UITF Notes

Opportunistic tests and long-term ideas off the top of my head

• Measure p spread on 703
  • Not trivial because contribution of beta function is significant
  • eta = length * tan(theta) = about 1.2 m
  • 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.
  • Assuming Gaussian distributions: momentum spread = sqrt(sigma^2 - epsilon*beta) / eta, yes?
  • epsilon*beta = 0 would give an upper bound of 4.6e-4.
  • We know the emittance (7.3 nm at 8 MeV/c). How do we get the beta function?
    • 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.
    • Elegant can calculate the betas directly from first principles, but we can't trust the model until we validate it.
    • 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.
    • 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.
    • Do the optics study for HKDL first. As soon as we know the Twiss parameters upstream of the quads and we convince ourselves that the quads do what they should, this special case becomes trivial.
• Is there anything we can learn from the BPMs / correctors to supplement the gun kick study at CEBAF?
• 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 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 value of this measurement is largely academic, though, in that what ultimately matters is the beam after the booster.
• In preparation for the simulation of the HKDL optics, we need to know the beam ellipse at the entrance to the quads.
  • We don't know what the booster does to the transverse phase space, and we also don't know if our model of the quads is correct. These problems need to be decoupled as follows:
    • Perform any reasonable pair of quad scans to determine the beam ellipse upstream of M501. Ignore the booster, just take the beam ellipse at its exit for what it is. What exactly "reasonable" means will be determined empirically on the first try. It can be refined once we know roughly what we are working with. Based on previous simulations of the whole beam line using Dennis's model, we should assume that the booster overfocuses at high output energy and therefore produces large betas at the first quad, so the first two quads probably can't be scanned too liberally. In principle, any quad or set thereof can be used to do this.
    • Put this beam ellipse into an Elegant model starting at M501 to predict the x and y beam size at the harp as a function of all quad strengths within reasonable parts of the parameter space. Confirm these predictions experimentally. If they are consistent, that means the quads are modeled correctly. This model will then give an accurate prediction of the beta function anywhere downstream (at this energy). Otherwise, find out what is wrong (distances, wiring issues) and iterate.
  • 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).

Random

• Harp axis calibration does not matter: It only changes the measured emittance but not alpha/beta, and its effect does not depend on the quad in use.
• Adding reasonable quadrupole moments to correctors is not enough to explain the inconsistency. It would need an extra quad with K1 ~ 5.
• At dp/p = 1e-3 (which is higher than what we observe unless the measurement is flawed), seeing significant inconsistencies in the quad scans needs a dispersion of many cm. In y, the only dispersion in this part of the lattice should come from the earth's field; this gives about 8 mm at the harp, much too low to see anything.

Urgent

• Edge focusing of the 601 dipole is not well-understood yet. Solve with tracking.
• The dispersion at 703 can be measured directly (though there's not really any reason to assume it's different from theory):
  • Vary momentum, steer back with dipole. This determines delta p as a function of delta GSET around the operating point without any effects from edge focusing (constant path length through the field).
  • Then, apply a well-known delta p to move the beam off-center and measure the displacement with viewer and harp.
• Make sure 700 quads are at zero field! Consider degaussing, measure with probe
• Make sure 700 correctors have no quadrupole moments (realign if necessary).
• Same for 201 and 401, can be verified by measuring beam size x/y vs. steering strength
• Take home an allsave of the 500 correctors (note polarity errors)
• Measure earth's field, I don't recall the z component being 40 µT anywhere in the UITF