Electron gun- what's wrong here?

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
David Kunkle
Posts: 285
Joined: Thu Apr 17, 2014 4:43 pm
Real name: David Kunkle

Re: Electron gun- what's wrong here?

Post by David Kunkle » Wed Jul 20, 2016 9:28 pm

Thanks for all the info and suggestions guys. Filament should be hot enough-haven't had problems getting e-'s to flow anymore- some experience with that now. Usually I melt them if anything.
I've ordered the inverter Steven recommended and a 1M ohm resistor. Found an isolation transformer on ebay. I plan on using a couple extra diodes laying around from microwave ovens.

Steven's suggestion for adding a gas feed makes it all look an awful lot like his patent. Not worried about patent infringement? ;)

Doesn't appear that I need to hack up what I already built. There does seem to be a difference of opinion whether the extractor ring will do anything useful or just cause problems. Looks like I can simply rewire things and try it several ways. Worst case, cut it off and get it out of the way. I am aiming for a diffuse cloud of e-'s.

Thanks everyone.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford

User avatar
Steven Sesselmann
Posts: 2096
Joined: Thu Aug 11, 2005 1:50 am
Real name: Steven Sesselmann
Location: Sydney - Australia
Contact:

Re: Electron gun- what's wrong here?

Post by Steven Sesselmann » Wed Jul 20, 2016 10:02 pm

David,

Let it be known that I am totally over patents, the patent process which was originally introduced by governments to encourage inventors by giving them a 20 year monopoly, has been hijacked by lawyers and large corporations who can afford to pay them. My patent applications have all lapsed and serve no other purpose than to put a name to the idea. When it comes to the fusion business a 20 year patent is totally useless, it's a lifetime project.

One note on the ion gun I suggested, It gets very hot, in fact the ones I made had cooling ribs and a tungsten ring around the filament.

Steven

These are the two I made for the late forum member John Hendron "starfire", John was an electrical engineer and a great source of inspiration for me in those early days. The ion gun project was a joint project between me and John and we became great friends even though I never actually met him in person.
ion source.jpg
Ion Source
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

David Kunkle
Posts: 285
Joined: Thu Apr 17, 2014 4:43 pm
Real name: David Kunkle

Re: Electron gun- what's wrong here?

Post by David Kunkle » Wed Jul 20, 2016 10:28 pm

I thought I'd read previous posts where you didn't care for or think much of patents anymore. Didn't quite realize it's been almost 10 years and that it only went as far as an application.

Always wondered why you went to all the trouble with machining that large nipple and cooling fins. Now I know- also why you use something more robust like the magnetron filament. Right now I just need the e- source, but if I get to the point where I need an ion source also, I wonder how long a light bulb filament will last if it gets so hot. Maybe at least turn down the power to the filament as the whole thing heats up to avoid burning it out- or convert to a magnetron filament.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford

David Kunkle
Posts: 285
Joined: Thu Apr 17, 2014 4:43 pm
Real name: David Kunkle

Re: Electron gun- what's wrong here?

Post by David Kunkle » Tue Jul 26, 2016 4:40 pm

I have the inverter that Steven recommended in his hyperlink above. 2 things though:

1) Didn't exactly come with an instruction sheet. Need to check my wiring with you guys. In the photo, the 2 wires at the top are 5V DC input with the left labeled GND- using that as -/ground wire. The bottom 3 wires are output. The 2 on the lower left labeled out1 and out2 being used as 900V positive output to the 2 diodes. And the lower right wire is labeled GND- using as ground for the 900V. Is this close to correct?

2) The 2kv diodes are out of microwaves. When I hook them to my DMM, I get no reading either way on the diode setting and OL either way when checking their resistance. At least one of them came from a brand new unit. Are they both bad or does it have something to do with their voltage rating and the DMM? Wanted to check before I order new 1kv diodes off ebay.

Thanks.
Attachments
inverter 001.JPG
Last edited by David Kunkle on Tue Jul 26, 2016 5:18 pm, edited 1 time in total.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford

User avatar
Dennis P Brown
Posts: 1521
Joined: Sun May 20, 2012 2:46 pm
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: Electron gun- what's wrong here?

Post by Dennis P Brown » Tue Jul 26, 2016 4:57 pm

What you said about wiring the unit agrees with my nearly identical unit. And no, high voltage diodes do not work with std checkers but should work with that PS. You will likely need a voltage divider since 900 volts tends to be at the upper limit of most meters (and will likely fry the meter.) Check the FAQ's on how to check HV diodes; I put such a unit together and it works. Now, with my HV x-formers (NST) and polarized HV meter I just test the diodes the old fashion way (explosion any one? Yes, I wear safety glass and assume the diodes will blow.)

Aside: the picture looks like you wired both diodes together at one end? Not sure that is a good idea. Don't remember if those two outputs on the converter PS are supposed to be connected. I never did that with mine. These units produce no significant current so don't see the point of wiring the two outputs together anyway. Also, there is a reason these units are cheap - they will take little abuse and fry easily.

If the diodes are wired together, undo them and try measuring the voltage again.

David Kunkle
Posts: 285
Joined: Thu Apr 17, 2014 4:43 pm
Real name: David Kunkle

Re: Electron gun- what's wrong here?

