Photon Monitors& Loss Monitors
at SuperKEKB
J.W. Flanagan, H. Ikeda, H. Fukuma, M.
Arinaga (KEK), G. Varner, J. Malin, B. Kirby(UH), C. Kenney, J. Segal (SLAC), G. Bonvicini(Wayne State), et al.
SuperKEKB Review
2014.3.3

Photon Monitors•

SRM: Synchrotron Radiation Monitor (MR, DR)– Visible light monitor. Interferometer, streak, gated camera, etc.
– MR: sz, sx (sy)– DR: sz, sx, sy•

XRM: X-ray Monitor (MR)– Pinhole, URA mask, etc.
– sy (sx)•LABM: Large Angle Beamstrahlung Monitor (IR)– SR-like radiation from interaction point (~300-600 nm)– Can measure size ratios and relative offsets at collision point.

•

Energy measurement based on inverse Compton scattering (MR)
–
–
–
–

•

MR

Not needed for Phase 1
In preliminary planning stages with SLAC.
Interest expressed by BINP as well.
Will not discuss in this talk.

Loss Monitors– Ion chambers and PIN diodes for monitoring and machine protection (~half are interlock inputs).

•DR– Ion chambers for loss detection for beam tuning (not part of interlock system).

MR SRM: Interferometers
SR Source Bend Parameterex

S-LER1(BSWFRP)
3.20E-09

S-HER(BSWOLE)
4.60E-09

k

0.27%

0.24%

ey

8.64E-12

1.10E-11

m

by

29.98

32.49

m

sy
Beam Energy
Bend effective length
Bend angle
Bend radius r
Observation wavelength l

16.1

18.9

mm

4
0.89
5.04
179.0
4.00E-07
1.0

7
2.90
5.00
580.0
4.00E-07
0.7

GeV
m
mrad
m
m
mrad

0.9
97%

mrad

Max. Visibility (fringe depth) gmax

0.8
98%

Min. measurable beam size sy min

15.7

18.5

mm

SR Opening angle qc (l)Slits opening angle D/F

Units
m

•Resolution fundamentally limited bymeasurement wavelength and opening angle
between slits from beam (D/F).
•Max. slit separation determined by beam
spread and mechanical considerations.

•Will primarily use for horizontal beam size measurements•Vertical beam size measurement is possible with interferometers, though is near
the limit of the interferometer resolution, and single-shot measurement is notpossible.
•But can be useful for cross-calibration purposes at larger beam sizes•To minimize deformation due to heat load, will use gold-coated diamond mirrors.
•Cavities below optics hut floors in D4 and D8 klystron galleries have been filled toreduce the amount of floor vibration, which had been a problem during KEKB
operation.

MR SRM: Diamond Mirrors• Monocrystalline diamond:Parameter
Energy(GeV)

Current (A)– Developed by Cornes Technology
Bending– 9 mm x 27 mm quasi-monocrystalline CVD diamond radius (m)substrate.
SR Power(W/mrad)– Surface: 1 mm Au, with thin Cr layer below that.
– Diamond surface is (nearly) a single crystal, so goodsurface flatness expected (Ra ~ 2 nm, <~λ/50)– Very good heat conductance and low thermal
expansion coefficient makes apparent change inmagnification smaller than that of Be mirrors usedat KEKB:

KEKB
LER
HER

SuperKEKB
LER
HER

3.5

8

4

7

2
85.7

1.4
580

3.6
177.4

2.6
580

48

136

72

149

• Berylllium: δmagnification = 43% @ HER full current• Diamond: δmagnification = 3% @ HER full current

Diamond mirror

Mirror surface distortion due
to 200W of SR power at
center of Be mirror

Mirror surface distortion due
to 400W of SR power at
center of Au+Dia mirror

Diamond mirror surface
distortion due to 400W of
SR power
ANSYS simulations: M. Arinaga

MR SRM: Extraction chamber,mirrorandmirrorholderExtraction
chamber

Mirror and mirror holder
prototypes••

Final mirror holder design:• Borrowed “cooling jet” feature from CesrTA x-ray optics heatsink• Mechanically simpler, good heat transfer• In fabrication now
Mirrors in fabrication now• 9 mm (W) x 28 mm (H) x 0.8 mm (D)• 3 monocrystalline joined segments• 1 um Au surface

Mirror holder final design(in fabrication)

MR SRM: Extraction
Chamber• Mirror set in 24 mm-highantechamber• Loss factor: k = 0.8e-6 V/pC
• P = I^2 k Tb
– I = 3.6 A– Tb = 4 ns
–  P = 41 mW

MR SRM: Schedule• Hut flooring has been strengthened to reduce vibrations. HER hut
expanded.
• Vacuum components designed and in fabrication (or alreadyfabricated):– Extraction chambers (vacuum group)– Mirrors– Mirror holders– Extraction windows• Optical transport lines from tunnel to surface to be installed startingfrom April 2014.
– Largely re-using KEKB components, with some modifications to reachnew chamber location.

• Vacuum components to be installed, optical transport lines aligned,
and above ground optical components to be reconstructed by
Phase 1 turn-on• From Phase 1 turn-on:– Commissioning of SRM

XRM: 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 highflux throughput for bunch-by-bunch measurements. Heatsensitive and flux-limiting monochromator not needed.
We need such a wide aperture, wide spectrum technique forshot-by-shot (single bunch, single turn) measurements.

