Fusor Forums

I have long cleaned many of my port windows. In the normal operational regime, you will have grid material deposited on your view port glass. Over a few years, they can become nearly opaque. Tungsten is particularly tenacious. In the old early days, I used SS grid wire and muriatic acid nearly instantly removed all such deposits. Not so with Tungsten. The solution is to abrade W off the window. I use a very heavy cutting compound liquid. It does take a good bit of elbow grease and concerted effort to remove the deposit. I always finish up with the fine liquid polish.

As I was packing up fusorIV, I removed all attachments that were removable and this included the long suffering view port. It was very heavily deposited. Before putting it away, I spent a rather hellish hour while watching an episode of Chernobyl on the big screen, polishing out the deposit. Finally all the deposit was gone. (You can tell, as even a trace mono-layer of remaining deposit will show interference diffraction banding). Alas, the window still retained a clean, yet, brownish tint. Then I remembered all of the x-ray tubes in my collection exhibit this. It seems that 16 years lashed to the mast in fusor IV, the window is solarized or tinted brownish from x-ray bombardment. I will just have to live with this and so will you if you operate at elevated fusion voltages for long runs over a number of years.

I obtained both the heavy abrasive paste, liquid and the fine abrasive paste, liquid at Harbor freight. They are not cheap!! However, there is a virtual lifetime's supply in each bottle. The stuff works great on metal and plastic.

There is some indication the browning will fade over time and might be accelerated by continuous exposure to high light levels or elevated temperatures. I submit this PDF URL.

http://birns.com/uploads/file/Radiation ... ration.pdf

Richard Hull

Richard, you might try annealing the radiation browning. Years ago I had a beer glass that I browned in a big cobalt source. One day, it accidentally was put in the dish washer instead if the usual hand was. The heat dry in the washer eliminated a good bit of the brown.

Perhaps your view port could use a slow bake in an oven.

Jim K

Hi Richard, a useful technique to removing tungsten deposits is melting a bit of sodium nitrite over the surface to be cleaned. It melts at low temperature and reacts with the tungsten. Then you wash thoroughly the window with distilled water.

Somewhere in my memory banks is a 1:1 mix of sulfuric and phosphoric acid to dissolve tungsten.

The PDF I supplied recommended heating as a cure as well as intense light. I have both phosphoric acid and sodium nitrite on hand, (doesn't every one?), I might try that next time I have a tungsten deposit. Now, I am down to just radiation browning.

Richard Hull

Slightly off topic.
My thinking is to cut up an inexpensive stainless camping mirror and stick it in an elbow to reflect the image through a window. The field of view is reduced but perhaps this is ok. Then place some lead between the web cam and the vacuum chamber and hopefully attenuate some of the X-ray induced sparkles.
This raises the question could one get away with an O-ring window seal.
-Peter