Beam Diagnostics
16 Feb. 2010, 15th 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. Bunch by bunch feedback system	

4. Synchrotron Light Monitor	

5. Gated Measurement	

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

LER	

Energy (GeV)	

7	

4	

Current (A)	

2.6	

3.6	

BPM, FB, SRM	Number of bunches	

2503	

2503	

FB, SRM	

Single bunch current (mA)	

1.0	

1.4	

BPM,FB, SRM	Bunch separation (ns)	

4	

4	

BPM, FB, SRM	Bunch length (mm)	

5	

6	

FB, SRM	

Emittance (nm)	

2.4	

3.2	

BPM, FB, SRM	Coupling (%)	

0.35	

0.4	

BPM, FB, SRM	Vertical beam size at IP (nm)	

59	

59	

BPM, FB	

Transverse damping time (ms)	

56	

37	

FB	

ante-chamber	

ante-chamber	

BPM, SRM	

Vacuum chamber	Beam current is twice as much as that of KEKB is.	

Very small beam size, especially in vertical plane.	

Relatedmonitors	

BPM : Beam position monitor	

FB : Bunch feedback	

SRM : Synchrotron radiation monitor	2. Beam position monitor	

Requirement	•Requirement to the BPM system is not fully specified yet. 	
•In order to start R&D we tentatively assumed that the required resolution of themeasurement is not far from the performance in present KEKB.	
Resolution : several micron, accuracy : 40 micron (by beam based alignment)	

Tentative functional specification	•Precise slow measurement - Repetition of ~1Hz.	
•Fast orbit measurement for the orbit stabilizing feedback whose repetition rate isseveral kHz.	
•Optics measurement during physics	

Turn by turn orbit measurement of a pilot bunch to obtain betatron phase and
X-Y coupling.	

•Fast orbit feedback to maintain stable collision.	

Factors affecting system design	a) Large beam current	•Large signal power to a detector, poor electrical contact of an electrode and acable and movement of BPM due to thermal deformation of a chamber.	
b) Use of ante-chambers	•Lowest cut-off frequency of about 900 to 990MHz of a beam chamber is below
a detection frequency in present KEKB system.	
c) Maximal use of present narrowband detection system based on VXI to save the cost.	

Design strategy	a) Development of a new button electrode.	
Button with small diameter, pin type inner conductor 	b) Development of a new detection module for 509 MHz detection.	
c) Development of a medium-band detection module for orbit stabilizing
feedback and gated turn by turn orbit measurement for optics
measurement.	
d) Development of a special detection module for collision feedback.	
e) Use of displacement sensors to measure the movement of BPM
due to thermal deformation of a chamber.	

Button electrode	LER chamber	

•A button electrode is under development.	
◊Diameter : 6mm	◊Flange type for easy replacement upon trouble
and TiN coating	◊Pin-type inner conductor for tight electricalconnection	
◊Ceramic vacuum seal	•Prototypes are installed in ante-chambers in Nikko
straight section and the south tunnel for test.
Problem is not found so far.	

volt	

0.4	

bunch current 	

0.95mA	signal of button with
6mmφ(cable length
84.8m）	

sec	

Electrode	509 MHz super-heterodyne detector	
•A narrowband super heterodyne receiver is being developed based on a present detector. 	

•At the previous KEKB review committee, 	

we reported that SNR of the detector was 60.9 dB
at a bench (SNR 90 dB<-> resolution 0.5µm). 	

Specification	

Detection frequency	

508.887MHz	

SNR at signal power of -60 dBm	> 89.8 dB	

by a signal level of a specific channel).	

◊A bug in power calculation of FFT was fixed.	

Absolute SNR was improved to 88 dB without
averaging (a switch module was bypassed). 	

< 7 dB	

18 bits / 102.4 kHz	-50 dBm	

2N (N=4, 5, ...., 12)	absolute SNR (dB)	

•Since then following improvements were taken. 	

Noise figure 	

◊A synthesizer to make a LO signal was replaced
ADC (bits/sampling freq.)	

to that with smaller phase noise. 	

