Beam Instrumentation and bunch
feedback systems
Makoto Tobiyama

SuperKEKB Beam Instrmentation

Introduction
SystemQuantity
HERLERDR

Beam position monitor (BPM)

46644483

Displacement sensor

1101080

Transverse bunch feedback system

221

Longitudinal bunch feedback system0(1)10Visible SR size monitor

111

X-ray size monitor

110

Beamstrahlung monitor

1

10

Betatron tune monitor

221

Beam loss monitor

200

34

DCCT

111CT

1

10

Bunch current monitor

111

SuperKEKB Beam Instrmentation

BPM system at Phase 1TypeFunctionResolutionRepetition

1GHz Narrow-band
system from KEKB

Number ofunits

Closed orbit
correction, CCC,
optics measurement

3m0.25Hz109

New narrow-bandwith 509MHzdetection

As above

2 to 3 m0.25Hz

133

Gated turn by turnInjection tuning,
optics measurement

50 - 100m100kHz/data

117

Medium-band

Measurement oforbit variation< 2 to 3 m

10kHz

4Fast orbit deviation

Orbit deviation abort ~10m<10 turn

100kHz4

One narrowband detector covers four BPMs.

SuperKEKB Beam Instrmentation

Configuration of main BPM system
GatedTbT• HER : 1GHz (old) detector used at KEKB.
• LER : 509MHz new detectors.
• All VXI main frames were replaced with newones.
• Rotation angle of BPM was measured prior
to operation for position-correction.
• Gain calibration, beam based alignment andin situ survey of bad BPM have beenapplied.
Instead of BPM mapping at bench.

GatedTbT• Movements of BPM blocks relative toadjacent sextupoles are monitored bydisplacement sensors to correct the beam
positions.
• Data acquisition software of KEKB is
modified to fit the new arrangement of thedetectors.

SuperKEKB Beam Instrmentation

Measured rotation angle of BPM

SuperKEKB Beam Instrmentation

Cabling check, Beam Based AlignmentCabling check– Cabling was checked by beam because final cabling check was
not done to reduce the cost.
– Wrong cable connection was found at 25 BPMs, then corrected.

Position offset of BPMs
– Beam based alignment has been applied to get position offset
between a BPM and the center of an adjacent quadrupole.
Sugimoto-san’s talk ??

SuperKEKB Beam Instrmentation

Obtained performancePosition resolution– Position resolution was estimated by beam by so called "three-BPM method"which measures correlation of the orbit among three BPMs.
– The result represents upper bound of the resolution because the measurement
can be affected by beam movement between switching interval of a multiplexer.
– The obtained resolution is better than 3m and 5m in LER and HER,
respectively, for most of BPMs.

Stability of relative gain among four signal paths– So called "consistency" is continuously monitored.
Consistency is defined as an rms value of 4 beam positions obtained by combination of3 electrodes.

– Consistencies are stable in LER where most feedthroughs and their cables arereplaced.
– Consistencies of some BPMs drifts or suddenly jumps in HER where old KEKB
hardware (cable, FTs) are used.
– Change of consistency is sometimes cured by cleaning of connectors and/or
signal cables. Otherwise, the gain is to be calibrated again

SuperKEKB Beam Instrmentation

Noise in 1GHz (KEKB) detectors
Larger noise level was found in the 1GHz detectors in asite building D7 where RF equipment's are located.
– BPM resolution at Oho and Nikko straight sections is affected probably
by the same cause.
– Small noise level in the 509MHz detectors is assumed to be due to their
better shielding of analogue circuits.
– Noise source is not identified yet.
– A measure is to replace the 1GHz detectors with the 509MHzdetectors.

SuperKEKB Beam Instrmentation

BPM troubles

Two 509MHz detectors have shown very low level detection.
– A disconnection was found in signal path in one of the detectors.
– Another detector is being investigated. Probably an attenuator was notcontrolled correctly.



Set up error of local oscillator's frequency was found at two
509MHz detectors, after rebooting.
A damaged feedthrough was found at a LER BPM QD3P4.

