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

Entry number 127388

This entry is a followup to: 127374

 
  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 
fluctuations?

  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.