Cold Cathode Electron Gun Mark I

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    1. P^2 - Paul 56 months ago | reply

      Looks like gas discharge. What's the pressure? (Rather, what's the electron mean free path?)

    2. nebarnix 56 months ago | reply

      Paul Its about 0.1 Torr. The mean free path is longer than you'd expect at this pressure for an electron. I will gather more data tonight. The pressure gauge was disconnected at the time of this experiment. Oops.

    3. P^2 - Paul 56 months ago | reply

      Well, that's just really cool.

      I know that filament temperature is important in EMs, since a hot filament imparts a wide velocity spectrum to the emitted electrons, which makes focusing harder. Is that an issue in a SEM? (lower resolution but also lower energy electrons) Does the cold cathode help?

      Also, I'm guessing you're low enough energy and fluence here that you don't have to worry about X rays, but if you're going above ~10 kV and a microamp then you should consider some kind of dosimetry and radiation protection.

    4. nebarnix 56 months ago | reply

      Paul Correct. I am sure that there are lots of drawbacks to the cold cathode design. However the largest plus is the fact that it can operate at such a low pressure. Its still not quite EnvSEM low, but it could be easily done given a differential pumping scheme.

      The voltage required to sustain arc ignition is about 12kV through a 10 meg current limiting resistor. Of course, the arc has a resistance so I'm sure the electrons are not that high energy. I also need to get a HV probe connected to the cathode to determine this.

      I'm sure I have a huge chromatic context here, that's ok though. At this point, I'm not trying to break any magnification barriers... And filtering can be accomplished using spray apertures to some extent.

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