Issues and Plans on Beam Diagnostics inSuperKEKB
10th Feb. 2009, KEKB review committee
M. Arinaga, J. Flanagan, H. Fukuma, S. Hiramatsu, T. Ieiri,
H. Ikeda, H. Ishii, K. Mori, M. Tejima and M. Tobiyama

1. Introduction
2. Beam Position Monitor
3. Synchrotron Light Monitor
4. Gated Measurement
5. Summary

1. Introduction•Parameters of SuperKEKB related to the beam diagnostics
HER

LER

Energy (GeV)

8

3.5

Current (A)

4.1

9.4

Bunch length (mm)35

Number of bunches

5018

5018

Bunch separation (ns)22Emittance (nm)1824

Transverse damping time (ms)4784

ante-chamberante-chamber

65x14(?)

50φ(?)

Vacuum chamber
Chamber cross section (mm)

2. Beam Position MonitorA)Requirement•Requirement to the BPM system is not fully specified yet.
•We tentatively assumed that the required performance is same as theperformance in present KEKB.
resolution : several micron, accuracy : 40 micron (by beam based alignment)•We also tentatively assumed that following functions are required
according to discussions in KEKB group so far.
a) Precise slow (about 1Hz) closed orbit measurementb) Turn-by-turn measurement during physics run to measure thebetatron amplitude and phase at BPMs.

B) Items to be considereda) Large beam current of about 10 A
•Large signal power to a detector, poor electrical contact and movementof BPM due to thermal deformation of a chamber◊Reduce the diameter of the button from 12mm to 6mm,
◊Use pin type inner conductor for tight electrical connection,◊Use displacement sensors.
b) Use of ante-chambers•Lowest cut-off frequency of a chamber is below 1 GHz which is a
detection frequency in KEKB system (cut-off frequency is 768 MHz fora chamber of 50 mm φ).
◊Change the detection frequency from 1018 MHz to 509 MHz,
◊Develop a new detection module for 509 MHz detection.
c) Maximal use of present system to save the cost◊Maximal use of present VXI modules, cables and so on.
d) Cold BPM•Several BPMs around IP might be at He or N2 temperature if cold bore
magnets are used as recently discussed.

e) Turn-by-turn orbit measurement in large current operation
A proposed solution1)Kick a pilot bunch, then measure its position.
2)Put a fast gate in front of a detection circuit to pick up a signal of thepilot bunch.
3)Increase the number of turn-by-turn BPMs.
Turn by turn BPM in KEKB
•38 log-ratio detection modules are installed.
•Slow measurement and turn-by-turn measurement are switched byswitch modules.
•120 turn-by-turn detection modules can be housed at the maximum topresent VXI mainframes.

◊Increase the number of turn-by-turn BPMs to 120.
◊These circuits cover 1/4 of BPMs in each ring.
◊A simulation shows that 90 BPM data are needed for the betatron phasemeasurement if the number of the power supplies of quadrupole issame as that in KEKB.

Button electrode•A button electrode is under development.
Prototypes are installed in ante-chambers inNikko straight section for test.
◊Diameter : 6mm◊Flange type for easy replacement upon trouble◊Pin-type inner conductor for tight electricalconnection◊Ceramic vacuum seal

Radiation‐resistant flexible PEEK coax-cable (3D)
•A radiation‐resistant PEEK cable is being developed.
•It will replace a present semi-rigid cable which connects a button

feed-through with a terminal.
A)Structure
inner conductor (4)insulator (3)outer conductor (2)covering material (1)copper lead
PEEK
corrugated copper duct
fireproofed non-halogen polyolefinB)Electric characteristics
peak voltage
characteristic impedance
VSWR
attenuation

1000 V AC
50 Ω
<1.15
82 dB/km (50 MHz, 20 deg.)C) Irradiation test
Source : γ ray (Co-60)

cables under test

•No significant deterioration of electric characteristics was observed after
irradiation of 30 MGy.
•Outer sheath was damaged after irradiation of 30 MGy (crack at bending).
•Estimated radiation level on the duct is 0.5MGy/year according to the datataken at KEKB in 2004.
•The cable will be tested in next run at KEKB.

