SETI always makes us ask what human-centered assumptions we are making about extraterrestrial civilizations. When it comes to detecting an actual technology, like the starships we’ve been talking about in the last two posts, we’ve largely been forced to study concepts that fit our understanding of physics. Thus Robert Zubrin talks about how we might detect a magsail, or an antimatter engine, or a fusion-powered spacecraft, but he’s careful to note that the kind of concepts once studied by the Breakthrough Propulsion Physics Project at NASA may be undetectable, since we really don’t know what’s possible and what its signature might be.
I mentioned zero-point energy in a previous post because Zubrin likewise mentions it, an idea that would draw from the energy of the vacuum at the quantum level. Would a craft using such energies — if it’s even possible — leave a detectable signal? I’ve never seen a paper on this, but it’s true that one classic paper has looked at another truly exotic mechanism for interstellar travel, the wormhole. These shortcuts through spacetime make space travel a snap. Because they connect one part of the universe to another, you go in one end and come out the other, emerging into another place and, for all we know, another time.
The fact that we don’t know whether wormholes exist doesn’t mean we can’t think about how to detect one, although the authors of the classic paper on wormhole detection make no assumptions about whether or not any intelligent species would actually be using a wormhole. The paper is “Natural Wormholes as Gravitational Lenses,” and it’s no surprise to find that its authors are not only wormhole specialists like Matt Visser and Michael Morris, but physicists with a science fiction connection like John Cramer, Geoffrey Landis, Gregory Benford and the formidable Robert Forward.
Image: A wormhole presents a shortcut through spacetime. Can one be detected? Credit: Wikimedia Commons.
The analysis assumes that the mouth of a wormhole would accrete mass, which would give the other mouth a net negative mass that would behave in gravitationally unusual ways. Thus the GNACHO (gravitationally negative anomalous compact halo object), which playfully echoes the acronym for massive compact halo objects (MACHOs). Observationally, we can look for a gravitational lensing signature that will enhance background stars by bending light in a fundamentally different way than what a MACHO would do. And because we have MACHO search data available, the authors propose checking them for a GNACHO signature.
In conventional gravitational lensing, when a massive object moves between you and a much more distant object, a greatly magnified and distorted image of the distant object can be seen. Gravitational lensing like this has proven a useful tool for astrophysicists and has also been a means of exoplanet detection. But when a wormhole moves in front of another star, it should de-focus the light and dim it. And as the wormhole continues to move in relation to the background star, it should create a sudden spike of light. The signature, then, is two spikes with a steep lowering of light between them.
The authors think we might find the first solid evidence for the existence of a wormhole in our data by looking for such an event, saying “…the negative gravitational lensing presented here, if observed, would provide distinctive and unambiguous evidence for the existence of a foreground object of negative mass.” And it goes without saying that today’s astronomy, which collects information at a rate far faster than it can be analyzed, might have such evidence tucked away in computer data waiting to be discovered by the right search algorithms.
Would a wormhole be a transportation device? Nobody knows. Assuming we discover a wormhole one day, it would likely be so far away that we wouldn’t be able to get to it to examine its possibilities. But it’s not inconceivable that a sufficiently advanced civilization might be able to create an artificial wormhole, creating a network of spacetime shortcuts for instantaneous travel. Matt Visser has discussed a wormhole whose mouth would be held open by negative energy, ‘…a flat-space wormhole mouth framed by a single continuous loop of exotic cosmic string.’ A primordial wormhole might survive from the early universe. Could one also be created by technology?
Civilizations on the Brink
More conventional means of transport like solar or laser-powered sails present serious problems for detection. In Jerry Pournelle and Larry Niven’s The Mote in God’s Eye, an alien lightsail is detected moving at seven percent of the speed of light, its spectrum the same as the star that it is approaching but blueshifted, which is how analysts have determined it is a sail. The novel’s detection occurs with far more sophisticated observatories than we have in our day, when finding a solar or lightsail in transit would be a tricky thing indeed. A fusion rocket, for example, would emit largely in the X-ray range and could be detectable for several light years, but a lightsail is a highly mutable catch.
I remembered reading something about this in Gregory Matloff’s Deep Space Probes (Springer, 2005) and checked the book to extract this:
If ET prefers non-nuclear travel, he might utilise a laser or maser light sail. If the starship is near enough and the laser/maser is powerful enough, reflections from the sail might be observable as a fast-moving and accelerating monochromatic ‘star.’ However, detection will depend on sail shape and orientation as well as other physical factors.
Therefore, it is not as easy to model the spectral signature of these craft as it is energetic nuclear craft. A starship accelerated using lasers or masers may be easier to detect during deceleration if a magsail is used.
Writing in the comments to yesterday’s post, Centauri Dreams reader James Jason Wentworth recalls Larry Niven’s short story “The Fourth Profession,” which has a lightsail detection something like the one in The Mote in God’s Eye:
“All right. The astronomers were studying a nearby nova, so they caught the intruder a little sooner. It showed a strange spectrum, radically different from a nova and much more constant. It got even stranger. The light was growing brighter at the same time the spectral lines were shifting toward the red.
“It was months before anyone identified the spectrum.
“Then one Jerome Finney finally caught wise. He showed that the spectrum was the light of our own sun, drastically blue-shifted. Some kind of mirror was coming at us, moving at a hell of a clip, but slowing as it came.”
Some sails could be truly gigantic, and we can imagine worldships large enough to require sails the size of a planetary radius, which could be detected when near their home or destination stars, but would be hard to find when in cruise. Matloff goes on to suggest that any search for this kind of ship should look near stars from which an entire civilization might be emigrating. A star like Beta Hydri is a possibility, a nearby (21 light years) solar-type star now expanding from the main sequence. This is the longest shot of all, but finding unusual signatures in visible light near a star leaving the main sequence would at least compel a second look.
The wormhole paper is John Cramer, Robert L. Forward, Gregory Benford et al., “Natural Wormholes as Gravitational Lenses,” Physical Review D (March 15, 1995): pp. 3124-27 (available online). See also Matloff and Pazmino, “Detecting Interstellar Migrations,” in Astronomical and Biochemical Origins and the Search for Life in the Universe, ed. C. B. Cosmovici, S. Bowyer and D. Werthimer, Editrici Compositori, Bologna, Italy (1997), pp. 757-759.
