Difference between revisions of "UITF Notes"

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== Opportunistic tests and long-term ideas off the top of my head ==
+
== MeV beam time ==
 +
* Test IHAM505
 +
* TM beam to 703 to see RF drift (full shift)
 +
* Verify optics setup for HKDL
 +
** To produce small beam at M703, first measure Twiss at 501 and then optimize beta_x with Elegant: try to make it small in the dipole AND at the harp if possible (keep the dipole from focusing)
 +
* Repeat buncher study, booster crested, 8 MeV, multiple scans per point
 +
** It may be interesting to do the buncher study with the 7-cell off.
 +
** This reduces microphonics impact, but optics of the low-energy beam are a problem
 +
** Crank 2-cell up?
 +
* Buncher power vs. GSET
 +
** Once correct buncher power is found, measure displacement at +/- 90 degrees on K501 again
 +
* Test booster off crest, scan buncher if results good
  
* Measure p spread on 703
+
== keV beam time ==
** Not trivial because contribution of beta function is significant
+
* LVQE scan at different voltages. Expect same result, provided different laser powers at same voltage give same result (avoid SCL).
** eta = length * tan(theta) = about 1.2 m
+
** Results are different, don't know if related to instrumentation (battery resistance etc.) or physics. If it's physics:
** sigma_x at 700 harp is about 0.5 mm. The intrinsic momentum spread is smaller than it looks; the beam moves visibly due to RF jitter, and the harp averages over that. In a sense, this is the "true" momentum spread; it depends on what we want to learn.
+
*** CST: Does thermal energy affect collection efficiency?
** Assuming Gaussian distributions: momentum spread = sqrt(sigma^2 - epsilon*beta) / eta, yes?
+
*** Ion current? probably too low to matter
** epsilon*beta = 0 would give an upper bound of 4.6e-4.
+
*** Try adjustable bias voltage source (Keithley)
** We know the emittance (7.3 nm at 8 MeV/c). How do we get the beta function?
+
* HVQE scan at different voltages. Expect different result.
*** It would be trivial if the 600 harp were placed at the same distance from the dipole as the 700 harp, but it is not.
+
* High current to FC2 for 12+ hours, check if drift is gone. Check with buncher ON and buncher OFF.
*** Elegant can calculate the betas directly from first principles, but we can't trust the model until we validate it.
+
* Look at [https://logbooks.jlab.org/entry/4022870 mains-harmonic BPM signals] as a function of parameters (buncher etc.)
*** qsUtility can measure alpha and beta upstream of Q504 using IHAM601 (already done in a test case). Elegant can predict beta at IHAM703 based on that. Sounds good enough to me? The prediction of beta_y is verifiable as the spot size in y is unaffected by dispersion.
+
* Measure bunch length upstream (chopper or Brock)
*** First, using Elegant, come up with a set of 501..504 quad values that will give a reasonably small beta_x at IHAM703, and verify that it is not too sensitive to the setpoints in practice. Making the intrinsic transverse size as small as possible (without it becoming unpredictable) will make sure the errors of beta and epsilon won't contribute too much to the error of the deconvolution result.
+
  
* Have the intermittent RF instabilities fixed
+
== Random things to change when it makes sense ==
* Measure how much juice the BPMs need for reliable positions, particularly in the keV region
+
* Is there anything we can learn from the BPMs / correctors to supplement the gun kick study at CEBAF?
+
* Implement QE tool per Joe's request. Got shopping list from Michele
+
** Sent her a list of existing PVs.
+
* It would be nice to have an extra corrector before the booster to get a nicer axis through both cavities. Prefer the duct-tape variety to nothing at all
+
* Permanently incorporate prep chamber stuff into EPICS
+
** stalk heater PS, temperature readback, ion pump current, anode current. Consider protection logic to disable heater if pressure or temp gets too high. Add oven timer. It should automagically post a completion notice to UITFLOG.
+
** maybe also an EPICS-switchable DC voltage for the auxiliary laser diode (replaces manual "beam shutter")?
+
** have a second PS for the dispenser; could be remote-controlled or not, don't really care... we can't automate the whole process anyway because of the manual valve
+
* Can we get decent, auto-aligning corrector mounts throughout the machine? The multipole moments are currently uncontrollable, presumably large, which is a bigger deal than one might think because the beam line alignment also looks terrible.
+
* Measure beam parameters downstream of booster as a function of gun energy. Maybe 4 or 5 energies. (Emittance, Energy spread)
+
  
