## Thursday, August 2, 2007

### Electron Guns

I have been looking at the electron gun question. How to design them how many amps of current they have to deliver.

Electron Gun Power

Electron Gun Suppliers [pdf]

Electron Beam Welding Primer

Joel, aka Tony Russi had this to say at NASA Spaceflight about expected electron gun currents (edited slightly for clarity):

The drive current in amperes to balance electron losses:
Ia = (Eq x Npcc x Vcc / Ts) x 1/ Gmj, where
Eq = electron charge in coulombs i.e. 1.602E-19,
Npcc = average inside electron density per cubic centimeter,
Vcc = volume of Polywell in cm3 i.e. 1.4E4, (4 π r3/3 )
Ts = electron transit time in seconds across Polywell(R=15cm),
Gmj = recirculation-corrected confinement factor.

The formula describes electron motion in a Polywell. The factor Npcc x Vcc is the total number of electrons inside the Polywell. Dividing this quanity by the time for each electron to cross from one side of the sphere to the other gives the rate at which electrons hit the confining B-field at the edge of the well i.e. the rate at which electrons try to escape. Dividing these factors by recirculaing-Gmj is the same as multiplying by the probability of escape per electron, which gives the rate at which electrons escape. Finally, multiplying all that by the charge on one electron gives the rate of charge loss in coulombs per second. An ampere(A) is, by definition, equal to one coulomb per second.

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Joel/Tony - I think that is an excellent first cut!

A Spread Sheet to calculate electron current requirements. It is called Electron Rqmts.xlr