Happy to oblige:
1. ISM not affecting particles: The ISM along a path of a few light years corresponds to a condensed layer of atoms roughly a thousand thick. Thus EVERY dust grain will hit MANY ISM atoms during its trip. You may easily calculate the momentum of a single atom at 0.2c, I guarantee that it is enough to impart a change in lateral velocity of more than 0.0005 m/s, even if you do not count the ejecta of the impact crater.
2. ISM magnetic fields being weak: The galactic field is around a nanotesla in strength. A light year has 10^16 meters. You mentioned 100 lenses a few meters thick, say generously 10 km worth of artificial fields per light year? In order to counteract fluctuations in the galactic field, which exists along the entire path, yours would have to be 10^12 times stronger, which comes to 1000 Tesla.
3. ISM magnetic fields being predictable: I don’t think so. See e.g. here: “The degree of radio polarization within the spiral arms is only a few %; hence the field in the spiral arms must be mostly tangled.”(http://www.scholarpedia.org/article/Galactic_magnetic_fields)
I am afraid these particular issues remain valid problems and so far your “refutation” of them amounts to little more than hand waving.
I have been wondering about the nature of these laws and the engineering of their application. This seems to be the most detailed description you have provided:
The first thing I notice is that the descriptions of the first and second layer are verbatim identical, which strikes me as a little bit weird. Simply stating that the two are identical in composition and function would have been less confusing.
The next thing I notice is your use of the term “electromotive force” as if it was an actual force, which a quick check of Wikipedia shows not to be true two sentences into the definition. This pretty much makes the whole rest of the argument null and void, until you clarify what you really mean by this term.
The third thing I notice is that you ascribe a dissipative quality to this force, since you say “will be given an electromotive force by the lens until this sideways speed will be nullified”, as if the effect of the force were proportional and opposite to the sideways motion of the particles. In physics, a force with this particular characteristic is called “friction”, and it is not something normally associated with magnetic fields. It would help if you could come up with some basic equations to derive this “electromotive force” and its characteristics.
Throw in a realistic field configuration, also, one that holds up to Maxwell’s laws. “Concentric circles around the center of the lens” that “get stronger as one gets from the edge of the lens to its center” is not one of these, I think. Best to specify the shape of the conductors generating the field, because that is what you will have to build and carry.
Eniac
I even know how I can decrease the electric field strength in the accelerator by 2 orders of magnitude (NOT only one) when increasing the diameter of the atom beam pipe from 2 m to 20 m.
Congratulations to this moment of enlightenment. I am just a little bit puzzled, because both physical common sense and this hypercard: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecyl.html say that the electric field of a linear charge density decreases linearly with distance. Perhaps you would like to share more details about this spectacular insight you have had which seems, on first glance, to defy the laws of physics?
Eniac
First – time for a new version of the interstellar system:
The half-circles accelerator will be 20000 km long. Its RFs will be 1 order of magnitude than the ones the LHC currently uses.
This half-circles accelerator will accelerate ~3,5 kg of atoms to 0,1 c every 20 minutes.
When exiting the accelerator, the atoms will be neutralized.
For a beam pipe with a diameter of 2 meters, the electric field strength will be 10^9 V/m*.
In ~10 hours, the accelerator will accelerate ~100 kg worth of atoms, a ‘batch’.
The first atoms of every batch will not be fuel atoms; their function will be to accelerate to ~0,1 c the container of this batch.
The container will be, at most, 100 times lighter than the fuel it will carry; made of ultralight materials. It will be equipped with electronics. Also, it will be able to receive energy via EM wave and to generate a magnetic field.
The first atoms of every batch will pass through lenses**, focusing them. When they are near the container, they will be given an electric charge by stationary lasers. The magnetic field of the container will repel these atoms, accelerating the container.
The rest of the atoms from the batch will be focused by the lenses, directed to enter the container now traveling at 0,1 c. Once all ~100 kg worth of fuel are inside the container, the container will close its door, carrying the atoms to the ship en route. To that purpose, the container will have systems that can change its course by a minute degree; as such, it will maintain the correct course.
Once near the ship, the fuel will be easily collected and used.
*As said, if you increase the diameter of the beam pipe to 20 meters, you can decrease the electric field strength by 2 orders of magnitude:
If you have only one atom beam traveling through the 20 meters beam pipe, then yes, the electric field strength by only 1 orders of magnitude.
If you don’t, though:
A circle with a radius of 1 m has the area =pi. In it, you can have only one beam pipe of 2 m radius.
A circle with a radius of 10 m has the area =100pi. Meaning, you can have ~100 beam pipes of 2 m radius.
In order for the accelerator to accelerate 3,5 kg every 20 minutes, through every beam pipe, you only need to have 100 times FEWER atoms.
As per
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecyl.html
the charge per unit length will be 2 orders of magnitude lower in each beam pipe.
This translates into an electric field of 10^7 V/m in each beam pipe. We have dielectrics today that can withstand this – mica, etc.
The cross section of an RF will have similarities with a honeycombed structure. The total mass of the RFs will increase increase by relatively little, though:
-their walls will be thinner – due to the fact that they must impart no larger kinetic energy to the atoms than the 2 meter diameter RFs,
-the dielectrics will be thinner – due to the decreased electric field strength.
Now you don’t even have the potential problem with the RFs not being able to function effectively with a 20 m atom beam pipe (Apropos this – please explain on what basis did you reach this conclusion, Eniac).
Am I to understand that you are now proposing to use a particle beam to push a container with fuel and accelerate it to 0.1c that way? This is yet another interesting proposal, albeit not a lot more realistic than the previous ones. Challenges I see here:
1) Getting the beam to provide the enormous acceleration needed while not turning the container into plasma.
2) Keeping the beam focused on the container over the enormous distance needed for this acceleration
3) Condensing the fuel inside the projectile without liberating enough heat to turn both into plasma.
Plus numerous others, too many to list.
In particularly, I would like to see some calculations about how strong a magnetic field is needed to “repel” the beam and how “lightweight” the magnet producing this field would be.
One flaw in this particular reasoning is that you overlook the fact that at any given point, the electric fields of the 100 pipes need to be added together, and we are back to one order of magnitude.
Even if you could produce fields that strong, the field you would need to keep the beam focused is one that is directed from the outside to the center. Maxwells equation require for the source of such a field to be at that center. This means you need to have a linear charge of the same magnitude and opposite charge of that of the beam, right at the center of the beam. That is similar to having a neutral beam, and I have trouble seeing how you would then accelerate that.
