Machine Review Committee 2009

Special Studies with Crab Cavities
Background of special studies
Special study 1: Controlled RF noise with crab cavities
Special study 2: Longitudinal kicked beam with crab cavities
SummaryYoshiyuki MoritaKEKBackground of the special studies
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Crab crossing was proposed for the upgrade of LHC.
KEKB is the first machine which applied the crab crossing.
We started collaboration for;1) Basic studies for LHC crab crossing using KEKB crab cavity.
2) Understand and solve luminosity reduction of KEKB at high current.
As a collaboration meeting between LHC and KEKB, we held a video
meeting on Aug. 5, 2008.
In the meeting CERN LHC people suggested several ideas for the KEKBmachine studies.
We picked up two studies;
1) Controlled RF noise study with crab cavities.
2) Longitudinally kicked beam study with crab cavities.
We conducted above studies on Dec. 12 with Rogelio-san from CERN.
Funakoshi-san conducted study1 again and obtained different results.

Presented at MRC2007 by Akai-sanPhase stability (cavity pick up signal)

Span 3MHz
No significant sidebands seen.

Span 200 kHz
Sideband peaks at 32kHz, 64kHz.
Phase error < ± 0.01 deg (fast)

LER

Span 200 Hz
Sideband peaks
at 32, 37, 46, 50, 100 Hz.
Phase error < ± 0.07 deg (slow)

According to b-b simulation by Ohmi-san, allowed phase error
for N-turn correlation is 0.1×√N (degree).

••Spectrum of pick up signal is consistent with phase detector data.
The measured phase error is much smaller than the allowed values
given by beam-beam simulation.

Special study 1Controlled RF noise study with the KEKB crab••••

Add controlled RF noise to the crab cavity
Measure beam size and luminosity
Controlled noise– Single frequency– Close to the horizontal betatron tune: νx (~50kHz)– Far away from νxBeam conditions– Single LER beam with a beam current of 100 mA– Single HER beam (100 mA)– Colliding beams (HER/LER: 65/100 mA)

Controlled RF noises study
LLRF of crab cavity
Vc FB system
Phase shifter

Klystron FB system

Tuner system

RF modulator

Crab cavity

Phase modulation

Added sinusoidal wave from a function
generator to a phase shifter of Vc PLL.

Control system
at D11 station

Phase modulation and phase error
Phase modulated oscillation

Vc & sin("t + # ) Phase modulation: " = " 0 sin(!t )= Vc{sin("t ) cos(# ) + cos("t ) sin(# )}% Vc{sin("t ) + # 0 sin(!t ) & cos("t )}% Vc[sin("t ) +#0{sin((" + ! )t ) $ sin((" $! )t )}]2sidebands
Phase modulation amplitude (phase error) ϕ0 is given by;" 0 (rad ) = 2 ! 10 X ( dB ) / 20
HER excitation: 47.5 kHz, -61 dB

No HER excitation

Study 1
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I?<JOKI?<?DSummarized by Rogelio-sanLER

Single beams

HER

Close to νx
47.5 kHz
HER: νx: .5226, νy: .6016

47.4 kHz
LER: νx: .523, νy: .583

Far away from νx
Close to νy42.0 kHz
LER: νx: .523, νy: .583

39.7 kHz
HER: νx: .5226, νy: .6016

Summarized by Rogelio-sanLER

Single beams
Close to νx

47.4 kHz
LER: νx: .523, νy: .5962

We tested again for LER single
beam with a different vertical tune.
νy: .589 →.5962

LER: νx: .523, νy: .583
HER: νx: .5226, νy: .6016

LER CC noise

Summarized by Rogelio-sanColliding beams

HER CC noise

Close to νx
47.4 kHz47.5 kHzLER σx

LER σx ,σyHER σyFar away from νx
Close to νy39.7 kHz
42.0 kHzLER σyHER σySummary of study 1
Beam condition

Noise

Beam size

LER single

LER νxLER σx↑ LER σy↑Threshold: -60dB

HER σx↑Threshold: -60dB

LER σx↑??