Max. input power	

◊Gain of a RF amp in front of the mixer was
FFT points (by DSP : SHARC)	

increased.	

◊Frequency characteristics of the IF filter was
improved. 	

◊A switch module was renewed.	

Relative SNR was improved to 88 dB by averaging data
8 times. ("Relatve" means signals of 4 channels are normalized◊A switch module is being tested at a company. 	

◊The module will be tested by beam in this spring.	

Freq. of input signal (MHz)	

signal freq.(Hz)	

Medium-band detector	
•Simple feedback model to determine repetition frequency of orbit measurement	
1G(s) = K(1++ TD s)−1
D(z)	
 disturbance	
T
s
Ts z
TD
I
−1
G(z) = K(1+

Yr	
 +	
€

-	

TI 1− z−1+Ts

(1− z ))

G(z)	
G	
€
P.I.D. control	
 €

Ym	

€

H(z) = 1

P1 (z) = z−T1 /Ts

+	

H(z)	

delay	
P1(z)	

kick to orbit	

delay : eddy current+P.S.	

€

+	
 Yo	

P2 (z) = z−T2 /Ts

Yr : reference orbit	

B(z)	

P2(z)	
delay : BPM
meas.+transfer
delay	

B(s) =Yo	

Yo : orbit	
Ym : measured orbit	BPM	

1
1+ a ⋅ s /ω c + b ⋅ (s /ω c ) 2

B(z) = B(s) s= 2 /T (z−1)/(z +1)

Bessel LPF : a=1.3617, b=0.6180	

Transfer function from Disturbance to Orbit	
€R(z) =€Yo (z)
1for Yr = 0	=D(z) 1+ H(z)G(z)B(z)P1 (z)P2 (z)sTs : sampling interval	Ts : 0.25ms, ωc: 12.6kHz, T1 : 0.5 ms, T2 : 0.25 ms, TI : 0.6 ms, TD : 0 ms, K : 0.8 	

Pole plot	

Im z	Abs(R(f))	

Re z	

f(Hz)	gain	50 Hz disturbance	gain = 1/0.45 = 2.2 @ 100Hz	100 Hz disturbance	

We set,	

sampling freq. fs as 4 ~ 5 kHz.	

Gain for 50 Hz disturbance of ~ 4.5.	

repetition of BPM measurement (kHz)	

•Evaluation circuit board for medium-band detector	

◊An evaluation circuit board with FPGA (Virtex5) is under development.	
◊Specification	

•Direct detection of 509MHz component with a sampling ADC and a digital filter.	

•Maximum repetition rate of 5 kHz for orbit stabilizing feedback.	

•Averaging data for slow but higher resolution measurement with rep. rate of 10 Hz.	

•Independent Log-Ratio detector with a fast gate switch (<6ns) with adjustable delay forturn by turn orbit measurement for optics measurement.	

•Electrical	

Input level	

-10 ~ -3 dBm	

Detection frequency	

509MHz	ADC resolution 	

14 bits	

ADC sampling frequency	

98.4 MHz (det.) / 40 MHz (log. amp.)	

Log amp.	

dynamic range > 80dB, freq. range 0.4 ~ 4GHz 	

Repetition	

5 kHz (max.)	

SNR	

>80 dB@-60dBm input and BW of 5kHz	

Fast gate 	width < 6 ns including rise and fall time	

◊The board will be tested in this spring.	

•Consideration to the standard BPM system 	◊Cost is a big problem. 	

◊If a price of the midium-band detector is 20000$ / unit,	

total cost is 20000$ x 938 units = 19M$. 	

◊Cost will be evaluated after the evaluation circuit is tested. Cost oriented
optimization of the system will be taken into account.	

◊Use of the narrowband detectors together with the medium-band detectors may be agood compromise of cost and performance. 	

For example, the medium-band detectors for orbit feedback can be used for
BPMs near sextupoles where optics will be sensitive to orbit deviation. 	