You are making some peculiar assumptions about scaling here. In my opinion, the wall thickness would have to be proportional to size or even thicker, otherwise the Q factor will go way down because of the extra resistance. Larger size of a resonator also implies lower resonance frequency, which would decrease rather than increase the resonator’s power.
I am certainly not an expert on accelerators, but it makes sense that for the above mentioned reasons (and others) scaling up of resonators is tricky business, at the least. If you would like to inform yourself about some of the issues, you might want to read this: http://cas.web.cern.ch/cas/Germany2009/Lectures/PDF-Web/Jensen.pdf
Judging from the pictures, it seems that typical beam channels through resonator cavities are only on the order of a centimeter, so to get to 20 m would mean scaling up by a factor of 1000 in size, which would most likely mean scaling around 1,000,000,000 in volume and mass. If they can be scaled much at all and still work, which I consider unlikely. Note that even these small ones look pretty hefty, already.
*Error correction:
“If you have only one atom beam traveling through the 20 meters beam pipe, then yes, the electric field strength by only 1 orders of magnitude.
If you don’t, though:
A circle with a radius of 1 m has the area =pi. In it, you can have only one beam pipe of 2 m radius.
A circle with a radius of 10 m has the area =100pi. Meaning, you can have ~100 beam pipes of 2 m radius.”
This should be:
If you have only one atom beam traveling through the 20 m diameter beam pipe, then yes, the electric field strength decreases by only 1 order of magnitude.
If you don’t, though:
A circle with a radius of 1 m has the area =pi. In it, you can have only one beam pipe of 2 m diameter.
A circle with a radius of 10 m has the area =100pi. Meaning, you can have ~100 beam pipes of 2 m diameter.
Eniac
“Am I to understand that you are now proposing to use a particle beam to push a container with fuel and accelerate it to 0.1c that way? This is yet another interesting proposal”
No, Eniac.
I’m proposing to accelerate the EMPTY 100 grams container to o,1c, and then fill it up with 10 kg worth of fuel.
“1) Getting the beam to provide the enormous acceleration needed while not turning the container into plasma.
2) Keeping the beam focused on the container over the enormous distance needed for this acceleration
[…]
In particularly, I would like to see some calculations about how strong a magnetic field is needed to “repel” the beam and how “lightweight” the magnet producing this field would be.”
The sailbeam proposal contains these calculations. But remember – now the payload/container has 100 grams, NOT 1-2 tonnes.
Meaning – 100 grams of particles at 0,1 c will impart 0,1c to the container over relatively short distances, even if they hit the container only a few at a time.
As for focusing the particles and then the fuel – at the accelerator and, if needed, en route (until the particles/the fuel reach the container) – I want to use my lenses, of course. Apropos them – I will write the post detailing it shortly – time permitting.
“One flaw in this particular reasoning is that you overlook the fact that at any given point, the electric fields of the 100 pipes need to be added together, and we are back to one order of magnitude.”
You have one beam pipe 2 m in diameter, containing 100 times less charged atoms, creating a 10^7 V/m strong electric field.
The RFs only have to impart 100 times less kinetic energy – they will be FAR smaller.
The beam pipe will be charged with a electric field of the same polarity – keeping the atom beam focused.
100 METERS AWAY (or more – I have ALL the space I’ll ever going to need), there’s another beam pipe, 2 m in diameter.
Its RFs and charge are the same as the first one’s.
ETC – until I have 100 beam pipes so arranged.
No, it does not. The equivalent to your container in Kare’s sailbeam proposal are the sails. They are accelerated by a laser, and no magnets are involved.
As I recall, Kare’s sails are much less than 100 g, and they do not include a magnet. Your ship, on the other hand, is a lot heavier than Kare’s ship, unless that changed? Also, Kare’s sails are allowed to self-destruct and turn into plasma to drive the ship. Your fuel must be stopped and collected in condensed form, which is incredibly more difficult.
In any case, what about the magnet that is to “repel” the beam? Any designs that fit within the 100 g weight budget? What is the field strength going to be?
Hint: It has to be wide and strong enough to bend the path of a heavy ion approaching at 0.1c by a substantial angle. Lorentz force at work. Similar to your accelerator, only now you have 100 grams to work with, instead of a bazillion tons.
Last time you spoke of 100 beam pipes 2 m in diameter, not just one, bundeled within a 20 m radius. Each would generate up to 10^7 V/m, but some would be further away from the point in question. The total for the bundle would add up to roughly 10^8, one order of magnitude less, as it should when the total width increases from 2 to 20 m..
However, that was yesterday. Now that there is only one beam pipe: You are right, the fields will be 10^7 V/m, still way more than enough to instantly disperse the beam. But now you have cut your throughput by 99%. Per accelerator, that is. It seems you are now planning 100 of these incredible accelerators. It would be interesting to hear how you would merge the beams. With your magic motion-stopper “lenses”, would be my guess. I eagerly await reading the promised new attempt at explaining their principle of operation.
In my humble opinion, 100 g of particles impacting a 100 g container at 0.1 c will produce nothing other than spectacular fireworks.
“The equivalent to your container in Kare’s sailbeam proposal are the sails. They are accelerated by a laser, and no magnets are involved.”
Eniac, the equivalent to my container in Kare’s sailbeam proposal is ITS SHIP:
Kare’s 1-2 tonnes ship is propelled by vaporized sails hitting a magnetic field – and he has calculations to this respect.
My FAR lighter 100 grams container is propelled by charged particles hitting a FAR weaker magnetic field.
“As I recall, Kare’s sails are much less than 100 g, and they do not include a magnet. Your ship, on the other hand, is a lot heavier than Kare’s ship, unless that changed?”
My ship is still 100 tonnes heavy.
The fuel comes to it in 100 g containers, each containing 10 kg worth of fuel. For 1000 tonnes of fuel, one must accelerate 10 tonnes worth of empty containers, then fill them with fuel.
The particles that propel the containers are FAR lighter than 100 g and are accelerated to 0,1 c by the accelerator.
“Also, Kare’s sails are allowed to self-destruct and turn into plasma to drive the ship. Your fuel must be stopped and collected in condensed form, which is incredibly more difficult.”
The particles that propel a container to 0,1c will be charged (by an external laser) before hitting the magnetic field generated by the container (with energy beamed to it).
Once the container is accelerated to 0,1 c, the 10 kg of fuel is sent to it, also at 0,1 c.
