Author Topic: Polywell Fusion: Path to SSTO and the Planets?  (Read 40401 times)

Offline Patchouli

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #20 on: 05/23/2009 06:59 pm »
Look what's been written:

"but the Navy provided a reported $1.8 million for Nebel and his colleagues to carry on Bussard's work."

http://cosmiclog.msnbc.msn.com/archive/2008/08/28/1301440.aspx


Hhahaahahahahaaa, that kind of investment for such important project is laughable for the capacity of the US Navy. They've got tens of billions of dollars, but can't give a reasonable sum of money for it....


What is NASA doing to investigate polywell fusion as a path to SSTO and manned interplanetary ships?
Right now all of the space agencies are wasting money from taxes to highly expensive and dangerous fire show, called chemical rockets and shuttles. No one ever cares that a Polywell fusor, or several Fusors, could provide the necessary energy for a Space Elevator , a Lightcraft, or WEAV.

Main problem at NASA and related is they just don't want to fund any long term research projects that carry any risk.

If it can't have a pay off in 5 to 15 years they don't pursue it.
I'm not saying a fusion powered SSTO is a waste of money far from it they should be researching things like this.
The issue is it may not produce anything useful for 20 years or more.

The big problem is risk aversion and short sightedness at agencies and by political leaders.

High risk long term projects are what government agencies should concentrate on as private groups can handle the near term stuff and are far better at fielding operational systems.
« Last Edit: 05/23/2009 07:04 pm by Patchouli »

Offline GI-Thruster

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #21 on: 05/23/2009 07:28 pm »
I think the problem may be a little different than you suspect.  NASA has many commitments that run back decades.  As I asked recently, isn't NASA funding Blended Wing Body research for more than 25 years now?  That's amazing especially considering it's Boeing who stands to benefit here, not NASA.

I think this all has more to do with VSE killing funding for so many other things.  MSFC had a new, $40 million complex just completed when it was closed because of VSE.  NASA was funding research into the Mach Lorentz Thruster and that ended very abruptly.  NASA was also funding research into Focus Fusion through JPL but that ended about the same time as VSE came along.  Not sure if it was a direct consequence or not.  And of course VSE killed hypersonic research and all NIAC funding.  NIAC is no more.

All this is not because the agency is particularly near-sighted.  It's been doing ion research for 4 decades.  The real reason is that in the '80's when we should have been thinking past STS and the financial demands from ISS, no one took action.  In order to maintain all the things NASA was doing in the 80's and do ISS and STS, NASA needed more funding.  Instead, its funding was cut.  So, it's no big surprise Mike Griffin got left holding the ball when VSE came along and he had to do what he was told: cut-cut-cut everything he could so there would be budget for VSE.  Obviously, we all wish POTUS had just given NASA a $6 billion increase so it could continue to fly STS until Constellation is ready, and keep all the programs that were cut.

So that's the context.  Add to that now the difference between last POTUS and this: Bush was a miser who never funded Constellation properly.  OBama spends money like a teenage girl in the mall with daddy's credit card.  If he doesn't write NASA an enormous budget increase, we can safely say he is no advocate of space.

Offline mlorrey

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #22 on: 05/24/2009 05:42 am »
I think the problem may be a little different than you suspect.  NASA has many commitments that run back decades.  As I asked recently, isn't NASA funding Blended Wing Body research for more than 25 years now?  That's amazing especially considering it's Boeing who stands to benefit here, not NASA.

Boeing is a tax paying constituent, ergo they are an obvious channel to commercialization of the technology. NASA generally doesnt do anything speculative that takes more than two presidential administrations, or even one if they can help it. They don't want something that is iffy causing them negative press from being proxmired.

Disruptive technologies are easy to proxmire.
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Offline GI-Thruster

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #23 on: 05/24/2009 02:18 pm »
Yes but look back on the history of flying wings.  Northrup didn't take 3 decades to fly.  They had troubles.  When these things stall, they flip head over heals and sometimes don't recover.  But this is stuff we've known about for 6 decades.  If Boeing wants to build a BWB, they should build it.  There is no onus upon the taxpayer to provide tech support for this research on ad infinitum.  I think it's just silly.

This sort of thing only happens when people are spending other people's money.  You'd never see this in private industry.

