# Presentation: 865584

## Tune Feedback for Polarized Protons

- Status of Tune Feedback at RHIC
- Peter Cameron

- RSC Tune Feedback Update

## Ramp Control Requirements

- Tune measurement and feedback
- Avoid resonances - betatron and spin
- Chromaticity measurement and feedback/feedforward
- Avoid tails on resonance
- Stability (right sign)
- Coupling measurement and feedback/feedforward
- Control tune
- Minimize higher order resonance strength
- Accomplish this without excessive emittance growth/halo formation

- RSC Tune Feedback Update

## Tune Feedback Block Diagram

- f ~ 245MHz

- Pkick < 1W

- Acceleration RF 28MHz

- RSC Tune Feedback Update

## Tune Feedback in early RHIC 2003

- Seven ramps attempted, all ‘successful’, but deuteron beam survival worse with TF on!
- Resonance between TF and power supplies? Radial loop? Beam-beam? Too much loop gain in PLL? Bad chrom?
- This problem was not observed with gold beam
- This problem has not been understood
- There have been no tune feedback ramps since the change to equal frequencies

- RSC Tune Feedback Update

## Ramp with Tune Feedback

- Blue (deuterons) Ramp with Tune Feedback RHIC 2003

- .24

- .23

- .22

- .21

- transition

- flattop

- Dots are kicked tune measurement

- RSC Tune Feedback Update

## Beam Buzz 

- .245

- .232

- Tune ‘buzz’ at beam loss

- f ~ 4Hz

- RSC Tune Feedback Update

## Broad 20Hz line – beam-beam?

- 12Hz cryostat
- vibration

- 18Hz beam-beam?

- 20dB

- Often
- >30dB

- RSC Tune Feedback Update

## Ramp with Tune Feedback

- Blue (deuterons) Ramp with Tune Feedback RHIC 2003

- .24

- .23

- .22

- .21

- transition

- flattop

- Dots are kicked tune measurement

- RSC Tune Feedback Update

## Ramp with Tune Feedback 2

- Amplitude and phase during
- Ramp with tune feedback

- transition

- flattop

- RSC Tune Feedback Update

## Transition Crossing

- Key to successful tune feedback is locking to a very small (~femptowatt) excitation signal in the presence of watts of coherent power
- Fundamental weak link is saturation of the first amplifier
- Resonate pickup difference mode for sensitivity and rejection of sum mode
- Above the nominal coherent spectrum
- Moveable BPM with position feedback to center pickup on the beam
- High Q cavity filters
- Transition defeats two of these
- Short bunch length puts pickup in the coherent spectrum
- Orbit shifts drive the pickup at the revolution line
- More kick required to stay above rising noise floor (due to saturation) creates emittance growth
- In addition, there are large tune jumps at transition

- RSC Tune Feedback Update

## Summary of TF in early RHIC 2003

- Tune control has not been a problem at a level that has been judged sufficient to warrant the additional complexity (and the associated learning curve) involved in making tune feedback operational - operations efficiency has been dominated by other issues
- Transition crossing presents problems that will probably be properly addressed only with a new pickup
- Feedforward has not yet been implemented - impeded use of tune feedback in ramp development
- Sufficient study time was not given to emittance growth

- RSC Tune Feedback Update

## Ramp Control Requirements

- Tune measurement and feedback
- Avoid resonances - betatron and spin
- Chromaticity measurement and feedback/feedforward
- Avoid tails on resonance
- Stability (right sign)
- Coupling measurement and feedback/feedforward
- Control tune
- Minimize higher order resonance strength
- Accomplish this without excessive emittance growth/halo formation

- RSC Tune Feedback Update

## Ramp Tune Measurement

- Ramp Tunes with 1Hz 200
- micron radial modulation
- for chromaticity measurement

- transition

- .24

- .23

- .22

- .21

- deuterons

- RSC Tune Feedback Update

## Chromaticity up the ramp 

- Ramp chromaticity

- PLL amplitude and phase

- 10

- -10

- 0

- Chromaticity Measurement on the Ramp - deuterons

- transition

- RSC Tune Feedback Update

## Chromaticity Scan 

- = 5

- 9

- 13

- 17

- vert

- horiz

- Search
- window

- Chromaticity scan

- .20

- .25

- Effect of Chromaticity on PLL

- RSC Tune Feedback Update

## Amplitude Response During Scan 

- = 9

- 13

- 17

- Amplitude and phase during chrom scan

- RSC Tune Feedback Update

## Ramp Control Requirements

- Tune measurement and feedback
- Avoid resonances
- Chromaticity measurement and feedback/feedforward
- Avoid tails on resonance
- Stability (right sign)
- Coupling measurement and feedback/feedforward
- Control tune
- Minimize higher order resonance strength
- Accomplish this without excessive emittance growth/halo formation

- RSC Tune Feedback Update

## Skew Quad Modulation

- 2Hz skew quad modulation, two families, 180 deg phase

- RSC Tune Feedback Update

## PLL FFT of Skew Modulation

- 0

- 0 Hz

- 40 Hz

- ~10-4

- 4Hz 35dB peak

- RSC Tune Feedback Update

## PLL FFT of Skew Modulation

- 0

- RSC Tune Feedback Update

## Ramp Control Requirements

- Tune measurement and feedback
- Avoid resonances
- Chromaticity measurement and feedback/feedforward
- Avoid tails on resonance
- Stability (right sign)
- Coupling measurement and feedback/feedforward
- Control tune
- Minimize higher order resonance strength
- Accomplish this without excessive emittance growth/halo formation

- RSC Tune Feedback Update

## PLL Amplitude vs Kicker power 

- PLL amplitude for kick reduced in 3dB steps

- Pmax ~ 2W

- -3dB

- -3dB

- -3dB

- -3dB

- P ~ 100mW

- ?12dB reduction in kicker power
- gives 6dB reduction in signal?

- -3dB

- RSC Tune Feedback Update

## What We’ve Learned this year

- PLL is greatly improved from last year
- PLL functions well over a large chromaticity range (but what are relevant parameters? – need good beam/PLL/magnet model)
- Chromaticity measurement on the ramp via radial modulation is viable
- Coupling correction is an issue - measurement via skew quad modulation is being actively investigated
- Preamp saturation is an issue, particularly at transition
- Emittance growth is an issue – optimization of kick amplitude and loop gain in progress

- RSC Tune Feedback Update

## Plan and Perspective for Polarized Proton Run

- Plan (what we want to complete before polarized beam)
- Additional ramps with TF during dAu run
- Add feedback to loop gain and amplifier power (in progress)
- Add image rejection hardware
- Simplified operator interface
- Feedforward of magnet corrections implemented
- Additional coupling studies
- Additional studies of moveable BPM control
- Perspective - Without transition crossing, and with smaller orbit and tune jumps, polarized protons look easy in comparison with dAu. Biggest issue seems to be smooth integration with operations

- RSC Tune Feedback Update