BPM for orbit feedback to maintain stable collision 	•Simple consideration on the BPM resolution and repetition rate of the measurement 	

1) Resolution	

Δy'
BPM	

BPM	

Q	
◊Beam-beam kick	

1.28m	

€ Δy' =

◊Orbit change at BPM	Q	σ *y /10

2π
2π
59nm
ξ
Δy
=
0.09⋅
= 12.4 µrad
βy* y0.27mm10

Δy' €Δy BPM = 1.28
= 7.9 µm2€
◊Required BPM resolution
will be ~ 1 µm. 	
2) Repetition	

€◊Measurement of vibration of IR quadupoles (M. Masuzawa et al., IWAA2004)	

Some peaks are seen at frequency less than 100 Hz.	

Vertical oscillation amplitude whose frequency is larger than 50 Hz is less than 1/10
of beam size.	

◊Feedback needs to have a gain in the region < 100Hz.	
Required rep. rate of the measurement of ~ several kHz (e.g. 5 kHz).	

•Signal processing of a detector	

◊Intrinsic resolution from thermal noise is 6nm for BW of 1kHz.	

◊Down covert 508.8MHz component of the beam to lower frequency
with an analog mixer.	

◊Convert IF to digital signal.	

◊Detect position through digital filters (CIC+FIR).	

Filter response (CIC and FIR) 	

SNR is relatively insensitive to a clock jitter than that in directconversion though additional analogue RF circuit is needed.	

Specification	

An evaluation system is under development in this fiscal year.	

Input level	

-10 ~ -3 dBm	

Detection frequency	

509MHz	LO frequency	

492 MHz	IF frequency	

16.9 MHz	ADC resolution 	

16 bits	

ADC sampling
frequency	

99.4 MHz	Sampling clock jitter(target value)	

<1ps	

CIC1	

5 stage, decimation 32	

CIC2	

5 stage, decimation 96	

FIR	

201 tap, decimation 7	

SNR	

> 110dB@-2.65dBm
sinusoidal wave	

Control	

EPICS	

BPM noise at 509MHz	

•The detection frequency is changed to 509 MHz from 1GHz of KEKB 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. The measurement showed that	

◊The noise came through signal pass from a feedthrough to a detector(shown at the previous KEKB review committee).	

◊The 508 MHz air waves enter from the klystron room to the control room. 	

At a module rack in the control room : 87dB µV/m, at a driver amp in the klystron room : 107dB µV/m. 	

◊Shielding of 9D coaxial cable is OK.	

A cable with length of 12m was fabricated. The signal was measured by a spectrum analyzer
when one end of the cable, which was terminated or covered by a meshed metal sheet, was put
near the driver amp in the klystron room. The 508MHz signal was not observed.	

◊The noise signal was detected by a VXI module in the shield tent where air waves were shielded. 	

The signal really comes through cables. 	
•Sources of a noise are still not identified yet. 	
•In operation the noise will be actually attenuated by an attenuator in the detector module which
adjusts an input level of the signal. From the measured signal and noise level, degradation of
the resolution is 0.045 / 0.7 µm at beam current of 1600 / 100 mA. 	

Noise voltage : Vn=1.7mV(rms) in 0 dB attenuator setting	Beam signal @ 1600mA : Vb=2.0V(rms) with 50dB attenuator setting	•Though the noise level will be small in usual operation, it may affect to theorbit measurement at optics correction which will be done at low current.	

Displacement censor	

Specifications	

method	electrostatic (capacitive)	

channels	

2	

range (mm)	

0.5 - 2.5	resolution (µm)	

< 0.2	

nonlinearity (%)	< ±0.3	frequency response (Hz)	

0 - 100	

Horizontal	

mm	

temperature 	

coefficient (µm/deg.)	

< 0.2	

sensor	x	

Gap detector developed at KEK.	

Cx	

metal	

•The number of censors to be installed and required
bandwidth are not determined yet. 	

50 µm	South tunnel(HER)	

800mA	

beam current	

x 10 sec	

Example of movement of BPM with respect to a
sextupole in KEKB	•Development of a new measurement target and arm	◊Measurement in KEKB showed that a big measurement error of about 10µm wascaused by thermal expansion of an aluminum target. 	

◊We are developing a new target made of ceramics in order to reduce thermal
deformation of the target and the arm of the sensors.	

