High Voltage properties at 350KeV (DC voltage)

[gee706]

Hi,

I'm working with a piece of kit which is used to accelerate ions in the manufacturing of silicon chips. We generate 350KeV using a high frequency power supply and a high voltage stack, basically a Cockcroft Walton Voltage Multiplier.

Bit of advice I'm looking for is based on the fact that the high voltage discharges to the ceiling of the enclosure when raised above 315KeV. The power supply, although rated to 350KeV, is only 0.5mA rated.

I'll try to explain using the photograph.



The red terminal above is approc 1.4m long, the main box section sits on the red insulators. From red terminal to floor (ground) is 74cm, from red terminal to side walls is 73cm, but red terminal to the ceiling (the ciling is grounded) is 65cm. We see discharge to the ceiling. So, may sound obvious that the ceiling is just too low, but can anyone justify with data to show that 350KeV and 65cm just don't match ? Or do they match ?

In addition to the ceiling gap being so small, I have 1 other thought. I've read about the bloke called Friedrich Paschen, whose Law (curve) proves the relationsip between HV breakdown and pressure. From the top of the red box to the ceiling of the roof, there is an extract pulling 2.9m/s which is required to extract toxic gas fumes.

My thoughts are "to raise the roof" (ceiling really) but I'd be greatful of any technical data that would justify my expense of doing so.

For interest, I have a youtube video of the high voltage discharge which you are free to watch and comment on.

https://www.youtube.com/watch?v=svQbKYvqMk4

 

[pepparz]

i understand the first ten words then i gets funny head hurt feeling

 

[Marvo]

Is it supplied by an inverter or directly from AC power?

Unfortunately I have very little knowledge of this type of equipment, is the output constant or pulsed? The only spark gap calcs I've been involved in are related to lightning strikes but I don't know if these would have any relevance to this equipment.

 

[Engineer54]

Why are you not asking these questions to the manufacturers that built and supplied the thing, instead of asking questions on an electricians forum?? Can't be that much of a process problem, as it seems you've been experiencing these discharges for nigh on a year now!! BTW what sort of high frequency are we talking about here??

 

[stitch]

Me too.

 

[DPG]

Bit specialised for an electrician's forum don't you think? Nice bit of kit though. Do you ever try any experiments with it (sitting in a faraday cage etc.) ? Daz

 

[gee706]

Hi Marvo,
Thanks for the reply. It is supplied from a power supply, the power supply generated up to 20KV at a high frequency, not sure, think around 60kHz. This 20KV is multipled through a full wave rectifying Cockcroft Walton, which charges at the first stage then passes to the next, eventually charging all stages to produce the 350KV. The red terminal that you see then sits at a potential of +350KV DC. What it does after that is irrelevant to the problem.

So, basically we need to drive the power supply to 350KV but when we reach 315KV, it arcs (jumps) to the earthed enclosure.

Thanks again for your help.

 

[gee706]

Why are you not asking these questions to the manufacturers that built and supplied the thing, instead of asking questions on an electricians forum?? Can't be that much of a process problem, as it seems you've been experiencing these discharges for nigh on a year now!! BTW what sort of high frequency are we talking about here??

Hi Engineer54,

I've asked these questions to the guy who supplied it but he's done his work and had his invoice paid and I'm left to try and sort it out now. The original manufacturer that built the kit 28 years ago no longer support it.
You're right about the timescale, Engineer54, we have about a dozen processes, the ones that operate at 50KV, 80KV, 100KV, 150KV etc are fine, there are just a few processes <300KV that we can't currently do. We've had multiple issues and we've also put the 350KV challenge on the back burner as our spare power supply was off to the repair shop - trying to running the system at 350KV can cause damage - so basically we've mitigated the risk by limiting our operations to 300KV. Pressure has been applied recently to go for the 350KV - hope that explains it for you.

 

[netblindpaul]

You are very confusing with your posts, you start off with 350 Kelvin electron Volts.
Now you are on to 50, 80, 100 etc. Kelvin Volts.
Are you talking about kilo Volts, kV, or kilo electron Volts, keV, can you please confirm what you are talking about and what you are trying to do.

