Fusion Paths Not Taken -3

Outlier LPP proposes Dense Plasma Focus and the hardest fuel!  Do they really have a chance?

In these final two posts, we discuss proposals that use magnetized target fusion ideas but both have the goal using p-11B fuel at successful start up.

We  discussed p-11B, earlier.  It generate 3 alpha particles (helium nuclei) and no neutrons; but it demands temperatures in the billions of degrees and it has a much lower probability of fusion-per-collision than either D-T or D-3He, the other commonly considered fuels.

There is a lot of skepticism in the fusion community relating to these two small companies. Each deserve its own discussion. Click any image to see its full sized version.

LPPF SpecificationsLPPF                                                      p-11B
Eric Lerner
DPF fusion, Focus Fusion power

Eric Lerner

Fig 1: Eric Lerner with the FF-1

2014 Dec 24 :  LPP announces pending name change to LPPF, initials only.  Currently, its web page is unchanged.

Dr. Lerner has been on the DPF quest for many years, and assembled his LPPF company for a realistic try at making an FF device operational.  His test bed is called FF-1.     Image source   AAAS

Hamad Yousefi

Fig 2: Hamid Yousefi

Lerner recently brought in Dr. Yousefi as his Chief Research Officer, After nearly a decade of interactions.  Yousefi, from the plasma research organization in Iran, had spent much effort in computer simulation of DPF operations and had influence the FF-1 design.

Dense Plasma Focus has been discussed in physics literature since 1957, but still is not well understood even by many technical people.  Laboratory plasma focus tests use the plasma guns similar to those of Hyperon Energy and HyperV Technologies (our discussion here) but optimized to tightly focus the discharge.

How a DPF works

Fig 4:  How a DPF works  (A)=3B, (B)=3E

DPF from fr.Wikipedia

Fig 3:  How a DPF works. Compare  (B) = 4A,  (E) = 4B

Fig 3 is from the French edition of Wikipedia.
Fig 4 is a composite from the LLPF website

3A A capacitor switches a high voltage across a hollow cylinder (cathode) and a central rod (anode), causing an arc between electrodes.  (LPPF uses a circle of rods for its cathode.  The LPPF anode is a rod with a central cavity to accept the jet from step 4D.)

3B, 4A The arc accelerates up the cavity, rotating about the central rod.

3C At the outer end, the arc focuses toward the anode.

3D The central discharge focus inwards to the 3E, 4B  twisted linear arc.

4C Chaotic instabilities in the focused line generate the knotted blob that lasts tens of billionths of a second and generates conditions for fusion.

4D Twin jets are emitted from the blob, electrons stream inwards, ions stream outwards, to be captured by a deceleration solenoid.

In 2012, Lerner and colleagues published a paper in a well respected journal that shows data from FF-1 where the knot reached temperatures in the range needed for p-11B fusion,  1.2×109 K,  1200 million Kelvin.  If accurate,  this is a milestone step.

There have been negative comments since early days in DPF proposals.  These are from physicists and not all are due to funding competition or envy.  Some of Lerner’s text is hard to follow and sometimes the notation is not explained or self evident.  Classify these as physics fights.

Physics fights are about as interesting for an outsider to watch as a food fight at a grade school dining hall.  If you are really trying to understand the DPF promise, though, such arguments matter.

Nevertheless, you have my permission to skip down past Comment 4.

Comment 1:  Symmetry Matters

Alignment and symmetry are crucial in DPF as it is in all implosion schemes.  Lerner admits on his web page that he has alignment issues. It sounds as though this is well understood.

Comment 2:  Survival of the fusion device

The collapsed fusing spark at the end of the DPF cycle is on surface of the material device anode tip.  When fusion micro explosions occur at NIF, the chamber is in a hard vacuum with materials far from the fusion spark.  This is to isolate the structures from explosive overpressure and fusion temperatures.  I do not see how any DPF could survive a single power generating fusion spark, especially at the temperatures required by the fuel.  Survivability for extended pulses as a problem implies successful completion of testing. LPPF would be happy to have this one.

