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User name Jin Huang
Log entry time 20:00:14 on October 9,2010
Entry number 334111
keyword=JT valve change, beam current adjustmentWe observed that Loop2 LH2 heater power dropped to 0W. Therefore we tried to increase JT valve by +1% (to 48%). There is little effect on heater power reading. Therefore we increased JT valve again by +2% to 50% and reduced beam curent to 8uA and the further to 5uA (from 10uA).
Now Loop 2 heater is barely 7W, just enough to keep loop at 19K (normal runing temp.). Loop1 heater is 0 to few walts. Not enough to fit it at 22K, although not too bad to increase temperature significantly. Since we are not using loop1, it's should be OK.
A permanent solution would be cut down 15K cryo use for iether Hall A or Hall C. For Hall A our options are
1. increase LD2 temperature by 1K. Then its 2K supercooled. OK for just keep it cold.
2. increase LH2 temperature by 1K. Then the liquid will be 2K supercooled. Still OK for running and enough room before it vapourizes.
3. Reduce beam current.
Run 7090 was take with 15uA.
Run 7091 was take with variable beam current (5uA to 8uA) as we try to stablize target
FIGURE 1
FIGURE 2
