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Optics Update


(KDP compiled these notes, but may not have understood perfectly. Please correct if necessary.)

  1. Ryan compared FocalPlane vs Transport definitions, apparently theta_FP is significantly dependent on x position.
    • We concluded that the FocalPlane variables don't easily project to "real" space, that, is, in transport coordinates one might calculate transverse position as x(z) = x_trans(z_fp) + theta_trans*(z - z_fp) but in focal plane coordinates this expression would look more complicated, and it isn't really apparent what x_fp(z) really means in physical space.
    • we suggest looking at transport coordinates for considerations of (for example) the waist locations.
  2. Ryan showed waist locations for two thin carbon runs. In both cases, it appears that the waists (calculated by projecting from x_trans and y_trans) occurred at roughly z=-1m for x and z=20-30cm for y.
    • The agreement between the runs wasn't perfect, and for one run the plot didn't go far enough on the x axis to be sure we were seeing the waist.
    • given the small variation of the beam size, it isn't clear that the differences in the waist positions between the runs is significant. The waist sizes themselves also didn't quite agree.
  3. Ryan showed the (previously seen) result that the ratio of quad field strength between StdTune and TuneB in reality, did not match the ratio of the quad strength that HRStrans finds when it 1) reproduces the StdTune 1st order transport matrix, or 2) optimizes for zero matrix elements to re-create TuneB (that is, finds fields such that <x|theta> = 0 and <y|phi> = 0, I think).
    • Ryan then pointed out that there is a negative sign in the definition of the PREX central angle (th0) and the HRS angle (th1) that he didn't understand.
    • Flipping that sign, then recalculating the TuneB setpoints, he finds that the StdTune/TuneB quad strength ratios agree (roughly) with the StdTune/TuneB ratios that were used during PREX-I.
    • This might be a total coincidence, but it gives a new avenue to check.
    • On a similar point: Bob thinks that the target-to-Q1 distance in HRStrans may be wrong (based on numbers given to him by Al Gavalya).
  4. We concluded that Ryan should look at the waist location calculated in HRStrans for various of these TuneB candidates:
    • the TuneB originally developed in HRStrans (for which the quad strengths do not seem to match what was used during PREX-I)
    • the TuneB developed in HRStrans after the th0 and th1 parameters are flipped in sign. (question: does he use these quad strengths while running HRStrans with the as-written signs, or his reversed signs? Maybe, try it both ways?)
    • The TuneB developed in HRStrans when using a target-to-Q1 distance to be provided by Bob.
    • (Another question: it was not clear to me what ray-packet should be used to calculate these waist positions. Presumably there is some reasonable model of rays accepted from a target?)
  5. A separate thought: I asked why we don't extract the first-order transport matrices from data, to compare with the first-order transport matrices being calculated by HRStrans. This might be a more quantitative or more informative comparison to make between data and HRStrans?
  6. Bob also suggested that Ryan check the definition of the variable "rho" in the HRStrans code. This is fairly complicated, and Bob hasn't cross-checked it recently.
    • I suppose we should try to deal with the sign of the th0 and th1 parameters correctly, also. Ryan doesn't think they should be defined with a negative sign. is he correct? Can someone explain why those signs really should be that way?