[Halld] Run update and plan for the next days

[Alexandre Deur]

Dear Collaborators,

Accelerator has been delivering beam to Hall D for a few days, although intermittently. We first got some beam on Monday, Dec. 14th. This was the first 12 GeV beam in Hall D, an important Accelerator milestone. After calibrating the ions chambers protecting our tagger equipment, we checked the beam quality. Radiation levels are about 5 times higher than what was seen with the 10.5 GeV last year. It is believed that this comes from a beam halo. However, these levels are acceptable for the type of works we will be doing during this period of commissioning. On the other hand, the beam position jitter is good: Hovanes wrote a program to provide an online analysis of the profiler data and the fast Fourier transform shows a x-jitter below 100 micron and a y-jitter of about 400 micron. Later on Monday, Eugene and Nathan optimised the beam position for maximum photon transition to the Hall. Following this, Alex Somov started to set-up the pair spectrometer trigger and we took data with the PS together with the microscope, hodoscope and TRD (Lubomir and Sergey's transmission radiation detector). Alex Somov and Nathan then did some hodoscope High Voltage scans. Meanwhile, Sergey took and analysed TRD data and those look good. 

Tuesday and Wednesday, we did not get the beam. RF separation to allow multi-hall operation was being commissioned. In addition, accelerator went on to achieve another milestone: high current 11 GeV beam to Hall A for several hours (~70 nA, 800 kW). The power of the RF separating cavity turned out to not be enough to separate the A and D beams so the beam transport was modified in order to facilitate the separation. This was successfully done. However, a fast shutdown system fault prevented to run with CW beam. This fault was fixed this morning and multi-hall operation should be now possible.

Meanwhile, the Hall D fast feedback commissioning, which was planned to start as soon as good beam is established in Hall D, had to be postponed to Thursday because of software problems. 

Today, Thursday 17th, we got the beam back early in the morning. But it was intermittent (for owl shift, we got in total 50 min of beam in packages of few minutes). The electron beam is also scrapping somewhere. The lower beam quality was traced back to the change of beam transport done in order to allow RF separation. After this optic change, the beam transport matching in the Hall D line had not been done. The rematching was done this morning. 
During the morning and beginning of afternoon, Alex Somov worked on the main detector trigger while accelerator started to commission the nA BPM. In the same time, radiation monitor data at different current and radiator thickness were also taken by Mark Ito and Eric in order to assess the beam quality.

The nA BPM commissioning quickly ran into software issues. Since the person responsible for it is busy with the (higher priority) commissioning of the fast feedback, we will most likely not be able to continue the nA BPM commissioning during the Fall 15 run.

We are now starting the fast feedback commissioning. Its first phase should last until 6-7pm. Then, accelerator will try to provide beam to Hall A and D. If this fails, Hall A will get the beam tonight, with the understanding that Hall D runs this week end. If the separation is successful, Alex Somov will finish the main detector trigger setup. Then Sergey Furletov will start studying the DAQ performance. If we have time, we will take pi0 calibration data tonight. We will continue with the same program tomorrow, with in addition some bias voltage study for the microscope.

Thank you,
 
Alexandre Deur, Hall D Run Coordinator.
 
RC cell: 757-383-5542
Office Phone: 757-269-7526