SuperKEKB Beam Instrmentation

Gated turn-by-turn monitor
509MHz/1GHz narrow band detector, or
medium-band detector

FPGA(Spartan6)

Pilot bunch signal orinjection beam
BPM
Fast gate
switch

BPF&Amp

Gate width~6ns

508.886MHz & FID

Log
Amp

TBT
Data

14bit
ADC

SuperKEKB Beam Instrmentation

1421B Gated turn-by-turn monitor

FPGA, DDR3
SAW filters andLog Amplifiers,ADCs

Fast Gate Switch

SuperKEKB Beam Instrmentation117 units have been installed

SuperKEKB Beam Instrmentation

Commissioning of GTBTRoughly adjusted ADC timing
using injection beam
– Contributed injection/storagetuningFine timing adjustments– Single bunched beam
– Using pilot(non-FB) bunchRough and fine timing
adjustment of fast gates usingpilot bunch during scrubbing
run.
– Ready to use with fast gatemode.

SuperKEKB Beam Instrmentation

IP orbit feedback detector (bb kick)Specification– Resolution <1um
– Repetition 32 kHz– Bandwidth <100 Hz (FB)

509MHz17MHz

frev X 990=98MHzSuperKEKB Beam Instrmentation

SuperKEKB Beam Instrmentation

Preliminary data(LER)

29mA

779mA

SuperKEKB Beam Instrmentation

Loss Monitor

We use beam loss monitors
for protection of thehardware against unexpectedsudden beam losses. Theloss monitor system provides
an trigger to the beam abortsystem.
The sensors are ion
chambers (32) and PIN
photo-diodes (114).
We optimize the threshold of
the abort trigger and the PIN
position by checking thebeam information at eachabort event.

SuperKEKB Beam Instrmentation

Loss Monitor : ex.1 LER Beam Loss

LER Vacuum Spike↓LER Beam Loss↓LM (PIN @ injection point) Abort↓
LER Beam Abort
It takes ～300μs

SuperKEKB Beam Instrmentation

Loss Monitor : ex.2 HER Beam Loss

HER Vacuum Spike↓HER Beam Loss↓
LM (PIN @ injection point) Abort trigger↓
HER Beam was aborted after 600μs
after beam loss started.
↓
LM（IC）Abort trigger↓
LER beam was aborted 1.5ms after
HER Abort.

SuperKEKB Beam Instrmentation

Betatron Tune measurement

Global tune measurement for multi-bunch, small beamcurrent
Gated tune measurement for pilot (or selected) bunch
only
PLL excitation of the pilot bunch using iGp12

SuperKEKB Beam Instrmentation

Tune measurement systemDue to large
feedback gain, thebeam response atlarge beam current
has been stronglydamped.

SuperKEKB Beam Instrmentation

Beam Spectrum @ CCR

SuperKEKB Beam Instrmentation

SuperKEKB Transverse FB systems

Collaborating SLAC(US-Japan) and INFN-LNF(KEK-LNF)

SuperKEKB Beam Instrmentation

SuperKEKB Longitudinal FB system

SuperKEKB Beam Instrmentation

iGp12 digital feedback filterSuccessor of iGp digital
filters developed under
US-Japan collaboration withSLAC.
– 12bit ADC/DAC– 10 – 20 tap FIR filter– 12MB memory to analyze
instabilities



10 iGp12s are used
– 8 with larger FPGA(VSX95T)– 2 with normal FPGA(VSX50T)

Single bunch excitation
using PLL

SuperKEKB Beam Instrmentation

Injection kicker adjustment using FB detector

SuperKEKB Beam Instrmentation

Bunch current monitor

MAX108 8bit ADC
Spartan6 FGPA
VME 2W size

Bunch current information is sent
through reflective memory (realtime) to the bucket selection
system at linac during injection
period( <20ms).

