FONT meeting notes October 27 2006
Present:
Glenn, Tony, Ben (Oxford)
Christine, Christina, Phil (SLAC)
Alexander (DL)
Hamid (Padova)
1. PCB BPM processors (Hamid)
-----------------------------
The PCBs are in.
The Minicircuits components are in.
3 amplifiers and 5 power supplies are in.
[1/11/06: 4 boards have been loaded and all parts are in hand for the 5th].
2. FONT4 board programming (Glenn)
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Glenn has sorted out the remaining 357MHz clocking issues.
He has set up the RAM for the timing strobes and checked it on the bench.
He is still working on the delay-loop logic.
He has a version of the code that is tested on the bench and good for testing
at ATF. Still to implement fully is the difference/sum division.
For now he is using 12-bit lookup tables which means we must be careful with
signal levels and overflows. If progress is good he could implement this fully
and test it with beam at KEK.
3. ATF visit
------------
Flights, rooms and a rental car are booked. Phil requested 2-3 shifts in week 1
and 2 shifts in week 2. Not heard back from Kubo-san.
** ACTION: PHIL: confirm with Kubo-san.
4. Feed-forward plans (Alexander)
---------------------------------
Alexander talked us through his memo (see www site) on thoughts for a feed-forward
test at ATF. The basic idea is to model the ILC RTML with 1 turn in the ATF ring,
and feed-forward a signal between the ring and extraction line. The system would
comprise 2 BPMs in the ring and 4 in the extraction line, with 2 kickers, allowing
for correction in x, x' (or y, y'). The feed-forward time is about 0.5 us.
Alexander proposes using stripline BPMs with resolution about 1um. We could start
with FONT-style processors. One development could possibly be based on
the 'needle' BPMs being developed for the crab cavity monitoring system.
He thinks a 14- (or even 16-?) bit ADC will be needed.
He proposes a 'double' amplifier system based on one coarse and one fine amplifier
gain stages.
Phil suggested discussing this promising proposal further with our SLAC and
ATF colleagues.
5. Modelling of FESA data (Tony, Christine) - see files on www
--------------------------------------------------------------
Christine discovered a 'feature' in her ESA beam code: she had an incoming beam
angle of 10 mrad, so the incoming beam was not hitting the module head on. A
quick check revealed that this makes big difference in the forward spray.
There also seems to be an issue with the method for counting particles in
GEANT, which Christine and Tony will try to resolve.
Tony updated the ESA beam scan simulations to show explicit scanning of the beam
from the nominal axis onto the module. The centred-beam counts of particles
pass the sanity check, which verifies Tony's counting method of using a 'vacuum'
disk volume element. Christine should check that centred beam gives her sensible
counts of 'spray'.
** ACTION: CHRISTINE
Tony also discovered that he has been modelling copper strips in the BPM, whereas
they are in fact steel. He finds this makes a big difference in secondaries.
He received a quote from CST for Particle Studio: £1439. Phil suggested going
ahead with the purchase. However the official release is not until mid November;
it would be good to extend our beta-version licence so Tony can work in the
meantime.
** ACTION: TONY
Christine has been working on scaling the ESA results to ILC. Last week with
'discrete' beam hits she estimated a BPM difference signal at the level of
4 X 10-5V. This week she added more beam hits and the estimate rose to
2 x 10-4V. Phil advocated dividing the azimuth into a largeish number of regions,
and summing up scaled results from ESA so as to reproduce the ILC 'ring of fire'.
This will not be quite right as we only have beam data for 4 quadrants, but
making some simple assumptions about hit densities within each sector
should give us some kind of 'worst case' estimates.
** ACTION: CHRISTINE
6. ESA flux measurements (Christina) - see file on www
------------------------------------------------------
Christina summarised the extrapolated beam flux measurements from the last
run. A tech Note is in preparation. The results cover a dynamic range between
about 10**6 and 10**10 primary beam particles, using 3 different techniques:
toroid
low-charge toroid
scintillator + PMT
Phil requested to see next time the actual data and details of the assumptions
used for the extrapolation into the unmeasured regions.
** ACTION: CHRISTINA
For next run possible improvements include an 'absolute' calibration of the PMT,
and better shielding of the CCD camera for the beam imaging.
7. Next meeting
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Friday November 3, 08.00/16.00
best wishes,
Phil
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