Target	Arm	

ZPF – E04	PSS – 50 	(Zero Expansion Ceramic)	

 (Metal Matrix Composite, SiC 50%, Si 50%)	

Thermal expansion coefficient (1/K)	

0.4 10-6 (@20±3°C)	

2.8 10-6	

Thermal conductivity (W/m/K)	

8	

175	

Resistivity (Ohm·cm)	

105	

0.02	

Density (g/cm3)	

2.6	

2.8	

Non-magnetism	

Non-magnetism	◊A problem is a cost (about 7,700$ / set).	

Estimated deformation (ANSYS simulation)	

The system can be used in critical place such as
sextupoles for local chromaticity correction.	

At local chromaticity correction sextupoles,	LER βy=2700 m, K2=1.47 m-2	Δνy=0.0003 for Δx = 1µm	HER βy=2140 m, K2=7.5 m-2	Δνy=0.0013 for Δx = 1µm	◊A set of the target and the arm is being fabricated.
The system will be tested in this spring run.	

MMC (ΔT 10°C)	

Hor. : 3 µm max.	

3. Bunch by bunch feedback system	
Features of feedback system in SuperKEKB	•Longitudinal feedback system will be required.	

•Noise in transverse feedback system should be minimized to reduce the blowupof the beam size during collision.	
•Vacuum components such as kickers, power cables, feedthroughs and BPM
electrodes should withstand large beam current.	

A. Transverse feedback system	
Requirement for damping time	Beam current of 3.6/2.6 A for LER/HER is assumed.	

•Coupled bunch instability (CBI) growth time	1) RF cavity	

2) Resistive wall 	

LER	

HER	

ARES (HOM)	

9 ms	

58 ms	

Super (HOM)	

---	

14 ms	LER (Cu)	

LER (Al)	

HER (Cu)	

3.6 ms	

2.8 ms	

3.1 ms	(Transverse radiation damping time : LER 37.4 ms, HER 56.4 ms)	3) Electron cloud instability (ECI) in LER	

0.5ms at the average/central electron density of 5 1010/1.1 1011 m-3 in drift space
without solenoid field (Y. Susaki at LER2010). The growth time will be increased ifsolenoids reduce the electron density. 	

4) Fast ion instability (FII) in HER	

0.3 ms (shown later) 	

LER : < 0.5 to 1ms (ECI) 	

◊Required feedback damping time 	

HER : < 0.3 ms (FII) 	

◊If the growth time of ECI and FII is larger than that of present estimation,required damping time for the feedback is relaxed to about 1 ms.	

◊The growth time of ECI and FII should be studied more.	

•Fast ion instability (FII)	

◊A simulation study just started with a tentative lattice parameterswith a code by L . Wang. 	

◊A very preliminary result is given here as an example. 	

Parameters for a simulation	

Vertical tune shift	

Amplitude growth	

unit : rms beam size	# of bunches / train	

100	

Bunch separation	

2 RF buckets	

Train gap	20 RF buckets	# of trains	

21	

Pressure	

1 nTorr	

Ion 	

CO+	

Coupling 	

0.2 %	

growth time 0.28 ms	

Critical mass	

◊Vertical amplitude grows 10 % of the beam size after 25 turns.	

◊Vertical tune shift by ions is 1.2 x 10-4 . 	

◊Critical mass is larger than mass of CO at some placesin the ring.	

◊Is FII not so strong in very low emittance lattice ?	

◊We need more study including a bunch by bunch feedback.	

Calculation by L. Wang	System	1) BPM	

◊Good time and frequency response.	

2) Low noise front-end electronics	

3)Digital filter using iGp	4)Power amp	◊Total 16 amps with 500 W output.	
5) Kicker 	

◊Two sets of a short stripline kicker per ringwhich correspond to two feedback loops
with 90 deg phase difference.	

iGp digital signal processing system	

•Features	

◊Developed under US-Japan collaboration (KEK-SLAC).	

Firmware is supplied by DimTel.	

◊Adaptable to almost any harmonic number.	

◊Operation at 509MHz is possible for KEKB.	

◊8tap FIR(KEKB) to 32 Tap FIR (DAFNE) are available.	

