Giorgio wrote:Dismantling and soaking with acetone is going to be quite time consuming, and will need anyhow a post treatment after reassembling.
Sorry if someone have no time.
Are you sure that the grease is problem if insulator is made of hydrocarbons too?
What will do your mix Ar+O2 with plastic insulator? Will your ultraviolet lamp not act on insulator?
Can that insulator after UV radiation and O2 discharge withstand 45kV without breakdown?
Would the insulator changing process be not time consuming in case of breakdown?
Actually we always used metal gaskets, so this was never an issue.
I am not sure if LLP people use metal or elastomer, but if they use elastomer it might be a good time to switch to metal gaskets.
They could also have the added bonus of a better vacuum too.
Giorgio wrote:Actually we always used metal gaskets, so this was never an issue.
I am not sure if LLP people use metal or elastomer, but if they use elastomer it might be a good time to switch to metal gaskets.
They could also have the added bonus of a better vacuum too.
Metal gaskets as electric insulator?
Actually selection of insulator material is a challenge for all pulse fusion devices. That's solvable. But I think elastomer or plastic would not a good choice.
PS: How you can provide vacuum tight (hermetic) joint between glass window and vacuum chamber? As I have no idea without elastomers.
I know about vacuum tight vacuum tight joint between metal wire and glass in vacuum tubes. But think that the shape also plays role. In any case that may be a challenge too.
Joseph Chikva wrote:Metal gaskets as electric insulator?
I do not know the FF-1 vacuum chamber layout in details, so I have no idea of what electric insulator you are worrying about.
Anyhow, not all elastomer undergo degradation under the UV+IR cleaning conditions.
A quick chat with the elastomer manufacturer can clear any doubt.
Joseph Chikva wrote:Metal gaskets as electric insulator?
I do not know the FF-1 vacuum chamber layout in details, so I have no idea of what electric insulator you are worrying about.
Anyhow, not all elastomer undergo degradation under the UV+IR cleaning conditions.
A quick chat with the elastomer manufacturer can clear any doubt.
I am worrying about nothing but only asking.
As quantity of residual grease will decrease by each shot even without degreasing.
For your note electric insulator in focus fusion device is one of critical parts.
UV radiation + O2 which dissociates by discharge will not degradate elastomer? I do not know such material.
For quick chat with the elastomer manufacturer I at least should know with whom I should speak.
Also I do not understand for what they use that watching window. Either they have not a hope to get any neutron or gamma flux or what they are going to observe through that?
Several considerations. What is the vapor pressure of the grease compared to hydrocarben gaskets? It the grease is not 'vacuum grease it may have significant outgassing. If the grease is vaporized during pumpdown or firing it could redeposit anywhere in the chamber. This might introduce an insulation issue.
Also, exposure plays a role. Exposed grease that is hit by UV light is much different from grease or gaskets that are tucked under a corner of the metal casing, especially if the casing is designed to minimize exposure of the gasket to energetic plasma or direct line of sight to the active regions of the device. The metel shell may have a shelf that when bolted down actually touches inside of the radius of the gasket. The gasket would be compressed to the extent nessisary to assure a tight vacuum seal just before the metal shelf meets it's opposisite metal surface, This would have extreamly small exposure to the plasma- only tiny defects / scratches in the metal shelf, plus designed bleed paths would allow communication between the gasket area and the intermal volume of the chamber.
kurt9 wrote:I don't know about plasma cleaning for the grease. I think they are just going to have to make sure that all of the parts are properly degreased prior to putting into the vacuum chamber. Ultrasonic bath in both acetone and IPA (two separate baths) can help with grease removal prior to putting into the vacuum chamber. At minimum, wipe everything clean with IPA before putting it in the chamber.
As far as removal of the Copper from the chamber walls, a simple DC glow discharge with Ar or O2 should do the job. The glow discharge would be simple capacitive DC with the bias plate at 500 or 1000 V bias. The Ar or O2 gas flow should be at around 1-10 torr with a base pressure of 0.1 torr (need only a roughing pump).
Dismantling and soaking with acetone is going to be quite time consuming, and will need anyhow a post treatment after reassembling.
Probably the best could be a UV+IR lamp to break the long carbon chains in short one followed by an Argon glow discharge to remove the remains.
I heave heard that lately Ar-O2 mixtures glow discharge are giving quite interesting results, but I do not know enough to offer an advice on this.
Needless to say that the way the chamber is designed will make quite a difference in the results that will be obtained with a system or the other.
