Performance of upgraded SPS damper in view of crab cavity tests

Complementarity to High Bandwidth Transverse Feedback

W. Hofle

CERN BE-RF-FB

Acknowledgement: A. Butterworth, F. Killing, G. Kotzian, T. Levens, E. Montesinos, A. Rey, D. ValuchG. Ledey, S. Mutuel (FSU-BE03)

Reminder: Principle of Transverse Feedback

Tsignal = Tbeam + n Trev

One or multiple pick-ups

Signal detection, signal processing, amplifiers, kickers

All LHC injector synchrotrons use transverse feedback systems, PSB, PS, LEIR (ions), SPS, in case of SPS since 1970’s

Challenging in Hadron Colliders due to need for low noise systems

LHC: transverse feedback system since 2010 at all times with high intensity bunches, during injection, acceleration and in collision

Feedback correction applied as correction in quadrature with position signal of oscillation

Matching of time of flight for wideband system

BPM

BPM Signal Processing

andCorrection calculation

Kicker

Power Amplifier

Ideal equilibrium orbitBeam trajectory

BPM Beam position monitor

Tbeam

Tsignal

Existing SPS Transverse Feedback System

Last upgrade 1997-2000 in preparation of the SPS as LHC injector

damping of injection errors and cure of resistive wall impedance driven coupled bunch instability (threshold ~5x1012 protons total intensity)

operates since 2001 between lowest betatron frequency and 20 MHz (V & H plane) to damp all possible coupled bunch modes at 25 ns bunch spacing

handles large injection errors of the order of several mm

Tetrode amplifiers with two tubes driving kicker plates in push-pull configuration installed in tunnel under kicker tanks

200 W drive power per tetrode 3 kHz to 20 MHz

Tunnel with kicker tank and tetrode amplifier in SPS LSS2

Served as starting point for the design of the LHC damper (ADT) kickers and power system

Technology of electronics of system used in SPS until 2012 dates from late 1990’s

Existing Transverse Feedback System

kicker effective capacitance:Cg+2Cp = 122 pF

not all circuit elements shown, e.g. matching at input

200 W drive power in 50 W

3 dB @ 4.5 MHzRA = 180 W, Ceff = 200 pF

Tube: RS 2048-CJC (V-plane) orTH561 (H-plane), max current 15A to 16Aclass AB

operational RF voltage 2.6-2.9 kVphase corrected 20 MHz

4.6 kV4.6 kV

RA=180

kicker 45p

32p 32pRA=180

L L

f < 25 MHzseries resonancewith L at 37 MHz

Existing Feedback: Kick Strength

+/- 2.6 kV @ 100 kHz, L=1536 mm, gap d=38 mm

15)-HFSS from(exact kV 215 2 d

LVV

Vs/m 102.7/ 4 eceVp

+/- 1.83 kV @ 4.5 MHz

kV 152V

Vs/m 100.5 4 ep

kV 46V

Vs/m 1058.1 4 ep

+/- 0.572 kV @ 20 MHz

G. Kotzian

integrated kick strength over the entire structure 41.375 V (transverse) for +/-1 V on kicker plates

Accurate kick strength evaluation with HFFS: example V-plane

Feedback kickers: Kick Strength

G. Kotzian

damps ~5 mm injection error (b=100 m) at 26 GeV/c in 20 turns (gain=0.1) in V-plane

• 26 GeV/c: kick per turn 8.3 mrad ( 0.54 mm at b=100 m) in V-plane• regularly running at 0.5 ms damping time (20 turns) • resistive wall growth rate for lowest mode: 0.5 ms to 1 ms

Horizontal kicker (BDH) Vertical kicker (BDV)

plane Length/gapmm/mm

DpeVs/m

kVtransverse

mradat 26 GeV/c

H 2x 2396/142 3.3x10-4 98 3.8

V 2x 1536/38 7.2x10-4 215 8.3

2.6 kV (with RS 2048 CJC tube)2.9 kV (with TH 561 tube)

Scope and Motivation for SPS damper upgrade under LIU

Why in LS1 ?