The collection of this fuel requires the fuel’s trajectory to be relatively exact (for a distance of light-days, perhaps light-weeks AKA the distance the container needed to be accelerated to 0,1c).
The fuel is NOT stopped by the container – both have ~0,1 c velocity.
“In my humble opinion, 100 g of particles impacting a 100 g container at 0.1 c will produce nothing other than spectacular fireworks.”
Only if these 100 g of particles hit the container ALL AT ONCE.
Not if they hit the container only one/a few particles at a time, for 10 weeks (distance of less than a light-week from the accelerator), for example.
“You are right, the fields will be 10^7 V/m, still way more than enough to instantly disperse the beam.”
10^7 V/m, still way more than enough to instantly disperse the beam?
Eniac, we have today dielectrics that can withstand this voltage (and not especially durable ones). Mica, for example.
And you think a material chosen by us to be sturdy (the material which will be charged in order to contain the beam) won’t be durable enough? When I’ve shown previously that we already have materials with a tensile strength large enough to withstand not only 10^7 V/m, but 10^9 V/m?
“But now you have cut your throughput by 99%.”
Yes, the RFs will only have to be 1/100 as powerful as the ones from the single atom pipe accelerator. Which translates into them being FAR lighter and easier to manufacture, not the opposite.
“It would be interesting to hear how you would merge the beams. With your magic motion-stopper “lenses”, would be my guess. I eagerly await reading the promised new attempt at explaining their principle of operation.”
Indeed, with my lenses**.
Not that I need them to merge these particle beams, seeing how, when exiting each accelerator, the particles will emerge, essentially, from point sources.
“Last time you spoke of 100 beam pipes 2 m in diameter, not just one, bundeled within a 20 m radius.”
My current, distanced, 100 beam pipes have a total cross section area of 100pi – equal to the one obtained by making one atom beam pipe have a diameter of 20 m.
As I already told you, Eniac – I know how I can decrease the electric field strength in the accelerator by 2 orders of magnitude (NOT only one) when increasing the diameter of the atom beam pipe from 2 m to 20 m.
With regard to this, thank you for your compliment: “this spectacular insight you have had which seems, on first glance, to defy the laws of physics”
The field can’t be weak if the particles are to be stopped before they hit the container. You have evaded my question: How weak did you have in mind?
This contradicts your previous statement:
It is also physically impossible, because the momentum does not add up. You actually need 100 g at 0.2 c to accelerate another 100 g to 0.1 c.
What materials we have is irrelevant. It is the beam that will disperse, not some material. We have already established that it is impossible to create the kind of electric field that would hold the beam together, since per Maxwell’s equations it would require negative charges inside the beam.
Relatively, yes. Instead of 10^12 times heavier than standard ones, they will now be 10^9 times heavier. But, you will need a hundred of them to keep your throughput… You may have a point here, though. Why not just build 10^9 LHCs? That way, we are working with known technology without the hazards of scaling up the size.
You have cheated though. Your latest design does not actually fit into the 20m circular cross-section we originally spoke about. You have decreased beam dispersion by dispersing the beam. Ingenious, indeed.
Yes, but a hundred of them. By “merging” I referred to the process by which you plan to combine them into a single narrow beam, which cannot be done by lenses or mirrors (unless they are magical).
This one we can tackle. Let’s see, 100 g in 10 weeks makes a mass stream of 1.6*10^-8 kg/s. The power for that is P=0.5*(m/[s])*v^2, comes out to about seven MW. Focused on what amounts to a 2 gallon bucket. Yup, fireworks.
Eniac:
“What materials we have is irrelevant. It is the beam that will disperse, not some material. We have already established that it is impossible to create the kind of electric field that would hold the beam together, since per Maxwell’s equations it would require negative charges inside the beam.”
?
Eniac, the atom beam is positively charged.
Are you actually saying that it’s impossible to take a cylindrical piece, charge it (while it’s in vacuum) positively to 10^7 V/m – this value NOT at 1 m distance from the cylinder, but at 1 mm distance from it?
Do detail Maxwell’s equations that show this.
“Relatively, yes. Instead of 10^12 times heavier than standard ones, they will now be 10^9 times heavier. But, you will need a hundred of them to keep your throughput… You may have a point here, though. Why not just build 10^9 LHCs? That way, we are working with known technology without the hazards of scaling up the size.”
10^9 times heavier than LHC’s RFs?
Eniac – with RFs 1 order of magnitude better than LHC’s, 20000 km wrth of accelerator can accelerate 3,5 kg to 9,1 c in 20 minutes. Don’t take my word for it – check how many RFs the LHC has, how long they are, how much kinetic energy they impart to the proton beam.
If you accelerate these 3,5 kg in 100 accelerators, NOT just one, with RFs 1 order of magnitude better than LHC’s, each of these RFs is 1OO TIMES LIGHTER than the LHC’s.
If you take RF no better than the ones in the LHC, each of these RFs is 10 TIMES lighter than the ones in the LHC.
You take the “10^9 times heavier”… from where exactly, Eniac?
“You have cheated though. Your latest design does not actually fit into the 20m circular cross-section we originally spoke about. You have decreased beam dispersion by dispersing the beam. Ingenious, indeed.”
Really?
My 100 beam pipes design is no heavier than the 1 beam pipe design (indeed, due to the electric repulsion being easier to solve, it’s lighter), has advantages relating to heat radiation, etc.
You call this ‘cheating’? Really?
It’s called thinking outside the box; solving a problem you considered unsolvable, Eniac.
Error correction:
“[…]with RFs 1 order of magnitude better than LHC’s, 20000 km wrth of accelerator can accelerate 3,5 kg to 9,1 c in 20 minutes.”
That should be:
[…]with RFs 1 order of magnitude better than LHC’s, 20000 km worth of accelerator can accelerate 3,5 kg to 0,1 c in 20 minutes.
**The LENSES:
“Throw in a realistic field configuration, also, one that holds up to Maxwell’s laws. “Concentric circles around the center of the lens” that “get stronger as one gets from the edge of the lens to its center” is not one of these, I think.”
Magnets arranged …NS NS NS…, forming a curved line, closing in a circle. The magnetic field lines will exit a magnet and enter the next, forming a circle.
The circles made of magnets (the inner circles, of weaker magnets, the outer circles, of stronger ones) are arranged in concentric circles, forming the lens.