509 MHz super-heterodyne detector
A 509 MHz detector is under development.
A) Consideration of signal to noise ratio (S/N) by thermal noise and position resolution•Assume,◊Size of button : 6mm φ◊Detection freq. : 509 MHz◊Transmission loss of cable (100m) : 9.14 dB◊Noise Figure (NF) of a detector : 9 dB

signal voltage
position x = K

V1 + V4 " V2 " V3
V1 + V2 + V3 + V4

For a sensitivity constant K of 30 mm,
S/N of83.5 dB corresponds to!
position resolution of 1 µm.
1
1" x,y # K x,y2
(S /N)

beam current(mA)!

•Resolution less than 1 µm will be obtained at beam current of 30mA which is a required minimum current for optics correction.

B) Specifications
Detection frequency

508.887MHz

S/N at signal power of -60
dBm> 89.8 dB

Noise figure< 7 dB

Mixer : Active image rejection mixer
ADC : 18 bits

ADC (bits/sampling freq.)

18 bits / 102.4 kHz

FFT of IF signal by DSP

Max. input power-50 dBm

DSP : SHARC processor

FFT points

2N (N=4, 5, ...., 12)

VXI module
4ch Switch : PIN & FET

Switch module

Analogue processor

C) Laboratory test

Results of FFT of IF signal
input : 508 MHz signal

1) S/N•The amplitude A was measured 16 times, then ascattering of A was calculated.

20

7.12 dB

0Amplitude [dBV ]•Assume that the noise is represented bya noise floor of the signal spectrum.
•Measured (S/N)noise floor was 85.1 dB.

-20data : 2048 points-40-60-80-100(S /N) amp. " # r.m.s. / A = 60.9 dB-120

resolution of 15µm

010000

20000

30000

40000

50000

40000

50000

Frequency [Hz ](S/N)amp is much worse than (S/N)noise floor
and should be improved.

!

no signal input
20

Some noise might be down-converted to IF(Intermediate Freq.).
•Measured NF (from the multiplexer input tooutput of 1st amp.) was 8 dB which is larger
than the spec. (= 7 dB).

Amplitude [dBV ]0Insertion loss of switches ?

-20-40-78 dB-60-80-100-120010000

20000

30000

Frequency [Hz ]SNR=7.12-（-78）=85.1(dB)

2) Linearity•Input vs. output characteristics of 4 channels was measured at the companyand fit to a 3rd order polynomial as,
3j
Vout,i = " a j,iVin,ii : ch no.
j= 0

2

1

Assume linear relations of!

(xbeam,ybeam)1
1(+ x beam + y beam )), Vin,2 = V0 (1+ ("x beam + y beam )),K
K
11Vin,3 = V0 (1+ ("x beam " y beam )), Vin,4 = V0 (1+ (+ x beam " y beam ))KKVin,1 = V0 (1+Positions are calculated as!

x out = K

Vout,1 + Vout,4 " Vout,2 " Vout,3,Vout,1 + Vout,2 + Vout,3 + Vout,4y out = K

Vout,1 + Vout,2 " Vout,3 " Vout,4Vout,1 + Vout,2 + Vout,3 + Vout,4The xbeam-xout was plotted as a function of xbeam.
!

34•Result
xbeam – xout at y=0mm

ybeam – yout at x=0mm

The error is about 0.1mm in -10 mm < x, y < 10 mm.
If offsets are removed and gains are equalized, position errors are 10µm
within -5 mm < x, y < 5 mm.
3j
Vout,i = " a j,iVin,iai,0 = 0, i = 1,4, a1,1 = a2,1 = a3,1 = a4,1j= 0!

!

The tolerance of the nonlinearity to the operation should be estimated.

Four channel gate
•A 4 ch gate was tested to measure the turn by turn orbit of a pilot bunch
separated by typically 6ns from a bunch train.
•Switches of a gate module for the bunch by bunch
diagnostics in KEKB are used.

