Tune and Coupling Feedback Implementation and Results from RHIC

Tune and Coupling Feedback Tune and Coupling Feedback Implementation and Results Implementation and Results

from RHICfrom RHIC

Peter Cameron

OutlineOutline

• A Brief History• Coupling and Coupling Feedback• RHIC Run 7

– anomalous BTF– tune scalloping

• Plans– ‘hybrid’ tune tracker– chromaticity feedback– continuous head-tail studies

Run00 LF Schottky Pickup, first tune tracker based on SRI lockin amplifierRun01 tune tracker based on RHIC BPM module

– experience gained with tune tracking, preparations for tune feedback beginRun03 tune tracker based on Pentek VME DSP system

– first successful tune feedback ramp was first try with gold (thru transition!)– performance good, but not consistent – failed ramps with no understanding of why

Run04 mechanism of failure of tune feedback in the presence of coupling is finally understood– efforts to ramp with tune feedback end– within one week the ‘eigenmode projection’ method of coupling measurement is running

Run05 no direct progress with tune/coupling feedback, however– early in the run Rhodri and Marek visit, first installation of 3D AFE in RHIC– understanding of mains harmonics is developed– last day of the run, BBQ tracks tune up the ramp

Run06 VME BBQ tune tracker - protons– AP/Controls finally ready for coupling feedback– first attempt delivers decoupled beam to full energy with ~.001 tune control– continued good success through the run, but mains harmonics prevent transition to full

operational status– last week of run - feedbacks used for first successful acceleration of polarized beam to 250GeV– the need for chromaticity control becomes ever more obvious

Run07 VME BBQ tune tracker – gold ions– chrom feedback planned for startup, but Controls Interface not completed– discovery of ‘anomalous BTF’ at injection– discovery of ‘tune scalloping’ on the ramp– mains harmonics plus tune scalloping gives a new problem

Brief HistoryBrief History

Measurement of Coupling using a Measurement of Coupling using a PLL Tune TrackerPLL Tune Tracker

Frequency

Am

plitu

de

FFT of Horizontal Acquisition Plane

Start with decoupled machine

Fully coupled machine: = |C-|

Only horizontal tune shows up in horizontal FFTGradually increase coupling Vertical mode shows up & frequencies shift

Hor

Ver

Set TunesHV

courtesy Rhodri Jones

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

Tracking the vertical mode in the horizontal plane &vice-versa allows the coupling parameters to be calculated



Eigenmode 2

Qx,0

Qy,0

|C-|

Eigenmode 1

Eig

en

mo

deo

r u

np

ert

urb

ed

tu

ne

va

lue

Co

up

ling

Am

plit

ud

e o

r u

np

ert

urb

ed

tu

ne

sp

lit

Eigenmode 2

Qx,0

Qy,0

|C-|

Eigenmode 1

Eig

en

mo

deo

r u

np

ert

urb

ed

tu

ne

va

lue

Co

up

ling

Am

plit

ud

e o

r u

np

ert

urb

ed

tu

ne

sp

lit

Fully coupled Tunes entirely defined by coupling – tune feedback would break here

courtesy Rhodri Jones

Tune Loop Simulink DiagramTune Loop Simulink Diagram

• PLL loop BW - a few Hz to 10Hz• Magnet loop BW ~1Hz, limited by magnet/power supply BW• Coupling loop has similar structure• Coupling loop BW ~0.1Hz• Loops are both ‘Single Input, Single Output’

OutlineOutline

• A Brief History• Coupling and Coupling Feedback

• RHIC Run 7RHIC Run 7– anomalous BTF– tune scalloping


RHIC Run 7RHIC Run 70. MAINS HARMONICS REMAIN THE PRIMARY OBSTACLE1. Anomalous beam transfer function – cause is not understood (next slide)2. Tune, coupling, and chromaticity drifts due to persistent currents at

injection (also next slide)3. ‘Tune scalloping’ 4. Mains harmonics plus tune scalloping gives a very tight ‘box’5. Effect of chromaticity and tune scalloping on tune feedback6. Large noise introduced when magnet loops were closed – again, from

anomalous BTF? Kills chrom feedback at injection7. A variety of other problems

– IPM, Artus, injection damper, button monitor all turning themselves on at inappropriate times

