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 Mario, very neat build, can you share the schematic for the filament supply circuit? also i was curious if you are able to modulate the current in the filament to control the x-ray hardness? In the past, I also tried to use galvanically insulated filament transformer to feed the glowing filament in the tube, with a small Chinese zvs module, but I found it very hard to control the filament current (and consequentially the HV current flowing in the tube) by varying the input voltage to the oscillating circuit.
Also more or less what is the power consumption of the HV system?

I don't want to be unkind, but may I ask why you want to produce something like that on a scale? currently, on the market there are plenty of these Chinese modules at low prices and high numbers, like the one you extracted the coil from, so what do you want to change from that? is there any particular feature you would add that would make it more original?
also, did you make the 3d X-ray photo? what apparatus did you use?

hi, thank you for your answer, the method you proposed to verify if the diode is overvolting is interesting, I think I will apply that in future build, maybe with a uA meter so it is easier.
regarding the diode overvolting being the problem I hadn't explained myself very well about the flyback voltage: the 0-10kV are P-P voltage, in fact I made this calculation: if the output is around 56kV, the input ac is 56000/4=14000vPP that is 5000v RMS, similarly if you calculate the flyback 12v in *2000/6=4000v, so that shouldn't be the problem or I am missing anything?

Hello everyone, thank you very much for the suggestions, yesterday I tried to add capacitance and it worked, unfortunately, I had only 50Hz capacitor for electric motor on hand, but I will now order some proper MKP capacitors and try with different values, for now, I had this result:
Vin=25v
Capacitance (uF)  Power consumption (W)
     0.45                5
     1                     10
     5                     100
with the 5uF capacitance, I could clearly hear sound coming from the transformer, this is a clear sign of the lower frequency, using my phone and a spectrum analyzer I determined the frequency to be around 8-10kHz.
Unfortunately, I had to lower the input voltage to 20V, because something happened with the electronic of the voltage regulator that doesn't make them to work properly, the following video shows the problem:
/>Maybe it is due to some high-voltage corona leaking, but I have insulated it very well and all the electronics are grounded so I don't know.
Anyway, I fixed the screen problems by restarting the two voltage regulator and proceeded to test with 20V at the input of the ZVS and now I still could hear the sound but there was no problem with the screens going crazy. With 20V at the input the power was at 50W.
I will do more testing after receiving the new capacitors and report the result.

Each multiplier stage gives a voltage equal to Vpp, which is 2.8 * Vrms for a sinewave. So 60 kV out (neglecting voltage drop from loadin) would correspond to 60 / (4*2. = 5.3 kV RMS, or 7.5 kV peak.

If I understand correctly, the problem is that the circuit is not drawing much power when you load the output of the multiplier? How are you loading the multiplier and what happens when you do so? Does the multiplier output voltage collapse? Does the transformer secondary voltage disappear?

yes exactly, the power consumption measured is not large enough compared to what it could and should be, I tried to load it with arcing through the air, with a gas lamp, and now I'm trying to use an x-ray tube as load, but the results are the same (low power), I don't think that the voltage out of the CW collapse, because it happened to me that the output high voltage arced over to ground as a result of poor insulation, I think that it wouldn't have happened if the voltage had collapsed

Hi everyone, I'm making this post because I can't solve this problem: I'm using a flyback transformer to feed a CW multiplier to get around 60kV, to power some vacuum tubes, but it is making me disappointed.
The problem is that the power output is always really low, lower than what it should be, the current setup is able to produce without any problem around 300-400W, but from the test I have made it won't go over the maximum at 30W, this is the setup:
DC variable power supply that powers the ZVS which then feeds a flyback transformer that produces around 15kV at around 30-60kHz and then gets multiplied by a 4-stage CW multiplier to around 60-70kV.
with 25v on the ZVS (the maximum allowable is 30V the minimum 10V), I get the best result (30W) to be safe I usually power with 25V, and at around 10v I get around 13W of power consumption, I tried a lot of tests, with a 3 stage CW multiplier, 4 stages and also tried only to play with the end of the flyback transformer itself, but the power consumption never goes above 35W.

is there something fundamental I am missing out on, or there is a problem with my setup?

