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Progress in Transverse Feedbacks and Related Diagnostics for Hadron Machines Wolfgang Hofle, CERN BE-RF

Progress in Transverse Feedbacks and Related Diagnostics

for Hadron Machines

Wolfgang Hofle

CERN

Beams Department

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Acknowledgements: G. Kotzian, D. Valuch, K. Li (CERN)

CERN BE department RF, OP, ABP, BI, CO Groups, TE-ABT Group

V. Zhabitsky (JINR)

J.D. Fox, J. M. Cesaratto (SLAC) for US LARP

PRINCIPLE OF TRANSVERSE FEEDBACK

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Principle of Transverse Feedbacks

• One or multiple pick-ups Turn by turn, bunch by bunch position with digitization and processing

• Widely used in high intensity

lepton colliders (B factories) and light sources to provide beam stability

• High intensity hadron machines

need feedback for stability as well • Use in hadron colliders more

challenging and restricted in past mostly to injection damping (low noise system needed)

• LHC collider uses TFB all the time including with stored, colliding beams, (protons and Pb ions) since 2010

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BPM

BPM Signal

Processing

and

Correction

calculation

Kicker

Power

Amplifier

Ideal equilibrium orbit

Beam trajectory

BPM Beam position monitor

Tbeam

Tsignal

Tsignal = Tbeam + n Trev

Projects and Future Needs for Transverse Feedbacks for Hadron Machines

• JPARC Main Ring: Tobiyama et al. IPAC’10 and TUPWA009

• GSI, FAIR facility planning to have transverse feedbacks M. Almuhaidi et al., IPAC’11

• RHIC injection damping, abort gap cleaning considering an upgrade

• CERN LHC Injector Upgrade Project (LIU): Upgrades for PSB, PS and SPS transverse feedbacks New generation of digital feedbacks planned

• Two stream instabilities (e-p) transverse feedbacks working at

proton accumulator rings at Los Alamos (PSR) and ORNL (SNS) R. McCrady et al., PAC’07; R. Hardin et al., IPAC’10

Past reviews and overviews: K. Balewski et al. (EPAC’98) D. Teytelman (PAC’03) D. Teytelman (PAC’11)

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LHC TRANSVERSE FEEDBACK AKA DAMPER / ADT

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LHC Transverse Damper (ADT)

o Initially designed for • Injection damping

• Feedback during ramp (coupled bunch instabilities)

o LHC Physics Run 1 (2010-2013) • Providing stability at all times in the cycle

(including with colliding beams !)

• Diagnostics tool to record bunch-by-bunch oscillations

• Abort gap and injection cleaning

• Blow-up for loss maps and aperture studies

• Tool to produce losses for quench tests

• Tune measurement (under development)

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7

LHC Transverse Damper Specs

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ADT Power and Kicker System W

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• Kicker length: each kicker 1.5 m • Max voltage: 10.5 kV • 2 mm kick to 450 GeV beam • Gain up to beyond 20 MHz • 16 kickers, • 32x30 kW tetrode amplifiers • Bandwidth up to 20 MHz

LHC transverse Feedback (ADT) kickers and amplifiers in tunnel point 4 of LHC, RB44 and RB46

Measured ADT frequency response. Green: bare power amplifier, blue: power amp + kicker.

ADT kicker. The beam is kicked by electric field

Power

beam observation

LHC

Built in collaboration with JINR, Dubna, Russia; E. Gorbachev et al. LHC Proj. Rept.-1165 CERN (2008)

40 turns, 1/40 = 0.025

1.2x1011 per bunch

Instability calculation by N. Mounet (CERN BE-ABP)

Instability Growth Rates versus Damping

50 ns spacing well under control with damper

Large impedance contribution by resistive wall effect

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10

50 ns bunch spacing

LHC

Drive Signal Generation

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Under ground cavern • 200 W driver amplifiers (25 MHz BW) • tetrode amplifier control

EMC • carefully designed to minimize • perturbances by noise • major EMC issue during commissioning:

8 kHz switching frequency of UPS

Electronics in surface building SR4 for easy access during commissioning • A/D conversion • all signal processing and D/A • computer controls

LHC

Q9

ADC

FPGA

S

...

S

...

SERDES

S

...

S

...

Q7

ADC

SERDES

SERDES

SERDES

SERDES

FPGA

Xilinx Altera

Q

I

fc = 40 MHz

fc = 40 MHz

ADC

ADCQ

I

fc = 40 MHz

fc = 40 MHz

DAC

ADC

FPGA

SERDES

ADC

SERDES

SERDES

SERDES

SERDES

FPGA

Xilinx Altera

Q

I

fc = 40 MHz

fc = 40 MHz

ADC

ADCQ

I

fc = 40 MHz

fc = 40 MHz

DAC

ΔxQ7

ΔxQ7

ΔxQ9

ΔxQ9

Δx

Δx

400.8 MHz

180º

180º

Coaxial Transmission Lines

Andrew HELIAX

7/8" Dielectric Foam

length ~ 650mlength ~ 450m

Macom H-9

2-2000 MHz

Comb Filter

400.8 MHz

Beam position VME module Signal processing VME module

Overview of ADT Signal Processing

Intensity nomalized bunch position digitized and synchronized (two pick-ups)

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Analogue RF signals

LHC

Beam Position Module W

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Transfer

switch

Low noise

amplifier

Hybrid

S

...