•A bunch was kicked then its position wasmeasured by a turn by turn BPM in KEKB.
mm
FFT of x positionx : linear scale
f/frev=0.5083

Specifications

 Frequency Range: DC - 4 GHz
 Impedance : 50 Ohms
 Number of channels : 4
 ON/OFF isolation : > 60dB @ 2GHz
 Channel Isolation : ~ 80 dB @2GHz
 Insertion loss ~ 3 dB
 Control Voltage: NIM level•The oscillation of the bunch was clearly identified.

Exciter of a bunch oscillation•The oscillation of a bunch is excited by shaking the bunch at
the frequency of a tune.
bunch
train

Deflector
feedback loop

#N-2!

Pulse
Modulator

CW orPulse%)#N-1

40 - 50 kHz#NDetector 1

ADC 1

ADC 2

BPM 1

#N+1

3.5

32.501000

Detector 2

Gate 2Clock2000

3000

4000

Turn

for #N bunch

ClockTrig.

Trig.

Gate 1!"#$%$&''()'&*)&'&

4
Horizontal position (mm)Gate Pulse
for #N bunch

BPM 2

for #N bunch

Button Pickups
File: BBB_Kick&Meas•A tracking exciter using PLL will be tried in next run in order to stably
kick the bunch.

BPM noise at 509MHz•In SuperKEKB the detection frequency is not 1 GHz but 509 MHz because
antechambers will be used.
•Noise from RF system might be troublesome.
•509 MHz signal was measured at Nikko straight section when RF cavities in HER
were powered.
noise power -134 dBm-114 dBm -120 dBm

CRAB

D10B

D10A

-130 dBm-110 dBm -132 dBm-127 dBm-131 dBm

D10D

D10C

QY2E.1QY2E.2QY3E.2QY4E.2QN1E.2QN2E.2

QN3E.2QN4E.2

QN5E.2

150φ

150φ

150φ

150φ

150φ

150φ

150φ

150φ

50x104QW2NP.2*noise level of the measurement : -136 dBm-118 dBm•A LER BPM also had noise, where no cavity
in LER is in Nikko straight section.

chamber size

•S/N from the measurement
signal : -51 dBm@30mA

noise : -110 dBm (QN2E.2)
1/(S/N)=-110+51=-59 dB = 0.0011

position error=1/2 x K x 1/(S/N)=1/2 x 33mm x 0.0011=18 µm•Second measurement was done to assure the noise did not came from the cavities
through the chamber.
CRAB

D10A

D10B

D10D

D10C

QY2E.1QY2E.2QY3E.2QY4E.2QN1E.2QN2E.2

QN3E.2QN4E.2

QN5E.2

150φ

150φ

150φ

150φ

150φ

150φ

150φ

150φ

50x104•The signals from QY3E.2 and QN2E.2 were measured connecting cables to feedthrough or terminating the cables to 50 ohm.
QY3E.2 (connect)
QY3E.2 (terminate)-90-90-100-100

-110
-120

QN2E.2 (connect)
QN2E.2 (terminate)-80level (dBm)level (dBm)

-80

-110
-120
-130

-130

noise level

noise level

-140

AB
C
electrodeD•Almost same level or larger
noise was observed when thecables were terminated.

-140

ABC
electrodeD

red : connected to the feed-through.
blue : terminated to 50 ohm.

•Noise comes from signal passfrom a feed-through to adetector.
Shielding is necessary for better
S/N.

Test of Libera Brilliance (Instrumentation Technologies)•Libera Brilliance is used in several lightsources such as Australian Synchrotron,
DIAMOND, Elettra, Soleil and SSRF.
•Libera has several data paths.
◊Turn-by-turn Acquisition◊Fast Acquisition (10kHz)◊Slow Acquisition (about 10Hz)•Libera might be a candidate of a signal
processor for special use, for example for
BPMs for IR orbit feedback where a fast
(1kHz to 10 kHz ?) continuous
measurement is required.
•A Libera Brilliance is under test inKEKB.

