HarmonicKicker-2021-06-18

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We should talk about the kicker test from a broad perspective to get a realistic sense of the difficulties and options.

What we need to measure

  • Measure kick angle of HK as a function of the kicker bucket number
  • Measure emittance degradation as a function of the kicker bucket number

What we don't need to measure; correct me if I'm wrong

  • impact of ludicrous bunch charges, unless they are needed for diagnostics
  • bunch train with multiple "different" buckets filled at the same time

Beam setup and diagnostic options

  • Filling all kicker buckets at the same time is possible, but having to geometrically separate the beams poses unnecessary difficulties in terms of beam line optics and temporally sensitive diagnostics.
    • Assumption: bunch frequency = f_RF / 121 = f_Kicker / 7 ~ 12 MHz.
    • All bunches then arrive at the same kicker phase.
    • The kicker phase knob selects the kick voltage.
  • Depending on how much space the kicker itself needs, it may need a new beam line of its own or not.
  • Measure kick angle with one or two BPMs downstream of the kicker. I feel like we will need two for a good determination of the tilt unless we take precautions to precisely align the launch into the kicker.
  • The available BPMs are most likely of a non-resonant type. John and Tom agree that they should be able to detect 12 MHz, though their LPF characteristic means the signal will be down by > 40 dB.
    • Because the signal is so quiet, the usual BPM electronics will not readily see it.
    • Tom: The signal can be measured directly with a 4-ch scope (preamp if necessary). While the pulses are far too short for any scope bandwidth, they could be dispersed relatively easily.
    • John: There is a circuit that will turn the signal into DC, which we're not fond of, but it's simple.
    • The detector likes long bunches, whereas the kicker does not.
    • Provided LHe + 12 MHz pulsed laser become available, the BPM readout should be tested ASAP to get a sense of how good the signal can be.
    • Baseline calibration of BPM readout can be done with CW or tune beam with kicker turned off.
  • Direct emittance measurement by way of quadrupole scan + transverse profile detector (e.g., harp).
    • Regardless of the kick, the beam always needs to be centered in the lens.
    • Unless I'm missing something, this needs three steering magnets downstream of the kicker to make a chicane that sets up a parallel launch into the lens + harp system (the kicker itself being the fourth steerer).
    • Because geometrically separating the bunches is unnecessary, this system can be kept short, alleviating requirements on focusing / aperture.

Prerequisites

  • What bunch length is really needed?
    • If the bunches were really short, the distribution of kick angles within the bucket could be measured directly. This would provide a cross-check for the emittance measurement or replace it entirely.
    • MeV bunch length measurement not currently available. Longitudinal optics of the machine without space charge can be simulated and should align with reality reasonably well.
  • We assume a 1497 MHz buncher is available. Would it work with the present setup hypothetically, i.e., 750 MHz buncher? Half the bunch frequency.
  • What is the expected impact of the new gun + booster?
  • Time scale?