“The next thing I notice is your use of the term “electromotive force” as if it was an actual force”
The increasing magnetic flux will create the ems within the particle
The ems will create an electrical current which, as per Lenz’s law, will have a magnetic field which opposes the change in magnetic flux.
The interaction between the lens’s magnetic field and the induced magnetic field will slow the particle down.
“The third thing I notice is that you ascribe a dissipative quality to this force, since you say “will be given an electromotive force by the lens until this sideways speed will be nullified”, as if the effect of the force were proportional and opposite to the sideways motion of the particles.”
The effect will be proportional to the change in magnetic flux, as per Faraday’s law of induction:
The change in magnetic flux will be 0 if the particle travels on a ‘horizontal’ trajectory.
The change in magnetic flux will be larger the larger the degree between the horizontal trajectory and the trajectory the particle has. And this degree will be larger the greater the sideways speed of the particle is.
Meaning, the larger the sideways speed of the particle is, the stronger the ‘friction’, nullifying this speed.
As the particle slows down, the ems decreases and the friction decreases.
When the sideways speed reaches 0, the ems reaches 0 the the particle ceases to experience friction.
“The first thing I notice is that the descriptions of the first and second layer are verbatim identical, which strikes me as a little bit weird. Simply stating that the two are identical in composition and function would have been less confusing.”
In the first lens, the magnetic field will get stronger as one gets from the CENTER of the lens to its EDGE (if a particle travels from the center of the lens to its edge, this lens will stop it).
In the second lens, the magnetic field will get stronger as one gets from the EDGE of the lens to its CENTER (if a particle travels from the edge of the lens to its center, this lens will stop it).
You charge something to Volts, not V/m. What I am saying is that the field inside such a cylindrical charged pipe would be exactly zero, according to Maxwell’s equation, or equivalently, Gauss’s law. Look it up, it is elementary physics. There would be nothing preventing the beam from spreading and hitting the wall, resulting in the by now familiar rapidly expanding cloud of plasma.
Here you are somehow assuming that the size of the resonators scales with the energy they provide to the beam. I think it is more likely they scale with the beam channel width, from about 2 cm to 2 m or 20 m, depending on your version. That makes up to 10^9 in volume or mass, which goes with the cube of the scaling dimension. Neither of us really knows how these really scale, though. It is quite possible they do not scale at all to such an enormously large beam channel.
Are the magnets end to end? Such a configuration of magnets would be the magnetic equivalent of a short circuit, i.e. most field lines would just run inside the magnets, outside there would be very little field.
Or are there gaps between them? In that case, you lose rotational symmetry, and particles will be deflected differently when they arrive near a magnet than when they arrive between two of them. This results in most of the particles not being directed where you want them.
In either case, of course, the amount of deflection will depend on the size, shape and conductivity of the particle, which again will result in most of them not going where you need them.
This may be the part that is wrong. When there is an induced opposing field, it will tend to drive the particle out of the field, not slow it down. I suppose it would be easy enough to build a prototype, where you blow smoke through a set of magnets and it emerges as a tightly focused beam? You should start there, as it seems it could be a nice desktop experiment, and potentially extremely useful.
Here is a nice lecture you could read up on to gain a little more facility with the laws governing electric fields:
http://web.mit.edu/sahughes/www/8.022/lec05.pdf
Pay particular attention to Corollary 1.
“Here you are somehow assuming that the size of the resonators scales with the energy they provide to the beam. I think it is more likely they scale with the beam channel width, from about 2 cm to 2 m or 20 m, depending on your version. That makes up to 10^9 in volume or mass, which goes with the cube of the scaling dimension. Neither of us really knows how these really scale, though. It is quite possible they do not scale at all to such an enormously large beam channel.”
I can always take the accelerator from 100 beam pipes, each of 2 m, to:
1000 beam pipes of 20 cm;
10000 beam pipes of 2 cm;
etc
I could move these beam pipes apart; after the electric field is weak enough, though, it may be better to position them in clusters.
Whether the mass of the RFs scales with the energy they provide to the beam or with the atom beam pipe diameter, under no circumstances, for the same kinetic energy, the RF will be heavier than the ones used in the LHC.
If the RFs mass scales with the size of the atom beam, they will be lighter than the LHC’s for the same imparted kinetic energy (I can make the atom beam pipe smaller).
If the RFs mass scales with the imparted kinetic energy, and they are an order of magnitude better than current ones (due to improvements in superconductors), they 10 times lighter than the LHC’s for the same imparted kinetic energy.
“Are the magnets end to end? Such a configuration of magnets would be the magnetic equivalent of a short circuit, i.e. most field lines would just run inside the magnets, outside there would be very little field.
Or are there gaps between them? In that case, you lose rotational symmetry, and particles will be deflected differently when they arrive near a magnet than when they arrive between two of them. This results in most of the particles not being directed where you want them.
In either case, of course, the amount of deflection will depend on the size, shape and conductivity of the particle, which again will result in most of them not going where you need them.”
I thought of a better configuration for the magnets:
Take wire, arranged in coils, bend it into a curve closing in a circle.
When electric current is circulating through this wire, it will generate a magnetic field whose field lines are contained within the coils.
That’s a circle.
The concentric circles will have increasing strength of the magnetic field.
“This may be the part that is wrong. When there is an induced opposing field, it will tend to drive the particle out of the field, not slow it down.”
When the particles enter the lens, they will experience a momentary stopping reaction on their forward direction of motion. Considering their speed – 0,5c – and the weakness of the magnetic field of the lens, this is all but negligible.
Inside the lens, the EMS/electric current/generated magnetic field, as per Lenz’s law, will only move the particles on the sideways direction.
“What I am saying is that the field inside such a cylindrical charged pipe would be exactly zero, according to Maxwell’s equation, or equivalently, Gauss’s law. Look it up, it is elementary physics. There would be nothing preventing the beam from spreading and hitting the wall, resulting in the by now familiar rapidly expanding cloud of plasma.”
Considering I make the accelerator have 1000/10000 atom beam pipes, magnetic fields should be sufficient for confinement.
Nevertheless, I am still searching for a solution involving electric fields.
Error correction:
“I can always take the accelerator from 100 beam pipes, each of 2 m , to:
1000 beam pipes of 20 cm;
10000 beam pipes of 2 cm;
etc
I could move these beam pipes apart; after the electric field is weak enough, though, it may be better to position them in clusters.”