Offline mlorrey

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #24 on: 05/26/2009 12:49 am »

Quote
I'm lost as to what you're referring to with regards gains as high as 12.  If we're talking about Q, what we're talking is fusion power out/power in.  Don't Poly people count X-Ray as part of fusion power out?  What I'm getting with Nebel's 1.7-12 Q depending upon how the physics breaks is that either way, he expects to do more than break even with B11.  Or was he talking about X-rays?

I think those are probably ultimate Q values - useful power out versus total power in.  I don't know if X-ray capture is included in those numbers, but even if it is, a gain of 12 is probably unreachably high for a reactor with the commonly-calculated thermal bremsstrahlung yield.  Most discussion on talk-polywell assumes bremsstrahlung is a total loss, but we've been wrong before (witness the 'first wall problem' that recently evaporated after a casual comment from rnebel)...

I suspect that the bremsstrahlung problem, subject to their proposed mitigation techniques, is the source of most of the uncertainty in the quoted values of Q.

Bremsstrahlung is a function of the average atomic number of the isotopes involved. With D-D fusion, you have an average number of 1 so bremsstrahlung is as low as possible. With straight p-B11 fusion, you have 1+5/2 or an average of 3, so bremsstrahlung will be significantly higher.

What Bussard found, however, was if the reactor ran in a proton-rich regime, this would bring the average down and he could reduce the bremsstrahlung to 5%. Another factor is that where the ions intersect, they are at a very low electrical potential. Bremsstrahlung is an issue in tokamaks because they operate at over 150 kEv or more, while Bussards WB-6 was running at only 12.5 kEv peak electrical potential, however the core of the reactor, where the magnetic fields are balanced, is at a very low electrical potential. So the particles are at high velocity and low electrical potential when they intersect, which also greatly minimizes bremsstrahlung and thermalization issues.
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Offline mlorrey

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #25 on: 05/26/2009 12:51 am »
Yes but look back on the history of flying wings.  Northrup didn't take 3 decades to fly.  They had troubles.  When these things stall, they flip head over heals and sometimes don't recover.  But this is stuff we've known about for 6 decades.  If Boeing wants to build a BWB, they should build it.  There is no onus upon the taxpayer to provide tech support for this research on ad infinitum.  I think it's just silly.

This sort of thing only happens when people are spending other people's money.  You'd never see this in private industry.

Much of what NASA does in this area is operate research facilities that are diseconomic for industry to operate, like wind tunnels, etc. NASA operates the facilities and lets various companies do research there in technology sharing agreements.
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Offline 93143

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #26 on: 05/27/2009 01:09 am »
Bremsstrahlung is a function of the average atomic number of the isotopes involved. With D-D fusion, you have an average number of 1 so bremsstrahlung is as low as possible. With straight p-B11 fusion, you have 1+5/2 or an average of 3, so bremsstrahlung will be significantly higher.

What Bussard found, however, was if the reactor ran in a proton-rich regime, this would bring the average down and he could reduce the bremsstrahlung to 5%. Another factor is that where the ions intersect, they are at a very low electrical potential. Bremsstrahlung is an issue in tokamaks because they operate at over 150 kEv or more, while Bussards WB-6 was running at only 12.5 kEv peak electrical potential, however the core of the reactor, where the magnetic fields are balanced, is at a very low electrical potential. So the particles are at high velocity and low electrical potential when they intersect, which also greatly minimizes bremsstrahlung and thermalization issues.

It's standard procedure to run hydrogen-rich, so as to reduce Z.  That alone isn't enough; a thermal reactor will still not break even unless a large fraction of the X-ray power can be recovered.

Bussard's reactor, on the other hand, has high-density fast ions at the core, along with slow, lower-density electrons.  The electrons are fast at the edge, where their density is at a minimum. The density of the electrons has a maximum (and their speed a minimum) at some finite radius, due to the virtual cathode potential bottoming out and starting to climb again towards the virtual anode generated by the ion focus.  One of the things you have to fiddle with to optimize bremsstrahlung is the height of that virtual anode, because it affects the speed of the electrons through the core.

Tokamaks typically don't run as hot as fusors and Polywells.  I am unaware of anyone ever managing to get a tokamak up to 150 keV (I thought it was usually about a 30th of that), although Hirsch did run fusors that hot.  Besides, that's temperature, not potential.  Potential has nothing to do with any of this; as far as fusion calculations are concerned it's just a mathematical construct, the gradient of which is the electric field.