• sharing pick-ups with Orbit System (MOPOS) from Beam Instrumentation Group incompatible with MOPOS upgrade foreseen

• requirements for single bunch damping for protons used for LHC p-ion Physics (closer spaced proton bunches, 100 ns)

• ions injection damping with fixed frequency scheme, closer spaced batches• individual bunch damping for crab cavity studies not possible with previous

system (sampling was not synchronous with bunch in previous system) • LHC doublet scrubbing beam incompatible with previous system• controls with G64 chassis and MIL-1553 are obsolete (MMI) new controls for

power system and LLRF, new RF function generators

implement this LIU upgrade already in LS1

Pick-ups dedicated for transverse FB

BPCR.214

BPCR.221

• 2 BPCR (H/V) for LHC type beams (couplers maximum ZT @ 200 MHz)• 2 BPH electrostatic PU (pFixedTarget)• 2 BPV electrostatic PU (pFixedTarget)

BDH / BDV kickers unchanged

RF Faraday cage

SPS Transverse FB

New Signal Transmission BA3 BA2

10

RF RX D(TRR)

EDA-01382FREV SPS

SynchronousRF Divider(MASTER)[120MHz]

80..420MHzDistributionEDA-01335

Clk DistriEDA-00594[380MHz]

ADCCLK/DACCLK (PFT)

ADCCLK/DACCLK (LHC)

ADCCLK/DACCLK (SCRUB)

Clk DistriEDA-00594

[FREV]

RF RX D(SRX24)

EDA-0138210MHZ REF 5..100MHzDistributionEDA-01334

Clk DistriEDA-00594

[10MHz]

LO 200 MHz pLHC H

LO 200 MHz pLHC V

FREVDistributionEDA-01336

FRF SHIFTED

RF RX D(SRX24)

EDA-01382

~2usFiber Delay + Distribution

LO 200 MHz (IONS PU214.H)

SynchronousRF Divider(IONS-A)[120MHz]

~3usFiber Delay + Distribution

LO 200 MHz (IONS PU221.H)

SynchronousRF Divider(IONS-B)[120MHz]

~10usFiber Delay + Distribution

~1usFiber Delay + Distribution

SynchronousRF Divider(IONS-C)[120MHz]

SynchronousRF Divider(IONS-D)[120MHz]

LO 200 MHz (IONS PU214.V)

LO 200 MHz (IONS PU221.V)

ADCCLK (IONS PU221.V)

ADCCLK (IONS PU221.H)

ADCCLK (IONS PU214.V)

ADCCLK (IONS PU214.H)

DACCLK (IONS H2)

DACCLK (IONS H1)

DACCLK (IONS V1)

DACCLK (IONS V2)

RF TX D(STX03)

EDA-01380

RF TX D(STX03)

EDA-01380

RF TX D(STX24)

EDA-01380

RF Phase Shifter

EDA-01618FRF SPS

BA2BA3

cfv-ba3-allfo1 cfv-ba2-allfo1

cfv-ba3-allfo1 cfv-ba2-allfo1

cfv-ba3-allfo1 cfv-ba2-allfo1

cfv-ba3-allsync1

5

5

4

SynchronousRF Divider(MASTER)[40MHz]

LO 40 MHz (SCRUB H)

LO 40 MHz (SCRUB V)

2

BPF200MHz

BPF10MHz

Clk DistriEDA-00594[400MHz]2

2

cfv-ba2-allclkgen

cfv-ba2-allclkgen

cfv-ba2-allclkgen

cfv-ba2-allclkgen

cfv-ba2-allclkgen

cfv-ba2-allclkgen

5x

4x

2x

5x

Stable phase (ppm)

Frequency program (ppm)

Ions (for implementationin 2015):4 different delays forpick-up and kicker (ADC/DAC) clocks

200 MHz RF

frev

10 MHz ref

+ inj. Pulse (copy of SPSCPS)

200 MHz LO

40 LO

120 MHzADC/DAC

expect over year20 degreesdrift @200MHz

1.48 km fiber links

Analogue Hardware developed in LS1 (1)

200 MHz filters during production in CZ Clock generation board (all beams)

• 200 MHz bandpass filters (S and D)• programmable gain/attenuation• down mixing (I,Q) to base-band• ADC protection• sampling @120 MS/s (on digital board)

LHC beam: 25 ns bunch spacing:

Mixers for down conversion

D. Valuch

Signal processing LHC 25 ns beam

Hybrid H9

Ga

uss

ian

typ

e lo

w

pa

ss,

f c=

40

MH

z

I+

I-

Su

m IF

to

dig

ital b

oard

Comb filterfcenter = 200MHZ4 pulses (20ns)

