Hi Carl:
I use freon bottles with the bottoms cut off as shatter shields.
I like to use both of my eyes!
Nothing says pain like glass shards.
Good advice Carl.
Safe fusoring!
Larry Leins
Fusor Tech
glassman hv supply
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Richard Hester
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Re: glassman hv supply
I would not use a glass chamber fusor in the continuous mode over about 20kV. Scott Little used a 6" conflat tee for a fusor chamber, and got a smattering of neutrons. As far as I know, he was the second one after Richard Hull to do this. Even at the lowly potential of 20kV, he had the problem of e-beams trying to make toast of his expensive conflat window, and had to install a grounded screen to fix this. I think there is a link to his site from Richard Hull's high energy hobby site, which can be reached from the "newbie" section of the forum. While you're there (if you haven't already) print out the two Tom Ligon fusor articles. They are full of vital information.
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Adam Szendrey
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Re: glassman hv supply
I just blew a hole in a lightbulb, by connecting it to my Tesla coil and putting the ground wire near the glass. A bright strong purple beam attacked that point of the glass wall , and in a moment a bright white glow appeared there and BANG! So that was what i was missing, that glass cannot be used at really high voltages, or only with certain safety measures.
Adam
Adam
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jlheidecker
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Re: glassman hv supply
Thank you everyone for your replies. This has brought up a few
more questions:
1) What is the problem with the electrons "seeing" the plastic cup?
Does charge build up and then alter the electric field?
2) Larry, how thick is your metal can? A couple millimeters thick
should do the trick right?
3) What causes these stray electron beams? They seem especially
odd to me since I am using a glass (insulator) bell jar. I mean, current
isn't flowing through this bell jar, so it seems charge should buildup
and then repel these beams. It's also hard for me to understand how
they make it out of the grid. Shouldn't they be attracted to the grid
and then go to ground?
It seems to me that Larry's idea of a metal can inside between the bell
jar and the grid should solve the problems of x-rays and glass
melting. The metal can will carry the electrons to ground, as well as
shield x-rays.
more questions:
1) What is the problem with the electrons "seeing" the plastic cup?
Does charge build up and then alter the electric field?
2) Larry, how thick is your metal can? A couple millimeters thick
should do the trick right?
3) What causes these stray electron beams? They seem especially
odd to me since I am using a glass (insulator) bell jar. I mean, current
isn't flowing through this bell jar, so it seems charge should buildup
and then repel these beams. It's also hard for me to understand how
they make it out of the grid. Shouldn't they be attracted to the grid
and then go to ground?
It seems to me that Larry's idea of a metal can inside between the bell
jar and the grid should solve the problems of x-rays and glass
melting. The metal can will carry the electrons to ground, as well as
shield x-rays.
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Richard Hull
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- Real name: Richard Hull
Re: glassman hv supply
Electron beams are every where in a fusor. About 12 to 15 in every fusor with a 5 wire geodesic. In poorly pumped fusors or fusors just shy of Star mode pressures, there always seems to be a single very very hot E-beam that will literally bore a hole in metal!!
We are talking continuous operation fusors here, not pulse mode jobs where the peak power can be in the megawatt range but the average power due to duty cycle is actually far less than that of a small average demo fusor. It is total, average, disappated power that heats glass and gives x-ray and neutron dosages.
I have run fusor I as a Nalgene desicator and it worked great up to 10kv absolute limit. Fusor II was a pyrex bell jar and I ran it up to almost 20kv to do the very earliest and tragically weak fusion, just to show it could be done. However I really didn't like to run the glass item over 12-15kv MAX! I would set an absolute limit on the glass item of 20KV PERIOD!! Fusor III was a nice stainless device and It got too hot to touch at 35KV and was doing fusion just fine. I found that at 38-40KV X-rays were starting to actually be detected through the casing!! Stainless is the ONLY material a serious fusor must be made from. The thicker the better with .050" thickness being a minimum. Fusor III was .060 thick. 304 SS is the preferred alloy as most vacuum fittings are made of 304 SS and welding is much easier with matched materials.
Glass WILL implode if you run the fusor over 20KV and the X-radiation will fry you as well. Nice fusion can be done between 25 and 35 KV in a .060" thick 304 stainless sphere with no x-ray shielding needed. ANYONE WORKING A CONTINUOUS FUSOR IN A GLASS SYSTEM OVER 20KV IS OPERATING AT THE PLEASURE OF GOD, THE FATHER, IN ITS CONTINUANCE.
If, as you say, you have a totally committed desire to go to 70kv, you absolutely MUST use stainless, preferably thick stainless, and provide a significant LEAD X-ray shield around the device as well. If you plan on a lot of fusion runs per week and a lot of time in the vacinity of the device, you will also need a separate borate/parafin neutron shield as well.
