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!
Top Related