== Preparation for HKDL ==
+
* The way MFQK403 is supposed to focus into both Aperture A4 and the booster is flawed for multiple reasons:
 
+
** The lens would need to produce multiple waists (DP can, A4, Brock cavity, RM11), so the focal length is a compromise. But interestingly, it is the same at CEBAF.
* The keV emittance can be measured at 501 provided intrinsic energy spread is negligible (buncher off). I'm not sure if it is, but at least in y the result may still be meaningful.
+
** The orbit needs to be very straight for the beam to make it all the way downstream, but to adjust this, we need both upstream correctors, 401A and 402, so centering in the lens at the same time is very difficult.
* qsUtility lacks harps to directly measure the optical functions prior to M601, especially directly before and after the booster. Need to measure them at M601 for a few suitable beam energies and backpropagate to M401 in preparation for simulations of the HKDL optics.
+
** We should do a GPT study and play with a potential extra lens, but I would intuitively suggest something like this:
** It may be useful to perform this measurement methodically for a variety of booster output energies. This could result in a separate tech note that contrasts the optical effect of the booster with what was measured at CEBAF (JLAB-TN-15-052). The quality of such results may, however, be affected by a poor understanding of the MeV optics, seeing as they will need to be adjusted. Maybe we can leave the last two quads off to alleviate this? Should be supplemented with Elegant simulations.
+
*** Remove Brock cavity, not needed
 +
*** Add corrector between MFQK403 and A4
 +
*** I think having the beam converge slowly into the booster is good, so I like that the lens is far away. Maybe the aperture should just be closer to the booster? At the very least, put it behind the BPM so we can see where we're at.
 +
* MFAK303 has a similar problem. Being single-wound, it is supposed to be equal and opposite to MFAK301, but this fixes its focal length, while it is supposed to focus in both the buncher and the dipole. This issue does not seem critical, but it could be pondered sometime.

Latest revision as of 13:43, 12 November 2022

MeV beam time

  • Test IHAM505
  • TM beam to 703 to see RF drift (full shift)
  • Verify optics setup for HKDL
    • To produce small beam at M703, first measure Twiss at 501 and then optimize beta_x with Elegant: try to make it small in the dipole AND at the harp if possible (keep the dipole from focusing)
  • Repeat buncher study, booster crested, 8 MeV, multiple scans per point
    • It may be interesting to do the buncher study with the 7-cell off.
    • This reduces microphonics impact, but optics of the low-energy beam are a problem
    • Crank 2-cell up?
  • Buncher power vs. GSET
    • Once correct buncher power is found, measure displacement at +/- 90 degrees on K501 again
  • Test booster off crest, scan buncher if results good

keV beam time

  • LVQE scan at different voltages. Expect same result, provided different laser powers at same voltage give same result (avoid SCL).
    • Results are different, don't know if related to instrumentation (battery resistance etc.) or physics. If it's physics:
      • CST: Does thermal energy affect collection efficiency?
      • Ion current? probably too low to matter
      • Try adjustable bias voltage source (Keithley)
  • HVQE scan at different voltages. Expect different result.
  • High current to FC2 for 12+ hours, check if drift is gone. Check with buncher ON and buncher OFF.
  • Look at mains-harmonic BPM signals as a function of parameters (buncher etc.)
  • Measure bunch length upstream (chopper or Brock)

Random things to change when it makes sense

  • The way MFQK403 is supposed to focus into both Aperture A4 and the booster is flawed for multiple reasons:
    • The lens would need to produce multiple waists (DP can, A4, Brock cavity, RM11), so the focal length is a compromise. But interestingly, it is the same at CEBAF.
    • The orbit needs to be very straight for the beam to make it all the way downstream, but to adjust this, we need both upstream correctors, 401A and 402, so centering in the lens at the same time is very difficult.
    • We should do a GPT study and play with a potential extra lens, but I would intuitively suggest something like this:
      • Remove Brock cavity, not needed
      • Add corrector between MFQK403 and A4
      • I think having the beam converge slowly into the booster is good, so I like that the lens is far away. Maybe the aperture should just be closer to the booster? At the very least, put it behind the BPM so we can see where we're at.
  • MFAK303 has a similar problem. Being single-wound, it is supposed to be equal and opposite to MFAK301, but this fixes its focal length, while it is supposed to focus in both the buncher and the dipole. This issue does not seem critical, but it could be pondered sometime.