Richard Hull
We are talking continuous operation fusors here, not pulse mode jobs where the peak power can be in the megawatt range but the average power due to duty cycle is actually far less than that of a small average demo fusor. It is total, average, disappated power that heats glass and gives x-ray and neutron dosages.
I have run fusor I as a Nalgene desicator and it worked great up to 10kv absolute limit. Fusor II was a pyrex bell jar and I ran it up to almost 20kv to do the very earliest and tragically weak fusion, just to show it could be done. However I really didn't like to run the glass item over 12-15kv MAX! I would set an absolute limit on the glass item of 20KV PERIOD!! Fusor III was a nice stainless device and It got too hot to touch at 35KV and was doing fusion just fine. I found that at 38-40KV X-rays were starting to actually be detected through the casing!! Stainless is the ONLY material a serious fusor must be made from. The thicker the better with .050" thickness being a minimum. Fusor III was .060 thick. 304 SS is the preferred alloy as most vacuum fittings are made of 304 SS and welding is much easier with matched materials.
Glass WILL implode if you run the fusor over 20KV and the X-radiation will fry you as well. Nice fusion can be done between 25 and 35 KV in a .060" thick 304 stainless sphere with no x-ray shielding needed. ANYONE WORKING A CONTINUOUS FUSOR IN A GLASS SYSTEM OVER 20KV IS OPERATING AT THE PLEASURE OF GOD, THE FATHER, IN ITS CONTINUANCE.
If, as you say, you have a totally committed desire to go to 70kv, you absolutely MUST use stainless, preferably thick stainless, and provide a significant LEAD X-ray shield around the device as well. If you plan on a lot of fusion runs per week and a lot of time in the vacinity of the device, you will also need a separate borate/parafin neutron shield as well.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Carl Willis
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- Real name: Carl Willis
- Location: Albuquerque, New Mexico, USA
- Contact:
Re: glassman hv supply
Hi Jason,
1)Electrons that hit the cup at high energy will vaporize plastic. This will ruin the vacuum (you'll see pressure rise and the discharge will turn dark bluish gray).
3) The electron beams are just the result of accelerating electrons "backwards" through the same field that accelerates the positive ions into the center. Plenty of electrons are liberated in the central region of the inner grid and these will gain full energy after falling through the field. The accelerating electrons are formed into rather narrow beams by the holes in the inner grid. In your picture of the bugle jet (nice photo by the way), a major electron beam is responsible for the heavy ionization that makes the bugle visible. The beam is on the bugle's axis. At 60 kV, there'd be a glowing bubble forming in the bell jar where the axis of the beam meets it.
The metal can idea will solve the big problems and is a good suggestion. It will cut down on x-rays. Surely it will protect the bell jar. At 60 kV with an estimated kilowatt of thermal power to dissipate, it will be getting very hot--I still recommend you don't plan on going that high. Make sure it covers the "top" of the grid system so electrons don't strike the upper parts of the bell jar. You could probably cut a small window in it somewhere so you can see in. Your grids are very well made and you'll probably get a good bunch of neutrons from the apparatus once you get the pressure down, the deuterium in, and the plastic out.
-Carl
1)Electrons that hit the cup at high energy will vaporize plastic. This will ruin the vacuum (you'll see pressure rise and the discharge will turn dark bluish gray).
3) The electron beams are just the result of accelerating electrons "backwards" through the same field that accelerates the positive ions into the center. Plenty of electrons are liberated in the central region of the inner grid and these will gain full energy after falling through the field. The accelerating electrons are formed into rather narrow beams by the holes in the inner grid. In your picture of the bugle jet (nice photo by the way), a major electron beam is responsible for the heavy ionization that makes the bugle visible. The beam is on the bugle's axis. At 60 kV, there'd be a glowing bubble forming in the bell jar where the axis of the beam meets it.
The metal can idea will solve the big problems and is a good suggestion. It will cut down on x-rays. Surely it will protect the bell jar. At 60 kV with an estimated kilowatt of thermal power to dissipate, it will be getting very hot--I still recommend you don't plan on going that high. Make sure it covers the "top" of the grid system so electrons don't strike the upper parts of the bell jar. You could probably cut a small window in it somewhere so you can see in. Your grids are very well made and you'll probably get a good bunch of neutrons from the apparatus once you get the pressure down, the deuterium in, and the plastic out.