Not significant

LER νyHER single

HER νxHER νyColliding

LER νxLER νyHER νxHER σy↓LER σx↑ LER σy↑HER νyHER σy↓LER σy↑How can we understand these behaviors?

HER crab controlled phase noise
39.1kHz (HER:νy)

Funakoshi
2008/12/17
1600/1037mA (L/H)
1585 bunches

HER σx
HER: νx: .5113, νy: .6062
LER: νx: .5056, νy: .5833

LER σyHER σyLER σx‐75dB‐70dB‐65dB‐60dB‐65dB

Noise amplitude added to HER crab

HER crab controlled phase noise
41.1kHz (LER:νy)

HER σx

HER: νx: .5113, νy: .6062
LER: νx: .5056, νy: .5833

Funakoshi
2008/12/17
1600/1037mA (L/H)
1585 bunches

H‐oscillation
HER σyLER σyLER σx‐75dB‐70 dB ‐65dB ‐60dB‐65dB
Noise amplitude added to HER crab

Study results
andcomparison with previous data

Funakoshi

Present data (Dec. 17) contradict previous data (Dec. 12).
These behaviors depend on tuning conditions.
Previous data
39.8 kHzHER σx41.1 kHz

Hor. Oscillation

HER σx39.1 kHzLER σyLER σyHER σyLER σyDec. 17
Physics run (LER 1.6A, HER 1.1A)
HER: νx: .5113, νy: .6062
LER: νx: .5056, νy: .5833

Dec. 12Beam study (LER 100mA, HER 65mA)
LER: νx: .523, νy: .583
HER: νx: .5226, νy: .6016

Funakoshi

x-y coupling parameters scanned
R4R4, x-y coupling parameter, was scanned as a tuning knob for both rings.
Measured Luminocity, Beam size, Beam life, etc. with and w/o RF noise.
No significant differences were observed.

Funakoshiwith noise:‐65dB (HER:νy)
Beam life

Beam size

Luminosity/GRLER R4

HER R4R4 scanning results

No significant variations.
Other parameters, R1,R2,R3
were also scanned, but novariations were found.

with noise:‐65dB (LER:νy)w/o noise

Special study 2
Longitudinally kicked beam with crab cavities••Longitudinal beam kick with ARES cavities
Monitor beam position by Turn-by turn BPM (by Ohnishi-san)– BOR for backup (by Flanagan-san and Fukuma-san)LLRF of the ARES normal conducting cavity
Fuji D8 station
Frequency: 2.44 kHz
Added to the PLL phase shifter by a function generator

Beam study conditions

LER single bunch operation: 1mA

Control system of ARES (D8 station)

Pickup signal of the ARES D8A

x-z coupling with crab cavity

Crab ON/OFF with longitudinal kick (-46.5 dB)
LER single beam: single bunch with 1 mA
Turn-by-turn BPM at no dispersion

Crab ON

Crab OFFCrab ON/OFF with longitudinal kickand horizontal kickHorizontal kick: injection kicker

Crab ON

Crab OFFCrab ON with low longitudinal kick (-55.3 dB)
and horizontal kick
Crab ON

Bunch oscillation recorder
independently measured
transverse spectrum.
(by J. Flanagan)Summary of study 1 and 2•

Study 1
– Controlled RF noise added to the crab cavity.
– Single beam σx blew up near νx (threshold: -60dB)– No significant effects near νy (far away from νx)– Colliding beams have much complicated behaviors.
– Those behaviors are dependent on tuning conditions.
• Dec. 17 data contradict Dec. 12 data.
– Need more studies to understand.

•Study 2– Longitudinal beam kick by ARES cavities.
– First observation of x-z coupling at crab cavity.
– Detailed data analysis in progress.