Log entry time 15:18:29 on June11,2004

Entry number 125365

This entry is a followup to: 125310

Followups:

• 125371 06/11/04 16:46 Armstrong revised target high power heater scan

  The Figure below shows the 4He target high power
heater during the owl shift current ramp (to 10 µA) and
a linear extrapolation to higher currents. 

   For the uninitiated, the higher power heater is there to stabilize
the cooling of the target. At zero beam current, it is in essence
a measure of the total cooling capacity of the cryotarget (under
the operating conditions present at that time); as the beam current
increases, the high power heater power level is automagically reduced
by the control system. Note that stable operation requires that the
heater power be non-zero, so the intercept is an overestimate of the
max. operating current.

  While the data are not very linear vs. beam current, they are
too limited based on this scan to determine a better functional form.

  We also may be able to adjust the operating conditions of the 
target to improve the heating power... butI don't have a good
intuition of by how much we can improve things.