◊Down sampling function for Longitudinal feedback.	

◊Bunch-selected FB ON/OFF and excitation.	

◊Transient-domain analysis for study of instability.	

◊Capable to monitor a feedback signal without disturbing
feedback. 	

•Status in KEKB	

◊Tested successfully for the transverse and longitudinal
system. 	

Now planning replacement of existing 2 tap filters to iGps.	

•Next generation system with a digital filter working at ~1.3
GHz using new FPGA, and ADC and DAC with higher
resolution is under development.	

•Example of transient-domain analysis with iGp at KEKB HER	FFT	

Amplitude growth of a bunch	

time	

turn	

◊FB turned off during 12 ms, then turned on again.	

◊Data of 1600turns of all the bunches were taken inthis sequence, then FFT was applied to get
oscillation modes.	

mode no.	

Amplitude growth of modes	

◊The result shows that 	

dominant mode of the coupled bunch instability is 5110,	

damping time of FB system is around 0.8ms at 800mA.	
time	

Development of Button electrodes and Lower noise front-end	•A feedthrough with low εr(~ 4) sealing is under development to get good time and frequency
response.	

φ8
φ6
φ1.8
1

φ4.1
3

φ1.3

D01

φ19.5

•Lower noise front-end for the transverse feedback system is under development. 	

detector out	◊A new detector is being tested by a beam simulator withrepetition of 127 MHz using step recovery diodes.	

◊An experiment measuring the effect of the feedback gain on theluminosity is planned with a new detector and the iGp which
replaces the existing two tap filter.	

KEKB-FB

Transverse kicker	
•Two sets of a short stripline kicker per ring	

Rsh=10kΩ per kicker, amp of 500W, 2 kickers -> Vkicker=8.9 kV	

Max. damping time 0.27ms(LER), 0.45ms (HER)
for max amplitude of 0.3mm.	

•Similar design with a present kicker	

◊Improved support structure for electrodes	A structure where electrodes are placed at samelevel as chamber surface is being considered. 	

The system needs consideration on trapped mode.	
◊Cooling of the electrodes will be fairly difficult.	

present LER kicker	

Effect of feedback noise on the luminosity	

•Higher vertical feedback gain in LER degraded the luminosity in KEKB operated without
Crab cavities. 	

•A simulation by K. Ohmi showed that fast beam noise whose amplitude is 2 % of beam size
degrades the luminosity by 20 %. 	

•An experiment was carried out in last December by applying
sinusoidal vertical kick to the beam by the feedback kicker. 	

•The result showed that, 	

◊The luminosity was degraded by the excitation of 0.2 σy,while a simulation showed that it was degraded by the
excitation of 0.05 σy . The luminosity seems not sosensitive that the simulation predicts.	

◊The beam could be excited by the kick with frequency
far from a betatron tune so large that the luminosity isaffected.	

•The measurement showed that the feedback noise should be
reduced as small as possible. 	

B. Longitudinal feedback system	
Requirement for the damping time	Beam current of 3.6/2.6A for LER/HER is assumed.	

•CBI growth time by cavity impedance	

LER	

HER	

ARES (HOM)	

15 ms	

75 ms	

ARES (0-π mode)	

29 ms	--	Super (HOM)	

---	

58 ms	(Longitudinal radiation damping time : LER 18.7 ms, HER 28.2 ms)	LER needs a feedback system with damping time of about 10 ms.	
Starting only with LER system might be better taking into account of cost.	

System	1) BPM, frontend electronics, digital filter	5) Back-end electronics	

◊Same as those of transverse system.	
A digital QPSK modulator from the ideaof Dr. John Fox (SLAC) is tested.	

2) Power amp	◊Four 500 W amps per kicker	
3) Kicker	
◊ DAFNE type kickers with Q value of about 5: two kickers in a ring	◊Rsh=650Ω/kicker, amp. 500W x 4 / kicker, two kickers -> Vkicker=3.2kV 	Max. damping time is 10ms if (ΔE/E)max. =4x10-4 (LER).	
◊Start with two kickers system (reserving a space for additional two kickers).	
◊Re-design with a better 3D code.	

