Started run 39.
We have the 15N+ beam with 426 keV/nucleon. We see a peak in detector top left (mostly) and bottom right, at 4600 keV. We think it is the beam (nominally 6400 keV) after going through silicon dead layer, which however seems to be thicker than expected (expected 0.7 um, but given 1.4 MeV/um energy loss it seems to be > 1 um).
To understand what was going on we first played with detector and beam position.
At 17:28 detectors are fully out, while we are playing with the electron cooler to try to remove this beam halo hitting the detector.
Detector DSSD0 top left periodically seems to get noisier (statistics up to >2E5) and we need to move the detector in and out to go back to normal operations.
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The beam halo in top left detector, as the detector gets moved in, gets elongated in the y direction instead of the x direction, as expected and previosuly observed.
Run 40 started.
18:36
Merger OK, Tape server OK
ADC data item statistics looks as before. OK
FEE temperatures look OK
System checks OK
Leakage current stable
Attachments 1-4
19:43
Merger OK, Tape server OK
ADC data item statistics looks as before. OK
FEE temperatures look OK
System checks OK
Leakage current stable
Attachments 5-8
21:15
Merger OK, Tape server OK
ADC data item statistics looks as before. OK
FEE temperatures look OK
System checks OK
Leakage current stable
Attachments 9-11
00;25
Merger OK, Tape server OK
ADC data item statistics looks as before. OK
FEE temperatures look OK
System checks OK
Leakage current stable
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Movements and observation in xy plot:
- Move right servo in by 20 mm and we see the halo in the top right moving accordingly (attachment 12)
-Move right pneumatic in, saw big increase on bottom right (attachment 13)
-moved beam position down vertical -6 mm and we see reduced beam spot on top left and more on bottom left
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Beam - target overlap:
We have yet to obtain an overlap
We cannot do this using the beam lifetime as from beam calc the lifetime from the ring is comparable to the lifetime with a target of 1e11 at/cm2
We have tried using Rutherford. However, we will have to move the detectors IN further as the Rutherford peaks at ~3.8 deg.
Possibly we may require other overlap detections from the ring?
I also think the beam requires some optimisation, electron cooler voltage seems to be fluctuating a lot and we see some features on the detectors when moving the beam / detectors as mentioned above.
02:25
The beam intensity has decreased signficantly (by about a factor of five) since about an hour. Operators tried different things, also consulted with Frank Herfurth, but they could not solve the problem.
There is no device which indicates malfunction.
So, during the rest of the night shift we will continue searching for the overlap (of the beam with the target) with the available beam intensity.
03:30
The beam intensity has improved without any aparent intervention.
We have started a new search for the overlap with 20 minute runs per horiznotal beam position.
Merger OK, Tape server OK
ADC data item statistics looks as before. OK
FEE temperatures look OK
System checks OK
Leakage current stable
03:40
After changing the horizontal beam position from 0 mm to 1 mm, the bottom right detector lost the Rutherford peak and its position spectrum looks to be half empty.
Moving it OUT and IN again did not change the situation.
There is no reason to think that this behavior has been caused by moving the beam by just 1 mm.
04:10
The beam intensity has dropped again without any apparent reason. So, at the moment we can not continue search for the overlap.
The bottom right detector seems to be counting normally again (also without any apparent reason).
06:45
Merger OK, Tape server OK
ADC data item statistics looks as before. OK
FEE temperatures look OK
System checks OK
Leakage current stable
07:18
Lost beam again. Gleb is looking for it. Moved right detector out temporarily.
System wide checks as before.
Merger OK, Tape Server OK.
Temperatures OK.
Rates currently OK.
Leakage current decreasing.
10:10
Beam is back. Target is unusually thick at 3-5E11
Checking beam overlap.
Merger & tape server OK.
Temps OK.
Rates OK, a bit higher in 01 and 04. |