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User name Sawatzky
Log entry time 01:40:26 on October 5,2000
Entry number 49353
keyword=heater oscillations in the cryotarget
Strange heater oscillation (HPHtr) in loop1 noted. It's a ~80 W sin^2 pattern with a period of 4 minutes. Temperatures and gas pressures track as you would expect with about a 0.1 degree amplitude oscillation in the loop1 temperatures, and a 0.4 degree oscillation in the target return (CTD7541). Pressure in loop 1 varies by about 5-8 psi during the cycle.
JP and Joe came in to take a look shortly after midnight and were a little mystified. JP enabled the automatic PID start (which had been disabled since the reboot) but it isn't clear if that actually has any effect with the current set-up. Joe thinks it might be some thermo-acoustic resonance that comes into play at these higher-than-normal pressures.
The cycling eventually stabilized and was OK for about 45 minutes, we changed to the carbon target, ran for 20 minutes and the oscillation began again. Restabilized after about 10 minutes...
Pressure in the target is about 236psi without beam loading, rising to about 240psi with 60 uA. This is a bit higher than anyone is comfortable with. If the pressure starts to exceed 250psi JP suggests that we try and *quickly* cycle the exhaust valve via the gui... Joe's taking 10:1 odds against it working -- no bet will be refused.