It is a pain in the ass, as I've have done such many times with vacuum chambers. However, I know of no other way to get rid of grease on parts that go into a vacuum chamber. De-greasing in acetone and IPA ultrasonic baths (10 minutes each) is common practice in the tool coating business (TiN, CrN, etc.) as most tool parts come coated in grease for corrosion protection. I used to do the same with vacuum chamber parts (flanges, etc.) when they were coated in any kind of grease.
Everything should be de-greased prior to going into the chamber anyways in order to prevent contamination of the chamber.
Also, once you do pump down, you will want to do an Argon glow discharge prior to each process run in order to completely rid of any contamination. I assume that they are running at high vacuum regime (10-3 to 10-7 torr).
If its UHV (ultra-high vacuum - 10-9 torr or greater), you will need to do a complete bake out process (usually takes 1-3 days) following the pump-down.
D Tibbets wrote:Several considerations. What is the vapor pressure of the grease compared to hydrocarben gaskets? It the grease is not 'vacuum grease it may have significant outgassing. If the grease is vaporized during pumpdown or firing it could redeposit anywhere in the chamber. This might introduce an insulation issue.
Also, exposure plays a role. Exposed grease that is hit by UV light is much different from grease or gaskets that are tucked under a corner of the metal casing, especially if the casing is designed to minimize exposure of the gasket to energetic plasma or direct line of sight to the active regions of the device. The metel shell may have a shelf that when bolted down actually touches inside of the radius of the gasket. The gasket would be compressed to the extent nessisary to assure a tight vacuum seal just before the metal shelf meets it's opposisite metal surface, This would have extreamly small exposure to the plasma- only tiny defects / scratches in the metal shelf, plus designed bleed paths would allow communication between the gasket area and the intermal volume of the chamber.
Dan Tibbets
We have two issues from Dr. Lerner's team:
First - contamination with hydrocarbons
The second - deterioration of transparency of observation window owing to copper deposition on it.
There was said that there is residual machining grease.
But I see also another hydrocarbon’s source: insulator and gaskets made from hydrocarbons too and contacting with plasma.
I am a little wondering as first (insulator) by idea should not made from hydrocarbon, and also I do not understand for what they need watching window?
And I am sure that occuring contamination by copper is more significant problem.
Joseph Chikva wrote:Also I do not understand for what they use that watching window. Either they have not a hope to get any neutron or gamma flux or what they are going to observe through that?
The DPF is in a room of its own that is kept sealed (and empty of people) whenever it is being fired. I'm guessing the window is primarily for the ICCD camera. I'm not entirely certain of the reason for the ICCD camera, but I suppose it helps with diagnostics.
Temperature, density, confinement time: pick any two.
Joseph Chikva wrote:I am worrying about nothing but only asking.
As quantity of residual grease will decrease by each shot even without degreasing.
For your note electric insulator in focus fusion device is one of critical parts.
UV radiation + O2 which dissociates by discharge will not degradate elastomer? I do not know such material.
For quick chat with the elastomer manufacturer I at least should know with whom I should speak.
Also I do not understand for what they use that watching window. Either they have not a hope to get any neutron or gamma flux or what they are going to observe through that?
You should post all these interesting questions to Focus Fusion Board, not here.
kurt9 wrote:It is a pain in the ass, as I've have done such many times with vacuum chambers. However, I know of no other way to get rid of grease on parts that go into a vacuum chamber.
You are right, but I guess it also comes down to understand how much contamination we are really talking about and from where it's coming.
For fingerprints type of grease contamination we used to clean it with presoaked pads. They were extremely costly but removed everything in a neat way.
Glass was cleaned using a no sharp edge stainless steel pad like this: http://www.opticsplanet.net/bel-art-cle ... 50000.html
The above was followed by an Argon glow discharge (as you mentioned) to remove any residue.
Joseph Chikva wrote:Also I do not understand for what they use that watching window. Either they have not a hope to get any neutron or gamma flux or what they are going to observe through that?
The DPF is in a room of its own that is kept sealed (and empty of people) whenever it is being fired. I'm guessing the window is primarily for the ICCD camera. I'm not entirely certain of the reason for the ICCD camera, but I suppose it helps with diagnostics.
I would guess the window is for the high speed ICCD camera also. They have published images of the forming plasmoid, This is a valuable tool, . For measuring x-rays, the viewport is probably more transparent that the thick stainless steel walls. The window would also allow for inspection of at lest some of the electrodes between fireings, in order to check for erosion and/ or breakage.
Joseph Chikva wrote:Also I do not understand for what they use that watching window. Either they have not a hope to get any neutron or gamma flux or what they are going to observe through that?
The DPF is in a room of its own that is kept sealed (and empty of people) whenever it is being fired. I'm guessing the window is primarily for the ICCD camera. I'm not entirely certain of the reason for the ICCD camera, but I suppose it helps with diagnostics.
