Building Wehnelt power supply? High voltage DC in series with low voltage AC

Question

I am trying to build a power supply in the following wehnelt/electron source configuration:

• The high voltage power supply is a DC supply with maximum of 30 kV, milliampere current range.
• The filament current supply is an AC supply of only a few, certainly less than 20 V.
• To power the supplies, the electric grid is used.

Is it possible to build a supply using individual DC and AC power supplies in series? I would assume in general no as the grounds are connected. Are there however at least some tweaks which would allow building a supply? How is the issue resolved in professional electron beam supplies?

Answer 1

Is it possible to build a supply using individual DC and AC power supplies in series?

Yes, but the supplies have to be isolated and each section needs to be able to support high voltages (the filiment current supply would need to be isolated to 30kV), otherwise you could get arcing across an individual supply. When placing supplies in series its advisable to use the same supply. It would be better to use a single 30kV supply. The current also matters.

If this is your first 'go around' it would probably take a lot of trial and error to build your own supply.

As far as the wehnelt supply goes if you could find a way to isolate a DC DC converter that would work, but it would need to be isolated to more than 30kV

Answer 2

A typical implementation is a transformer with very high isolation. Here is a classic Tektronix example:

^{From: File:Tek-RM35A-HV-Section.jpg | TekWiki}

The high voltage transformer is a ferrite E-core, with single-turn windings wrapped around the outer legs. Wire with thick insulation or sleeving is used to achieve the necessary breakdown voltage (here, a few kV). The same approach, with 50kV rated wire, could be used for your application. If your system requires DC heater power, a rectifier and filter will also be needed (the vacuum tube rectifiers used here are perfectly happy with high frequency heater power). Since the load is consistent, varying the AC input will suffice for purposes of regulating output. Adjust for desired output, as measured with a meter while the high voltage is disabled.

Further details cannot be determined as you have provided nothing about the particular system (your question was more of a "does a proof exist" than "show me a proof", I guess).

Answer 3

The Van de Graaff generator I worked on had the power transferred from the ground to the 4 MV terminal via the rotating belt. This supplied power to the top deck as well as for the filament supply. The generator was from an aircraft and produced AC at 440 Hz.