Fusor Safety Note

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Dan Knapp
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Real name: Dan Knapp

Fusor Safety Note

Post by Dan Knapp »

It has been regularly noted here that it is hazardous to operate a glass system at fusion producing power levels since an electron/ion beam impacting upon the glass wall can lead to wall failure. I had not previously heard of any such wall failure risk for a stainless steel fusor. At the Osaka IEC workshop, Masuda showed a 17 cm diameter stainless steel fusor system where a beam had burned a hole through the 4 mm thick wall (see photo below of the cutaway chamber). This system even had a water cooling jacket, but the failure occurred at a point where a baffle in the water jacket limited the cooling. In discussion of this wall failure, it was noted that intense beam formation results when there is an asymmetry in the grid openings resulting in a more intense beam in a larger opening.
This failure occurred in a very high power compact system (120 kV, 24 kW). Since an amateur fusor is unlikely to be operated a such high power levels, there is low risk of such wall failure occurring in a stainless steel system. However, it is worth noting that it is possible, and for those operating with aluminum (lower melting point) or thin stainless chambers, it could pose a possible risk at higher power levels.
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cutaway chamber showing hole burned through 4 mm wall.
cutaway chamber showing hole burned through 4 mm wall.
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Richard Hull
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Real name: Richard Hull

Re: Fusor Safety Note

Post by Richard Hull »

Thanks for the report Dan. Fusors not built to withstand the rigors of fusion should not attempt fusion. In this case, as you note, over 25kw was poured into the system. Still, it is important to continually emphasize that no fusion or even high power demo fusor work should be attempted in a glass or thin metal chamber.

I was rather sorry to see the makezine artical on the small demo fusor. It is inherently a weak system as someone, some where, might try to up the power with a bad outcome.

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
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