BBQ and Other Developments

APEX Cameron BBQ 3Nov06

BBQ and Other DevelopmentsBBQ and Other Developments

Peter Cameron


OutlineOutline• 60Hz harmonics - covered yesterday• Chromaticity measurement/feedback

– slow (1Hz) radial modulation – the baseline– slow (<0.5 fs) or fast (>>fs) phase modulation– multitone– continuous head-tail

• e-cloud tune shift along the bunch• Central frequency measurement

– two parameters – non-lin chrom and momentum offset

• BTF– optimize (Wolfram) – BBTF for lumi,…

• Monopole squid


Chromaticity Measurement and FeedbackChromaticity Measurement and Feedback

• Chrom feedback – the final step in ramp ‘automation’?• “Present measurement quality is questionable” – AD et al• Possible alternative techniques for continuous measurement

(desirable for feedback)– phase modulation (SPS, Tevatron, RHIC)

• advantage - does not stress tune tracker (mod freq beyond PLL BW)• disadvantages – frequency must avoid synchrotron frequency, possible beam

loss, not clear S/N is better than slow radial

– 3 tone method (Hermann’s suggestion – 100 tone) (SPS, RHIC?)• advantage – no momentum perturbation• disadvantages – additional excitation/emittance growth, complication of

synchrotron satellites, requires knowledge of eta, bunch length,…

– continuous head-tail (SPS, Tevatron, RHIC)• advantage – no momentum perturbation• disadvantage – no proper theoretical understanding (yet)


Summary of Chromaticity

t

t

vert

horiz

+5

-5

dp/p of +/-10-4 gives ~+/-100 radial modulation (RHIC&LHC)

-5

-5

+5

+5

Q'

Q'

Q'ramp 6380

ramp 6382

ramp 6381

in RHIC modulation is at 1Hz

chrom - good results under sequencer control





• advantage - does not stress tune tracker (mod freq beyond PLL BW)• disadvantages – limited to <~1/2 synchrotron frequency, possible beam loss,

not clear S/N is better than slow radial





SPS testing Sep 2006courtesy Ralph Steinhagen


so far – S/N poor for comparatively large dp/p











courtesy C.Y. Tan


courtesy C.Y. Tan


Multi-tone methodMulti-tone method

• Recent (yesterday) results from SPS– 3 tones – central lock plus 2 side tones– same kicker power at all 3 lines– 40Hz offset– PLL BW 20 Hz– fs ~100Hz to 200Hz – general statement - “good results” - no quantitative data yet

• Difficult to implement at RHIC– varying synchrotron frequency on ramp, as low as ~10Hz at transition– PLL BW ~10Hz– just the same, it is worth studying, especially in light of……

• Hermann’s suggestion – 10 tone? 100 tone? – 3D AFE gives headroom on S/N before emittance growth becomes an issue– with FPGA-based BBQ it becomes somewhat trivial (at least from

hardware/software point-of-view) to lock MANY loops on the beam – starts to look more like continuous BTF











continuous continuous head-tailhead-tail


Rhodri Jones – continuous head tail 500 turn simulation results, phase difference between head and tail (settling time evident)


head tail

lowpass filtered head x tail

1 second

mean = .758

mean = .283

February 2006 RHIC Run 6 - continuous head-tail chromaticity measurement using BBQ (no momentum perturbation)

Marek and Rhodri


Chromaticity Measurement and FeedbackChromaticity Measurement and Feedback• Chrom feedback – the final step in ramp ‘automation’?• “Present measurement quality is questionable” – AD et al• Possible alternative techniques for continuous measurement






– continuous head-tail (SPS, Tevatron, RHIC)• advantage – no momentum perturbation• disadvantages

– no proper theoretical understanding (yet – effort at both CERN and FNAL)– RHIC results not repeated at SPS

• Marek is working on improved detector




• e-cloud tune shift along the bunch – use 3D AFE?• Central frequency measurement

– two parameters – non-lin chrom and momentum offset


• Monopole squid





– ‘two’ parameters – non-linearities and momentum offset


• Monopole squid


Tune spread measurement methods

• Sliding window fit to response to Artus kick • gives amplitude dependence of coherent tune

• Schottky – difficult to get needed resolution• (upper width + lower width) - (2 x rev width) • gives tune spread due to octupole and higher, (plus beam-beam,…)

• Zoomed Schottky • width of central line of incoherent betatron distribution • gives tune spread due to all contributions (sextupole, octupole, beam-beam,…)

• Central Frequency - all contributions

from 23 Jan 04 BMX meeting


LF Schottky at Injection

chrom = (lower - upper) / dp/p

tune spread =(lower + upper) - (2 x rev)

gives tune spread due to octupole and higher, (plus beam-beam,…)


zoomed HF Schottky - revolution line

At store with storage RF on

central line ‘infinitely narrow’

Synchrotron freq ~ 250Hz


LF Schottky at injection - 9 Dec 03

BH ~ 41 Hz~ .0005

BV ~ 29 Hz ~ .0003

YH ~ 81 Hz~ .001

YV ~ 30 Hz ~ .0003



• Data from Dec 03 RHIC BMX• Max beam lifetime was not at central frequency• At that time not obvious how to improve RHIC performance using this measurement

• Steve Tepikian presentation a few weeks ago

• effect of NL chrom on tune footprint, beta fcns,…• suggests why CF not optimal

A possible relatively simple APEX:• two knobs – amount beam is off-momentum, and non-lin corrector strength• explore this parameter space for beam lifetime





– ‘two’ parameters – non-linearities and momentum offset


• Monopole squid


Monopole squidMonopole squid• just a heads up• squid based monopole detector proposed

to PAC by Chaudhari et al• committee recommendation was to get

experience with squid in RHIC IP radiation environment – concern is spurious radiation-induced quantum flux jumps

• test installation is in preparation for IP10• will need ~1hr access at start of APEX to

transfer helium to the dewar

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BBQ and Other Developments