◊Improve cooling structure of a body.	

4) Power cable and feedthrough	◊R & D will be required against a large beam current.	

A beam test of longitudinal feedback system	Grow(Excite)/Damp experiment	
Excite	synchrotron sidebands	

Damping time ~3 to 6 ms	

Damp	

Amplitude of modes	4. Synchrotron light monitor	
A. Visible light monitor	

Interferometers	

•Resolution fundamentally limited bymeasurement wavelength and opening angle
between slits from beam (D/F).	

•Max. slit separation determined by beam
spread and mechanical considerations.	

•Beam size measurement is possible with interferometers, though is at the limit of theinterferometer resolution.	

•Measurement wavelength needs to be lowered to fit beam size into dynamic range.	

•Limitation on slit separation is due to antechamber height (14 mm).	

◊Extraction mirror will be in antechamber for reduced impedance.	

◊If we could increase antechamber height by factor of two for 2 m (LER) or 4 m (HER)
in front of extraction mirror, we could correspondingly reduce minimum measurable
beam size by factor of two. Appears difficult due to presence of upstream quads.	

Visible light options	
•Standard interferometer using σ polarization	

•Rotate polarizer -> interferometer using π polarization	

Point Spread Function of πpolarization light in LER	◊All wavelengths come to minimum at center, so can use
broader spectrum.	

•Rotate polarizer, remove slits 	

-> Vertical polarization monitor (proposed at PSI)	

◊Resolution similar to interferometer with slits
set at π polarization peaks.	

Not as good theoretical resolution as interferometer(which can push slit separations out into tails of light
distribution).	

◊Greater open aperture than vertical polarization interferometer	m	Convolved image of verticalpolarization monitor	LER : σ=20,40,80[μm]	

◊More complicated beam current dependence due to heatinduced mirror distortions	Must understand and correct for distortion of whole mirror
rather than just two small regions.	

•All above options under consideration for applicability for
different types of measurements	

•Longitudinal measurements: streak camera	m	Extraction Mirror	

•Heat load at high beam currents causes mirror distortions.	

•Increase in power load with nano-beam option is much less severe than with high-current option.	

LER bend radius doubled.	

•Investigating new mirror structures, e.g., thin
Be on thin water-cooled Cu plate.
SR	

Cross –section:	

Projected slit positions	m	

400 W	

Be	
Cu

H2O	
•Simulation showed that deformation decreases withthin (2.5 mm) Be mirror, but laminar cooling waterflow will be needed in back rather than parallel coils
as used at present, to avoid surface distortions.	

•We plan to make a mirror of this type to test.	

m	

B. X-ray Beam Size Monitors	

•Purpose is to provide high-resolution bunch-by-bunchmeasurement capability, with low beam current dependence(low distortion).	

Intensity	

•Developing system based on Coded Aperture Imaging.	

◊Technique developed by X-ray astronomers using a mask tomodulate incoming light. 	

◊Resulting image must be deconvolved through mask response(including diffraction and spectral width) to reconstruct object. 	

◊Open aperture of 50% gives high flux throughput for bunchby-bunch measurements. Heat-sensitive monochromator notneeded.	

Detector signal measured at CesrTA.	

Beam size ~16 µm.	

σy(um)	

Uniformly Redundant Array(URA) for x-ray imaging being
tested at CesrTA	

turn	

Turn-by-turn single-bunchmeasurements at CesrTA	X-ray Source	Simulated detector response fordifferent beam sizes.	

Beam to mask: 6 m, Mask to detector: 24 m	

HER: 5 µm pitch coded aperture	

•Use last arc bend before straight section(LER: Fuji, HER: Oho)	

•Simulation with 5(10) µm pitch coded
aperture in HER(LER) shows required beam
size resolution is achievable.
	

LER: 10 µm pitch coded aperture	R & D of X-ray Beam Size Monitors	

•Collaboration with Cornell (CesrTA ILC damping ring study
machine group) and U. Hawaii (Belle detector group)+SLAC.	

•Beam size measurements down to 15-20 µm demonstrated so far.
Looks promising for SuperKEKB.	