– 5 FEC VME crate would hang frequently– ‘cache corruption’ problem would break feedback ramps

=30 deg

conventional delta-wye 6 phase 12 pulseconventional delta-wye 6 phase 12 pulse

LOAD

A

B

=30 deg

1 3 5

4 6 2

1 3 5

4 6 2

firing order:A1, A2B1, B2A3, A4B3, B4A5, A6B5, B6

Phase between A and B bridges

depends on mains voltage (booster

on/off, ???...)

With phase shift between A and B

bridges, this reproduces the

pattern used in the simulation.

RHIC 6 phase 12 pulseRHIC 6 phase 12 pulse

The simulationThe simulation• 12 free parameters for main dipole PS

– turn-on time of each of the 12 SCRs– also controls turn-off time of preceeding SCR

• 24 free parameters for simulation– turn-on time of each of the 12 SCRs– pulse length of each of the 12 phases

• SCR rise time ~10usec• Simulation time resolution ~14usec

– this is what was convenient– later reduced to ~7usec, no qualitative difference

familiar pattern

3D AFE

M Turn BPM

Simulation

Seen heremains harmonicsIPM firingArtus firingpower supply oscillating?

Mains Harmonics in Time DomainMains Harmonics in Time Domain

1.67msec

720Hz

Amplitude is tens of micronsBBQ sensitivity is ~10nm

Vertical Artus kicker firing

main dipole power supply turns on

main dipole power supply turns off

Chrom needs fixing here

This difficulty with acquiring lock was aggravated by persistent current decay, causing large and fast drifts at injection • tune ~.02 (tunes cross!!!)• coupling - full coupling• chromaticity ~3 unitsThese drifts are compensated for Run 8?

Anomalous beam response at injection • tunes separated and well decoupled• not power line, synchrotron freqs• similar in all 4 planes• serious obstacle to acquiring lock• serious contributor to ‘noise’• not seen with 245MHz PLL• disappeared with start of ramp• not understood – speculation on power supply regulation/phase shift at low current

BlueVert

‘Unexcited’ spectrum at betatron line

>30dB above noise floor!

The consequence of the previous slide - procedure to lock the The consequence of the previous slide - procedure to lock the tune trackers in the presence of multiple peaks and persistent tune trackers in the presence of multiple peaks and persistent current decay was ~40 steps!current decay was ~40 steps!

1. take BTFs to determine where the optimum line is for locking2. reduce proportional gains (can’t acquire initial lock with optimal gains)3. set the search windows so that H cannot lock on V, and V cannot lock on H4. turn on the H kicker, acquire a lock. This inevitably is not a lock on the line you

want, but rather a lock on the first line the BBQ comes to.5. nudge the search window to push the BBQ onto the correct line. This often

requires repeated nudges.6. tweak the phase to optimize response amplitude - because of many peaks BTF

app does not reliable give optimum phase information, has to be done manually7. turn up proportional gain8. adjust desired amplitude for kicker feedback9. open the search windows10. turn on kicker feedbacks11. repeat steps 1-10 for vertical. If we are running both beams repeat this whole thing

for the other ring12. tell shift leader BBQ is ready

‘Tune Scalloping’ with TF loops open• BBQ very precisely drives a slice up out of the tune distribution• tune shifts as amplitude increases (sextupoles dominate? Large octupole for t?) the slice moves off resonance, depopulates• BBQ falls off that slice, locks back in the center of the distribution• the process repeats

Contributing factors• large kicker excitation• large loop gains• small chromaticity

Kicker turned down here, then started locking on mains harmonics

scalloping

Makes for a tight ‘box’• need large kicker excitation because of mains harmonics• need large loop gains for reliable tracking of fast tune changes• chromaticity feedback not yet implemented – chrom control is not particularly good

