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    User name Armstrong

    Log entry time 15:53:20 on June29,2004

    Entry number 127388

    This entry is a followup to: 127374

    keyword=notes on hydrogen boiling

      Target boiling with hydrogen racetrack cell
      How does the present 20 cm racetrack cell compare with the 
    Hall-C style cigar-tube machined cells, in terms of target density 
      Using Hachmemi's Lumi analysis results 
        entry 27374 
       of the recent target boiling run (Run 2498), I extract the following:
      With 60 Hz fan speed  and a 3.5 x 3.2 mm raster, the lumi's see roughly
       150 ppm of boiling at 45 µA;
       314 ppm of boiling at 64 µA; 
     In comparison, from the studies Riad, Bryan, and I did in Nov. 2002
    with the 15 cm machined cells,  
      (see our technical note)
      with 60 Hz fan speed and a 4 mm x 4 mm raster, we saw
       950 ppm of boiling at 45 µA;
       3000 ppm of boiling at 64 µA; 
      i.e. about an order of magnitude worse. Note that comparisons
     of 4 cm and 15 cm machined cells indicated that shorter cells had
     less boiling, so presumably a 20 cm version of the machined cells
     (more direct comparison with racetrack cell) would be even worse.
    Caveat - the Lumi's were not at the same angles/locations
     for the Nov. 2002  tests as for the present data, so perhaps the 
     boiling results are not directly comparable, given our experience
     that the Lumi's at present see worse boiling effects than do the 
     HAPPEX detectors. 
    Conclusion - Dimitri's racetrack cells are a major improvement 
       over the cigar-tube machined cells. However, it is not yet clear 
       that they are an improvement over the "beer can" cell - we would
       need to run at 100 µA and look at detector widths to 
       get a direct comparison.