Lawaranceville E-Newsletter

[Henning]

Okay, they got a question for chemists and vacuum experts: how to easily clean the chamber.

For the chemists out there, we have a few cleaning questions. On the one hand, we sometimes (including right now) get accidental contamination within the vacuum chamber with lubricating grease from machining that gets stuck in unseen places and is not totally cleaned before we get the pieces into the vacuum chamber. Is there any gas we could use that would clean up hydrocarbon deposits formed after the plasma interacts with the grease, which won’t harm our stainless steel vacuum chamber or our copper electrodes? If we could just have a cleaning gas, it would be much faster than opening up the chamber and taking everything apart.
Second, copper eroded from the anode gets deposited on our glass viewing windows. We can take these out easily enough but what is good to clean the copper off the glass that won’t scratch or harm the glass or the surrounding steel?

If you know anything about it, please post your answer at http://focusfusion.org/index.php/forums/viewthread/952/ or add a comment here. Hopefully someone from LPP will look at it - or I'll point them to here.

[Giorgio]

IR + UV lamps or Glow discharge with Argon.

See here:
http://www.vacuumlab.com/Articles/VacLab52.pdf

They could also contact directly the guys at vacuumlab.com for additional suggestions.

[Joseph Chikva]

Okay, they got a question for chemists and vacuum experts: how to easily clean the chamber.

For the chemists out there, we have a few cleaning questions. On the one hand, we sometimes (including right now) get accidental contamination within the vacuum chamber with lubricating grease from machining that gets stuck in unseen places and is not totally cleaned before we get the pieces into the vacuum chamber. Is there any gas we could use that would clean up hydrocarbon deposits formed after the plasma interacts with the grease, which won’t harm our stainless steel vacuum chamber or our copper electrodes? If we could just have a cleaning gas, it would be much faster than opening up the chamber and taking everything apart.
Second, copper eroded from the anode gets deposited on our glass viewing windows. We can take these out easily enough but what is good to clean the copper off the glass that won’t scratch or harm the glass or the surrounding steel?

If you know anything about it, please post your answer at http://focusfusion.org/index.php/forums/viewthread/952/ or add a comment here. Hopefully someone from LPP will look at it - or I'll point them to here.

I know only well known thing.
That first fusion experiments wall was made from glass. And plasma was contaminated with silicium, oxygen, etc.
Then when walls were made from stainless steel especially after some "trainings" (multiple heating-cooling cycles up to 300 deg) plasma contaminations has been dramatically decreased.

[kurt9]

Okay, they got a question for chemists and vacuum experts: how to easily clean the chamber.

For the chemists out there, we have a few cleaning questions. On the one hand, we sometimes (including right now) get accidental contamination within the vacuum chamber with lubricating grease from machining that gets stuck in unseen places and is not totally cleaned before we get the pieces into the vacuum chamber. Is there any gas we could use that would clean up hydrocarbon deposits formed after the plasma interacts with the grease, which won’t harm our stainless steel vacuum chamber or our copper electrodes? If we could just have a cleaning gas, it would be much faster than opening up the chamber and taking everything apart.
Second, copper eroded from the anode gets deposited on our glass viewing windows. We can take these out easily enough but what is good to clean the copper off the glass that won’t scratch or harm the glass or the surrounding steel?

If you know anything about it, please post your answer at http://focusfusion.org/index.php/forums/viewthread/952/ or add a comment here. Hopefully someone from LPP will look at it - or I'll point them to here.

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).

[rjaypeters]

Second, copper eroded from the anode gets deposited on our glass viewing windows. We can take these out easily enough but what is good to clean the copper off the glass that won’t scratch or harm the glass or the surrounding steel?

Change to sapphire windows and scratching during cleaning becomes less of a problem. 'Course the sapphire windows may be out-of-budget.

Alternatively, treat the glass windows as replaceable items and don't bother cleaning them.

[Joseph Chikva]

Okay, they got a question for chemists and vacuum experts: how to easily clean the chamber.

