[Solid_hgc] Question about radiation on O-ring

[Zafar Ahmed]

I did not attend the meeting and now there is question about how
radiation resistant the O-rings
will be because during PREx O-ring at the end of detector chamber
melted. I talked to Robert
Michaels about it and following is the conversation between Bob and me.
Ahmed's Comments:-------------------------------------------------------------------------
The O-ring at the end of detector chamber and before septum magnet in
HallA during PREx melted when we turned on the raster on the optics
target.Two factors are responsible for this. One, due to raster, the
beam washitting the solid rack which holds the optics foils. Second,
distancebetween O-ring and origin of the radiation source was short.
We wererunning PREx at 50 uAm but I don't remember what current did we
use forthe optics run.
On the other hand in SIDIS configuration of SoLID the target is
liquidHelium, beam current is about 10 uAm and distance of O-ring of
HGC fromtarget is about 2 to 3 meter so I think there is no danger of
melting ofO-ring by the radiation from the target.
-------------------------------------------------------------------------
Bob's reply:-------------------------------------------------------------------------
You have to evaluate the radiation load, and there are ratings for
howmuch radiation O-rings can take. There have always been O-rings on
thetarget chamber but they were at much larger angle; they go around
thewindows.
Regarding the PREX experience, it was a little more complicated
thanwhat you wrote. It is true there was an accident early in the
runwhere a rastered high-current beam was put on the optics target,
whichhas small foils. Some beam scraped on the heavy aluminum frame
ofthe target. But that was a brief incident. It probably weakenedthe
O-right, though. There was a much longer exposure to radiationjust due
to the target, and there was some evidence that hurt us,too. Remember,
we went through 2 or 3 of those O-rings duringthe run (cannot remember
how many but at least 2 and probably 3).
-------------------------------------------------------------------------




Ahmed
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