[Hps] RC Day Summary

[maurik]

Dear HPS,

This is a quick summary to update everyone on the status of the run and what happened in the last 24 hours. Details should be in the ELog!!!

ACCESS FOR SVT Issues.

Since the power out event the SVT and the SVT wire scans had not been consistent and painted a very confusing picture. At the end of yesterday’s RC meeting, we decided that the only thing to do was to open up the SVT and take a look. The thought was that the SVT was not on the correct pivot, which would explain some of the behavior observed. Just before 4pm we called for a controlled access and Stepan, Bob Miller (engineer) went down into the hall to remove the beam pipe so Tim could see if the SVT could be “wiggled” into place.
What Tim found when the SVT was opened was that the entire SVT box, which sits inside the vacuum chamber and holds the SVT, was shifted downstream (backwards) by close to 1cm, as judged by the gap between the SVT box and a ridge in the vacuum chamber, which should have a 1/2 inch gap. The motor shafts which control the layer 0-3 opening angle were slightly bent backward and were now chafing against the holes. There were “skid marks” not the G10 plate. Tim observed that the SVT box weighs something like 100 lbs, so significant force was needed to cause this move. It is not clear how this force got applied to the box, but the thinking is that eddy currents in the metal plates caused this when the magnetic field collapsed during the power off event.

Solution:
A custom “grabber” was quickly constructed by Bob, which could be connected to a threaded rod, which with an end plate and a nut could gently and accurately pull the SVT forward. The motor control rods were disconnected and the grabber rig was used to slowly pull the SVT forward. Some care was taken that this would not cause a misalignment. Tim measured the position with a caliper, and also had a 1/2 inch piece of aluminum in the gap to make sure the distance was correct. After moving the SVT box, the motor control rods could be re-connected without stress, and their movement was verified. Tim also checked the target grounding. Everything was closed up again and the area around the HPS detector cleaned. All work was completed around 2am. Vacuum took a while to restore and the valve between upstream and the HPS vacuum could not be opened before the HPS vacuum was good enough (not clear what value that was.)

 
Tim and Bob moving the SVT back in place.

Follow up:
Once we were back for beam permit, we did several SVT wire scans, which now showed consistent results between the top and bottom scans to ~100µm. We think we are recovered to a workable state that will allows us the take production data.

Additional SVT work:
Tim, with Omar working remotely, worked on the SVT. One of the 5V power supplies is not able to provide enough current to power the FEB. (FEB8, which powers layer 6 top) which means that one hybrid must be turned off. We decided the best choice would be to turn off Layer 6, stereo, on the electron side. Another hybrid that is causing trouble is FEB 5, hybrid 3, which means that Layer 4, axial positron is also off. If I understood correctly, this hybrid is acting up for reasons that are not fully understood, at least by me.
It will not be easy to do better than turning off these two hybrids.
Omar took a new SVT baseline run.

Next downtime period:  Replace the coolant from water to 7500 so that we can run the FEBs colder.

ECAL:
There are some “flakey” channels in one high voltage group on the ECAL. Nathan and Rafaella swapped out the HV supply channel, but this did not resolve the issue. Further investigation is ongoing.

Magnet Chicane:
After any access, you can turn on the magnet chicane as soon as the hall goes to “power permit”. Don’t wait until MCC calls to turn on the chicane. When turning the magnets back on, “10% of the time this does not work with the automatic button”. When turning on the magnets, check to make sure the magnets actually come on. If they do not, use the manual turn on procedure, if you know how, or call the slow controls person on call.

Trigger:
Valerie presented a v7 of the trigger, with a mix of all trigger channels. This should give a rate of 22kHz at 200nA. It contains a new and improved muon pair trigger. The trigger was tested briefly in run 100010, which showed it can run at 200nA and 93% live time. This will be the new production trigger.

Collimators:
Since the beam is now back at y=~0.5mm on 2H02Y, we are repeating the centering of the HPS collimator.
The upstream collimator, which has prevented us from going to high current running will need to be investigated. Over the weekend we plan on running production at ~150 to 200nA with the 8µm W target. On Monday we may try to go to higher currents, which could involve some time improving the upstream optics.

RUN:
Once production running is established again, with the SVT at 0.5mm and at least 150nA on the 8µm W target.
Do a quick check of the halo, as described in the “Short Term Schedule” point 5.
Go to production running. 
Once per shift, do a quick harp scan with 2H02, and check beam quality, position, width and halo. There is no need for an SVT wire scan if beam has not changed.

Best regards to all,
	Maurik


 

  

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