Science/Engineering/Technical forums

OK
I whet the whistle with what i was doing on the water cooler
but it has dissappeared
The following pics are of the modified system that can go to 100kV+ with plenty of mA
x-rays are a real hazard with measured values in the many
100s of mSv/hr
A radiation wall of concrete filled cinder blocks has been constructed. Interesting to note the wall works very well but turning the detector with its sensitive face upwards gives us around 150uSv/hr being reflected (backscatter) off the roof. The new spellman supply STR series 150kV @ 40mA is remote controllable, although the supplied software is extremely clunky with a mind of its own. So we will set up and enable the supply then make ourselves scarce while we wind up the voltage remotely over the ethernet connection to the supply. Only 1 high voltage breakover outside the tank so far and alot of work to clean up the charring of the big plastic insulator.
We have a camera inside the terminal area that is repeated on the 19" monitor at the control console so we can check on arcs etc
pics are of the system into the view port @ 33kV and then 90kV note the plastic is trying to track internally
The vertical stack of resistors in the centre of the outside pic is the ballast resistors 150k ohms
enjoy

Nice stuff! Yeah, once you get over about 60kv, funny things happen with electricity in air...it stops doing the obvious, and I've personally seen arcs over 10' long that made u-turns in mid air at 125kv. It gets into "big boy" stuff really quick. All it takes is for a small "streamer" to form, then it works like lightning - it follows it's field-emission "nose" through cosmic ray tracks, dust, you name it. And here I am about to commission a 100kv supply...the first 100k of ballast will be in the supply and under oil - I use 225w cartridge WW resistors that are about 11" long per 50kv - that's about what they'll hold off without arcing between the turns internally in the event of an arc outside them. And since the cable itself has enough capacity to store some energy, some of my ballast is right at the feed through point, after those few pf's of stray, to really limit the peak current in an arc (destroys grids in my fusor if I don't). Even then, I have around 50 pf just in the feedthrough/grid - doesn't store much energy, but it's such a "high quality" capacity that it can still make peak currents that will blow pits in metal, which tend to wind up in general failure (now I have sharp-point field emitters due to the ridge at the edge of the pit).

I wasn't able to easily determine what your ballast looks like from the pics, maybe you need to add some words there.

Being a moderator, if you want something to stay around on the water cooler, just make it "sticky". It applies to the whole thread you do it too. I created that one at the suggestion of Carl Willis as a way for us to have some fun, but not have it hang around to be embarrassing or confusing later on, for most things. But now and then we get up to something worth keeping, and one of us mods has to decide to do that and mark a topic sticky for that to happen. Every thread in every other forum here is "permanent" unless the ISP fails, or a mod for some reason decides to wipe it out.

Doug

okay the ion source is held on the 8" CF in the centre of the plastic insulator
red arrows are the input ballast resistors
the green arrow is the input end from the Spellman

Got it. Looks like you use the same type ballast R's I do here. Great big honking WW resistors that are long enough to not arc over in the event of a short (arc) on the other end of them. As you know (but not everyone has been here like you have) I have to fan-cool mine. That also seems to make arcs a bit less likely, as ozone can't build up as easily.

I admit to a bit of surprise you're not having "lightning" right off the top end, though, at 100kv - I have when I have something that "pointy" and that much voltage, and they can be really scary and NOT go to the nearest ground, but all around the shop on the way. Well, my scary incident happened at closer to +125kv, but you're in the range, I believe.

Doug
Yes
check pic three very carefully ie in the monitor pic there are now corona rings on the resistors to mitigate corona a drop of 2 mA @ 85kV

merry xmas
hope you are warm

Hi John,

I just caught up on this thread, nice big chamber, are you doing this at work?

What is the significance of the grid shape?

Steven

OK
Massive changes
to get rid of x-rays I have now put in an accelerator section so the chamber only sees the first accelerator plate in the accelerator tube.
This equates to about 15kv when the ion source is at 100kV.
X-ray flux has reduced by a factor of a couple of thousand and now is around 100uS @ 65kV 2Ma of ion current
It has worked, corona is now down to a few uA @ 105kV the standing current is from the resistors setting the acceleration plate voltages ie 8 x 50 meg Vishay high voltage resistors.

Been up to 65kV with a 2mA ion beam and we will have to decrease the acceleration section resistors as too many ions are hitting the first plate changing its voltage too much causing a few little zips back to the ion source on the outside

Elliot my summer student has been a terrific help . Just show what I want and its done yehah

Tee hee...I'm just waiting for you to fire D's at a target with that baby...2ma @ 100kv showed on the order of a million neuts/second per microamp for a frozen heavy water target for Phillips in the '50s sometime...that would be quite serious at 2k times that! The X rays (really, gammas) from the neut capture alone would get darned loud.

Doug

that may be on the agenda after we get what this has been setup for
Another pic
Here we are running a 5mA beam @ approx 90kV
We have increased the accel section current to control the accel plate voltages better no zips between plates
the funny red light is rad warning not good to stand around toooo long

The funny blue line on the monitor I put down to Philips monitors not handling a few rads

It's funny that it's a vertical line. Is there rotation going on at either end? Most monitors scan horizontal, as do most cameras. I could see taking out a line (one transistor) easier.
I gotta get me a gamma spec going soon again. The thing with simple geiger counters etc is that you don't get the energy of those rads. They might be a lot lower than the 100kv or so you put in by the time they scatter off air, bricks, etc and get to your sensor. It'd be nice to know the *actual* energy that's leaking.