Delay equalization

SA

B

Coax lineTunnel-BA2

(300m, 7/8" Flexwell)

Stripline pickupfcenter = 200MHz

beam

4-way

4-way

0°

90°

Q+

Q-

ADC driverGain

Dip

lexer

<400MHz

>400MHz

Dip

lexer

<400MHz

LO1200MHz/

IF -

3 (

0)

dB

m

ADC

Dual 16bit ADCVin 1-2Vpp

Vcm = 0.7-1.25VDDR CMOS out

ADC

- 16 bit data- 1 bit ovf- 1x ENC clock- 1x /CS- 2x SCK+SDI

I+

I-

Del

ta I

F to

d

igita

l boa

rd

Gain control

0°

90°

Q+

Q-

LO1200MHz

ADC

ADC

- 16 bit data- 1 bit ovf- 1x ENC clock- 1x /CS

Hybrid H9

Ga

uss

ian

typ

e lo

w

pa

ss,

f c=

40

MH

z

I+

I-

Su

m IF

to

dig

ital b

oard

Comb filterfcenter = 200MHZ4 pulses (20ns)

Delay equalization

SA

B

Coax lineTunnel-BA2

(300m, 7/8" Flexwell)

Stripline pickupfcenter = 200MHz

beam

4-w

ay

4-w

ay

4-way

4-way

Gain control

0°

90°

Q+

Q-

ADC driverGain

Dip

lexer

<400MHz

>400MHz

Dip

lexer

<400MHz

LO2200MHz

IF -

3 (

0)

dB

m

ADC

ADC

- 16 bit data- 1 bit ovf- 1x ENC clock- 1x /CS

I+

I-

Del

ta I

F to

d

igita

l boa

rd

Gain control

0°

90°

Q+

Q-

LO2200MHz

ADC

ADC

- 16 bit data- 1 bit ovf- 1x ENC clock- 1x /CS

- 10 bit data- 1 bit WR

- 1 bit WR

- 1 bit WR

- 1 bit WR

200MHz LO2 in

Firmware

t

t

t

t

- 1 bit /CS

- 1 bit /CS

- 1 bit /CS

DAC1- 16 bit data

- 1x /CS- 2x SCK+SDI

t

DAC2- 16 bit data

- 1x /CS

t

- 1 bit WR

- 1 bit switch

120 MHz clocks

DA

C Gain control

- 1 bit switch

DA

C

- 1x /CS- 2x SCK+SDI

Module 1 outputH1 (or V1)

Module 2 outputH2 (or V2)

4-w

ay

4-w

ay

Gain control

200MHz LO1 in

ADC1 ADC2 DAC1 DAC2

ADC2 CLK 120 MHz

ADC1 CLK 120 MHz

DAC2 CLK 120 MHz

DAC1 CLK 120 MHz

Digital Boardanalogue front-end(here for LHC beam)

variable delaysfor clocksADC/DAC(120 MHz)

H1 (V1)

H2 (V2)

BPCR.214 (H/V)

BPCR.221 (H/V)

Digital Hardware developed in LS1

• eight installed for SPS start-up • separate boards for H- and V-plane and beam type (pFT, pLHC, pSCRUB, Ions)• tested up to beyond 120 MHz clock frequency, Xilinix ARTIX 7 FPGA• features ADCs and DACs with four different clock domains for delay adjustment

New development !

8 ADCs4 DACs

outputgain control via DAC a laLHCADT

Board will be usedfor ADT (independent gain control on DACs)

T. Levens, D. ValuchG. Kotzian (firmware)

Feedback electronics uses LHC RF VME standard

RF functiongenerator

pFT signalprocessing

pLHC signalprocessing

signal combination/selector

timing

Crate management

clock distr.

