KitemanSA wrote:Hmm, I always pictured the ions as going much more slowly at max KE than the electron, maybe almost as slowly as the electrons at min KE. Does anyone know the velocities off hand?
Taken from Bussard's comments for WB6. With a potential well of ~ 10 KeV the electrons had a speed of ~ 1 billion cm/s or ~ 10 million M/s. The ions have the same KE, but the speed is KE=1/2 MV^2, so the velocity difference is ~ the square root of the mass difference. The deuterium ion has a mass of ~ 7200 times that of the electron so the speed would be ~ 1/85th or rounded down to ~ 100,000 M/s.
These numbers could be calculated directly, but I generally use my recollection of Bussard's statement. I'm uncertain though if he was using the average velocity, the maximum velocity, etc. so I consider the numbers ball park close and of course dependent on where the charged particle is in the potential well at the time.
In WB 6 with 100,000 electron passes before loss equates into a travel distance of ~ 20-30 KM and the lifetime was a few milliseconds. That works out to ~ 10 KM/ms or 10 million M/S average velocity for the electrons.
If you take statements of ~ 20 ms lifetime for the ions (read that somewhere) and multiply that by the average (?) velocity of 100KM/s, then the ion would travel ~ 2 KM. That would be ~ 10,000 passes in WB6. This is similar to what Bussard said was required for a chance for fusion to occur (50% chance, 90% chance?).
This can be compared to ChrisMB's number of ~ 300,000 KM travel distance needed (or at least my recollection of a few hundred thousand KM) in a Tokamak to achieve good chances of fusion. Using the density difference between the two machines of 100-1000X and the fusion rate scaling as the square of the density means that in the Polywell, the confinement time in terms of ion travel distance needs to be only ~ 1/10,000th the distance or less. That would be ~ 30 KM, or as little as 0.3 KM. This shows that the ion confinement claims are consistant with sucessful fusion rates - the all important Triple Product. Confinement times per fusion event is similar, though the raw numbers are way different. This does not include thermalization distribution differences and possibly confluence, which would only help the Polywell picture, and is reflected in Nebel's estimate that the Polywell is ~ 60,000 times as energy dense as the Tokamak- at least the current low Beta Tokamak. If someone can develop a higher Beta Tokamak the numbers would change accordingly, but the Triple Product is a constant.
Dan Tibbets
To error is human... and I'm very human.