SuperKEKB Beam Instrmentation

PerformanceStrong transverse coupled-bunch instability has beenobserved in both rings even with fairly low storedcurrent at very early stage of the commissioning.
– LER : Both H and V instability, V was much stronger and limited
the stored current in the beginning.
– HER : Both H and V. Both instability limited the stored current
less than 0.5mA (total current with multi-bunch mode) in thebeginning.

BxB feedback systems have been contributing to thering commissioning– Vacuum scrubbing– Coupled-bunch instability study(EC, Fast Ion)

SuperKEKB Beam Instrmentation

Example of G-D experiment(HER-H)

SuperKEKB Beam Instrmentation

LER-VSuperKEKB Beam Instrmentation

LER longitudinal FBLongitudinal instability starting with beam current>660mA with by 3 mode.
Wide modes around 500?

SuperKEKB Beam Instrmentation

Tuning of LFBPEAKRMS

PB_20160513_LK2_2
15PEAK

1050-50500

1000

1500

2000
Delay

2500

3000

3500

4000

SuperKEKB Beam Instrmentation

Successfully suppressed instability

1/16 down sample
Growth~40ms, Damp~25ms

SuperKEKB Beam Instrmentation

Difficulty in FB systems(1)2GHz(=508MHz x 4) reference stability– Phase of 508MHz clock has changed frequently without
correlation of beam.
– Found broken 508MHz phase shifter at reference line(RF).
– Also make slow feedback loop by using iGp(L) fast memory.

SuperKEKB Beam Instrmentation

2GHz feedback loop

SuperKEKB Beam Instrmentation

Difficulty in FB systems(2)Saturation of FB bunch position detectors– LNA just after comb filter saturates with bunch current >0.5mA– Couldn’t stop abnormal single bunch injection >5mA/bunch– Changed power-balance in FB detector

SuperKEKB Beam Instrmentation

Saturation of FB detector

Found MITEQ LNA saturates with bunch
current >0.5mA.
Bunch current alarm did not work with settingof >0.5mA/bunch which caused over current
accident at HER (stored ~5mA/bunch).

Similar configuration
on bunch feedback
detectors.
Need modification!

SuperKEKB Beam Instrmentation

Revised FB/BCM detector

SuperKEKB Beam Instrmentation

Difficulty in FB systems(3)Burn-out of the water-cooled dummy loads for LER
longitudinal FB systems due to stop of water chiller.
– Status of the chiller and temperature around LFB system havebeen monitored but no automatic interlock was implemented.

Automatic beam abort request has been implemented– Chiller stop
– Temperature increaseSuperKEKB Beam Instrmentation

Burning of LFB kicker dummy loads

SuperKEKB Beam Instrmentation

Difficulty in FB systems(3)New transverse FB kicker for LER seems broken?
– Completely short-circuit at FT2(?) after short maintenanceperiod.

SuperKEKB Beam Instrmentation

LER TKW2 troubleNo signature observed before trouble– No abnormal temperature rise.
– No reflection.
– No vacuum burst.

SuperKEKB Beam Instrmentation

Summary

Most of the beam instrumentation prepared forSuperKEKB rings (phase 1) are working well.
– COD measurement system
Narrowband position monitors Gated turn-by-turn monitors
 IP position monitors– Beam current/ bunch current monitor– Loss monitor– Bunch by bunch feedback systems
Tune monitors
 Transverse FB (HER and LER)
– LER transverse kicker trouble Longitudinal FB (LER)SuperKEKB Beam Instrmentation

For Phase 2 operation


Replacement of damaged BPM heads.
Transverse FB kicker– Need to investigate the cause of trouble.
– High beam power kicker (with collaboration of SLAC)IP feedback systems– Simulation of feedback (with dithering feedback)– Implementation of IP feedback algorithm.

SuperKEKB Beam Instrmentation

Backup slides

Narrowband BPM system

SuperKEKB Beam InstrmentationFeatures•1GHz detectors of HER are those used in KEKB.
•Detectors of LER are newly developed 509MHz
detectors.
•All VXI main frames in KEKB were replaced with new
main frames.
•Gain calibration and beam based alignment are appliedinstead of BPM mapping at a laboratory and in situ
survey of BPM position respectively.
•Rotation angle of BPM was measured prior to operation for position-correction.
•Movement of BPMs against adjacent sextupoles is monitored bydisplacement sensors, then used for correcting the beam position.
•Data acquisition software of KEKB is modified to fit the newarrangement of the detectors.