CPU

Scrubbing Doublet Beam

Scrubbing beam position detection:• Bandpass formed by LP and strip-line coupler response• Synchronous sampling at 120 MHz• Compute position from 3 samples digital down conversion

LP filterStrip-line couplerCombination (BP)

Position detection: doublet beam

Scrubbing beam position detection:

• Long bunches injected on unstable phase• Bunch splits into doublet• 200 MHz component low at injection and phase

changing cannot use pLHC 200 MHz demodulation, damper must work from turn 0

• 40 MHz component stable during• After splitting could switch to pLHC 200 MHz

demodulation

effective Bandpass transfer function

PU signal

single bunch doublet

200 MHz BP filtered

40 MHz BP filtered(120 MHz sampled)

Performance Doublet beam: bunch train

25 ns spaced doublets

Analog signals before digitization:

Doublet beam: phasing ADC clocks

hR [𝑛 ]=[1.0 ,−0.5 ,−0.5 ]

3𝐻 RBPM input

120 MHz sampling clockbunch synchronous

ADC120 MSPS 40 MSPS

tagging of bunch[0]

Setting-up: open loop BTF measurement

• open loop BTF measurement: H damper, example fixed beam, NWA, remotely• Sweep across two betatron lines (example ~ 3 MHz)• adjustments using phase setting and loop delay• synchrotron sidebands visible

CommissioningSPS Start-up In 2014

Performance for Doublet beam - first results

• bunch-by-bunch position data available in internal memory• damping time of 20 turns reached as in previous system• commissioned for three types of beams, pFT, pLHC, pDoublet optimization ongoing

batch of48 doublets

Plans for single bunch damping

Dense spacing 100 ns Truly isolated bunches 250 ns

scheme for largespacing

what we propose

best for isolated bunches

issue: full kick strength only available for frequencies up to < 5 MHz need to play some “tricks” as for LHCADT

Full kick strength available with peak hold

Relevance for crab cavity tests with single bunches

Single bunch damping example: LHC ADT

large bunch spacing:peak hold (25 x 25 ns = 625 ns)pre-distortion of drive signalto compensate for phaseresponse of power amplifiers

50 ns, 75 ns operation:peak hold for 2-3 samples

25 ns operation:without peak hold

Easier in SPS as frequency up to which full kick strength availablefour times larger than in LHC ADT case

drive signal (200 W level):

kick voltage (power amplifier return, kV level):

zoom: 500 ns/div

500 ns/div

10 ms/div

Diagnostics potential for headtail motion

Normalized transverseposition

Transverse oscillation

pattern

Movement of centre-of-charge

Longitudinal profile

symmetricasymmetric

even symmetricodd symmetric

Str

iplin

e p

icku

p

Q9

I

Q

ADC

Nor

mal

ized

pos

itio

n ca

lcu

latio

n

Beam Position module

COMBFILTER

A

B

S

180°HYBRID

beamADC

I

Q

ADCCOMBFILTER

ADC

Ra

w e

lect

rod

e si

gna

ls

Pos

ition

an

d in

ten

sity

sig

na

ls

Ban

dw

idth

lim

itatio

n

Gai

n co

ntro

l

Do

wn

co

nve

rsio

n

Dig

itiza

tion

No

rma

lize

d b

unc

h

by

bu

nch

po

sitio

n ca

lcul

atio

n

S

Relevance for crab cavity and instability studies !

Normalized beam position

I

Q

S

I’S

Q’S

I’Q’

S

0 0.5 1 1.5 2 2.5 3-0.2

0

0.2

0.4

0.6

0.8

1

1.2

Frequency / GHz

De

tect

ed

Am

plit

ud

e [N

orm

aliz

ed

]/ m

m

xN(f

x)

xbar(fx)

The normalization scheme sees the symmetric (even) oscillation patterns (needed for the closed loop feedback)

Damper sensitivity to symmetric intra-bunch motion is a function of the longitudinal beam spectra

For the anti-symmetric case no oscillation amplitude is detected, odd modes not visible to the damper, provided bunch is symmetric in shape

normalized transverse positionas computed

LHC ADT case (f scales 1/bunch length)

Phase rotation in digital part to align Sum and Delta in I, Q; required angle measured during set-up

G. Kotzian, EDMS 1404633LHC vs SPS feedback: 400 MHz 200 MHz, bunchlength

center of gravityoscillation amplitude

Headtail oscillation detection

• This algorithm can detect odd-mode oscillations• Algorithms cannot resolve the original oscillation frequency, and absolute oscillation

amplitude accurately• However, can detect activity and distinguish between symmetric (even) and

asymmetric (odd) modes of every bunch valuable diagnostics !

