[Bteam] Notes from Yesterday's B-team meeting
Matt Poelker
poelker at jlab.org
Thu Oct 22 14:05:22 EDT 2009
Yesterday, while troubleshooting gun high voltage problems, we found a
problem with a splice between the gun HV cable going into the gun
ceramic and the cable coming from the Ross probe tank upstairs in the
service building. The problem at the splice.....speculation is that we
suffered an arc to ground. Not so drastic that the cable was completely
shorted, rather it behaved like a small and variable resistor to
ground. As a result, we were taking away voltage from the gun. This
introduced beam steering downstream of the 15 degree dipole bend
magnet. Probably started happening on September 29 when we first
noticed via the archiver that the 100kV orbit was drifting around. So
on one hand, we regret not identifying the problem sooner. On the other
hand, maybe we have made some progress understanding the puzzling
injector drift problem (e.g., why we would need to adjust capture phase
on daily basis....we thought those days were over, and maybe they are,
once we fix our HV cable and run with constant gun bias). Granted, this
is still speculation, but if indeed we were taking away voltage from the
gun, it could explain some of our observations. And once we fix the
splice, we might find it easier to operate the Compton.....
Matt
Arne Freyberger wrote:
>
>
> B-team Meeting Agenda (2:00pm Wednesday MCC conf. room)
>
>
> 1 2009-10-21 Wed 14:00 Agenda
>
>
> 1.1 Compton Status Happex III
>
> What is the status of the electron and photon compton signals after
> the last injector optimization?
>
> * Photon counting
> o Injector tuning on October 15th
> <http://opweb.acc.jlab.org/CSUEApps/elog/entry/1492644>
> resulted in good photon rates. Compton photon rates are
> very sensitive to the settings of the injector.
> o Retune required on October 19th
> <http://opweb.acc.jlab.org/CSUEApps/elog/entry/1493141> to
> get photon rates back to acceptable.
>
> -- orbits were adjusted -- capture gset by 2 out of 6000
> -- increased prebuncher by 0.02 -- capture phase by 1.3
> degrees -- A laser phase by 0.5 degrees
>
> o new spectrum look similar to old spectrum (for my crude eyes)
> * Electron counting
> o electron data appears to be a bit cleaner.
> o electron detector moved closer to the beam (about 6mm).
> o zero crossing clearly observed.
> * Flash ADC photon data
> o 1800V operation except when beam conditions degrade and
> the things trip off.
> o Low photon rate count (number available to MCC) is not a
> guarantee that the flash ADC spectrum is clean.
> o MCC has no way to know if beam quality is good enough for
> the flash ADC analysis.
> * Summary
> o beam quality is good for photon compton
> o electron detector still has a high level background. But
> there might not be enough time to address this. Cleaning
> the electron background is not as high priority as
> accumulating statistics.
> * Q/A
> o most sensitive signal is a PMT current.
>
>
> 1.2 Injector optimization for Happex-III Kazimi Reza
>
> What knobs are best? Stability and drift? Additional parasitic monitors?
>
> * Continuously monitor the time of arrival at the YAO cavity. Reza
> is exploring continuous readout of the 6GHz bunch length cavity
> to look for changes in the arrival time at this point.
>
>
> 1.3 Hall-A Transport optics Ryan Tief
>
> What did ray-trace tell us about Hall-A optics?
>
> * horizontal pseudo phase space looks reasonable through the
> Hall-A line
> * vertical mis-match at the beginning of the A line
> * IP02A BPM area significant distortion to the ray-trace ellipse
> * distortion is correlated with beam loss in the A line. So
> scraping is causing the distortion which starts in the compton
> chicane. The ellipse excursion in this region is of order 1.8mm
> full width. So there is a tight 1mm vertical issue at the front
> end of the compton. The distortion shows up on the negative
> side, so the tight aperture is below the beam.
> * Detail look at the vertical plots, suggests that the problem
> resides somewhere between 1C16 and 1P02A. Better data would help
> narrow down the source of the problem.
>
>
> 1.4 Energy change
>
> Date
> 2009-10-29 Thu
> Energy(5-pass)
> 6.068 GeV, symmetric setup.