Post by David Kunkle » Tue Jul 26, 2016 6:19 pm

Good to know about the diodes. I'll assume they're OK for now unless I can't get the right output from the whole contraption after I get the wiring correct.

As a matter of fact, the negative ends of both diodes are wired together, then the resistor would come after that. I was thinking the 2 outputs were out of phase AC, and the diodes would convert that to constant DC. Of course, now that maybe doesn't sound right in my head. :)

If that's wrong, where do the 2 diodes go?
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford

User avatar
Steven Sesselmann
Posts: 2096
Joined: Thu Aug 11, 2005 1:50 am
Real name: Steven Sesselmann
Location: Sydney - Australia
Contact:

Re: Electron gun- what's wrong here?

Post by Steven Sesselmann » Tue Jul 26, 2016 9:54 pm

David,

The USB ground crosses over to the ground pin on the HV side and the two HV pins are connected together.

If you use fast switching high voltage diodes you can get away with two diodes.

After that you just put in a 3KV capacitor and a load resistor and if you like another capacitor across after the load resistor as well.

I hope it's needless to say, "DANGER HIGH VOLTAGE" these little inverters look harmless but can bite you.

PS: When you rectify 900V AC the output potential increases to around 1400V DC

Steven
ccfl.png
Diagram
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

Rex Allers
Posts: 236
Joined: Sun Dec 30, 2012 8:39 am
Real name:
Location: San Jose CA

Re: Electron gun- what's wrong here?

Post by Rex Allers » Tue Jul 26, 2016 10:38 pm

David, what you are doing does not look reasonable to me. I didn't look back in the thread to figure out what you want to drive with this and I didn't find a link where Steven mentioned this inverter, but from the pic, it looks exactly like one I have, made by TDK.

These inverters were made to drive CCFL lighting. For reference about what's in them you can look for the topic "CCFL inverter" on Wikipedia.

I think you have it right about how you connected the 5V DC input. IF you make the 5 V adjustable (say 2 to 5 V) you can control the output voltage somewhat.

The two outputs you have connected are the part that is not reasonable. The transformer has one high-voltage secondary winding. The two blue things on the HV-end of the inverter board are caps (capacitors). One end of each cap is connected to one of the two output pins. The other end of the caps is tied together and connected to the x-former hv output. The caps are there to limit the drive to CCFL lights. In this case the board was designed to drive two lights but they both come from the same secondary wire of the transformer.

So for the best use as a generic HV supply, you don't want these caps in series with the output. You'll just be limiting the power you can get from the supply. You also only want one output since the two come from the same place anyway. You can solder a wire to the other end of one of the caps as your output, or you could jumper across one cap and use that one output pin. Or you could remove the caps and re-purpose them as filters on the other side of your diode rectifier. (With the caps removed, you'd need to jumper the HV across to one of the output pins or solder an output wire to the inside end of where one of the caps was removed.)

These inverters are switching supplies that run at 10's of kHz through the transformer. To rectify the HV efficiently you need fast diodes. I think most microwave oven diodes are intended for 50 or 60 Hz so they are not fast. Probably not a good fit for this application. The key diode spec is reverse recovery time. I think diodes for this kind of frequency would typically be about 80 to 100 nS trr.

One last thing. Most of these small inverters have low end of the secondary (output ground on this board) tied to the input ground. That should be fine, but I think on this one it is easy to isolate the two grounds so that the secondary is not tied to the input ground. If you look, I think you will see a GND jumper running very close to one corner of the transformer on the top of the board. Removing this will float the secondary side from the input ground.

I hope all that made sense.
Rex Allers

Rex Allers
Posts: 236
Joined: Sun Dec 30, 2012 8:39 am
Real name:
Location: San Jose CA

Re: Electron gun- what's wrong here?

Post by Rex Allers » Tue Jul 26, 2016 11:45 pm

I see Steven also gave a post about using this inverter, complete with schematic.

Since, in my last post, I talked about removing or bypassing the caps in the output of the inverter, I thought I would comment about Steven's circuit. His configuration, with two diode strings, is a voltage doubler. In this case the two caps on the inverter are put in parallel as the charge storage for the first stage of the doubler. That's a valid approach and doesn't require any hacking on the inverter board.

Steven also mentions using fast diodes, but the 1N4007's in his schematic aren't particularly fast; about 2 uS trr, I think. For this kind of application I ordered some surface mount BYG23M diodes from Mouser, a while back. They are spec'ed at 1 KV, 1.5A, 75 nS trr. Overkill on the current for this but pretty cheap, if I remember right. Maybe others have recommended part numbers to look for.
Rex Allers

David Kunkle
Posts: 285
Joined: Thu Apr 17, 2014 4:43 pm
Real name: David Kunkle

Re: Electron gun- what's wrong here?

Post by David Kunkle » Tue Jul 26, 2016 11:56 pm

Steven Sesselmann wrote:David,

The USB ground crosses over to the ground pin on the HV side and the two HV pins are connected together.
If you use fast switching high voltage diodes you can get away with two diodes.
After that you just put in a 3KV capacitor and a load resistor and if you like another capacitor across after the load resistor as well.
As far as the diagram goes- thank you, thank you. Now I know what the heck I'm supposed to be putting together. No electrical engineer here, but I can read that perfectly well!

As far as a 3kV cap, what farad rating should I look for?
Another cap across the load resistor will further smooth out the ripple?

Thanks.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford

Post Reply