-Carl
Re: glassman hv supply
If you want to operate at 60kV or higher, you will need stainless steel in the thickness of 1 cm, or thicker. This is what we use to shield 65 kV, 30 watt ebeam tubes. We also verify they are undetectable above background from about 2 KeV. I personally, would be quite uneasy operating a .050" thick fusor shell at above 40 kV without measurements and probably some external shielding.. Especially if you are thinking of mA levels or higher.
Actually, a couple mm of lead is a quite practical shielding material, for the amateur. Probably more so, than the very thick stainless steel, particularly for spherical shapes.
No one should be operating these devices above about 10 kV without a decent Xray detector. Low energy xrays are a serious skin cancer hazard, and the high energy xrays can penetrate quite deeply. Below about 10 kV, most health physicists are not too worried. We use the Monitor 4 rad detectors which use the LND mica window, halogen quenched Geiger tube detectors. We have verified these will detect 1.5 KeVxrays. The units run about $400 new..
Dave Cooper
Actually, a couple mm of lead is a quite practical shielding material, for the amateur. Probably more so, than the very thick stainless steel, particularly for spherical shapes.
No one should be operating these devices above about 10 kV without a decent Xray detector. Low energy xrays are a serious skin cancer hazard, and the high energy xrays can penetrate quite deeply. Below about 10 kV, most health physicists are not too worried. We use the Monitor 4 rad detectors which use the LND mica window, halogen quenched Geiger tube detectors. We have verified these will detect 1.5 KeVxrays. The units run about $400 new..
Dave Cooper
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jlheidecker
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Re: glassman hv supply
What if I use a glass belljar as a vacuum chamber, but then place a
thick stainless "can" or whatever inside the bell jar? Won't this
prevent the electron beams from frying the glass? And also shield
some x-rays? I could even use lead shielding outside the bell jar if
necessary.
thick stainless "can" or whatever inside the bell jar? Won't this
prevent the electron beams from frying the glass? And also shield
some x-rays? I could even use lead shielding outside the bell jar if
necessary.
Re: glassman hv supply
Hi Jason:
If you really want to go that way.
You will have to cool the top electrode in order to prevent the
red glowing can to soften the vacuum seal where the feed through enters. All my in can fusor units are a bit different from your setup.I have a bell jar with an entry hole in the top of it.
My grid is bottom fed from a conflatted 1500 amp 20 kv
cerma seal insulator. That way I can work the vacuum without the threat of electricution.
If you want to see it in the flesh...I will be bringing the Kenmore 4 fusor to Richard's HEAS meeting in October.
Safe Fusoring!
Larry Leins
Fusor Tech
If you really want to go that way.
You will have to cool the top electrode in order to prevent the
red glowing can to soften the vacuum seal where the feed through enters. All my in can fusor units are a bit different from your setup.I have a bell jar with an entry hole in the top of it.
My grid is bottom fed from a conflatted 1500 amp 20 kv
cerma seal insulator. That way I can work the vacuum without the threat of electricution.
If you want to see it in the flesh...I will be bringing the Kenmore 4 fusor to Richard's HEAS meeting in October.
Safe Fusoring!
Larry Leins
Fusor Tech
-
Carl Willis
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- Contact:
Re: glassman hv supply
Jason,
It's a big safety improvement over just the bell jar but my recommendation is not to run full power with it because of the high temperatures involved and the fundamental fragility of a hot glass bell jar under vacuum. Also, you must have coverage over the top of the can so you have a sort of full-coverage metal belljar inside the glass belljar.
One of the potential problems will be heat. I left up the notes below of the calculation I did because I was curious just how hot such a cylinder might get with effectively no convection cooling. It would be in the neighborhood of 720 K at equilibrium with hot spots due to electron bombardment maybe 100-200 K higher, using a fusor power of 1200 watts which may be about right for your 60 kV aspirations. So you have some things to be careful about, like not letting it touch the glass inside, not using any solder joints on it, picking an alloy that won't outgas or undergo some physical transformation, etc. Basically with that kind of temperature you'd be on your own, which is not at all a bad thing but just means you want to progress with extra caution.
E = S * T^4 (Stefan-Boltzmann law)
T = 4th RT OF[ (1 / (5.67 * 10^-8 W / m^2 / K^4)) * 1 / 0.08 m^2 *1200 W]
T = ~ 720 K
-Carl
It's a big safety improvement over just the bell jar but my recommendation is not to run full power with it because of the high temperatures involved and the fundamental fragility of a hot glass bell jar under vacuum. Also, you must have coverage over the top of the can so you have a sort of full-coverage metal belljar inside the glass belljar.