> ?_wien
> Equal pain, ?_wien =75
> ?_wien
> During first four days when only B is taking beam, ?_wien = 65
> Special Request
> Vertical spin alignment in Hall-A for two shifts. Hall-B will want
> to go to 1-pass beam during this test. PVDIS will want this in the
> middle/end of the run, not at the beginning.
>
> * Comments on PVDIS startup
> Would like to address the beam quality issues at the beginning
> of the run. This includes:
> 1. phase advance from modulation coils
> 2. compton photon rates
> 3. compton electron rates
> 4. raster size at target
> 5. FFB setup
> 6. 85? A current
> 7. ?_wien
>
> Most of these issues require close collaboration with Hall-A
> experimenters since they provide the measurements and Q&A. The
> goal is not merely to reach acceptable beam, but to achieve the
> requirements with a robust (stable) setup with minimal
> compromises. Time invested at the start of the run to get things
> right, should pay off over the duration of the run.
>
> * Energy Change Strawman
> This will be discussed in more detail at the next B-team meeting.
> o defer cathode bake/activation until 2009-11-02 Mon if
> possible
> o Thursday 2009-10-29 Thu
> + A and C go offline
> + ESR T1 turbine swap out, remove FNAL turbine and
> install repaired JLAB turbine.
> + radcon survey of A line from 1C16 to 1P02A, search
> for hot spots.
> + Helicity board swap
> + energy change to 6.068 GeV. -- review last June
> test, is this allsave ok? -- symmetric setup --
> watch the cryoload
> + 5-pass A to dumplette
> + 5-pass B to F-cup
> + 5-pass C to BSY dump
> o Friday--Monday 2009-10-30 Fri-- 2009-11-02 Mon
> + 5-pass CW to B, physics
> + 5-pass 5uA CW to BSY dump for stability
> + periodically 5-pass to A dumplette for quad scans
> with 1C05
> o Monday 2009-11-02 Mon
> + 12 hours gun bake/activation
> + MO ? f 12 GeV studies
> o Tuesday 2009-11-03 Tue
> + ?_wien =75 change
> + 5-pass to B when possible
> + 5-pass to A -- day shift, injector optimization of
> compton rates -- day shift, ray trace collection or
> other optics work -- day shift, beam will be high
> current for compton
> o Wednesday 2009-11-04 Wed
> + 5-pass to B
> + 5-pass to A -- day shift, more beam studies to
> optimize compton -- ray-trace -- aperture scans --
> matching -- phase advance -- raster setup
>
>
> 1.5 Optics-on-call
>
> Outgoing
> Tiefenback
> Incoming
> Roblin
>
> * Recent Machine issues
> o Compton rates -- highly sensitive on injector
> configuration, see notes above.
> o Power outage -- 9:20pm Tuesday all power was lost on site
> -- 8:30am Thursday still dealing with issues
> o FFB in A is sometimes problematic to configure properly
> * Upcoming Week
> o Hall-B goes to 1-pass (from 5-pass) -- 2009-10-22 Thu
> 11:00 start change to 1-pass -- 2009-10-26 Mon ??:??
> Return to 5-pass
> o Brinkman, Director of the Office of Science visits on
> [2009-10-28 Wed]. The machine will go to control access
> for a tour of the injector. The tour will also visit the
> halls. Opportunity for short duration beam studies.
> o Prepare for energy change on 2009-10-29 Thu
>
> Date: 2009-10-22 08:47:18 EDT
>
> HTML generated by org-mode 6.31trans in emacs 23
>
>
> --
> Arne Freyberger
> Director Operations Department
> Jefferson Lab Phone: (757) 269-6268
> 12000 Jefferson Avenue Pager: (757) 584-6268
> Newport News, VA 23606 Email: freyberg at jlab.org
>
> ------------------------------------------------------------------------
>
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--
Matt Poelker
Jefferson Lab
MS Bldg 5A, Rm 500-17
12000 Jefferson Ave.,
Newport News, VA 23606
poelker at jlab.org
757-269-7357 office
757-584-7357 pager
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