I tried calculating the impedance of my CW multiplier at a frequency of 40kHz and 2.2nF capacitor I got 540kOHM, which at 60KV should give a current for 0.1A and a power of 600W which is not nearly close to what I am experiencing.
This is the schematic for the ZVS and also the CW multiplier before I put it in epoxy resin:


any advice is welcome, many thanks.

hi, I think that for your application a van de Graff generator or any other electrostatic generator might be better.
For example using a van de Graff you might be able to control very accurately the potential varying the speed of the belt in the machine, because the electric field and so the potential is in direct relationship to the number of charged ions contained in a given volume, in the atmosphere the charge accumulated by a Van de Graaff generator are naturally dissipated by the ions flowing away in the air, so you have a situation where you can control the total number of charge in a given volume by balancing the input flow of charge versus the output flow, if you want to raise the potential, the speed of the motor is increased, the rod accumulates more charge than what can leave and so the potential is increased.
This setup would be more stable in terms of ripple compared to the 30KV generator, but I think it would also be more useful because accurately controlling the flow of charge from a flyback transformer would be very hard, and even if you can do that you would be limited by the 30KV that is not that high compared to what you might be able to reach with an electrostatic generator.
can I ask for what kind of experiment you need this setup?

Hi, if the PSU transistor blows, then I am pretty sure you are encountering the same problem I had a short time ago, the problem was grounding.
The solution was earth-grounding (so connecting the negative side of everything to the same ground that then is connected to the building earth) so I connected the PSU and the voltage regulator negative to the earth of the PSU, (in my PSU only the chassis was grounded)after this all the problem with static electricity (the voltage regulator screen going mad), and the transistor blowing, disappeared.
You can find more information here: https://highvoltageforum.net/index.php?topic=2449.msg18037#msg18037 .
Just out of curiosity, what type of HV power supply are you using?

Hello, I'm making this post because I would like to hear your opinion about a problem I encountered today when I tested my homemade x-ray power supply:
I start by describing the schematic: it uses a switched mode power supply to transform the 220v to 24v, then regulator 1 makes it possible to regulate the voltage between 0 and 23v, for this test, I used 7v (this gives me around 30kV at the output of the multiplier), then the output goes to a ZVS driver which feeds a flyback that gets multiplied with 3 stages CW voltage multiplier, the output then goes to the x-ray tube, which itself is powered by a second regulator that emits few volts and around 2-3 A for the filament of the x-ray tube.
Schema2_230507_122610.pdf
while testing (see video below) the high voltage is turned on by pressing the push button with a stick as shown in the video, you can hear the high voltage hissing. No x-ray is seen on the fluorescent paper in front of the tube (this might be due to low high voltage or low current in the filament, but is not the problem) then after some time you can hear an explosion, that is some sort of component dying.
/>I checked and the main power supply doesn't work anymore, the lower left transistor (D13009K) haves some black residue near the base and by testing it with a multimeter it seems to be the problem.

I have checked the rectifier and it is ok, the model of the transformer is S-360-36.
The two regulators are reg 2: "ZK-4KX" , and reg 1: "DPS5015".
I didn't ground the negative side of the power supply and the other part of the circuit because I thought that there may be some problem with connecting the earth ground (that is connected to the chassis of the power supply) to the negative polarity of the different voltage regulators, mainly because by using a multimeter I have seen that the negative (input/output) side of the regulator doesn't have continuity so by connecting them I thought I might cause some problem (note that the earth ground of the chassis is not connected internally to the negative side of the switch mode power supply).
So this is my question: the reason for the transistor exploding is that I didn't ground the power supply? I can only think of this as an explanation, but it seems unreasonable, mainly because the power supply has the chassis earthed so it should act as a Faraday cage and protect the internal component from any static electricity.
Do you think that I should ground only the power supply, the supply and the 2 regulators and the CW multiplier or only part of the component?
if you have any other comments or suggestions I would love to hear that.