A New Cube, or Two

[Rich Gorski]

Liam,

Super first rate system you've put together.

I noticed that there is no water cooling for the turbo. I would keep an eye on the motor/bearing case temperature especially during bakeout.
Also check turbo manual to see how necessary water cooling is during normal operation.

Rich G.

[Liam David]

Thanks Rich. Indeed, I don't have the water cooling connected, but the gas load is surprisingly low, as is the ambient temperature. I've been keeping an eye on the temperature and have a chiller unit on standby for both the fusor and turbos. I've no intention of breaking this turbo after expending so much effort cleaning it up.

With the chamber at 100C - 150C (location dependent by design), the vacuum is at ~3e-6. That unrestricted 200 l/s pumping speed really does wonders.

[Liam David]

Ultimate pressure after a ~4hr bake at 120C and overnight pump is 8e-8 torr. The chamber was wrapped in multiple layers of aluminum foil, then with a 1" ceramic insulating blanket, and then with some more foil. Parts for the fusor are now marinating in the chamber at 140C and 1e-6 torr. All but the cube fusor itself are clean and ready for baking. The turbo pump continues to run flawlessly, and now with the additional gas load and higher temperature it's being water cooled.

[Liam David]

The vacuum system is now mostly assembled with the final batch of parts in the bakeout chamber, including the cathode at 400C and 1e-6 torr. I'm aiming to get the cathode mounted, aligned, and under vacuum tomorrow. After that, it's a few days of pumping and baking out targeting the low e-8 torr range, followed by glow discharge cleaning, feedthrough conditioning, and finally a fusion test.

[Rex Allers]

Hi Liam, Fantastic work you have been doing from the time you started and even more so as your work continues.

I just read where you said, "then with a 1" ceramic insulating blanket"
I don't know what that is (the ceramic part). I presume it must be flexible. Can you provide a link or just a bit more description of the material?

[Rex Allers]

Another trivial question.

In that same Christmas eve post one of the pictures shows your primary pump on the floor. There is a brownish cylindrical filter on the exhaust, presumably to reduce oil mist that might be expelled.

Is that a vacuum-pump-specific part or something you adapted for the purpose?

[Liam David]

The ceramic blanket is a CeraTex product made for kilns and furnaces: https://www.amazon.com/gp/product/B08KBSVXVF. Like fiberglass, or worse in fact, it likes to shed small bits of fibers which are bad to breathe so PPE is a must. It's covered in many layers of aluminum foil where possible. With part of the chamber at 400C, I was able to hold my hand on the outside with a single layer of the stuff and some 5 layers of foil total above and below the blanket.

The brown cylinder is an oil mist filter from McMaster: https://www.mcmaster.com/9850K55/. I works well for low flow rates when the pump is at less than ~1 torr but when first beginning a pump-down lots of oil vapor still makes it through. I believe this behavior is the same as filters directly from vacuum pump manufacturers.

[Dennis P Brown]

Your cycling to 400 C means a lot of stress on joints. Do check that all bolts are still properly tight (and not over tighten, either.)

Rarely see anyone do that high a bake out except for super clean systems but certainly you have a clean system. I assume you use filtered dry air or argon as a back fill for service and to prevent air entry.

[Matt_Gibson]

Hi Liam,

I might have missed it, but could you give a few more details about the ss mesh screen that you have protecting your viewport? Looks like you have a nifty way of fitting one inside your viewport…

Thanks!
Matt

[Liam David]

I've done a couple different things.

I have a piece of sacrificial glass (McMaster #8477K28 x 1/4") which fits just inside the viewport and I use a piece of flattened 1/4" OD metal braided sleeving to hold it in place. I don't need the sacrificial glass anymore as it was initially meant to shield from the on-axis beam of the Doug Coulter-style cathode. I have a picture of the shield here: viewtopic.php?p=88149#p88149

The other viewports I've had were "protected" by a fine SS mesh which were just press-fit into the recesses of my cube ports. The mesh is for field shaping rather than protection, however, and it wouldn't do much against a concentrated e-beam anyways. I don't have any aftermath pics on hand, but in the picture below is a sub-mA e-beam absolutely cooking a SS mesh that I had lining the conflat tube (pre-cube days when I was using the Coulter grids). There was a ~1/4" hole in the mesh.

If you really need to protect a viewport against an e-beam, deflection is the best option. Sapphire would survive much better than borosilcate or quartz because of its high thermal conductivity and isn't too expensive in smaller sizes, e.g. https://www.knightoptical.com/stock/sap ... mmthk.html.

[Matt_Gibson]

I’ve been using a sacrificial glass as well. It gets sputtering pretty fast so was hoping for a better solution, but it might be the best for now.

-Matt

[Jim Kovalchick]

I use a sacrificial piece of glass in front of my huge viewport. I just packed some foil to wedge it in place. It’s been there for years without issue.

[Matt_Gibson]

Thats the 4k screen of fusors, for sure!

-Matt