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Debuncher “phase jump” project

Decouple Debuncher RF frequency from MI 120 GeV frequency 53.103080 MHz could move by ~1-2 kHz Can center beam in Debuncher (Steve W’s ESME graphs) Added degree of freedom will facilitate 8 GeV energy match with RR Could even stack at higher flat-top energy. Debuncher “phase jump” project.

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Debuncher “phase jump” project

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  1. Decouple Debuncher RF frequency from MI 120 GeV frequency 53.103080 MHz could move by ~1-2 kHz Can center beam in Debuncher (Steve W’s ESME graphs) Added degree of freedom will facilitate 8 GeV energy match with RR Could even stack at higher flat-top energy Debuncher “phase jump” project

  2. MI RF at 120 GeV (say 53.103 MHz): Desired Debuncher RF (say 53.101 MHz): digitally synthesized with DAC driven by programmable logic On MIBS $79 event, jump phase of synthesized Debuncher RF to match measured phase of MI RF, plus programmable offset phase jump  bucket-to-bucket transfer still works

  3. Implementation: reprogram spare MI damper board DAC output (x4) 12 bit, 424 MS/s Ethernet (Acnet etc) • Fast ADC + digital logic measures MI phase • Digital logic + fast DAC replaces VCO in Debuncher LLRF CPU slow control FPGA signal processing ADC input (x4) 12 bit, 212 MS/s TTL I/O

  4. The FPGA (programmable logic) coding looks like something in between writing a program and drawing a schematic.

  5. Debuncher LLRF (AP50) Damper board

  6. For now, we swap out VCO module during tests (DDS signal replaces raw VCO)

  7. Initial test: looked at MI RF, new RF, and BPM signal on scope, to see that MI RF and new RF line up on first turn • Last Friday: Dave P. and I plugged in modified VCO module toward end of Keith’s bump studies, and stayed in once stacking started back up • Flux capacitor scope showed that once we set synthesizer’s phase offset, it continued to match up on future $29 cycles • Is there a way to plot measured phase on a FTP? • Stacking rate (~3.7E10/hr, with a stack of ~180E10) with synthesizer was about the same as stacking rate once VCO was put back • But cavities had detuned by the time we started stacking, so we couldn’t check the bunch rotation • Is it easy to look at momentum spread just after bunch rotation? • Other good Debuncher diagnostics I should learn to use?

  8. Next test (this week?) • Get DDS amplitude right (took us a while last time) • See if stacking works OK during a long test • Plot flux capacitor error signal over many cycles? • Look at momentum spectrum after bunch rotation, before and after swapping VCO modules • Try moving MI frequency (to MI central orbit), keeping Debuncher constant, and see if stacking rate is preserved • How long to retune if Debuncher moved down from 53.103 to 53.102? (Then look at tails in post-bunch-rot momentum spectrum.) • How easy for me to learn what these studies could break and how to fix it or re-tune it?

  9. Rotator cavities on, 219us before beam arrives; stay on for 306us (DRF1-2 fanback shown). Need phase stable before this (no problem: phase jump occurs 295us before beam).

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