A delicate balance to tune the tracking

Ramp 8245

Indication of small chromaticity

Limit of tune shift defined by dynamic aperture?

dots are Artus kicked tune measurements

Three successive wiggles ramps during beam commissioningThree successive wiggles ramps during beam commissioning

second ramp – turn down kickers, BBQ captured by mains

first ramp – we see scalloping

Ramp 8253

Ramp 8254

Ramp 8255

third ramp – turn kickers back up, again see scalloping

Third ramp, and effect of scalloping on chrom measurementThird ramp, and effect of scalloping on chrom measurement

This is NOT problem with chrom algorithm phase

tunes

During Run 7 BBQ worked very well, despite many issuesDuring Run 7 BBQ worked very well, despite many issues

0. MAINS HARMONICS REMAIN THE PRIMARY OBSTACLE1. Anomalous beam transfer function – cause is not understood (next slide)2. Tune, coupling, and chromaticity drifts due to persistent currents at

injection (also next slide)3. ‘Tune scalloping’ 4. Mains harmonics plus tune scalloping gives a very tight ‘box’5. Effect of chrom and scalloping on tune/chrom

measurement/feedback6. Large noise introduced when magnet loops were closed – again, from

anomalous BTF? Kills chrom feedback at injection7. A variety of other problems

– IPM, Artus, injection damper, button monitor all turning themselves on at inappropriate times

– 5 FEC VME crate would hang frequently– ‘cache corruption’ problem would break feedback ramps

Saturday – ramp 8211 (the first wiggles ramp)Chromaticities and tunes

Chrom measurement affected by tune scalloping here

dots are Artus kicked tune measurements

The first wiggles ramp came 10 ramps after the first

successful TF ramp. Chrom was not corrected until

the following Wednesday evening

Effect of chrom on TF

Loops open ‘ungracefully’, BBQ continues to track

Effect of chrom on Tune and Coupling Feedback – ramp 8217

Scalloping with TF loops closed

Chrom small here

Vert amplitudeand phase

horiz amplitudeand phase

vert tune scalloping with TF on

Loop gains and kicker excitation turned down here, back up here, down again here

H tune

V tune

Ramp 8667IBS lattice

Chromaticity via radial modulation with BBQ in RHIC Run 7 two successive ramps for correcting and measuring result

Chromaticity corrected here and here

With ongoing tuning we eventually had reasonably good chrom measurements on

the ramp

first ramp

second ramp

Simultaneous tune and coupling feedback in both rings , ~97% transmission

Loops closed thru transition

Ramp 8498

Yellow beam current

H tune

V tune

Blue beam current

H tune

V tune

Slight tune swing down to keep between mains during ramping

With ongoing tuning we eventually had good feedback ramps

OutlineOutline

• A Brief History• Coupling and Coupling Feedback• RHIC Run 7

– anomalous BTF– tune scalloping


• Dynamic range at transition was the showstopper for the 245MHz PLL• 3D AFE and BBQ appeared to be the solution to this problem

– Large dynamic range of the diodes – first components in the signal paths– ~160dB suppression of the revolution line plus ~10nm sensitivity

• However, BBQ operates in the coherent spectrum– We discover mains harmonics, which are ~70dB above BBQ noise floor, ~50dB

more severe in RHIC than Tevatron or SPS– We discover the ‘anomalous BTF’ at injection with ions– No obvious solution on the horizon for either of these problems in the coherent

spectrum, they both are solid obstacles to making tune tracking feedback operational

• lock acquisition at injection cannot be automated• needed kick (due to mains harmonics) blows up emittance

• So how about a ‘hybrid’ system? Direct diode detection of 245MHz pickup• Some data from last run (following slides), many questions

– Noise floor? At high frequency?– Coherence at high frequency?– Performance of 3D AFE peak detector with resonant pickup?– Phase compensation? Mix in tunnel?