LHC ADT case (f scales 1/bunch length)

different combination of Sum and Delta I,Q componentsindicates headtail motion

LHC vs SPS feedback: 400 MHz 200 MHz, bunchlength

longitudinal

LINE OF CHARGES

tran

sver

se

I-Component

Q-C

ompo

nent

longitudinal

tran

sver

se

I-Component

Q-C

ompo

nent

MEAN TRANSVERSEOFFSET

MEAN TRANSVERSEOFFSET

MEAN TRANSVERSEOFFSET

pure movement of theCENTRE-OF-CHARGES

only HEAD-TAIL activity,constant transverse offset

Visualization of bunch motion

TAIL HEAD

longitudinal

tran

sver

se

I-Component

Q-C

ompo

nent

TAIL

HEADMEAN TRANSVERSEOFFSET

mixed HEAD-TAIL activity withcoherent CENTRE-OF-CHARGESmovement

longitudinal

tran

sver

se

I-ComponentQ

-Com

pone

nt

MEAN TRANSVERSEOFFSET

Visualization of bunch motion

MEAN TRANSVERSEOFFSET

HEAD-TAIL activity has some phase-advance w.r.t. the CENTRE-OF-CHARGES movement

HEAD-TAIL activity is in-phasewith CENTRE-OF-CHARGESmovement

extend to include influence of long. motion and non-symmetric bunches in analysis

Visualization of bunch motion

Rapid identification of• quiet bunches• bunches with transverse center of mass motion• bunches with head tail motion• bunches with combination of center of mass and headtail motion with correlation

800 1000 1200 1400 1600 1800 2000 2200-1000

-800

-600

-400

-200

0BPOS-Q7-H-B2

Delta

examplefrom LHCscrubbing run

Added value of upgraded SPS damper to crab cavity tests in SPS

Efficient damping of single bunches will become possible

Studies with stored beams and a state-of the art low noise damper should serve as test bad for the LHC case with respect to noise issues

Similarity of SPS damper and LHCADT permits to investigate interplay between transverse feedback and crab cavities

Diagnostics potential of damper hardware in area of headtail motion analysis

Above is possible before LS2 as a result of realizing the SPS damper upgrade in LS1

significant effort which will pay off for crab cavity tests between LS1 and LS2

Complementarity of Feedbacks

Upgraded BA2 Damper

• detects center of mass oscillations of bunches, feedback in “base-band”• LIU upgrade successfully implemented:

- dedicated new standard SPS pick-ups (BPCR coupler)- New eletcronics, bunchlet scrubbing beam

• kHz to 20 MHz, high kick strength (good for mm’s of oscillation) high kick strength• Headtail “intergral” diagnostics possible• LL electronics could drive wideband kicker (up-converted signal)

BA3 Proposed High Bandwidth Feedback (V-plane)

• New approach: Intra-Bunch System similar to stochastic cooling in some way• advanced Digital Technology 4-8 GS/s • ~5 MHz to >~ 1 GHz, not so high kick strength• addresses intra-bunch motion, diagnostics potential by direct sampling• potential to damp intra bunch motion inside doublets interesting with respect to

requirement to provide a high quality doublet beam for LHC scrubbing• kicker and Amplifier development crucial for success• applicable to other accelerators including colliders such as FCC and LHC.

HBTFB - High Bandwidth Transverse Feedback

• Wideband feedback system (GHz bandwidth) for SPS• Intra-bunch GHz transverse feedback system• Help stabilize beam against Ecloud and TMCI effects• Under development with LARP

supported by: US-LARP (SLAC, LBNL)LNF-INFN (kicker study)CERN SPS LIU Project

AnalogFrontEnd

Analog BackEnd

SignalProcessing

BPM Kicker

Power AmpADC DAC

Beam Active closed loop GHz Feedback

transverse position

pre-processed sampledposition“slices”

calculatedcorrection data

correctionsignal

pre-distortion drive signal

Summary

SPS damper was consolidated with respect to power system and controls

completely new electronics developed, installed and commissioned

required Performance reached including for critical doublet beam

upgrade opens possibilities to use the system for tests with crab cavities including diagnostics for headtail motion.

diagnostics potential complementary to monitors and feedback that directly sample in time domain at high sampling rate

Implementation of electronics for LHC ion beams before LS2

THANK YOU FOR YOUR ATTENTION!