SuperKEKB Beam Instrmentation

Cabling•Cabling was checked by beam because final cabling check was not done toreduce the cost.
•Wrong cable connection was found at 25 BPMs, then corrected.

Position offset of BPM•Beam based alignment has been applied to get position offset between a BPMand the center of an adjacent quadrupole.
H. Sugimoto's talk ?

SuperKEKB Beam Instrmentation

Performance
Position resolution•Position resolution was estimated by beam by so called "three-BPM method"which measures correlation of the orbit among three BPMs.
•The result represents upper bound of the resolution because the measurement canbe affected by beam movement between switching interval of a multiplexer.
•The obtained resolution is better than 4um and 4um in LER and HER
respectively for most BPMs.
H. Sugimoto's talk ?

Stability of relative gain among four signal paths•So called "consistency" is continuously monitored.
Consistency is defined as an rms value of 4 beam positions obtainedby combination of 3 electrodes.
•Consistency is stable in LER where most feedthroughs and their cables are replaced.
•Consistency of some BPMs drifts or suddenly jumps in HER where KEKB
hardware is used.
Change of consistency is sometimes cured by cleaning of connectors and/or
signal cables. Otherwise, the gain is to be calibrated again.

SuperKEKB Beam Instrmentation

Noise in 1GHz detectors•Larger noise level was found in the 1GHz detectors in a site building D7
where RF equipment's are located.
•BPM resolution at Oho and Nikko straight sections is affected probably by thesame cause.
•Small noise level in the 509MHz detectors is assumed to be due to their bettershielding of analogue circuits.
•Noise source is not identified yet.
•A measure is to replace the 1GHz detectors with the 509MHz detectors.

SuperKEKB Beam Instrmentation

Troubles•Very low signal level was found in two 509MHz detectors.
A disconnection was found in signal path in one of the detectors.
Another detector is being investigated. Probably an attenuator was not controlled correctly.
•Set up error of local oscillator's frequency was found at two 509MHz detectors.
•A damaged feed through was found at a LER BPM QD3P4.

SuperKEKB Beam Instrmentation

Beam loss monitor & Abort logger

SuperKEKB Beam Instrmentation

2GHz Comb filter output

LER (DS) 0.12mA/bunch、-30.6dBm

SuperKEKB Beam Instrmentation

MITEQ LNA output-4.87dBm (G=25dB)

SuperKEKB Beam Instrmentation

MITEQ LNA

Low noise amplifier
G=20dB（Spec)NF 1.5dB
P1 10dBm
At 2mA/bunch, the output of the comb filter will be-6.16dBm– with 25dB amplifier, the linear output will be18dBm : Completely saturated!.
– The BCM has saturated after 0.5mA/bunchSuperKEKB Beam Instrmentation

MITEQ LNA response
MITEQ

1510

Calib Out(dBm)

Calib Out(dBm)

50-5-10-15-20-45-40-35-30-25-20

Calib In(dBm)-15-10-5

SuperKEKB Beam Instrmentation

MCL ZX60-3011+ LNAGain = 11.5dB
P1dB >21dBm
NF ~1.7dB

SuperKEKB Beam Instrmentation

MCL ZX60-3011
MCL-ZX60-3100+

20
Calib out(dBm)

Calib out(dBm)

100-10-20-30-40-30-20-10

Calib In(dBm)010

SuperKEKB Beam Instrmentation

Idea 1(bad idea..)Remove MITEQ LNA after Comb filter
Leave original Level7 DBM
Add DC amplifier (G=14dB) after output

Large low frequency noise!

SuperKEKB Beam Instrmentation

HER #0が真ん中SuperKEKB Beam Instrmentation

LER #0は67.556ns後