Comb filter

fcenter = 400.8MHz

I

Q

LO 400.8MHz

DA

C

DA

C DC Offset

compensation

Gaussian type low

pass, fc=40MHzI+

I-

Q+

Q-

30dB step

attenuator

VME

control

I

Q

DA

C

DA

C DC Offset

compensation

Gaussian type low

pass, fc=40MHzI+

I-

Q+

Q-

30dB step

attenuator

VME

control

Su

m IF

to

dig

ita

l b

oa

rd

De

lta

IF

to

dig

ita

l b

oa

rd

Transfer

switch

Attenuator

S

...

Comb filter

fcenter = 400.8MHzDelay

calibration

D

SA

B

Coax line

Tunnel-SR4

(500-700m,

7/8" Flexwell)

Stripline pickup

fcenter = 500MHz

• Low noise amplifier for for good S/N ratio before • Adaptation of signal levels to beam intensity • Challenge for multi-bunch operation: keeping reflections under control

LHC

ADC / Signal Processing / DAC

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• Beam Position VME board • bunch spacing: 25 ns, 40 MS/s • bunch by bunch normalised position • 16 bit ADCs • 2 mm rms resolution • Gbit serial link to transmit data for

processing or storage

• Processing VME board • 80 MHz clock frequency • amplitude and phase correction by FIRs • adjustment of delay and feedback phase • generation of excitation signals • 14 bit DAC

LHC

LHC Transverse Feedback - Post LS1 W

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Pickup

Q7

Beam

position

module

Q7

Pickup

Q9

Beam

position

module

Q9Analogue output to

the power amplifiers

Digital signal processing unit

DAC

Gain control

(CCC)

CLEANING

DAC

Pickup

Qx

Beam

position

module

Qx

Pickup

Qx

Beam

position

module

Qx

DACBeam transfer

function meas.

Observation

box

Tune/

instability

diagnostics

box

Fast b-by-b

Instability

diagnostics

CCC, users, logging

• doubling # of pick-ups

• complete re-cabling of PUs

• new digital hardware

• multiple ADCs and DACs

• reduction of noise

• flexibility for gain control

• instability diagnostics (trigger !)

• tune diagnostics (GPU)

Major upgrade in LS1

(2013-2014)

D. Valuch, CERN BE-RF

LHC

TRANSVERSE FEEDBACK KICKER AS AN EXCITER

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Abort Gap Cleaning W

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Abort gap viewed by abort gap monitor with RF switched off, Cleaning by ADT (DDS) in V-plane stepping through a range of frequencies Also used for injection gap cleaning prior to every injection (H-plane)

Tim

e (t

urn

s)

Time (within turn)

3 ms

(Abort Gap Monitor (Synchrotron Light)

M. Meddahi et al. IPAC’10 B. Goddard et al. IPAC’11 E. Gianfelice-Wendt et al. IPAC’12

LHC RHIC also uses damper for AGC, A. Drees et al. EPAC’02, pp. 1873

Selective Transverse Blow-up

stops at 18 mm aperture

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aperture measurement using blow-up with transverse damper

Wire scanner measurements (normalized transverse emittance)

18 mm

2 mm

• “White noise” generated on FPGA

clocked at 40 MS/s

aperture measurements by blow-up

loss maps for collimation set-up

dynamic aperture

any kind of excitation can be gated

(also DDS produced narrow band)

gate, 11 ms (example)

• Blow-up functionality very important In a future

very large HC (to balance

emittance damping by

synchrotron radiation damping)

Loss Maps: V. J. Moens, S. Redaelli et al. MOPWO050

LHC

evolution of beam oscillation amplitude Fast losses (BLM signal)

Fast Losses with ADT Simulating “UFO” Type Losses for Quench Test

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1 ms

M. Sapinski et al. WEPME044 and THEA045 (Fast Losses and Quench Tests)

Transverse Feedback was used as exciter in three quench tests carried out in February 2013

LHC

OPERATIONAL EXPERIENCE WITH TRANSVERSE DAMPER IN LHC

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21 W. H

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Injection Oscillation Logging and Analysis

• All injection oscillation data of the first bunch of every batch logged since Summer 2010

• Can retrieve performance at

injection from logging • Data also logged for post mortem

when beam is dumped • Memory to log 73 turns x 3564

possible bunch positions (25 ns spacing) for observation Injection damping fill 1268 (August 9, 2010)

horizontal plane beam 1

LHC

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A. Macpherson CERN BE-OP & BE-RF

Automated Fill Analysis: Damping Time

• Injection oscillations damping of first bunch in a train systematically logged

• Fill analysis tool computes

damping time and tune for every injected batch and fill

• Data quality check challenging • Variations over time in part due to

chromaticity settings (V-plane !)

