Tune/Coupling/Chromaticity Measurement and Feedforward/Feedback

LARP Berkeley Apr 2006

Tune/Coupling/ChromaticityTune/Coupling/ChromaticityMeasurement and Measurement and

Feedforward/FeedbackFeedforward/Feedback

Peter Cameron


OutlineOutline

• Decoupling• Ramping• 3D AFE ‘Beam Noise’ Susceptibility• Plans


x

y

Q1

Q2

A1,xA2,x

A1,y

A2,y

x

y

Q1

Q2

1,x

1,y

2,x

2,y

x

y

Q1

Q2

A1,xA2,x

A1,y

A2,y

x

y

Q1

Q2

A1,xA2,x

A1,y

A2,y

x

y

Q1

Q2

1,x

1,y

2,x

2,y

Schematics showing the two eigenmodes rotated with respect to the horizontal and vertical planes due to coupling. The left hand figure shows the special case where the projections of each mode in each plane are in phase. The right hand side shows the more general case where coupling introduces a phase shift into the eigenmode projections.

C-A/AP/174 - Possible phase loop for the global betatron decoupling, Y. Luo et al C-A/AP/204 - Towards a Robust Phase Locked Loop Tune Feedback System, R. Jones et al both at http://www.rhichome.bnl.gov/AP/ap_notes/cad_ap_index.html


Manual DecouplingManual DecouplingSkew chrom

0

Chrom measurement


You will see this slide again


Coupling Echoes Coupling Echoes

½ synchrotron period

1 sec

Coupling coefficient ‘C’

0

.02


OutlineOutline



First Ramp with FeedbacksFirst Ramp with Feedbacks


First Ramp with Feedbacks 2First Ramp with Feedbacks 2


Last Blue Ramp with FeedbacksLast Blue Ramp with Feedbacks


Next Ramp with Feedbacks OffNext Ramp with Feedbacks Off


OutlineOutline



Beam NoiseBeam Noise

• Steve Peggs – “declare Victory”

• Peter Cameron – “Mission Accomplished”

• One messy little detail– 3D AFE sensitivity to

‘beam noise’– No free lunch


3D AFE ‘beam noise’3D AFE ‘beam noise’• Beautiful when looking at amplitude

– Very sensitive ~10nm– Resistant to dynamic range problems (bunch length, beam offset,…)

• But, when you put it in a phase loop…. • Possible sources

– Radiation Damage?– Beam loss? Direct impingement on electrodes? Amplitude modulation?– High frequencies - longitudinal ‘hot spots’?– Low frequencies - broadband magnet noise? Power supply bit toggling?.....– Instabilities (weak – not noticed by anything except 3D AFE)?– Long range beam-beam?

• Complicating factors– Mains harmonics, IPM– ’10Hz noise’ – cryostat vibrations?– Anomalous tune dependence– Islands– Anomalous phase shifts– Synchrotron satellite sensitivity? Pulsed excitation?


BBQ and PLL S/N ComparisonBBQ and PLL S/N Comparison- static conditions- static conditions

BBQ H

I and Q

PLL both

I and QBBQ V

I and Q


Initial SymptomsInitial Symptoms• BBQ AFE problems – gain chain?

– dropouts– saturation

• First suspicion was radiation damage of the in tunnel electronics– Specifically, gain control– Move electronics out of tunnel – Bench check revealed no problems– Operation with electronics out of tunnel perhaps

showed moderate improvement – capacitance of heliax between pickup and diodes?


Yellow horizontal – Yellow horizontal – ‘dropouts’ during ‘dropouts’ during fillingfilling• signal goes away completely at times• At other times attenuated


Blue Vertical- ‘Saturation’ Blue Vertical- ‘Saturation’ during rampingduring ramping


BV ‘Saturation’ Spectra at storeBV ‘Saturation’ Spectra at store

78KHz span 4.8KHz zoom


APEX ExperimentAPEX Experiment

• The goal – gain understanding of the effect of beam loss on the BBQ, and specifically on the Direct Diode Detection (3D) analog front end

• The procedure– Apply a bump upstream of the BBQ pickup– Observe effect of beam loss on BBQ I and Q signals– Simultaneously observe loss monitors and Schottky


Max bump ~3cm!

BBQ pickup Schottky


BBQ SchottkyBump effect

Total beam loss was ~3X1010


Effect of beam loss on BBQ I and Q was observed only early in the bump Change in loss pattern? Islands?

next slide


Schottky also showed effect only early in the bump, and only in horizontal

times of large losses

Schottky vert

Schottky horiz


Effect of beam loss on BBQ I and Q was observed only early in the bump Change in loss pattern? Islands?

next slide


Zoom on effect of beam loss

next slide


Further zoom on effect of beam loss

~180 degree phase shift= temporary ‘loss of lock’


Similar data from fill 7614, showing progressive deterioration of lock quality as beam loss increases


Effect of beam loss on signal amplitude – ‘AM effect’

~0.5%/turn


Actual loss rate 5 amp/sec (Don Bruno) ~0.025T-m/s~150rad/sec at 25GeV, ~100

~0.5%/turn

1 sec for bump10-4 loss gives 10-9/turn


Polarimeter EffectPolarimeter Effect


100MHzHi-Pass no filter

50MHzLo-Pass

100MHzHi-Pass plus50MHzLo-Pass

Effect of filtering in front of diodes


BTF MethodBTF Method

• Excite beam ~10 microns• Phase synchronously

demodulate response to get amplitude and phase

• Can get – Direct– Coupling– Beam-beam

• Lockin plus 3D AFE gives excellent sensitivity


• Transverse instability• Not fixed by chrom• Frequently present at a

level not detectable by anything other than BBQ

• Upper half of sideband


Effect of long range beam-beam on the ramp


3D on the Ramp - 1 Jan 05

dominant

spacing

is 180Hz

60Hz onset

60Hz end

IPM every

100 turns

(780 Hz)


coupling excitation is horizontal

vertical

horizontal


Anomalous tune dependenceAnomalous tune dependence

• Next slide shows odd behavior of BBQ phase noise during a tune scan– Tunes are fully decoupled– But, somehow for small tune separations tune phase

noise (fluctuations in Q) is small, and for separations greater than ~.01 it becomes large

– Additional phase noise in horizontal late in the tune scan can probably be attributed to beam loss

– ???


BBQ during tune scan (BBQ during tune scan ( const) const)

Vert I and Q

Tunes and beam decay

HorizI and Q

~.01 units of tune

Effect of beam loss?

decoupled!!! dqmin<.001


Summary on 3D AFE ‘beam noise’Summary on 3D AFE ‘beam noise’• We don’t know where it comes from• With other pressures of RHIC operations easing, time

available to start investigating more intensively• What we have tried

– Filtering – both in front of diodes (MHz range) and digital (tens of Hz range)

– Hybrid– Reversing diodes– Pickup centering with motion control – no effect– Changing time constants – suspicions here

• Need to make a plan


Short term plan Short term plan • Investigate 3D AFE

– Rhodri visit 2 days next week– Marek visit before RHIC turns off?– 3D in phase loop at Tevatron?

• Chromaticity measurement and feedback• Implementation on DAB board

– CERN visit early July– CERN visit September – PLL on SPS

• See behavior of 3D in phase loop

• Longer term – more Tan involvement

Tune/Coupling/Chromaticity Measurement and Feedforward/Feedback

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