Going to 28 cm beta* at end of store
update 9/2/05
Jerry Annala
Most of the documentation needed for going to 28 cm beta* is contained in the studies sequencer aggregate called "go to 28 cm beta* at EOS". The acknowledges contain only a few words of instructions though, so more detail is given here.
Step 1 (Getting prepared to transition) - Several plots are started to verify that supplies ramp smoothly, and beam stays in the machine. C23 compares are made in Proton Removal mode at various places in the study so that trouble shooting can be done if things don't go well.
Step 2 (Setting up the machine) - Beginning at the START_PGM C49 command, we start actively preparing the machine for the study. No power supplies change yet, so this can be done as before the study actually begins. We take a short cut with page C49 to load some of the ramps we need to play. We first activate the QBS ramp (this only sends a TECAR ramp). We then activate C49 file 4 (TECAR only). The activation of the QBS ramp was necessary in order to get the choice of Tecar only when activating file 4. The next thing to do is a send to hardware for only the "End of Store" and the "After Proton removal" ramps. These are the two right most columns on the send to hardware page. Send the following groups:
Proton Tune
Chromaticity
Coupling
Hor Separators
Ver Separators
Feeddown Circuits
Setting T:MDAT12 and the ACL script to follow are also for setting up and can be done without affecting the experiments. The use of MDAT12 is a kluge. Some of the low beta quads are powered by 460 cards which need to use MDAT scaling for the time ramps to work (bug in the 460 code). Anyway, we use MDAT 12 for scaling because this frame is not used. We set it to 4096 because this gives us unity scaling in the card.
Step 3 (Going to the new lattice) - After the ACL script plays, the next acknowledge will really start changing things, so you must be ready before continuing. The first thing is the retraction of the collimators (similar to what is done at the end of Halo Removal). Next is a polarity command given to the A17 separator. The switch should not actually occur until the middle of the ramp to 28 cm, but the command is given before the ramp. Event $69 triggers everything. The beams are separated in the first 5 seconds, and the A17 separator should switch polarity. At the 20 second point, the quads should begin ramping to their new values. After 10 seconds, the quads should be at their new values, and the separators should quickly bring the beams back into collisions. There is a check of the A17 separator polarity because there have been some hardware issues with this switch. The sequence should truncate at this point as the ramp to 28 cm is complete. The sequence can be started again from below the truncate command to gracefully exit the studies.
Step 4 (Running at 28 cm) - If the experiments are going to run, it might be necessary to tune, and re-scrape to reduce losses and improve lifetimes. If a re-scrape is needed, just begin with TEVCOL move 4. A double scrape should not be needed.
Step 5 (Getting back to HEP conditions) - Continuing the sequence from the Acknowledge just above the kill beam will gracefully get out of the 28 cm study condition. Event $6C causes everything to ramp back to sequence 25 of the squeeze. At this point, the Un-squeeze should be done from the Collider sequencer. Do not execute the the ACL END28CMSTUDY until the un-squeeze has begun. Once the unsqueeze has been triggered (event $C9), the rest of the studies aggregate can be run. The steps here are the opposite of the setup steps. The ACL script un-does the configuration of the low beta quads. From page C49 we activate the QBS file. Then, C49 file 1 is activated (TECAR only). We then send the same ramps to hardware that we did in step 2. Make sure that C49 indicates that file 1 is active before sending these ramps to hardware. Once the sequence is complete, the Collider sequencer is used to decelerate and you are back in the normal sequence of Collider operation.
Step 6 (One final check) - Once the Tevatron is sitting on the front porch, go to page I14 and look at the C:B7SHM. Click on Menu, and select Diagnostics. Next, select :Display MDAT readings (right column, 4th from the top). Record the value of frame 10 (Left column - first row below the gap). Next close the Diagnostics widows, and click on interrupt level B. Display the G table independent values (Middle box, left column) in raw data. Verify that the value of MDAT 10 that you recorded when on the diagnostics page is less than the value of the breakpoint on the line numbered 2. The images below show which numbers to compare.
