Log entry time 14:37:23 on October 25, 2010

Entry number 202572

Followups:

• 202611 10/25/10 20:19 buddhini FFT of 3H09BX and 3H09BY for run 6206

Jay Benesch called for a meeting among some accelerator optics and
instrumentation experts after the MCC meeting this morning.  The subject
was the double peaks we see in our y position difference distributions.
This is a summary of some things discussed and a near term action plan.

1. I explained exactly what our position difference distribution
represents, and indicated that the "double-peak" does not actually mean
that the beam is at those two different positions.   For example, one way
it could come about is noise on the beam at a quarter our sampling rate
(~ 943 Hz / 4 ~ 236 Hz).  If we were in phase with that, it would cause
two peaks in our position difference distribution (one corresponding to
the helicity pattern +--+ and the other corresponding to the helicity
pattern -++-).  The peaks would have opposite signs and be centered
around zero.  Even if we were slipping a bit in phase, it would still
generate two peaks spread out a bit, kind of like what we see.  I think
that example made it clear to them what this distribution was, even if it
may not be exactly what is happening.

2. Fast feedback: We claimed that we saw it with Fast Feedback was off. 
But in the discussion it became clear that we did not have it completely
off.  It showed as in "standby" on the General Tools screen, meaning that
the part that corrects 60 Hz and some higher harmonics was off.  But the
"feed forward" part that corrects over a broad spectrum up to 1 kHz was
not off.  It continues to interact with the corrector coils.  We will try
again tonight with that turned off.

3. Coil modulation: We also discussed our coil modulation.  It was "off",
but not completely disenabled from MCC.  That invokes a relay that
completely disables control of the coils through that system, so we will
try that too.

4. We were also requested to generate fast fourier transforms of our data
for both X and Y to pick out what frequency might be causing this.  Then
Pete Francis can put an oscilloscope on the drive leads to these coils to
check for any evidence of noise at that frequency.