This is:
I can always take the accelerator from 100 beam pipes, each of 1 m radius (2 m diameter) , to:
10000 beam pipes of 10 cm radius;
10000 pipes of 10 cm radius, each containing 100 beam pipes of 1 cm radius (2 cm diameter)
etc
Of course, the electric field strength decreases to 10^7 V/m in the 10000 beam pipes of 10 cm radius (and it can be made smaller).
And this would be:
Of course, the electric field strength decreases to 10^5 V/m in the 10000 beam pipes of 10 cm radius (and it can be made smaller).
Of course, ultimately, you can achieve the 9 order of magnitude in beam density by building 10^9 of your mega-accelerators, each using plausible, existing technology. You would then have 10^9 beams, which you would need to somehow combine, or build a separate set of enroute lenses for each. It is much like combining the light of a billion flashlights into a deadly laser beam. Not feasible.
What about the spaces between coils, where there is no field? Also, can you really control the field strength everywhere to within the required accuracy of 10^-14?
What about the variation in particle properties? You have not yet addressed it, even though I pointed it out multiple times and it is absolutely fatal to your lens proposal, in my opinion.
Eniac
“Of course, ultimately, you can achieve the 9 order of magnitude in beam density by building 10^9 of your mega-accelerators, each using plausible, existing technology. You would then have 10^9 beams, which you would need to somehow combine, or build a separate set of enroute lenses for each. It is much like combining the light of a billion flashlights into a deadly laser beam. Not feasible.”
Except I don’t have to build 10^9 mega-accelerators.
I only have to build:
“10000 beam pipes of 10 cm radius;
10000 pipes of 10 cm radius, each having a honey-comb stricture, containing 100 beam pipes of 1 cm radius (2 cm diameter)
etc”
And the RFs of these accelerators are NOT heavier than the LHC’s.
Indeed, I assume they are an order of magnitude lighter than the LHC’s, due to improvements in superconductors or due to atom beam pipe geometry.
10000 accelerators are NOT 10^9 mega-accelerators. And are feasible. As for combining the beam, my lenses should be sufficient.
“What about the spaces between coils, where there is no field? Also, can you really control the field strength everywhere to within the required accuracy of 10^-14?”
My current plan involves accelerating containers of 100 g for every 10 kg worth of fuel.
The acceleration will take only as long as is needed in order not to break the containers apart. For example – for a constant acceleration lasting 2 years, bringing the container from 0 to 0,1c, I must only need to keep the fuel particles on track (targeted for the container) for 1,2 light-months, (NOT 4 light-years) across which, I can plant as many lenses as I want. Which translates into an accuracy for the fuel particles of FAR less than 10^-14.
Also – the space between the wire coils circles can be made arbitrarily small.
“What about the variation in particle properties? You have not yet addressed it, even though I pointed it out multiple times and it is absolutely fatal to your lens proposal, in my opinion.”
Let’s take an example:
We have to particles; both have the same speed, but one has a larger area, experiencing more change in the magnetic flux.
The larger particle will receive a larger emf, will achieve the correct 0 sideways velocity sooner, after which it will no longer change sideways velocity.
The smaller particle will achieve the 0 sideways velocity later.
When exiting the lens, both particles will fly parallel to each other.
More precisely, 10^-15 per meter of lens radius, multiplied by the number of lenses along those 1.2 light months. You tell me which combination gives you something feasible like, say 1% accuracy? 0.1%?, 0.01%? 100,000 lenses of 100 km diameter might just do….
How were you going to let the buckets pass through the lenses? Is there a hole in the middle letting particles escape? You know, with 100,000 lenses there are not very many particles you can let escape before there are none left at the end.
This is not how lenses work. And it is not how particles behave in a magnetic field. Any field.
Eniac
“And it is not how particles behave in a magnetic field. Any field.”
As per Faraday’s law of induction, that’s how particles behave in a magnetic field and in a changing magnetic field.
“How were you going to let the buckets pass through the lenses? Is there a hole in the middle letting particles escape? You know, with 100,000 lenses there are not very many particles you can let escape before there are none left at the end.”
The lenses are made of coils of wire – VERY thin wire, due to the weak magnetic fields they generate being enough to negate the VERY small sideways velocity of the particles.
Very few particles will hit these coils of wire.
“More precisely, 10^-15 per meter of lens radius, multiplied by the number of lenses along those 1.2 light months. You tell me which combination gives you something feasible like, say 1% accuracy? 0.1%?, 0.01%? 100,000 lenses of 100 km diameter might just do….”
When the particles exit the accelerators, they’ll exit, essentially, from point sources. They can be focused into a beam with a fine-tuned direction.
Afterwards – do tell, Eniac, what will change the particles’ sideways velocity to any significant degree across 1,2 light-months?
With a lens arranged every light-day – a small lens, due to the particles not dispersing to any significant degree in the intervening space.
If need be, on this interval one can even arrange stations to deflect the incoming ISM before it reaches the fuel particles.
So, then, now you have 10,000 accelerators, each with a bundle of 100 beams, each carrying 1,000 times the charge density of an LHC beam. The 100 beams are bundled within a 10 cm radius, as I understand, so they must share the hole in the RF resonators? Which makes those 10 times bigger than today’s. If they can be scaled at all, and still work.
Good luck with that …
And I am still calling them mega-accelerators, given they are each roughly the size of the Earth. Now that there are 10,000 of them, they are starting to crowd the solar system… :-)
No, not really. Your wire coils need a certain thickness to carry the required current. Particles which hit the coils are obviously lost (the coils too, probably, come to think of it), so are the ones between coils. With 100,000 lenses, you can afford to lose only less than 0.001% of the particles, which makes for VERY thin wires.
Are the coils round? If so, particles entering near the coil center are deflected more than the ones entering at the periphery. With square coils, all bets are off about the degree of homogeneity of the field, my guess is much worse than 1%. For “only” 100,000 lenses of “only” 100 km radius, you need 0.001% accuracy. I guess it will have to be 10,000,000 lenses of 1,000 km radius, at least.
But the buckets will…
You have not really told how you can aim them to such exquisite accuracy to begin with. “As per Faraday’s law of induction” does not cut it. It is vague, not to mention wrong. If it is not wrong, then it is revolutionary and you should work it out and publish it. I’ll be happy to proofread if you so wish ….