• Difference H/V: large V inj. error first bunch on edge of kicker pulse

2012 Proton Physics Run Horizontal

2012 Proton Physics Run Vertical

LHC

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A. Macpherson CERN BE-OP & BE-RF

Automated Fill Analysis: Damping Time

Beam 1 H: 16 turns V: 27 turns

Beam 2 H: 13 turns V: 26 turns

H

H

V

V

LHC

Performance with Bunch Trains in LHC 2012 W

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50 ns bunch spacing standard + hold 144 bunches (4x36)

25 ns bunch spacing enhanced bandwidth 144 bunches (2x72)

Injection oscillation damping

W. Hofle et al., WEPME43 LHC

Operation Through Cycle W

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Gain

Phase shift

Injection

probe

beam

Injection

physics

beam

Prepare

rampRamp

Sq

ue

eze

Physics

Abort gap

cleaning

Injection gap

cleaning

Intensity

Energy

10's turns

100's turns

500's turns

Q injection

Q collisions

Inje

ctio

n

Inje

ctio

n

Inje

ctio

n

Inje

ctio

n

Inje

ctio

n

Inje

ctio

n

Adjust

Tune feedback

LHC

TRANSVERSE FEEDBACK AND TUNE DIAGNOSTICS

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Impact on Tune Measurement System (LHC)

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with damper, max gain used

• less broadening with lower gain • reduction of tune peak, i.e.

residual oscillations by more than 20 dB

solution deployed in 2012: ADT gain modulation within turn and gated BBQ 6 bunches are used for the Tune Measurement, these have low ADT gain

R. Steinhagen PAC’11, N.Y.

feedback gain

LHC

Closed Loop Transfer Function W

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system input system output

G(s)

)(sY)(sX

feedback

F(s)

)()()()( sNsFsGsY

)()()()()()()( sYsFsGsNsFsGsY output of closed loop

closed loop transfer function

open loop

)()(1

)()(

)(

)()(NCL,

sFsG

sFsG

sN

sYsG

N(s)

visible to damper

PU perturbation

beam

See also formalism with z-transform treatment: C.-Y. Yao et al. WEPME56 (Argonne NL) Tune measurement from in-loop signal: C. H. Kuo, IPAC’11, pp. 514-516

Spectra with feedback on (LHC) W

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Measurement from a single bunch, two pick-ups, spectra averaged over 45 minutes (2010 data, V plane) W. Hofle, V. Lebedev et al. IPAC’11

(tune is trench)

Beam oscillating due to external excitation (not instability !) reduced by feedback

Simulation: Single bunch 8000 turns

PU signal Beam (invisible to FB) Kicks by TFB

LHC

Tune Measurement with ADT (LHC)

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cleaning (injection)

high gain (@450 GeV) (trench @tune)

lower gain (average over 6 bunches) parasitic lines ! (ramp)

tune change at start of squeeze (0.280.31) (4 TeV)

tune (H)

time

Based on recording of 6 bunches (horizontal plane) (also considering and tested excitation by short burst gated on 6 bunches)

Courtesy: F. Dubouchet (CERN)

LHC

MITIGATION OF TRANSVERSE INTRA BUNCH MOTION BY FEEDBACK

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Intra Bunch Transverse Feedback

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Analog Front End

Analog Back End

Signal Processing

BPM Kicker

Power Amp ADC DAC

Beam

transverse position

pre-processed sampled position “slices”

calculated correction data

correction signal

pre-distortion drive signal

CERN PS Transverse Feedback W

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PS TFB ON

10 ns/div

PS TFB ON

10 ns/div

A. Blas et al. WEPME011 D. Perrelet (CERN BE-RF)

10 ns/div

PS TFB ON

10 ns/div

PS TFB OFF

1.4 GeV 26 GeV Challenge: Time of Flight Compensation Fully digital implementation

SPS High Bandwidth Damper Project W

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ECI (limitation at 25 ns spacing) TMCI (single bunch intensity limitation)

• Feedback Project addresses limitation in the SPS in intensity due to E-Cloud Instability (ECI) and Transverse Mode Coupling Instability (TMCI)

• Recent Simulations with Head Tail Code confirm feasibility

• SPS is test bed for deployment of such a system in other accelerators (e.g. LHC)