Now, tokamaks do have a wide spread of particle energies, whereas Polywells are supposed to be nonequilibrium machines with a much narrower distribution.  So there is a high-energy tail on the tokamak particle energy distribution that results in the bulk of the bremsstrahlung.  It also results in the bulk of the fusion, so...

Offline mlorrey

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #27 on: 05/27/2009 07:55 am »
Bremsstrahlung is a function of the average atomic number of the isotopes involved. With D-D fusion, you have an average number of 1 so bremsstrahlung is as low as possible. With straight p-B11 fusion, you have 1+5/2 or an average of 3, so bremsstrahlung will be significantly higher.

What Bussard found, however, was if the reactor ran in a proton-rich regime, this would bring the average down and he could reduce the bremsstrahlung to 5%. Another factor is that where the ions intersect, they are at a very low electrical potential. Bremsstrahlung is an issue in tokamaks because they operate at over 150 kEv or more, while Bussards WB-6 was running at only 12.5 kEv peak electrical potential, however the core of the reactor, where the magnetic fields are balanced, is at a very low electrical potential. So the particles are at high velocity and low electrical potential when they intersect, which also greatly minimizes bremsstrahlung and thermalization issues.

It's standard procedure to run hydrogen-rich, so as to reduce Z.  That alone isn't enough; a thermal reactor will still not break even unless a large fraction of the X-ray power can be recovered.

Bussard's reactor, on the other hand, has high-density fast ions at the core, along with slow, lower-density electrons.  The electrons are fast at the edge, where their density is at a minimum. The density of the electrons has a maximum (and their speed a minimum) at some finite radius, due to the virtual cathode potential bottoming out and starting to climb again towards the virtual anode generated by the ion focus.  One of the things you have to fiddle with to optimize bremsstrahlung is the height of that virtual anode, because it affects the speed of the electrons through the core.

Tokamaks typically don't run as hot as fusors and Polywells.  I am unaware of anyone ever managing to get a tokamak up to 150 keV (I thought it was usually about a 30th of that), although Hirsch did run fusors that hot.  Besides, that's temperature, not potential.  Potential has nothing to do with any of this; as far as fusion calculations are concerned it's just a mathematical construct, the gradient of which is the electric field.

Now, tokamaks do have a wide spread of particle energies, whereas Polywells are supposed to be nonequilibrium machines with a much narrower distribution.  So there is a high-energy tail on the tokamak particle energy distribution that results in the bulk of the bremsstrahlung.  It also results in the bulk of the fusion, so...

All I can say is Tom Ryder tried to make your arguments and Bussard showed that Tom was trying to apply tokamak conditions to a polywell to get those numbers, and the real numbers were much much lower. Evidently Nebel and the Navy think so too. EMC2 now has another 2 million in funding.
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Offline 93143

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #28 on: 05/27/2009 04:59 pm »
All I can say is Tom Ryder tried to make your arguments and Bussard showed that Tom was trying to apply tokamak conditions to a polywell to get those numbers, and the real numbers were much much lower. Evidently Nebel and the Navy think so too. EMC2 now has another 2 million in funding.

I'm not disagreeing with you; I'm just trying to correct some apparent misapprehensions.  Read my posts more carefully.

Also, it's Todd Rider, not Tom Ryder.

Offline go4mars

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #29 on: 02/01/2011 08:19 pm »
Also in the comments, Nebel mentioned that we should have a yes or no answer on this technology in 1.5 to 2 years. 

Any minute now...   

Hopefully this becomes a superheavy lifter in the next 5 years.  :)
« Last Edit: 02/01/2011 08:19 pm by go4mars »
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Offline Cinder

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Offline space_man

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #31 on: 02/02/2011 02:21 pm »
Please somebody explain to me how to channel alpha particles from a polywell reactor to form a jet without forming any instabilities at the bottom of the "well"?

Until somebody explains to me how to do that, I remain convinced that there is no clear way to make a thruster from a polywell reactor.

Offline Downix

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #32 on: 02/02/2011 02:57 pm »
Please somebody explain to me how to channel alpha particles from a polywell reactor to form a jet without forming any instabilities at the bottom of the "well"?

