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    User name Armstrong

    Log entry time 16:50:32 on August 09, 2005

    Entry number 151279

    keyword=Target fan speed test

    Target Fan Speed Test

    When we were in controlled access earlier today, I did a quick study of increasing the target fan speed even higher than the 70 Hz we have been running.

    Conditions   (no beam): 

       CHL flow =  24 g/s  
   Pressure =   206.5 psi    
   Cell Temperature =  6.70 K  
   HTR_fore Temperature= 6.77 K
   Cellf_aft Temperature 6.82 K

     (all of these remained steady during the test)
    I reset the software limit on the target fan speed, following instructions from Chris Keith, to 36% maximum (86 Hz), then moved the fan speed up in steps:

        Fan Speed   HighPower Heater
      (Hz)         (W)
    ---------   ----------------
      70           311
      74           278
      79           243
      83           211
    The target ran stably at 83 Hz.

    However, we dump   100W more   power in the target when moving from 70 Hz to 83 Hz! The increase is more than I expected.

    So, to reduce our target density fluctuations further by raising fan speed, we would need to do one of:

    1. Increase CHL flow (not possible, we are near the agreed-to 25 g/s max).
    2. Decrease beam current (aargh...)
    3. Increase cell temperature, which means reducing density to keep pressure safely below the venting point.
    There may be some dependence of the fan heating on density or cell temperature, of course. We also don't know if the density fluctuations might also depend on density or cell temperature as well.

    A bigger raster would be a preferable solution.

    However, I think we may not be fully optimized, and I will think about whether we should explore raising the temperature.

    I moved back to 70 Hz after the test.

    A copy of this log entry has been emailed to: jpchen@jlab.org