Comment 3:  Thermalization and Quantum Magnetism

The fusion snap of the DPF spark in Fig 4C lasts about the long as the 10-20 ns laser blast at the NIF laser facility. This is the time that the fusion event will take place.  Although this sounds short, there is plenty of time for thermalization to happen.

So:  is the focus plasma near thermal equilibrium?  If so, the ions and electrons would exchange energy and temperature – heating to the billion degrees would be that much harder.

Lerner says NO.  He invokes what he calls  Quantum Magnetism to say the snap will never be in equilibrium – so equilibrium arguments need not apply.

His discussion compares the electron’s Larmor (gyro) orbit about the magnetic field with the electron’s de Broglie (quantum) wavelength.  When gyro shrinks to the quantum, the electron will not absorb any more momentum from an ion and will not drain power from the ion distributions. I believe that Lerner says that when   λquantum = Rgyro, ions that hit an electron cannot heat it because the gyroradius would have to become smaller than the probabilty distribution that is the electron.

Lerner estimates self-generated magnetic fields need to be 10 G Gauss [same as 1 M T in mks metric units … G means “thousand million” or U.S. “billion.”  T stands for tesla and 1 T is 10,000 Gauss. Compare: a compass needle is moved by  Earth’s field of ½ Gauss.]

Apparently FF-1  has not yet generated this monster field, but expectations are high for the device after the current upgrade is complete.

Physics point A:   LPPF’s  huge B value is much too small.

Back-of-Envelope indicator-only estimate when  λquantume = Rgyro  has
B = 2(m/e) kT/h  (standard physics symbols.)
For the magnetic field B = 1 M T,  electrons should be not much hotter than 4 Million K, about the temperature of the surface of the sun, nowhere near temperatures of p-11B fuel.  I have to admit that the solar cold shocks me.

Point B  – Momentum is a vector not a value. This result is only a rough estimate.

Part of the momentum causes the electron to gyrate about the magnetic field but the rest (the parallel part) moves it along a field line. The above simple formula assumes the non-parallel momentum is the same as the total. But the estimate could be off but by a factor closer to 1 than 10. Also, it is a semi-classical estimate, does not use full quantum mechanical equations, might be off again by a small margin. No matter.  Squeezing the perpendicular gyration to 0 would not affect kinetics in the parallel direction

Inhibition for the non-parallel part will not inhibit parallel momentum exchange and thermalization should take place.  Further, ion-electron collision can cause “pitch angle” scattering where gyro velocity converts to parallel flow velocity which will thermalize with the ions.    maybe I am missing Lerner’s argument?

 Comment 4:   p-11B Fuel

We will discuss this at the end of our next post. It is another controversial issue.

Final comments on DPF and LPPF’s work

click for our list of other fusion strategies

LPPF has built a prototype plasma focus device and have published interesting results. They are looking for funding to move on the the next step. They think that all they need is what one can get from internet crowd sourcing!  This is a technology has been studied by only a few labs about the world and has yet to reach acceptability.  My prediction:  unknown effects lay in wait for the researchers and LPPT will need more funding than they expect.  Only time will tell.

The baseline truth in Focus Fusion will lie in FF-1’s ultimate performance and repeatability, independent of all the physics arguments made before the fact.  Lerner knows there are problems ahead, he can point them out. But what he does not know are the unknowns he cannot point out.  If we only knew what we don’t know, wouldn’t life be easier?

Eric Lerner is an irritating guy.  He believes in his own work, he does not believe the Big Bang happened, he does not believe the universe is expanding.  I would bet he does not believe that the light speed is the maximum velocity Relativity allows!  He sounds a lot like today’s version of Nikola Tesla.   …  are we wrong and is he right? (Maybe with a communication problem?)   The physicist in me does not believe the FF idea before the fact and really does not want to fuss with it.  But reality wins in the end, and the panoply of human beliefs do not matter;  so the romantic in me urges him onwards.

……………………………….

Charles J. Armentrout, Ann Arbor
2015 Jan 2
Listed under Technologya post in the Fusion-Other thread
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About LastTechAge

I am a physicist with years of work in fusion labs, industry labs, and teaching (physics and math). I have watched the tech scene, watched societal trends and am alarmed. My interest is to help us all improve or maintain that which we worked so hard to achieve.
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