•Fermionics InGaAs detector tested at Cornell and KEK PF.
Time resolution sufficient for bunch-by-bunch measurements,
but efficiency low at high critical energies. Investigating
further detector options (KEK/UH/SLAC).	

STURM ASIC for high-speed readout (G. Varner).	

Ver. 1 tested at KEK PF in March 2009.	

Ver. 2 in fabrication now. Ver. 2 specs:	

•STURM (Sampler of Transients for Uniformly Reduntant
Mask) readout ASIC designed at U. Hawaii.	

Signal flow diagram for x-ray monitor system	

Fermionics InGaAs detector array.	

Also being used at CesrTA (with Cornelldeveloped mount and readout).	

Illustration of two of the detector concepts to be
explored in next phase of x-ray detector
development. At left, a regular pattern of n and pelectrodes, at right, a trench structure, which
provides a more uniform drift volume.	

Hamamatsu MPPC test
array: high gain (“silicon
PMT”), but low resolution:
candidate for slow x-ray
monitor.	

Direct-detection X-ray monitor	

•Basic principle is to use X-rays penetrating
chamber walls downstream of bends directly
to measure beam emittance (very oldfashioned method).	

•System is simple. No optics elements are
required. It requires small thin region (~1 mm)
on antechamber outer wall to extract X-ray.	

Consulting with vacuum group	– cooling an issue, but may be possible.	

•Some potential candidate locations are in
local chromaticity correction sections
around IP with huge beta functions and nooverlap (final evaluation pending lattice
finalization).	

LER BL2LP	

 LER BL2RP	

 HER B2ERA	 HER BL7RE	

βy (m)	

1200.00 	

1000.00 	

418.00 	458.70 	

σy (µm)	

123.94 	

113.14 	

59.61 	

62.44 	σ'y (mrad)	

0.10 	

0.11 	

0.14 	

0.14 	

Spot size (µm)	

145.62 	

137.16 	

98.52 	

102.96 	

Change in spot
size fordoubling of
beam size	

1.78 	

1.74 	

1.45 	

1.45 	SR Fans: HER right side of IR	

SR Fans: LER right side of IR	

•
•
•
•

SR Source Bend Parameters 	

BL2RP.1: ×	

BL2RP.2: ○ ?	

BL2RP.3: ×	

BL2RP.4: ○?	

••B2ERA: △	

BL7RE: ○ ?	

C. Beamstrahlung Monitor	

Transverse view	

•Developed by G. Bonvicini (Belle, Wayne State U.)
originally for use at CESR.	

•Uses relative strengths of x- and y-polarization ofwide-angle beamstrahlung to diagnose quality, e.g.
beam separation and beam size of collision.
•Estimation of signal and background level has juststarted with a simulation code.
•Standardized, compact light spectrometers to be
implemented at each viewport, with 0.2 mrad angularresolution, and 8 PMTs (2 polarizations, 4 wavelengths).	

•Device has background discrimination rejection throughsimultaneous detection of 4 different wavelengths.	

Two beams at IP	

Most important change: much stronger beams at KEKB.
Comparison at θ=5mrad, λ=300-600nm, 0.5mrad2 acceptance) 	

CESR-cSuperKEKB

Ratio

Sx (Hz)

6E4

3E11(L),1E11(H) (Prel.)

2-6E6

Sy(Hz)

6E4

6E10(L),2E10(H) (Prel.)

0.3-1E6

Bx(Hz)(∝N/γ)

2E6 (est.)

2E5(L),1E5(H)0.05-0.1

By(Hz)(∝N/γ)

2E6 (est.)

2E6(L),1E6(H)0.5-1

B(from beam)

Very small

Very small

S : Signal, B : Background	

By G. Bonvicini	

Polarization	

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

5. Gated Measurement for Bunch-Tune, -Orbit and -Phase	

Development of a fast gate module	•A fast gate module is developed for a fast gate to measure the tune, orbit andlongitudinal phase of each bunch separated by 2ns.	