 

[gee706]

Bit specialised for an electrician's forum don't you think? Nice bit of kit though. Do you ever try any experiments with it (sitting in a faraday cage etc.) ? Daz

Hi Daz,

Yeah, maybe too specialised for this forum, but at the end of the day I'm talking about high voltage (350KV DC) arcing. Surely a common theme with high voltage ?

Our approach to health and safety is such that there is no messing about or experimenting with this stuff, the closest we get is having the doors wedged open and the interlocks defeated, lights switched off - and stand back - so that we can see where the arcing is coming from.

Cheers,

G.

 

[Marvo]

Hi Marvo,
Thanks for the reply. It is supplied from a power supply, the power supply generated up to 20KV at a high frequency, not sure, think around 60kHz. This 20KV is multipled through a full wave rectifying Cockcroft Walton, which charges at the first stage then passes to the next, eventually charging all stages to produce the 350KV. The red terminal that you see then sits at a potential of +350KV DC. What it does after that is irrelevant to the problem.

So, basically we need to drive the power supply to 350KV but when we reach 315KV, it arcs (jumps) to the earthed enclosure.

Thanks again for your help.

There's many variables in this environment that would encourage arcing. This arrangement sounds like a fairly standard particle accelerator so the immediate one that would spring to mind would be background radiation causing avalanche and dielectric breakdown. If this issue has been persistent for a long time I assume you've already done most of the obvious diagnostics and tests so I'm not sure you'll get much meaningful assistance from here.

 

[gee706]

You are very confusing with your posts, you start off with 350 Kelvin electron Volts.
Now you are on to 50, 80, 100 etc. Kelvin Volts.
Are you talking about kilo Volts, kV, or kilo electron Volts, keV, can you please confirm what you are talking about and what you are trying to do.

Hi netblindpaul,

Sorry for any confusion.

Not sure where you get the kelvin electron volts from ? kelvin being a measure of temperature is nothing to do with this.


I am talking about KeV, sorry for using abreviations, but it's Kilo electon Volts.


Just to clarify for you, netblindpaul, our piece of kit runs a dozen different processes. The red terminal in the original post is energised to a certain level of energy (KeV's) for the proocess. The maximum capability is 350KeV, and we can't at the moment achieve 350KeV as it discharges as per the youtube video at 315KeV.

We can set the red terminal from anything between 0KeV and 350KeV.

Some processes only require 50KeV. These can run no bother. Sorry for making it sound confusing.

We can command the red terminal to 150KeV, 300KeV, but when we command 315keV or over, we have arcing.

Guess it's like having a car that should do 120mpg, but can't get over 90mph. It can drive at 30mpg, 50mph, 80mph,. ....... do you now get it ?????????

Thanks anayway for your support

 

[Marvo]

I think Paul is picking up on the fact the capital K is Kelvin, small k is kilo so your thread title would suggest ....

 

[gee706]

There's many variables in this environment that would encourage arcing. This arrangement sounds like a fairly standard particle accelerator so the immediate one that would spring to mind would be background radiation causing avalanche and dielectric breakdown. If this issue has been persistent for a long time I assume you've already done most of the obvious diagnostics and tests so I'm not sure you'll get much meaningful assistance from here.

Hi Marvo,

Actually, biggest factors are humidity, surface condition (sharp points are bad, large radius are good), obviously the gap, dust, particles.

I've just asked the forum incase there is someone out there with experience that might provide me with data on High Voltage (DC) versus gap (distance).

Anyway, nothing ventured, nothing gained.

The kit is so old, although new to us, I think there were only about 50 of them made and less than 6 still in use, so getting support is impossible.

bye

 

[gee706]

I think Paul is picking up on the fact the capital K is Kelvin, small k is kilo so your thread title would suggest ....

Thanks for that clarification, Marvo. I stand corrected.

Thanks for educating me, Paul. I was unaware the it was keV and not KeV, but there you go, every day is a school day.

 

[Marvo]

Thread cleaned up and moved to DIY forum