Hello everyone, recently I recently started a project at my university in witch I will try to build an electron gun using some of their equipment, it needs to shoot electrons at a target material to study the emission of light using different machines like spectrophotometer ecc. the parameters for the build are: accelerating voltage variable between 0-30kV, it would be better to reach 50KV, but 30 are ok, high current is not all that important, so in the order of mA, deflection of the beam is not necessary because the target can be positioned where the electron goes, but it wouldn't hurt to have a way to steer the beam, more important is the collimation, that is necessary and important to achieve a more or less focused beam.
The first try I made was to take apart an old oscilloscope and extract the CRT tube from that:

and this is the complete system:

on the right the tube goes to a turbomolecular pump, that can reach 1*10^-5 mbar, my goal was to try and reuse the crt tube controls grid to create the beam and steer and collimate it using the already existing structure, but unfortunately, that is too complicated, also this kind of crt should normally operate at 1-2kV, so using this system at 7,10 or even 30 kV seems really hard, and also it uses an indirectly heated cathode, that from what I found can only operate at an anodic voltage of <5kV (https://www.r-type.org/articles/art-249.htm)
and also I don't know at which potential the collimating plate should be set, so I decided to change strategy:

I want to use this x-ray tube filament that came from a broken tube (the glass was broken in transit but the filament has continuity so should be ok) that should be made of tungsten, and I want to build a very primitive and as simple as possible collimating system, that should be electrostatic, if anyone has a clue on how to do magnetic collimation I'm open to that option too, but electrostatic collimation seems easier to me because I'm also building the high voltage power supply, it will be made of a zvs+ac flyback, going into a 4 stage + polarity CW multiplier, that will give me 5-40kV without many problems.
I tried to do some research on the topic but I have found only superficial instructions or extremely theoretical books, the only useful one is the following: https://sbe.org/handbook/fundamentals/Video/Video-Electron_Optics.pdf
I need specific construction/engineering information, like at which distance the electrode should be placed, at which potential, how many focusing plates and relative potential, how to calculate the focal spot ecc.
From what I understand, if the ratio of the voltage at which the different electrodes are placed with respect to each other is more or less constant the focal spot should remain the same, (in my case it is in the order of 20cm) so I was thinking of using different output from the voltage multiplier coming from different stages, to be able and achieve different voltages all at once, that can be changed by changing the input ac so that the ratio of the voltage is kept constant and so the focal spot, in this way I should be able to maintain the same focal spot varying the accelerating voltage, right?
so if anyone has any practical information on how to build such a focusing system I would be really happy to hear, and also if I made any mistake in the reasoning or principle please correct me;
Many thanks!

Hi everyone, today I will describe to you a very strange problem that happened to me while experimenting with a CW multiplier:
first of all, here is the circuit:

the CW multiplier consists of a 4-stage, negative output polarity, made of 30KV 10nF disc ceramic capacitor, and 2CL2FP 30KV 100mA diode.
The AC input uses a transformer that shouldn't go over 10kV and is driven by a ZVS with an input voltage of 6-30V.
With this kind of specs, nothing bad should happen because the diode and capacitor are rated at more than 3 times the voltage each stage should encounter right?
unfortunately no and here is what happened:
yesterday I was using a 1Gohm resistor and uA meter to measure the output voltage with respect to the input at the ZVS, everything was good until I reached 50/60KV, at that point I heard a high pitch sound and the voltage dropped catastrophically, after trying to bring it back on the voltage got to 20kV for a fraction of a second and then gradually decreased over 1/2 seconds.
Today I tried to replicate the experiment and filmed everything, the exact thing happened again, this is the video:
/>in the video, you can see me increasing the input voltage to the ZVS from 10V (which gives an output of 40kV) to 11V, when all of a sudden the normal sound changes, and the voltage drops, then you can see me trying to turn the system back on but it responds with a strange sound and a voltage drop.
in this video you can see exactly what is happening now and what happened yesterday after I got to the voltage at which the system broke down: />this is a photo of the CW multiplier and the measuring system:

The hypothesis I formulated yesterday evening was that maybe a voltage spike killed the diode?, it would not be the first time I killed a diode, but the one I killed in the past was because I was working very close to the datasheet limit voltage, this time I am using a diode rated for a full repetitive 30000V, and the AC voltage can't even jump a 5mm gap so this option is quite improbable.
Another option is overcurrent, but that shouldn't also be the case, because the diode is rated for 10A spike and 100mA continuous, and they were drawing 50uA, and also potted in epoxy.
so I am left with 2 options: the CW multiplier has acquired a mind of his own and is trying to communicate with us humans, or there is a very strange thing happening that I can't think about.
So I ask to you high voltage expert, if anyone has any idea or suggestion or anything at all please write it here so maybe this problem will be solved.
Thank you.

Hi everyone, I'm having some problems with my PSU which is a DPS5015, unfortunately, while building a new machine I placed the back ( ) of the board on a metallic surface, which made it act erratically after I saw that I fixed the problem by adding a plastic insulator behind the board to prevent this from happening, but now I have another problem when turning on the PSU, the screen light up but shows the following image that is not normal:

I discovered by trying that it is possible to exit from this only by long pressing all the buttons (V,A,set,ON) and it reboots and now shows the normal screen, but it is like frozen because it is impossible to modify the voltage or current regulation by pressing the relative buttons, so it is stuck on whatever voltage and current settings was before, another aspect is that I can no longer use the Bluetooth function because it won't show on my device, even if the Bluetooth module's led is blinking.
Besides this, it is possible to use the SET button, but not navigate through the menu because the A,V buttons do not work, and the ON buttons also work so it will power up with the fixed voltage and current regulation, which are unfortunately impossible to change.
If anyone with some experience with these kinds of power supply knows what is happening, I would be very grateful if they could tell me.