Drawing of the Hall A beamline
This is out of date! Requested a new song sheet from Joyce. Please check this link for the drawing of Hall A beamline done by E. Forman in 2014. It shows the locations of the different beamline components, their names and the labels. (NOTE that the beamline near the target needs to be updated to reflect the addition of new parity BCMs which was done in Fall 2015.)
Hall A HARPs
All harps in Hall A have been switched to the accelerator style, so any reference to PMT HV is out of date.
As our harps are now accelerator standard, the accelerator should be able to run their standard gui's.
1H04A & 1H04B are the two harps near the target.
In the ARC, we use 1C07A & 1C07B and 1C18A & 1C18B to get the bend angle of the beam.
1C12 is the middle of the Hall A arc.
COMMON SENSE TIPS for Rastered Beam Spot Size
- If you ask for 2x2 mm2 raster, you probably will NOT get that. Why? Because of quadrupoles between the raster and the target; note, the control software assumes a 23-m drift with no magnetic fields. What to do? With target out, ask for 2x2 mm2 (for example) and observe whatever you observe as the real spot size. Then multiply the requested size by the ratio of what you want to what you observe, and then ask MCC for that. This should give you the desired spot size.
- Do not confuse the "rastered spot size" (of order 4 mm) with the "intrinsic spot size" (typically 10 to 100 times smaller).
- If your purpose is to check the spot size and dwell time to avoid destroying the target, then test at low current, say 1-2 μA, before going to high current on target or test with no target in the beam. Note that the beam position lock does not work well below 1 μA.
- A good double check is the oscilloscope trace of the raster current, seen in the middle room (electronic rack room) of the counting house.
- If you see a funny looking plot with a lot of scatter? Possibly the beam was off, or sometimes off. Make sure the beam is on (> 2 μA).
Initial BPM/Raster checks/Beam centering [3-4 hours]
- First MCC centers the beam on the beam dump using the ion chambers.
- Establish CW beam.
- Note that we will NOT be going through the Compton chicane.
- With no more than 5 μA of stable beam find the center of the target using the steps below:
- For each step, make sure to record both the rates from the right and left HRS and the BPM positions at BPMA and BPME.
- Move the target to the BeO target. Find the unrastered beam on the BeO target.
- Then have MCC restore beam at 5 μA with a nominal 2x2 mm2 rastered beam size at the target.
- Make sure you read the section above on COMMON SENSE TIPS, regarding the rastered beam spot size.
- Use the target OTR to help get a square raster (see How to view Target OTR).
- Move the target to the Empty 1 position.
- Before asking for beam, check the right and left HRS (T1 trigger) rates. Record these rates in the HALOG.
- Run rastered beam with the target in the Empty 1 position at 5 μA, while checking the right and left HRS (T1 trigger) rates. Record the rates and the beam positions.
- Move the target to the Carbon hole position.
- Check the rates in the right and left HRS (T1 trigger). Record these rates.
- If you can see a difference in rates between the foil and no foil, then continue. Otherwise contact the run coordinator.
- Use the spot++ tool on both L-HRS and R-HRS (see Raster calibration, spot++)
- Verify that the raster is approximately centered on the Carbon hole target. If it is not, ask MCC to move the beam position in x and y until the
hole is roughly centered on the raster image.
Do not increase the raster size. If you cannot find the hole with the raster ON, please contact the run coordinator (Contact information is on the white board).
- After the raster is centered on the hole, have MCC turn off the raster. Since the hole in the Carbon foil is 2 mm in diameter, and the beam spot is much smaller than this, the rates should drop to the rates with the Empty target.
- Now move to the "Raster Target". Ask MCC for 5 μA of beam with a 2x2 mm2 raster. If the beam is centered, the rates should match the rates of the empty target.
- If you notice excess rate, then slowly move the beam position until the rates are the same as those with the empty target.
- After beam centering, update on the white board the nominal beam positions and the "MCC" raster size to get 2x2 mm2 raster on target.
- Make sure you make a detailed log entry with the results of the position scan.
- Superharp Scan with Raster off to check if they are working and provide signals:
- Have MCC scan the two superharps (IHA1H04A and IHA1H04B) near the target with raster off.
- Request MCC to make an ELOG entry with the Harp results.
- Make sure the three wires are clearly visible and have reasonable resolution for each harp: ~200-500 μm.
- If the harp scans are successful, then proceed with the bullseye scan below.
- Make a record of the results of the harp scans in the HAlog along with the ELOG entry numbers.
BPM Calibrations (Bullseye Scan) [1-2 hours]
How to perform a bulls eye scan:
1. You need unrastered beam:
- caution you should not do this with a target requiring rastered beam - use carbon, BeO, optics, or in the worst case empty instead
2. Ask MCC to steer the beam to the nominal center of the target.
3. Wait until beam is stable and have MCC perform a harp scan for the two superharps near the target (1H04A and 1H04B) and take a CODA run for both the left and right spectrometers during the same time. Start the coda run first before asking MCC. Request MCC to make an ELOG entry with the Harp results, you should see all three harp wires. Record ELOG entry numbers.
4. Ask MCC then to steer the beam to positions around the nominal center:
- cover at least the area the raster will cover: (2,2), (2,-2), (-2,-2), (-2,2) and repeat (0,0) - repeat harp and CODA runs for each position
5. Record Harp scan run numbers and corresponding CODA run number for each beam position. As an example, see HALOG # 3324009.
6. Make a record of the harp scans and CODA runs in the HAlog.
How to analyze the bulls eye scan:
- detailed instructions can be found at the Analyzing BPMs website. - the shift crew is not expected to analysis the bulls eye scan.
BCM Calibrations [2 hours]
Accelerator has a written procedure to follow if you wish to cross check the current at the injector with the current in the Hall.
- Warn MCC a few hours beforehand.
- The Hall A BCM and scalers need to be cross-calibrated to the Faraday cup and a BCM in the accelerator (OLO2) and the Hall A Unser.
- Before beginning the procedure, make sure the Hall A BCM logger and the HRS DAQ are started, which will record the signals from all relevant BCM used during the calibration. http://hallaweb.jlab.org/equipment/BCM/BCM_logger.html Here is how to start the logger, choose the BCM logger script (solution 2).
- Also start a HRS run to record the scalers during the calibration procedure.
- It is useful to have someone over in MCC to help coordinate the calibration with them.
- Take data on carbon target with I = 0, 3, 0, 5, 0, 7, 0, 10, 0, 15, 0, 20, 0, 25, 0, 30, 0, 40, 0, 50, 0, 60, 0, 70, 0, 80, 0 μA (or as high a current as available).
ARC Energy Measurement
- The procedure will be conducted by Douglas Higinbotham.
- With the ARC in achromatic optics, the energy measurement can be done at any time though with more uncertainty as the effects of the ARC quads need to be taken into account.
- If you wish to do a full dispersive optics measurement, it need to be coordinated well in advance by the run coordinator as it is invasive to the other halls. Yves from accelerator should be in MCC if the procedure has been done in while. It is presently unclear if it is even possible to do a full dispersive optics measurement with 11 GeV beam due to the energy spread of the beam as well as sync. radiation.