For the chemists out there, we have a few cleaning questions. On the one hand, we sometimes (including right now) get accidental contamination within the vacuum chamber with lubricating grease from machining that gets stuck in unseen places and is not totally cleaned before we get the pieces into the vacuum chamber. Is there any gas we could use that would clean up hydrocarbon deposits formed after the plasma interacts with the grease, which won’t harm our stainless steel vacuum chamber or our copper electrodes? If we could just have a cleaning gas, it would be much faster than opening up the chamber and taking everything apart.
Second, copper eroded from the anode gets deposited on our glass viewing windows. We can take these out easily enough but what is good to clean the copper off the glass that won’t scratch or harm the glass or the surrounding steel?

If you know anything about it, please post your answer at http://focusfusion.org/index.php/forums/viewthread/952/ or add a comment here. Hopefully someone from LPP will look at it - or I'll point them to here.

The second thought I would propose is to disassemble device and to wash each metallic part in solvent. E.g. acetone.
Then a few heating-cooling cycles for removal of absorbed on the surface contaminators. This is important.
From what insulator is made?
As I remember the word "Mylar". Hydrocarbon? Plastic? Or ceramic?
The best insulator material less contaminating plasma is Beryllium Oxide: good electric insulator, better thermal conductor than even aluminum (metal!), low atom number of beryllium and so, lower Bremsstahlung in case of erosion, etc. One disadvantage of beryllium and beryllium oxide that both they are toxic and require qualified working.

Also I do not quite understand. What is a problem with hydrocarbon contamination if that is caused by machining grease and if that may be removed after a few shots?
I see more significant problem. If they have problem of deterioration of transparency of observation window at the expense of copper deposition, won't that copper contaminate also plasma as well?
Why not as a last resort to try beryllium electrodes instead of copper?

[Henning]

Thanks everyone for your suggestions. If you have more, these are welcomed nevertheless.

I don't know exactly where this lubricating grease comes from. As they write it's somehow hidden in unseen places. More some kind of an accident.

That Mylar (boPET) is used in insulating the conducting aluminium sheets, from switches to the DPF. I don't know whether the base insulator of the electrodes are PET too, but I think they are. But it seems insulators aren't the problem here.

Beryllium is hard to machine, because of its toxicity. As long as we don't need to mess around with beryllium, that's a good thing. Now the experiments of testing several dimensioned DPFs are starting the next few weeks, for determining the optimum parameters for fusion. Electrodes will have to be replaced quite often, and copper is easier to handle than beryllium.

[Giorgio]

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.

[Joseph Chikva]

I don't know exactly where this lubricating grease comes from. As they write it's somehow hidden in unseen places. More some kind of an accident.

I don't know whether the base insulator of the electrodes are PET too, but I think they are. But it seems insulators aren't the problem here.

Beryllium is hard to machine, because of its toxicity. As long as we don't need to mess around with beryllium, that's a good thing. Now the experiments of testing several dimensioned DPFs are starting the next few weeks, for determining the optimum parameters for fusion. Electrodes will have to be replaced quite often, and copper is easier to handle than beryllium.

I think that lubricating grease comes from machining from coolant liquid. As after machining the parts that should be clean obligatory should pass degreasing operation.

But also if they use plastic insulator I am not sure which one make more significant contribution in contamination: grease or eroded and dissociated insulator.
As contamination by grease will be lesser by each shot.

Yes, beryllium is harder machinable than copper. But we already see the problem with copper deposition on watching window. As I understand before deposition copper's particles should pass through plasma. Will they not contaminate plasma? Atom number of copper and beryllium? Which one will give less Bremsstahlung?

[Joseph Chikva]

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?

[Ivy Matt]

Beryllium is hard to machine, because of its toxicity. As long as we don't need to mess around with beryllium, that's a good thing. Now the experiments of testing several dimensioned DPFs are starting the next few weeks, for determining the optimum parameters for fusion. Electrodes will have to be replaced quite often, and copper is easier to handle than beryllium.

Well, that's news. Does that mean you'll be introducing nitrogen soon?

Just an informational note: for the reasons given only copper electrodes will be used in the current experiment, but my understanding is that a production DPF reactor would use beryllium electrodes.

[Giorgio]

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.

[Joseph Chikva]

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.

[Giorgio]

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]

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?