Specifications

a) Laboratory test by a signal generator (Turn-by-turn Mode)•Resolution

Kx=Ky=10mm, Libera att. 0dB, Libera input -20dBm(Kx=Ky= about 30mm in KEKB)

0.5µm

0.5µm

σx = 0.18µm, σy = 0.18µm in 10000 data for K=10mmb)Beam test (Turn-by-turn Mode)
FFT - 65536 points (power spectrum)xmmx

LER 1430 mA20µm

50kHz

turn38.1Hz
50.4Hz2x" = $ S(# )d#

100.7HzS(ω) :power spectrum density of noise floor

σx : 3.2µm, σy : 2.4µm!

σx,y is not the resolution of the BPM. It could be
affected by the movement of the beam.
*Sudden change of the data is observed in Slow Acquisition Mode. The reason is not clear yet.

freq.

Cold BPM in IR•Several BPMs in IR may be at low temperature (He or N2 temperature).
•Heat dissipation was roughly estimated.
iZ0buttonroom temp.

Z0
cold mass
CLER
bunch current : 1.84 mA, bunch spacing : 2ns, bunch length : 5mm,
button diameter : 6 mm, chamber radius : 47 mm " 0 I˜(" )bunch spectrum of i(t)%1I˜ (" ) =& i(t)e$"t dt
2# $%!

!
"!

1 1 1 $
1 1 1 µ0"$2$
R(" ) =( + ) &l=( + )& l, % =2# a b %2# a b2µ0"

red : copper conductor

ρ : resistivity, δ : skin depth, l : length of conductor
$!

P=

1
(" 0 I˜ ( p" 0 )) 2 R( p" 0 )%2 p=#$

a=1.5 10-3 m, b=0.4 10-3 m (LHC BPM cable), l=0.1 m!

4K for copper (He temp.) : ρ =9.3 10-11 Ωm
δ =4.0 10-8 m, R=0.12Ω@15GHz, P=0.03 W
77K for copper (N2 temp.) : ρ =1.55 10-9 Ωm
P=0.14 W•Questions
Is the heat load within the ability of the cryogenics ?
Structure of a feed-through, a connector and a signal cable ?
Alignment, movement of BPM at low temperature ?

•KEKB has no experience of this kind of BPM.
Need R&D if the cold BPM is really required.

3. Synchrotron Light MonitorA)Visible light monitor•Beam size at source points of light

σx(µm)
σy(µm)
σmin (µm) : minimum measurable beam sizeby an interferometerLER1490
97

LER2
420
68

HER73046121324

D : slit separation,
F : distance from beam to slits,
θc : critical angle" min. = Minimum(Dmax /F, 2# c )•From standpoint of beam sizes, we can still use:!

Dmax=aperture

θcF

Interferometers
Streak Camera
Gated Camera•Extraction mirror
Heat load at high beam currents causes serious mirror distortions.
LER1

LER2

Energy(GeV)
Current(A)Bending radius(m)

3.5
9.4
180

3.5
9.4
120

LER1(KEKB)
3.5
260

Power(W/mrad/A)
Total incident power(W)

11.5
231

17.3
204

34.5
147

First step: increase bending radius of source
magnets (HER 2x, LER1 3x, LER2 2x).

ANSYS simulation

m48.7
364

97.5248

Next step: Investigate new mirror
structures, e.g., thin Be on thin watercooled Cu plate.
Projected slit positions
mm

84.1
1160

HER(KEKB)
81.4580

HER400 WmA simulation showed that deformation decreases to the level of KEKB with 2mm Be
and a water channel. We are trying to find a better solution.

B) X-ray Monitor•Purpose is to provide high-resolution bunch-by-bunch measurement
capability, with low beam current dependence (low distortion).
•Currently we are investigating and developing (in collaboration withCornell U. and U. Hawaii) an x-ray monitor system featuring:1) Coded Aperture Imaging
Being tested in collaboration with Jim Alexander et al.
at CesrTA at Cornell U..
2) High-speed readout
STURM readout being developed at U. Hawaii (Gary Varner).

1) Coded Aperture Imaging•Technique developed by x-ray astronomers
using a mask to modulate incoming light.
•Resulting image must be de-convolved throughmask response (including diffraction andspectral width effects) to reconstruct object.
•Open aperture of 50% gives high flux throughput
for bunch-by-bunch measurements.
•A heat-sensitive monochromator not needed.
* : convolution
P=O*AOˆ = P * G = O * (A * G)Oˆ : reconstructed object, P: picture, O: object,!!

