North Damping Ring RF

Transcription

1 North Damping Ring RF

2 North Damping Ring RF Outline Overview High Power RF HVPS Klystron & Klystron EPICS controls Cavities & Cavity Feedback SCP diagnostics & displays FACET-specific LLRF LLRF distribution RF Feedbacks: RF scope (TEK scope) Feedback triggers Tuning tips

3 System Overview: Purpose From P. Krejcik s Damping Rings RF Users Guide The RF system provides a synchronous accelerating voltage to make up for the energy individual particles lose due to synchrotron radiation and the energy a bunch can lose from higher order mode losses. In addition, the RF provides a longitudinal restoring force that keeps the particles bunched together inside the RF bucket.

4 Some Damping Ring Paramters Beam Energy 1.19 GeV RF Frequency 714 MHz Revolution Frequency 8.50 MHz Harmonic number (buckets) 84 Energy Lossper Turn Either 93.1 kevor 79.2 kev? RF voltage 800 kv Phase 6.7 Synchrotron Frequency khz Storage Time 16.6 ms Available Klystron Power 50 kw Bunch Length 5.25 mm (4.5 of 714 MHz) Energy damping time 1.78 msec Horizontal damping time 3.5 msec Vertical damping time 3.53 msec Pi mode cavity damping time 100 μsec

5 High Power RF

6 HVPS SLAC-built CW klystron, no modulator, no VVS. No PIOP, just DAC/SAM readout in SCP On/off control only, through EPICS

7 NDR Klystron One CW klystron, located inside the vault, SE corner. Capable of 60 kw peak AMRF sets voltage locally, usually ~800 kv, designed to be capable of >1MV Klystron has no PPS interlocks Two cavities driven through isolator and magic tee to prevent reflected power from the cavities from reaching the klystron

8 NDR Klystron Controls Klystron Mode: OFF: No LLRF TUNE: Allows tuners time to adjust at a lower RF power level OPER: Running with full gap voltage To reset after a trip: Clear interlocks, turn on HVPS, Change modes from off to tune, wait until cavities turn green, change mode to operate.

9 RF cavities RF Cavity 590 Two cavities, two cells in each. Unit numbers 590 (Cavity A) and 810 (Cavity B) Cavity tuners : mechanical plungers moved by stepper motors Tuner feedback controls in EPICS

10 RF cavities Cavity tuner feedbacks in EPICS In Automatic, feedback moves the phase loading angle, a phase comparison of the 714 MHz waveguide pickup signal and the cavity pickup signal ~1 Hz feedback In Manual, users have control of the position slider. Option to have the feedback disabled when beam is not present (could prevent tuner from walking away when there is no beam loading)

11 πmode Cavity Passive Cavity, meant to damp πmode oscillations in twobunch operation If the tuner ends up in the wrong place, power can get absorbed, structure heats up, create vacuum problems.

12 Klystron EPICS displays

13 SCP displays

14 Status Displays Update every 2 minutes

15 LLRF Distribution

16 LLRF Distribution Functional Schematic

17 Simplified RF cartoon (SLC era)

18 Simplified RF cartoon (FACETrelevant only)

19 Voltage Control Oscillator Can use to change the frequency of the incoming LLRF Used during comissioning Used during comissioning mostly

20 Station Phase Adjusts phase of the ring RF at injection relative to the injector RF OPS set to maximize OPS set to maximize capture

21 DR RF Feedbacks Most feedbacks are mostly hardware, adjustments need to be made locally.

22 Question for Mike/Howard Does the gap voltage still go to some intermediate value when we rate limit? Does this attenuator thing that was part of the feedback that we are no longer using do that?

23 Beam Phase detectors 714 and 2856 MHz phase detectors The signal from a BPM pumps an LC circuit, phase of oscillation changes when the beam phase changes.

24 S-Band Phase Loop Phase locks the phase of the damping ring beam to the S-Band phase of sector 2 (and NRTL compressor) Gated: switches on 1.3 ms after injection and then ramps to the desired extraction phase. Makes extraction phase independent of injector phase drifts The change in phase is calculated by the DROPP camacmodule, which has triggers for start and stop times and calculates an appropriate ramp. S-Band desired phase setpointis set by Phase Ramp NREX feedback actuator is an offset to the S-Band feedback

25 Phase Ramp Reference phase at the end of the phase ramp prior to extraction, relative to linac

26 SCP S-Band Feedback Controls

27 S-Band Feedback Triggers

28 Phase Compensation Fbck EPICS feedback, 10 khz Maintains a constant phase between the klystron and cavity. Intended to compensate for power supply variations or phase changes across attenuators used for amplitude control Readbackvalue should normally be zero. If it starts becomes unlocked, it can be reset by opening the loop, adjusting slider until readbackis close to zero, and closing the loop again.

29 Synchrotron Loop Provides external damping of the synchrotron 0-mode bunch oscillations Beam phase is compared to Beam phase is compared to the 714 MHz reference and fedbackto a fast 714 MHz phase shifter

30 Direct loop fbck Many names: Direct Loop, Fleming loop, beam loading feedback MHz feedback. Meant to combat bunch length instability at high current (sawtoothinstability) for SLC (where the bunch would damp to a certain size and then blow up, damp down and blow up) as well as beam-loading transients at injection Adjusts the klystron drive to compensate for the change in beam loading for different bunch lengths. May or may not use for FACET.

31 Status Displays Update every 2 minutes

32 DR TekScope CH1, CH2 can be many things: Beam phase relative to 714 MHz reference or cavity frequency, S-band phase, BPM sum signal peak, cavity gap voltage, etc. HVS thinks remote control doesn t work, so someone will have to drive down, set it up how we want it, and then document which channels are hardwired to which signals.

33 S-Band beam phase 714 MHz beam phase

34 RF Scope Images

35 RF feedback triggers

36 Tuning/Setup tips To get the first two turns: launch, septum bumps To get multiple turns (up to ~20): make sure tunes are right Can get up to 200 with RF off if the tunes are right, per Lanny Adjust Station Phase (Phas1) for max capture (tweak far enough to both sides to see appreciable loss, leave phase in the middle).

37 The end TBD: Supplimentalstuff about SLC things, references