Linac design considerations

[3l]

Hi Guys:

Under construction:

There are two kinds of linacs one needs to design for:

# 1 high voltage but low amperage
# 2 lower voltage but higher amperage

First thing to consider is the linac electrode spacing.
First you need to decide how many electrodes you might need.
I have filled pads of paper sometimes trying to strike a balance between electrode spacing and the length of the linac.
Some times you just go with the least of the bad.

The second consideration is space charge impeding the ion flow
If the electrode is too small.

When I design a linac , I pick a prefabricated glass oil cup then cut the ss electrode to the needed length.
I would rather go to the dentist than cut glass tubing again!
Fiddly ,messy, low workable parts yield plus blood transfusions.

Let's say for example our design voltage is 500 kv.
Lets say we will use 10 electrodes in a voltage drop method.
Then each electrode will carry 50 kv per section.
The gap size is determined by Paschen's Equation for spark discharge (This is where studying the Pspark pays off)....You want No discharge at all.
Vs = Pd
Minimum spark voltage Vs (kv)
P = gas densty (mbar)
d = gap distance in mm
If you don't do this
the tube won't accelerate properly or at worst case not at all.
You simply plug in the operating pressure and voltage of the stage to get the zero discharge value. Most linacs operate at 10^-6 Torr which is a hard vacuum.

Happy Fusoring!
Larry Leins
Fusor Tech

[jst]

Problem; isn't 10^-6T a little too hard a vacuum in a fusor environment?

At some point it would be nice if these linacs ran in a fusors vacuum circuit.