I would guess the window is for the high speed ICCD camera also. They have published images of the forming plasmoid, This is a valuable tool, . For measuring x-rays, the viewport is probably more transparent that the thick stainless steel walls. The window would also allow for inspection of at lest some of the electrodes between fireings, in order to check for erosion and/ or breakage.
Dan Tibbets
Yes, for high speed camera that is an argument. But if the critical plasma contamination will observed, may be some indirect measuring methods would be more preferable.
For X-rays not sure. As I remember that read earlier that Philipov (if recall correctly) found the plasmoid's forming position via collimating of X-rays without any window.
Also I think that after number of shots structure of device will have secondary radiation (certainly if they achieve significant neutrons yield) and, so, some simple robotic device would be preferable for changing of electrodes.
Ivy Matt wrote:Well, that's news. Does that mean you'll be introducing nitrogen soon?
Actually I don't know much more than you in that respect. Probably not too soon.
Joseph Chikva wrote:Also I do not understand for what they use that watching window. Either they have not a hope to get any neutron or gamma flux or what they are going to observe through that?
It's for proving the theory of kinking of the filament and the formation of the plasmoid.
Joseph Chikva wrote:Also I do not understand for what they use that watching window. Either they have not a hope to get any neutron or gamma flux or what they are going to observe through that?
It's for proving the theory of kinking of the filament and the formation of the plasmoid.
One of the main goals is to focus the plasma correctly, and a camera is the best way (?) to assess that.
Ok, thanks.
Responsing on your questions I think that any elastomer/plastic gasket required for providing hermeticity degradating itself will contaminate plasma with hydrocarbons. Even if all internal parts of reactor will be absolutely grease free.
If insulator made of Mylar that also would be the second hydrocarbons (mainly carbon and also oxigen) contaminaton.
But if next generation of reactors will not have glass window and will have right insulator: e.g. beryllium oxide, this type of contaminations will not be observed.
But also I am sure that any time contamination with electrode material will be very signficant.
For etching of deposited copper I can propose the following (sorry for Google translation from Russian): Preparation of etching substance.
There are various structures for etching, coiled a material at manufacturing of printed-circuit boards.
The recipe №1.
For forced (during 4—6 mines) etchings it is possible to use the following structure (in mass parts): 38 % hydrochloric acid in density of 1,19 g/sm3, 30 % peroxide (peroxide) of hydrogen-pergidrol. If hydrogen peroxide has concentration of 16-18 % on 20 mass parts of acid take 40 parts peroxide and as much waters. At first mix with water peroxide, and then add acid. Printing conductors and contact platforms should be protected an acidproof paint, for example nitroenamel НЦ-11.
The recipe №2.
In a glass of cold water dissolve 4—6 tablets of peroxide of hydrogen and carefully add 15—25 ml the concentrated chamois of acid. For drawing of drawing of the printed-circuit board on coiled a material it is possible to use glue БФ-2. Etching time in the given solution approximately 1 ч.
The recipe №3.
In 500 ml hot (approximately 80 °С) waters dissolve four table spoons of table salt to two spoons grinded in a powder of a copper vitriol. The solution gets dark green coloring. It is ready to application right after cooling (at a heat-resistant paint, see above, it is unessential). The solution suffices for removal of a foil of 200 sm3. Etching time nearby 8 ч. If printed-circuit board drawing is executed enough heatproof by a paint or a varnish, the solution temperature can be finished approximately to 50 °С and then intensity of etching will increase.
The recipe №4.
Dissolve 350 г chromic anhydride in 1л hot water (60—70 °С), then add 50 г table salt *. After the solution will cool down, start etching. Time of etching of 20-60 minutes If in a solution to add 50 г the concentrated chamois of acid etching will be more intensive.
The recipe №5.
In 200 ml of warm water dissolve 150 г chloric iron in a powder.
Preparation of chloric iron.
If there is no chloric iron in a ready kind (in a powder) it is possible to prepare it most. For this purpose it is necessary to have 9 %-s' hydrochloric acid and small iron sawdust. On 25 volume parts of acid take one part of iron sawdust. Sawdust falls asleep in an open vessel with acid and leaves for some days. Upon termination of reaction the solution becomes light green color, and in 5—6 days Colouring changes on yellow-brown-solution chloric iron is ready to application. For preparation of chloric iron it is possible to use powdery iron minium. Thus on one volume part of the concentrated hydrochloric acid 1,5—2 parts of minium are required. Components mix in glasswares, adding minium in the small portions. After the termination of chemical reaction to a bottom the deposit and a solution of chloric iron drops out. It is ready to application