Log entry time 00:14:11 on January16,2003

Entry number 92061

keyword=IA slope tuned

Summary: the IA waveplate rotation picomotor S2 was set to -2000, giving
an IA slope of approx 340 ppm/Volt. This change was necessary after this motor
setting was changed by the source group during beam studies.

The IA system used to control charge asymmetry has a rotating waveplate
which can be used to adjust the IA slope (and so the dynamic range). This
wave plate was rotated today during beam studies by the source group to
study a rumored effect of this waveplate setting on Hall B 60 Hz noise (which
wouldn't make any sense at all, so luckily it was shown to not exist).

Unfortunately, the picomotor (S2) adjusting the waveplate position is highly
unrepeatable. Even though S2 was returned to its nominal setpoint, the IA slope
was changed from -190 ppm/Volt to +10 ppm/Volt.

So in order to recover a suitable dynamic range for the IA system, it was necessary
to tune this waveplate angle. Because S2 is so non-repeatable, this is an empirical
process. We got lucky, and found a huge slope, ~340ppm/Volt, very quickly.

This large slope should make our feedback more reliable. However, the slope has
not been well-measured (we were in a hurry to get out of the way of production) so
feedback convergence will be a bit slow. It is very desireable to measure this slope
more precisely soon.



       Run#   IA    S2   A_Q 

11:10  1323    5     0     350

11:17  1324   10     0     400

11:21  1325   10  -1000   1240

11:24  1326   10  -2000   2050

11:30  1327   10  -2000   feedback started

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User name paschke/vacheret

Log entry time 00:14:11 on January16,2003

Entry number 92061