One of the potential problems will be heat. I left up the notes below of the calculation I did because I was curious just how hot such a cylinder might get with effectively no convection cooling. It would be in the neighborhood of 720 K at equilibrium with hot spots due to electron bombardment maybe 100-200 K higher, using a fusor power of 1200 watts which may be about right for your 60 kV aspirations. So you have some things to be careful about, like not letting it touch the glass inside, not using any solder joints on it, picking an alloy that won't outgas or undergo some physical transformation, etc. Basically with that kind of temperature you'd be on your own, which is not at all a bad thing but just means you want to progress with extra caution.
E = S * T^4 (Stefan-Boltzmann law)
T = 4th RT OF[ (1 / (5.67 * 10^-8 W / m^2 / K^4)) * 1 / 0.08 m^2 *1200 W]
T = ~ 720 K
-Carl
Re: glassman hv supply
Jason - Putting the metal electron and xray shield inside the bell jar does help, but as Carl notes, you need xray shielding on all sides. Depending on whether you bell jar is sitting on a stainless or aluminum base plate. you may not need shielding on the bottom...If stainless, usually the base plate is amply thick for xray shielding. Lead is good outside the glass, so it doesn't help for thermal stress. Its vapor pressure may be high enough to spoil you needed level of vacuum.
Dave Cooper
Dave Cooper
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jlheidecker
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Re: glassman hv supply
Let's say I keep the pyrex bell jar for a vacuum chamber. If I use a
0.1" stainless can with a top to cover my cathode and grid, this
should absorb the heat and dissipate it through my aluminum
baseplate. Of course my belljar will heat up since it touches the
baseplate, but I believe the air should help cool the baseplate enough
to keep the bell jar from overheating.
Does anyone feel that this is worth a shot? As long as I monitor the
temperature of the glass of course. Or strongly feel it is a disaster
waiting to happen?
0.1" stainless can with a top to cover my cathode and grid, this
should absorb the heat and dissipate it through my aluminum
baseplate. Of course my belljar will heat up since it touches the
baseplate, but I believe the air should help cool the baseplate enough
to keep the bell jar from overheating.
Does anyone feel that this is worth a shot? As long as I monitor the
temperature of the glass of course. Or strongly feel it is a disaster
waiting to happen?
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Richard Hull
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Re: glassman hv supply
Subject: Glassman Supply
Last group of messages: bell jar/ x-ray safety.
Someone searching on post titles will not get the value of this valuable discussion on bell jar/ X-ray safety. In many ways it is, effectively, lost data.
Let's change to a new title post and thread if the subject changes from the title of the original posting.
Last group of messages: bell jar/ x-ray safety.
Someone searching on post titles will not get the value of this valuable discussion on bell jar/ X-ray safety. In many ways it is, effectively, lost data.
Let's change to a new title post and thread if the subject changes from the title of the original posting.
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
-
jlheidecker
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- Joined: Thu Jan 23, 2003 3:11 am
- Real name:
- Contact:
Re: bell jar safety
Richard,
You said you wouldn't recommend going beyond 12 - 15 kV in a glass
Fusor. What would say are maximum currents at these voltages? I
ask because the higher current will of course bore through the glass
quicker. And I am just about ready to work at this
voltage.
Thanks,
Jason H
You said you wouldn't recommend going beyond 12 - 15 kV in a glass
Fusor. What would say are maximum currents at these voltages? I
ask because the higher current will of course bore through the glass
quicker. And I am just about ready to work at this
voltage.
Thanks,
Jason H
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Richard Hull
- Moderator
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- Joined: Fri Jun 15, 2001 9:44 am
- Real name: Richard Hull
Re: bell jar safety
It is beam energy that messes up the glass. At 15kv you would be getting high localized heating at only 5 ma. I actually detected my first neutrons at about 16kv in Fusor II (bell jar) I actually saw a flake of glass flip off the inside of the jar where a beam was hitting and land on the base plate. Within moments after seeing that, I shut down fusor II forever and realized glass ain't in fusion territory and built the stainless steel fusor III.
Richard Hull
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Re: bell jar safety
Richard,
What power levels were being used in Gerado Meiro's demo fusor? It is apparently producing neutrons and is using some sort of bell jar or glass container of some sort. What was going on there? Was that safe?
Definately in "all due caution" mode now,
Bill Allen
What power levels were being used in Gerado Meiro's demo fusor? It is apparently producing neutrons and is using some sort of bell jar or glass container of some sort. What was going on there? Was that safe?
Definately in "all due caution" mode now,
Bill Allen
-
Richard Hester
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- Joined: Thu Jul 05, 2001 12:07 am
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Re: bell jar safety
The best way to find out would be to send a message to Mr. Meiro. As far as I can remember, he never reported any operating parameters, and hasn't posted here in quite some time.