Dr Park speaking at University of Maryland on September 9th

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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D Tibbets
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Joined: Thu Jun 26, 2008 6:52 am

Re: Dr Park speaking at University of Maryland on September

Post by D Tibbets »

ladajo wrote:Here is further thought on Lawson Criteria for Polywell courtesy of Jaeyoung Park;

"In high β cusp, plasma confinement time is sufficiently long to satisfy Lawson Criteria without the need for non-Maxwellian distribution. "

Theoretically conjectured loss current per cusp by Grad and NYU team:

I e,i / e = π / 9 * n e,i * υ e,i * π(r e,i ^ gyro)^2

means: 0.5s confinement time for 100 keV electron with 7 T, 1m radius 6 coil cusp which is favorable for a net power device.

So what is:
- 100 keV e-injection: τ e ~ 0.5 sec per Grad for 1 m device (longer τ for larger size)

- β=1 condition, therefore plasma density of 1.2x10^15 cm-3 at 7 T magnetic field

- If Polywell can achieve 30% efficiency of converting electron beam energy to ion energy via electric potential, T ion ~ 30 keV.

Polywell nTτ ~ 1.8x10^16 keV s/cm3 > Lawson triple product of 1-10x10^15keV s/cm3
and, it is also noted that Polywell does not require alpha heating to achieve net power"
Again, just to add my two cents worth-

Confinement time to meet the Lawson criterion is long enough, but not so long that full Maxwellian thermalization is inevitable, thus the 'monoenergetic' moniker. It is almost a Goldie Locks situation.

The potential well depth is a product of two factors, The efficiency of electron injections and the resultant depth of the potential well relative to the injected electron energy. In WB 6 the potential well depth was reported ~ 80% of the electron energy/ voltage on the magrid. 10,000 Volts / 12,000 volts. What is less certain is the electron injection efficiency. In WB6 , if the injection efficiency was ~ 3% (from some BOE calculations I did in another thread(which may be erroneous), the final efficiency would be 0.03 * 0.8 or ~ 2.4 %. This is why I understand the electron injection efficiency is the big research challenge right now.


Not requiring alpha heating means no ignition contribution, no self heating, The alphas, and other high energy charged particles leave the system naturally through convenient cusps. Importantly, this also means that the confinement times , while adequate, are not so long- especially for these fusion products, that you have to actively extract this ash from the plasma. This is the extractor problem in Tokamaks, and it seems that this component by itself will be a Herculean effort to make work in a Tokamak. In the Polywell this consideration is nearly non existant.

The Polywell, based on it's physics, presents many fewer engineering challenges than the Tokamak and perhaps most of the other ignition based machines. Ignition implies that not only the fuel ions, but the fusion product ions are contained sufficiently for thermalization to occur between them. The Polywell avoids this whole can of worms, along with having other simpler (at least in theory) processes that that eliminate some of challenges of the Tokamak/ magmetized plasma based machines. The risks are thus reduced from a bunch of interrelated and often competing processes to only a few.

Or, at least that is my contention. Once the few major risks are addressed, you do not have this crowd of secondary considerations that might block the road. So, the risk assessment and perceived stage of development is a different beast.

Dan Tibbets
To error is human... and I'm very human.

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