As for what will change direction before flight: Coulombic dispersion in the accelerator, the process of neutralization, the process of condensation. All of these (in addition to being impractical to begin with) are going to exert strong uncontrollable forces on the particles. And en-route: There is the interstellar medium, which each particle will encounter many times. Dust is always charged, it is impossible to completely neutralize a dust particle down to the last electron. That will make them bend in your lenses and in the galactic magnetic field. Each one a little differently according to its charge.
These are just a few selected examples.
Only with a VERY accurate lens. Your coils need not apply. And only one beam at a time. Since the beam origins do not coincide in space, their focused versions will not coincide in direction. And one centimeter is not a point, which alone will introduce more dispersion than you can tolerate. It is the billion flashlight scenario, again. Or a million, or 10,000, whatever the case may be.
RFs:
“So, then, now you have 10,000 accelerators, each with a bundle of 100 beams, each carrying 1,000 times the charge density of an LHC beam. The 100 beams are bundled within a 10 cm radius, as I understand, so they must share the hole in the RF resonators? Which makes those 10 times bigger than today’s”
I have 10000 bundles of accelerators, each bundle having a 10 CM RADIUS.
Each bundle contains 100 accelerators, each accelerator having a 1 CM RADIUS aka the radius of the LHC’s atom beam pipe. Meaning, the RF geometry will not have to be scaled up at all.
And have I mentioned that the RFs will have to impart to the atom beams 1000000 LESS POWER than the LHC’s RFs? This translates into FAR smaller RFs.
“And I am still calling them mega-accelerators”
By comparison to every other mechanism aimed at imparting a payload (far lighter than 100 tonnes) a delta v of 0,2c, my ‘mega-accelerators’ are tiny.
““As per Faraday’s law of induction” does not cut it. It is vague, not to mention wrong.”
Faraday’s law of induction is mathematically exact.
http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction
As is Lenz’s law.
http://en.wikipedia.org/wiki/Lenz%27s_law
As said, They describe exactly how neutral particles behave in a magnetic field and in a changing magnetic field (aka 0 and non-zero change in the magnetic flux).
If you can create and control inside the lens the magnetic field to the required fine-tunning, the neutral particles will lose their sideways velocity (as per the mechanism I’ve described in my previous posts) to said required fine-tunning.
“Are the coils round? If so, particles entering near the coil center are deflected more than the ones entering at the periphery. With square coils, all bets are off about the degree of homogeneity of the field, my guess is much worse than 1%.”
One lens will have the magnetic field inside the coils stronger near the coil center and weaker near the coil periphery.
I will put several lenses one behind the other – 2-4 lenses, at most, should form an unit – arranged so as, per total, the effects of the magnetic field average out and are uniform for a particle crossing the lenses.
“Your wire coils need a certain thickness to carry the required current. Particles which hit the coils are obviously lost (the coils too, probably, come to think of it), so are the ones between coils. With 100,000 lenses, you can afford to lose only less than 0.001% of the particles, which makes for VERY thin wires.”
The coils will be put one behind the other – so as, if the particle missed the first few coils, it will miss all the subsequent coils (unless it has improbably high sideways energy – most of the lenses will be there for fine-tunning the sideways velocity to the required degree).
“Dust is always charged, it is impossible to completely neutralize a dust particle down to the last electron.”
But it is possible to neutralize atoms/molecules down to the last electron and then merge them.
“Coulombic dispersion in the accelerator, the process of neutralization, the process of condensation”
I already solved the Coulombic dispersion problem: a field strength of 10^6 or 10^5 is eminently manageable – quite the opposite of impractical.
As for neutralization and condensation – they are at least as practical as the schemes proposed for some of the Bussard ram-scopes/the sailbeam/etc requirements. They require fine-tunning, yes, but are far from impossible.
PS – Do you have any knowledge about the effects of extremely low frequency EM waves on particles (charged or otherwise)?
And now, a new iteration of my HALF-CIRCLES ACCELERATOR:
Take a circle. On the edge of this circle, in 10000 equidistant points, position the 10000 accelerators (bundles of accelerators, to be exact).
The fuel atoms will be ejected by each accelerator, having a direction tangential to this circle (direction which will change slightly in order to follow the container as it flies).
The atoms will be neutralized. They may or may not be condensed into particles (it may not prove necessary).
Then the atoms/particles will be focused by my lenses (the precision required being FAR smaller than in my previous iterations of the half-circles accelerator).
Take a 100 grams container, meant to ultimately contain 10 kg worth of fuel. The container will be made to go in a circle – just beyond the circle described by the 10000 accelerators – by the Lorentz force.
Between 1 10000 accelerators station and the next, the container will be accelerated by the momentum of atoms/particles coming from the first accelerators station, focused by a lens.
The distance between 1 10000 accelerators station and the next can be made so small that ISM and interstellar magnetic fields are no longer problems.
While those laws are valid and exact, they do not, as you claim, say anything about “how neutral particles behave in a magnetic field”. While you certainly could use these laws to derive equations of motion for such particles: You have not done so, nor referenced someone who did.
Those equations of motion would very much depend on specific properties of the particles (conductivity in particular), and I bet they would be nothing like what you expect.
You solved nothing. We have previoulsy determined that an electrostatic field will not stop dispersion. The impracticality of condensing neutral atoms emerging at near light speed from an accelerator into dust may be surpassed by that of fusing protons gathered from the ISM, but that does not make it practical.
I will not comment on your proposal to build a meta-mega-accelerator for charged buckets.
“Those equations of motion would very much depend on specific properties of the particles (conductivity in particular), and I bet they would be nothing like what you expect.”
You bet, but support your assertion with little.
“You solved nothing. We have previoulsy determined that an electrostatic field will not stop dispersion.”
And?
A magnetic field will – and is quite practical at 10^5-10^6 field strengths.
Your ‘Coulombic dispersion problem’ has become a straw-men.
“I will not comment on your proposal to build a meta-mega-accelerator for charged buckets.”
An accelerator that solved your ISM and interstellar magnetic field problems.
AND is tiny by comparison to your atomic rocket.
Unless you’re referring to a PERFECT (no losses) atomic rocket. Talk about NOT practical!
Bets do not need to be supported. They are to be settled by an outcome. I will patiently await the derivation of these equations and happily concede my bet if it so happens.
No it won’t. And if you are referring to 10^5-10^6 Tesla, no, such field strengths are entirely not practical.
75 % efficient would be quite sufficient, and is infinitely more practical than your fantastically accurate bucket-throwing machine.
“And if you are referring to 10^5-10^6 Tesla, no, such field strengths are entirely not practical.”