Agilent HMMC-2027	

Beam test	Specifications	Input/Output Impedance
50 Ω	

Input Power> +20 dBm	Bandwidth
1.0 MHz - 5.0 GHz	

Switching Time200 ps	

ON/OFF Isolation> 50 dB @2GHz	

Insertion Loss
< 10 dB@2GHz	

Control
0 - - 0.8 V	

1 ns/div	Excitation of a pilot bunch by PLL	

Excited amplitude of a bunch	

FFT of the oscillation	

PLL	

A betatron oscillation of a pilot bunch was successfully excited by PLL.	

Gated Measurement of a pilot bunch	•A gate circuit was tested by beam to pickup a signalof a pilot bunch located 6ns after a bunch train. 	

mm	

FFT of x position	

x : linear scale	

f/frev=0.5083	

gated signal	

•X-Y coupling was measured by eight-electrodesBPMs with a gate module during physics run.	

FFT of a gated signal measured by a turnby turn BPM	◊The pilot bunch was kicked by the PLL exciter, then its turn-byturn position was measured with the gate module. Detection
modules were log-ratio circuits supplied by Bergoz. 	

single beam	colliding beam	

◊The experiment showed that the system had a sensitivity tomeasure R parameters. 	

◊A fast switch of a specific channel in the gate module wasdamaged twice during measurement. The cause is being
investigated. The experiment is planned in next run withimproved calibration of the system and the repaired gate
module.
	by K. Ohmi	

6. Summary	1)Beam position monitor	
•Standard BPM	◊Prototype of the button electrode was successfully tested with beam.	
◊Two detection circuits, namely the narrowband detector and the medium-band
detector, are under development. 	
◊Selection of two detectors is not done yet. Both detectors may be used together
to reduce a cost.	

•BPM for collision feedback	◊A prototype of the button electrode and feedthrough has been ordered andwill be tested in this spring. 	
◊Development of the detection circuit has already started. The evaluation
circuit will be tested in this spring. 	
•RF noise in RF straight section might be still a problem though the orbit
error due to the noise is estimated to be a level of 0.7 µm at 100mA. 	
•If the requirement from optics which is not specified yet is much tighter than that of
KEKB, the BPM system should be reconsidered. We need specification as soon as
possible.	

2) Bunch by bunch feedback system	• Common components to transverse and longitudinal system 	
◊The iGp digital filter will be used for whole system.	
◊The low noise 3 GHz frontend electronics and BPM which has
better time and frequency response are under development.	

• Transverse feedback system	
◊Two stripline kickers for each ring will be used.	

◊ New stripline electrodes with improved support structure and goodcooling is to be designed. 	

◊ Expected damping time is comparable to growth time based onpresent status of simulations of ECI and FII. 	

The study of ECI and FII has just started. More study is needed todetermine target values of the damping time.	

• Longitudinal feedback system	
◊Two DAFNE type kickers will be used in LER.	

◊Power cables, connectors and feedthroughs against large beam
current need to be developed.	

3) Synchrotron light monitor	

•Visible light monitor	
◊The interferometer and streak cameras will be used for measuring transverse sizeand longitudinal profile of the beam, respectively. 	
◊Vertically polarized synchrotron light might be used to determine the verticalbeam size.	
•X-ray monitor	
◊Fast measurement of the transverse beam size by the coded aperture method is being
developed and will be implemented in SuperKEKB. 	
• Beamstrahlung monitor	

◊The monitor has a capability to be a useful monitor to get information of beamcollision.	
◊A way of installation and detailed simulation study will be carried out along with theprogress of IR design. 	
• Items to be considered hereafter	
◊Design of the extraction chamber and a transfer line for the X-ray monitor	
◊Design of a vacuum chamber for extraction mirror	
◊Thermal deformation of extraction mirror for visible light	4) Gated measurement	•A fast gate capable to gate a bunch signal separated by 2 ns was successfully
tested by beam.	
•A beam test kicking a pilot bunch by PLL was successfully done.	
•A beam test showed that the detection of oscillation of a pilot bunch with thegate module had a sensitivity to measure the X-Y coupling.	

5)DCCT, CT and loss monitor	
•Similar system as that of KEKB will be used.