Run Coordinator report: Fall 2017

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Summary of the Fall 2017 Hall D run

The original schedule was to start physics operations on Dec. 1st and end it on the Dec. 21st. For the accelerator, it was to be a 4-hall operation, a first for JLab. Among the consequent challenges was that Halls D and B would share the same chopper slit at the source. It also implied that RF beam separation must work. RF separation had been demonstrated and used during the previous runs, but only for a short time (about a day). One implication of Halls B and D sharing a slit was a constraint on their beam currents and the ability to tune one beam without affecting beam delivery to the other hall.

The setup for Hall D was a beam energy of 11.6 GeV (the same value as Fall 2016 and Spring 2017), nominal operation at 200 nA of electron beam current with 250 MHz frequency, and operating the solenoid at 1350A. (It operated for 24 days without troubles!) Most of the run was expected to be done on the 60 μm diamond radiator (JD70-100) with the 5 mm collimator hole.

Since the Fall 17 run was expected to be 20 days, priority was given to 1) make sure the equipment was ready for the longer Spring 18 run; and 2) do as many tests/commissioning as possible in order to allow for more time for data taking in Spring 18. Physics data taking for Fall 2017 was secondary.

The tests/special tasks we planned were (in rough order of priority):

  1. Beamline, trigger, DAQ and detector checkouts in preparation for Spring 2018. This also included:
    1. 60 μm diamond alignment;
    2. Microscope yield study;
  2. High-intensity trigger and DAQ tests;
  3. Total Absorption Counter (TAC) V-wire radiator commissioning;
  4. CDC and FDC HV scans;
  5. CDC and FDC readout test;
  6. ToF non-linearity test;
  7. Straight track runs for DC alignment studies;
  8. Systematic TAC study (runs with different materials in the photon beam line. Run with main solenoid off);
  9. Systematic PS acceptance study (runs with collimator position offset);
  10. Align a thin 17 μm diamond (JD70-104) and take enough data to achieve ~1% statistic on rho polarimetry;
  11. Fast raster beam characterization;
  12. Beam halo measurements to assess background for PRad target TAC runs;
  13. Muon chamber test (parasitic);
  14. TRD/EIC gem tests (parasitic).

This constituted about 1/3 or the scheduled time. The remaining 2/3 were to be for production on the 60 μm diamond (4 orientations, 150 nA), Al. radiator (230 nA), weekly empty target runs, and other special tasks pertaining to production, such as daily harp scans.

In addition, Accelerator/RadCon groups planned some Hall D related tests:

  1. Test nA BPM and stripline BPM.
  2. Test fast raster operation.
  3. Evaluate Hall D Rapid Access.

Beam restoration in CEBAF started on Nov. 27th. Circulating the beam up to 5.5 passes took longer than expected but it was achieved on Dec. 7th. At that point, the beam was tuned up to the Hall D electron beam dump. However, shortly after this, RF separation problems appeared: the IoT powering the 5-pass separation cavity developed an arc that kept tripping all the separators (except for the one for 1st pass, which was powered independently). This prevented the 4-hall operation and it was decided to suspend Hall D operation until the arc problem was fixed. The reasons for this choice of priority were that Halls B and C had their central equipment to commission, and that Hall A was using a Tritium target, which associated program called for quick completion.

Given this and the reported progress on fixing the separator problem, we hoped to still be able to run for 3 or 4 days during the fall. We revised our runplan to match this much shorter schedule, keeping only the highest priority tasks and removing all the physics runs/empty target/harp scans. The tests/special tasks for the reduced runplan were:

  1. Beamline, Trigger, DAQ and detector checkouts, including testing the goniometer by aligning the 60 μm diamond for one configuration only. This was important because the goniometer had been removed from the beamline after the spring 17 run.
  2. Microscope yield study;
  3. High-intensity trigger and DAQ tests;
  4. Total Absorption Counter (TAC) V-wire radiator commissioning;
  5. CDC and FDC HV scans;
  6. CDC and FDC readout test;
  7. ToF non-linearity test;
  8. Taking a few hours of data in standard production configuration on the Al. radiator and on the 60 μm diamond (one polarization direction only). In addition we wanted a short 15min run in DAQ long mode.

Eventually, the separator arc problem was fixed and beam delivery started in Hall D on Dec. 18th after 6pm. The next 12h were dedicated to characterize the beam and establish whether it was good for our short program. Although the beam quality would have not been adequate for physics data taking (the beam horizontal width was too large, and there were signs of beam scraping), it was judged to be sufficient for our reduced program: trying to better the tune would not be a good investment given our short run time. We went on to achieve all the reduced runplan goals. Our operation went very smoothly, without any major problem. The only significant issue was that accelerator was not able to deliver more than 100nA to us, presumably because of the less than ideal beam tune. This prevented us 1) to push the DAQ and trigger as much as we wished, 2) to take data in standard GlueX production condition, and 3) to run in the conditions that RadCon wanted to validate the Rapid Access system. However, we still managed to do most of the high rate tests for the trigger and DAQ by inserting at the same time both our 60 μm diamond and 30 µm Al. radiators.

Most of the time, we ran with both Hall B and C operating. While we ran, Hall A was down: a target issue stopped their run earlier than expected. Nevertheless, we kept sharing the slit with Hall B rather than using the now freed Hall A slit, in order to test the set-up we expect for Spring 2018. Although there were only up to 3 halls running concurrently, the successful beam concurrent delivery to B,C,D essentially validated the 4-hall operation of CEBAF. It is a significant milestone for accelerator (and of course, also very important for GlueX).

Regarding the parasitic/accelerator tests, all the tests for the TRD/EIC gem were successfully completed. No test was carried with the muon chamber. It is unclear that the data gathered by the newly installed radiation monitors will be enough to certify the Hall D Rapid Access. In fact, we were told to not expect it for the Spring 2018 run. The fast raster tests were not done, and I do not have information yet on the status of nA and stripline BPMs tests.

In all, given the short amount of running, we had an excellent and efficient Hall D operation, in which we maximized the use of the beam we received. All tasks on the reduced runplan were accomplished. This will be extremely valuable for the upcoming spring run.


Alexandre Deur, Hall D Run Coordinator for the Fall 2017 Run.