Until somebody explains to me how to do that, I remain convinced that there is no clear way to make a thruster from a polywell reactor.
Linear accelerator. Once particles become too heavy to suspend they drop and   are shot out.
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Offline kkattula

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #33 on: 02/02/2011 03:45 pm »
Actually the alpha particle fusion products have far more energy than the fuel ions. That is the whole point. So they leave both the potential well and the magnetic confinement PDQ.

For direct power generation, they would be slowed down by charged grids, outside the confinement. For a Direct Fusion Product rocket engine, their paths would be bent by magnetic fields until they all head in the same direction.

Offline Downix

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #34 on: 02/02/2011 07:46 pm »
Actually the alpha particle fusion products have far more energy than the fuel ions. That is the whole point. So they leave both the potential well and the magnetic confinement PDQ.

For direct power generation, they would be slowed down by charged grids, outside the confinement. For a Direct Fusion Product rocket engine, their paths would be bent by magnetic fields until they all head in the same direction.
Right.  A Polywell design lends itself for this very well.  We did a Fusor (earlier, primitive form of the concept) which did just this, giving us a Neutron jet.
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Offline 93143

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #35 on: 02/02/2011 10:25 pm »
And, of course, directly channeling the alphas is only necessary for outer-solar-system missions or interstellar probes, where you need Isp in the range of 105-106 seconds.  For SSTO, and for higher-thrust space drives useful as far out as Jupiter or possibly Saturn, you would use direct conversion of the alpha particles' energy to electricity, which would then be used to run an electric thruster like any other power source (though the high voltage does add a wrinkle; the engine design may need to take this into account).

Ultra-high-Isp applications aside, the Polywell's primary advantage in terms of space propulsion is direct conversion, which enables fusion-to-electric power conversion efficiencies of perhaps 70-90% and eliminates the need for a heavy thermal plant.  As a result, neither the power conversion system nor the waste heat radiators weigh very much compared with those required for a fission nuke of comparable power.  (In fact, for SSTO operation, the required Isp is low enough that it should be possible to use propellant to "regeneratively" cool the reactor and power conversion system, resulting in an effective conversion efficiency of ~100% and no radiators at all.)  Also, since the waste heat isn't at the bottom of a thermal cycle, the radiators can be quite hot, further reducing the required area as 1/T4.  In addition, a Polywell requires no fissionables, produces no nuclear waste (even neutron activation of core materials is insignificant if EMC2 is right about p-ııB), and could potentially have significantly higher core power density than a comparable fission reactor, at least in the GW range.

Assuming, of course, that they get it to work, and that p-ııB with direct conversion turns out to be feasible...
« Last Edit: 02/02/2011 10:32 pm by 93143 »

Offline space_man

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #36 on: 02/03/2011 02:19 pm »
Actually the alpha particle fusion products have far more energy than the fuel ions. That is the whole point. So they leave both the potential well and the magnetic confinement PDQ.

For direct power generation, they would be slowed down by charged grids, outside the confinement. For a Direct Fusion Product rocket engine, their paths would be bent by magnetic fields until they all head in the same direction.

Really? The alpha particle fusion products have more energy then fuel ions? Then explain to me how do the fuel ions get hot enough to ignite?

Observe the geometry of a polywell reactor, its is essentially a cube with ions leaving in ALL direction, un-preferentially. Now you saying you want to bend all the paths into a single tube using magnetic fields, good, but did you consider magnetic field penetration inside the polywell and the consequences from that?

Offline tnphysics

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #37 on: 02/03/2011 03:06 pm »
The fuel ions are moving fast. The fusion products, though, are still faster. That is how energy gain is achieved. You put some energy in, you get more out.

Offline space_man

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #38 on: 02/03/2011 05:13 pm »
The fuel ions are moving fast. The fusion products, though, are still faster. That is how energy gain is achieved. You put some energy in, you get more out.

I agree with that, except what you are talking about is a non-ignited mixture. From what I gather you guys plan on running a polywell reactor where you are not even using the energy released by fusion to heat the fuel to necessary temperature required by fusion, how is this a self-sustaining plasma? seems very inefficient.

Offline GraphGuy

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Re: Polywell Fusion: Path to SSTO and the Planets?
« Reply #39 on: 02/03/2011 05:15 pm »

Really? The alpha particle fusion products have more energy then fuel ions? Then explain to me how do the fuel ions get hot enough to ignite?


Because the byproduct of an exothermic reaction (chemical or nuclear) has more energy than the reactants?  Boron-proton fusion releases a good deal of energy.

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