Revision as of 14:58, 6 October 2022 by Bruker (Created page with "How to reproduce the beam that made https://logbooks.jlab.org/entry/4051717 this x-ray image: * Load save #781. This setup has the Wien filter set to 90 degrees (we think...")
How to reproduce the beam that made [this x-ray image]:
- Load save #781. This setup has the Wien filter set to 90 degrees (we think) and should give 5.5 MeV/c after the booster. Cycle all magnets if not done automatically.
- Insert FC1 or FC2, send TM beam, making 15 to 20 nA, which is enough for BPMs and well below the MeV current limit. With the present laser setup, you will need an attenuator setting of about 550.
- Retract cup, sending beam all the way to the end.
- Open relative BPM screen and steer out any obvious differences in the keV part (of course, there shouldn't be any). If there are still significant differences in the MeV line only, it may be due to RF phases.
- Assuming nothing is terribly wrong upstream and you only want to put the beam spot where we had it for the test: Reproduce M604 and M605 BPM readings by steering with correctors M604, M605 and M605A. We had M606 at zero the whole time. Verify M605 beam position with harp (compare with picture from log entry).
- With the 302A and 302B solenoids set to 0, the keV line is fairly straightforward to steer through, with two exceptions:
- Corrector K401 is used to center in the buncher, K401A to center in aperture A3, and then K401B to get the downstream orbit close to the axis. If you see something on K401 but not on K402, there's no way to know where you're stuck, so you'll have to sweep the parameter space until you see something. Centering in the buncher is then done with MLHK401 but only makes sense if the phase is already right; otherwise, start with the buncher off. Then, centering in aperture A3 is done with K401A but needs K401B to countersteer so you'll still see the beam on K402 while finding the edge of the hole. You want to be roughly centered in the hole.
- Finding the beam on K403 is similarly painful because the DP can, aperture A4, and the Brock cavity will intercept it. You need the K403 lens to be well centered for the beam to make it through, but you can't find the center until you're already close to it. Once you see the beam, play with K401B and K402 to find a lens-centered orbit that goes through all elements without scraping.
- The MeV line is a hen-and-egg type of thing in that the steering and optics rely on correct RF parameters, but you can't find those without already having steered and focused to M703. Starting with a decent setup, you can hope for everything to be roughly correct.
- If you want to check the phases, put beam on viewer M703 if you can. MDLM601 BDL should be about -9200. Play with quads to minimize horizontal beta. Both booster cavities are phased for maximum individual energy gain, i.e., beam goes to the right. There is currently no easy way to authoritatively find the correct buncher phase, so try to find the setting that gives minimum horizontal size, perhaps sigma = 5 pixels on the viewer or sigma = 0.5 mm on the harp (note, x is the right peak on this harp!). Horizontal dispersion at viewer/harp is about 1.3 meters. Cycle the dipole to 0 and restore quad settings to go to M600.
- Once RF is good, center in the M501...M504 quads using viewer M505 or M506. Find a good launch with M201 and M401; try not to use the M501 corrector.
- The rest is straightforward.