Mode Spectra without feedback

CERN SPS

Simulations with Feedback W

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K. Li et al., WEPME042

ECI TMCI

Bandwidth need at SPS injection 450 GeV/c from simulation (2.7 ns bunch length)

• ECI: 500 MHz

• TMCI: 200 MHz

increasing FB gain increasing FB gain

CERN SPS

CERN Headtail Code

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J. Dusatko et al. (SLAC) WEPME061

Hardware Development for the SPS feedback

• 4 GS/s sampling rate • 16 5-tap FIR for single bunch control

CERN SPS

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37 J. D. Fox et al. (SLAC) WEPME060

Single Bunch instability control with SPS HBTFB

FB switched off no feedback feedback

chromaticity chromaticity

CERN SPS

Beam Response in Closed Loop W

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• Note the different response of the beam for different positive feedback gains. • Many modes get excited with higher gain in positive feedback.

Turns

Feedback “gain”

gain = +64

-16 -16

Frequency Sweep 0.19 – 0.17

Turns

gain = +16

-16 -16

Frequency Sweep 0.19 – 0.17

2012-2013 experimental results: J. D. Fox et al. (SLAC), WEPME060 CERN SPS

Kicker Design for SPS Feedback W

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J. Cesaratto et al. (SLAC) WEPME061

Need for high Bandwidth requires new kicker for the SPS: • Inspired by Stochastic Cooling

Systems Faltin type kicker considered (strip-line with slotted shield to beam pipe)

L. Faltin, Nucl. Instrum. Methods 148 (1978) pp. 449.

CERN SPS

Conclusions

• Advances in Technology for ADCs and DACs permit today the design of digital transverse feedback electronics for Hadron Colliders thanks to a high number of bits, successful example is LHC

• Transverse feedback essential for beam stability and emittance preservation used in LHC since 2010 with colliding beams

• Interferences with tune measurement system promotes use of in-loop feedback signal for tune analysis as pioneered also in various electron machines; large number of bunches, need for on-line averaging a challenge

• Further improvement in S/N desirable, multiple PU, multiple ADCs an interesting option, also pursued at different labs, good analog front-end key

• Intra-bunch feedbacks work well for long (10’s ns long bunches in proton machines), high speed ADCs/DACs permit extension to short bunches (ns range with GS/s) new wideband feedback system is being pioneered for CERN SPS, potential future use also in colliders such as LHC

• Major applications of transverse feedbacks for purposes of beam excitation

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SPS High Bandwidth Transverse Feedback Selected Bibliography 2009-2013

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[1] J. R. Thompson et al., PAC’09, (2009), pp. 4713-4715.

[2] J. D. Fox et al., PAC’09, (2009), pp. 4135-4137.

[3] J.-L. Vay et al., IPAC’10, (2010), pp. 2438-2440.

[4] C. Rivetta et al., PAC’11, (2011), pp. 1621-1623.

[5] R. Secondo et al., IPAC’11, (2011), pp. 1773-1775.

[6] M. Pivi et al., IPAC’12, (2012), pp. 3147-3149.

[7] J. M. Cesaratto et al., IPAC’12, (2012), pp. 112-114.

[8] K. Li et al., WEPME042, these proceedings.

[9] J. Dusatko et al., WEPME059, these proceedings.

[10] J. D. Fox et al., WEPME60, these proceedings.

[11] J. M. Cesaratto et al. WEPME61, these proceedings.

Thank you for your attention

Work presented on the CERN SPS High Bandwidth Transverse Feedback

is a collaborative effort supported by the US LARP Program

J. D. Fox, J. Cesaratto, J. Dusatko, J. Olsen, M. Pivi, K. Pollock, C. Rivetta, O. Turgut, S. Johnston (SLAC)

S. De Santis, H. Qian, Z. Paret (LBL)

M. Tobiyama (KEK)

D. Alesini, A. Drago, S. Gallo, F. Marcellini, M. Zobov (LNF-INFN, Frascati)

G. Arduini, H. Bartosik, W. Hofle, G. Iadarola, G. Kotzian, K. Li,

G. Rumolo, B. Salvant, U. Wehrle, C. Zannini (CERN)

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ADDITIONAL SLIDES

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Impulse Response – Linearization of Phase W

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Linearization of phase makes system usable as feedback up to 20 MHz

W. Hofle et al., WEPME43 32 tap FIR for phase equalization

Courtesy: G. Kotzian

LHC

Shaping Time Domain Response W

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Condition for h(nTb) = 0 symmetry of roll off

• Motivated by appearance of single bunch instabilities

• Used operationally for squeeze

and 25 ns spacing tests

LHC

beam 1: transverse injection transient, pilot

H Q7, no dispersion H Q9, dispersion 0.9 m

V Q7 V Q9

low chromaticity low chromaticity

high chromaticity high chromaticity

transient in energy of beam

Diagnostics: The Fixed Display Damper off

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LHC