10^5-10^6 is referring to the strength of the electric field:
-if you have 10000 beam pipes of 10 cm radius (20 cm diameter), the strength of the electric field is 10^6 v/m.
-if you have 10000 pipes of 10 cm radius, each having a honey-combed stricture: containing 100 beam pipes of 1 cm radius (2 cm diameter), each of these 1 cm radius beam pipes being encased in a Faraday cage, the strength of the electric field is 10^5 v/m.
-And, of course, I can make these 1 cm radius beam pipes being encased in a Faraday cage to have a radius of 10 cm (the diameter of the LHC beam pipes is 6,3 cm):
the electric field strength is 10^4 v/m;
the radius of the bundle of 100 beam pipes will be only 1 meter.
The containment of the 10^4 v/m electric field will be done via magnetic fields.
BTW, the electric field generated by the RFs, for a 20000 km long accelerator is 50 Mv/m.
“your fantastically accurate bucket-throwing machine”
A circle (or oval-shaped form) made with 10000 (or more, smaller) accelerators spread out?
The distance between 2 accelerators will be of a few light-minutes, at most.
Not so “fantastically accurate” has become more than sufficient.
“75 % efficient would be quite sufficient”
“75 % efficient would be quite sufficient”
A mature fission rocket technology could have efficiencies of 60-70%. I outlined above the astronomical numbers relating to the amount of fuel you need to have. Not really practical.
We would be VERY lucky to have a fusion rocket efficiency in the 50-60% range – you want, essentially, to create a highly efficient fusion reaction in the nozzle of a rocket, expelling propellant (when we cannot even do it efficiently in closed structures, with no complications relating to propulsion). This results in astronomical numbers for the amount of fuel aka NOT practical.
Do mention the steps you propose to make these approaches more feasible than a Bussard ram-scoop (or other interstellar propulsion schemes that require mega-engineering and a LOT of “ifs” with their physics), Eniac.
Throughout this thread, you only formulated the problems. Do you have any solutions – or not?
Simple: Make do with a lower velocity. A fission rocket at 50% energy efficiency would have an exhaust velocity of roughly 0.02 c, which would allow us a delta-v of 10% of c with a mass ratio of 1:150. A similarly effective fusion rocket would get 0.03 c exhaust velocity, or 0.15 c at 1:150. A somewhat larger mass ratio of 1:1000 this could get us all the way up to 0.2 c.
This means that with good, but less than perfect fusion rocket, we can make the goal that you have set, and with a fission rocket it would just take us a little longer. A 1:1000 mass ratio is not pretty, but mega-engineering it is not. To propel a 1000 ton payload, you would need one million tons of fuel, which would fit within a cube of 100 m or less, depending on density. Not more than a large building, really.
All that needs to be worked out is the engine, with a comparatively low power density because it runs over many years. No impossible precision, no Earth sized structures, no magical lenses, no buckets blown up by intense particle beams. No rapidly expanding cloud of plasma, with a little bit of luck….
Eniac
“Make do with a lower velocity. A fission rocket at 50% energy efficiency would have an exhaust velocity of roughly 0.02 c, which would allow us a delta-v of 10% of c with a mass ratio of 1:150.”
Eniac, we’re talking about velocity 0,1c, delta v of 0,2c. You’re moving the goalposts:
For a velocity of 0,05c, my accelerator only has to be a LOT smaller (everything accelerated to only 0,05c). It would never qualify for being megaengineering.
What about delta v of 0,2c?
‘The rocket equation – for an effective exhaust velocity of 0,017c, if you wish to reach a delta v of 0,2c, the propellant mass must be ~125000 larger than the payload!
In the quoted paper, the payload is 60 tonnes. That’s literally a toy starship – it’s doubtful 60 tonnes can sustain 12 astronauts for 80 years (a trip to Alpha Centauri).
Still, you must carry 7500000 tonnes of propellant for these 60 tonnes.’
This makes my accelerator look TINY!
“A similarly effective fusion rocket would get 0.03 c exhaust velocity, or 0.15 c at 1:150.”
As such a thing is not known in the art, do tell how you intend to reach 50% efficiency in a fusion reaction existing in a rocket nozzle (as already aid, we would be VERY LUCKY to get here – and have not idea how).
“No impossible precision”
First – my accelerator doesn’t require anything close to ‘impossible precision’
Second – you were about to tell me how you intend to obtain that highly efficient fusion reaction.
“no Earth sized structures,”
For a delta v of 0,2c? I beg to differ.
“no magical lenses, no buckets blown up by intense particle beams. No rapidly expanding cloud of plasma”
All these assetions are supported by little. You just put them here.
BTW – as it turns out, electrostatic fields will do just fine for containment.
You only have to charge two – or more – separate pieces (made of conductors) and arrange them so that the containing electrostatic field around the atom beam has the same strength at a given radius from the center of the atom beam.
I am curious about what this mysterious arrangement might be. Are you keeping it secret?
As it turns out, and you apparently agree, our common goal of 0.2c can be achieved either by
1) A 50% effective fusion rocket and a 1:1000 mass ratio, about 100x100x100 m in size fully fueled, or any non-cubic variations of that.
2) A unspecified atomic rocket fueled from flying buckets accelerated and filled using an arrangement of many neutral particle guns of unheard-of beam intensity which at least according to your previous descriptions are about Earth sized. If you have thought of smaller ones, do tell how long they are now.
I am tiring of my efforts to let you see the absurdity of your design. Let us just leave it at the above and let the readers decide. I doubt there are more than 3 by now…
One light minute is 2*10^10 meters. Assuming your buckets are no more than a meter across, you’d have to have an aiming accuracy of 5*10^-11. Groping for an analogy, I think this corresponds roughly to hitting a quarter on the moon, shooting from Earth.
I do not think this is true.
If you look back, you will see each of my assertions backed up by either a back-of-the-envelope calculation, or by reference to a well-known law of physics. Which is more than can be said for most of your assertions, which usually run along the lines of “arrange this and that so that it does (something truly incredible)”, or “this and that requires (something reasonable or tiny, without supported numbers)”, when in fact the requirements are astronomically difficult.
Just to be specific: “magical lenses” is backed up by the law of conservation of radiance, “buckets blown up by particle beams” is backed up by a calculation of the power impinging on such buckets, and the “expanding cloud of plasma” is backed up in several instances by realistic calculations of the energy that would be released in designs that you have put forward.