‘‘Hybrid’ tune trackerHybrid’ tune tracker

Ramp 8687 yellow BBQRamp 8687 yellow BBQ

Ramp 8687 yellow LF SchottkyRamp 8687 yellow LF Schottky

Ramp 8687 (early May)Ramp 8687 (early May)

Yellow LF Schottky 245MHz signal as seen thru 3D AFE

Yellow 1m long stripline signal

as seen thru 3D AFE

What is this???• ‘clock’ jitter? Blue is master• higher order transverse modes?

• we consistently see stronger beam response below t

• else?

Ramp 8687 around transitionRamp 8687 around transition

Yellow LF Schottky 245MHz signal as seen thru 3D AFE

Yellow 1m long stripline signal

as seen thru 3D AFE

Ramp 8687 time domain around transitionRamp 8687 time domain around transition

-13 sec 0 +12

IPM firingYellow LF Schottky 245MHz signal as seen thru 3D AFE

Yellow 1m stripline signal as seen thru 3D AFE

245MHz pickup

existing 3D AFE

245MHz kicker

Possible ‘Hybrid’ Tune Tracker Block DiagramPossible ‘Hybrid’ Tune Tracker Block Diagram

existing BBQprocessing

AGC

tunnel

1002a

beam

motion control

pickup sum mode

30.625 MHzbandpass

diode doubler

61.25 MHzbandpass

diode doubler

122.5 MHzbandpass

diode doubler

245 MHzcavity filter

245 MHzcavity filter

Advantages of this approach to ‘hybrid’:• minimal phase compensation needed• excite the same spectrum you are measuring• ‘bleedthru’ less problematic• minimal modification to existing BBQ

• Transition Chromaticity Monitor• ‘Hybrid’ tune tracker?• Chromaticity measurement and feedback• Other Stuff

– Beam transfer functions– Streaming audio– Coupling echoes?

OutlineOutline

• Scenario 1 – no anomalous BTF at injection with ions– Early on (before any ramps in blue?)

• turn on tune and coupling feedback, turn on radial wiggles, assess quality of chromaticity measurement (all hardware and software is in place)

• If good, ramp in this configuration (it will improve chrom measurement on the ramp, therefore will speed ramp development)

– When controls infrastructure is sorted out, do APEX ramps with chrom feedback

– During proton ramp development – use chrom feedback (250GeV!!!)

• Scenario 2 – anomalous BTF at injection with ions, no anomalous BTF at injection with protons– During APEX at store with ions

• turn on tune and coupling feedback, turn on radial wiggles, assess quality of chromaticity measurement

• If good, close chromaticity feedback loop and explore

– During proton ramp development – use chrom feedback

• Scenario 3 – anomalous BTF at injection with ions AND protons– Hybrid tune tracker

Run 8 Plan for Chromaticity Feedback Run 8 Plan for Chromaticity Feedback (assuming present BBQ tune tracker)(assuming present BBQ tune tracker)

p

we excite ‘on-momentum’

longitudinal beam profile

p

sum signal

(with positive chromaticity)In betatron phase• particles from the head arrive at the tail early• particles from the tail arrive at the head late

(scaled) difference signalis time shifted

sum signal

(scaled) difference signalis time shifted

the (scaled) difference of the sum and difference signals looks like this

the (scaled) difference of the sum and difference signals

rectified difference of the sum and difference signals

sum signal

FFT showing relative amplitudes of the 3 signals for a 0.1 radian phase shift and 1ns rms bunch length

the (scaled) difference of the sum and difference signals

rectified difference of the sum and difference signals

sum signal

zoom on the previous FFT

BPM off-set

hi-pass

BBQ AFE

a possible processing chain

Other Stuff• Beam transfer functions – improvements?

– White noise? Chirped?– Beam-beam transfer functions?

• Coupling BBTF for LHC orbit feedback - Steinhagen

• Streaming audio of BBQ – Internet radio• Coupling echoes?

Backup material

Documents

Tune and Coupling Feedback Implementation and Results from RHIC