A : mask or aperture, G: post processing array
A*G : system point-spread function~ δ function

Uniformly Redundant Array (URA) mask
being tested at CesrTA

Simulated detector response forvarious beam sizes
preliminary
red : datagreen : simulation

Example of beam size measurement
at CesrTA (σ y =~ 45 µm)

2) High-speed Readout: STURM(Sampler of Transients for Uniformly Redundant Masks)‫‏‬•Designer: G. Varner, U. Hawaii (Belle)•8 Channels/ASIC, 32 samples/channel•Up to 8 external timing strobes•Each timing strobe can fire 4 timing samples,with minimum spacing < 5 ps.
Examples:8 bunches, 4 samples/bunch
32 bunches
8 trains, 4 bunches/train•Total readout time 8 µs
Turn-by-turn measurement is possible.
•Beam test planned March 2009 at KEK PF•Detector
Fermionics InGaAs sensor array being tested at
CesrTA and KEK PF.

C) Beamstrahlung Monitor•Developed by G. Bonvicini (Belle,Wayne State U.) originally for use atCESR.
•Uses relative strengths of x- and ypolarization of wide-angle beamstrahlung
to diagnose quality, e.g. beam separation,
beam size, of collision.
•Monitor and Vacuum groups are assisting
Prof. Bonvicini with design of system foruse at SuperKEKB.

Polarizing Beam Splitter
infrared
PMTredPMTCESRred
infraredmirrorTwo beams at IP•Need to understand background due tohalo in IR quadrupoles.
•Need to make room for extraction mirror
and window in beam pipes near IR, andevaluate resulting HOM.

polarization

G. Bonvicini et al., Phys. Rev. E 59, 4584 (1999)

PMTPMT4. Gated Measurement for Bunch-Tune, -Orbit and -Phase
A) Development of a gate module•A fast gate module is being developed for a fast gate to measure thetune, orbit and longitudinal phase of each bunch separated by 2ns.
•Two switches are being tested.
1) Agilent HMMC-2027

Specifications
Input/Output Impedance
50 ΩInput Power> +20 dBm
Bandwidth
1.0 MHz - 5.0 GHz
Switching Time200 ps
ON/OFF Isolation> 50 dB @2GHz
Insertion Loss
< 10 dB@2GHz
Control0 - - 0.8 V2) AVAGO AMMC-2008•Beam Test

HER: 0.5 mA/bunch
HMMC-2027

AMMC-2008
Bunch Train

Gated Bunch

1 ns/div

1 ns/div

ON/OFF Isolation: >60dB@2GHz, Switching Time: <500 ps, VSWR ~1.5
•A compact 4 channel module will be fabricated and tested with beam in next
fiscal year.

5. Summary•Tentative plan of beam diagnostics system in SuperKEKB is as follows.
•BPM system
1) Flange type feed-through with a button electrode of 6mm φ,2) All BPMs are processed by narrow band detection at 509 MHz,3) 120 BPMs can be turn by turn BPMs with a fast gate,
4) Some BPMs, for example BPMs near IP, might becommercial products.
Issues to be solved or not addressed yet are1) Improvement of S/N of the prototype 509 MHz detector andimprovement of its linearity if necessary.
2) RF noise at 509 MHz in RF straight sections,3) System of a cold BPM if it will be used.

•Synchrotron light monitor system1) Visible light monitor•Use of an interferometer, a streak camera and a gated camera like KEKB.
2) X-ray monitor•Coded aperture imaging and high-speed readout for turn-by-turn or bunch-bybunch measurements (a backup might be a pinhole mask for slow
measurement).
Issues to be solved or not addressed yet are1) Thermal deformation of an extraction mirror for visible light,2) Design of a mirror chamber for reduced HOM losses at higher beam
currents and short bunch length,3) Design of an extraction chamber and a beam line for X-ray monitor.
•Gated measurement system with newly developed fast gates.
•Remaining instruments such as DCCT, CT and loss monitors will bestraightforward extension of those in KEKB.