Uniformly Redundant Array(URA) for x-ray imaging to be
used at SuperKEKB

Source distribution:+
Kirchhoff integral over mask(+ detector response) Detected pattern:

Simulated detector response
for various beam sizes at
SuperKEKB LERXRM: Coded Aperture tests at CesrTA

Example of bunch-by-bunch data
(electron-cloud blow-up study data)
Single-shot data average for each bunch

Example of turn-by-turn size andposition data (one bunch out of train)

D Line layout

Detector box

Optics box

V. tuneBunch-bybunch
position
spectraXRM: Coded Aperture tests at CesrTA
 High-energy mask high-power tests:
 Au+Si mask tested at 120% of SuperKEKB LER SR power load Melted!
 Au+Si mask survived at 100% previously.

 Au+CVD (diamond) mask tested in April 2013

 Survived 120% LER power load
 Applicable improvements in heat sink design identified -- will change design for
SuperKEKB.

 High-energy mask imaging tests
 Detector: Gained familiarity with characteristics of Fermionics InGaAs pixel
detector
Au+Si mask after 100%
SuperKEKB equivalent power:

Au+Si mask after 120%
SuperKEKB equivalent power:

Factory-damaged Au+CVD
mask for burn test:

XRM: Tests at ATF2 beam line
Duringconstruction

Rotating
mask holder

Detectortable

XRM: Coded Aperture tests at ATF2
Data: Dispersion Knob Scans

Simulations

Measured beams of <7.5 um with scanned-pixel measurements
World record for low-energy coded aperture measurements

XRM: Coded Aperture at Diamond LSXRM: Coded Aperture test at Diamond LS•

Using spare high-energy optic (Au+Si)
designed for SuperKEKB:––•

Detector:––•

10 mm x 59 URA
18.2 mm Au mask on 625 mm Si
substrate
200 mm LuAG:Ce screen
1024(H)x768(V) pixel camera

Not single-shot measurements, but
sufficiently detailed data to use toprovide input for modellingbackground due tocoherentscattering effects (Rayleighscattering)–

Modeled detected spectrum

Data taken from single-pixelwidth line near center

Significant at high energies

Best-fit:--Beam size: 10.5 mm--Mask position relative to
beam: 166 mm

Best-fit:--Beam size: 10.4 mm--Mask position relative to beam:
5 mmBest-fit:--Beam size: 10.6 mm--Mask position relative to
beam: -126 mm

XRM: SuperKEKB x-ray monitor•

Xray Source Bend Par. S-LER(BS2FRP.1)
3.20E-09exk
0.27%
8.64E-12
ey
50.0
by

S-HER (BS2E.82) Units
4.60E-09
0.24%
1.10E-11
11.5

m

sy
Beam Energy
Effective length
Bend angler
Critical Energy

11.3
7
5.9
55.7
105.9
7.1

mm
GeV
m
mrad
m
keV

20.8
4
0.89
28.0
31.7
4.4

m
m

Uniformly Redundant Array(URA) for x-ray imaging to be
used at SuperKEKB

Mask:
•

•

In-hand for Phase 1:•
High-power, 59-element, 10 mm/element URA•
10 mm Au mask on 625 mm Si substrate•
Under development:•
10 mm Au mask on 800 mm CVD diamond(monocrystalline) substrate•
Substrates manufactured, samples given to
NTT-AT to test masking method.
•
New pattern planned for improved resolution
Detector:•
Phase 1: 64-channel, 50 mm pitch•
More channels desirable, for background subtraction and toaccommodate beam deviations.

Simulated detector response
for various beam sizes at
SuperKEKB LERXRM: Detector• Tests with Fermionics detector at Photon Factory and CesrTA showed that
detection efficiency at high energies is very low– Active pixel depth is only 3.5 microns.

• Detector development needed for the future– Higher efficiency at hard x-ray spectrum seen at SuperKEKB– Fast response for being able to directly diagnose head-tail instabilities at SuperKEKB.
– Active edge (Deep-pixel ) Si design being built in collaboration with SLAC:• Deep but narrow pixels: 2 mm deep, 50 um pitch, 128 pixels• Can stack 2 detectors for greater collection efficiency– Also making simple spectrometer using sideways-mounted detector with variable pixel widths

X-rays incident direction

J. Segal, C. Kenney (SLAC)XRM Spectrometer
X-raysincident
direction

LER Spectrum in Spectrometer
0.35000

Fraction of signal0.30000
0.25000
0.20000
0.15000
0.10000
0.05000
0.00000
1

2

3

4

5

6

7

8

9

10

11

12

11

12

Strip

HER Spectrum in Spectrometer
0.25000
0.20000
0.15000
0.10000
0.05000
0.00000
1

2

3

4

5

6

7

8

9

10

J. Segal, C. Kenney (SLAC)XRM: statisticalresolution
35 um pinhole

Detected image simulations (LER):
59x10 um URA
mask

13151 pattern

Modified
Fibonacci patternSingle-shot resolutions:••

Mask pattern:
Blue: Single bunch, full current•
URA mask better than single pinhole.
Red: Single bunch, 1/128 current•
Other patterns found with even better resolution.
Detector pitch:(optics correction mode)•
For a range of mask types, most of the benefits are gained at 50 um. Below that, the only difference is at ~a few
um, which we do not expect to see at SuperKEKB.
–•

Decision: Go with 50-um pitch, 128 pixels

If we need better single-shot resolution at low beam intensities, we should add detector layers to increase
detected flux.

XRM: Detector
resolution -- blooming
CASINO simulationsof electron
propagation in Si:

Power absorbed in 2 mmdeep Si detector

LER with 200
um of Be in
path

Blooming vs energy

HER with
1.42 cm of
Be in path

Blooming = ~2 um at 20 keV: Looks OK w/50 um pitch

XRM: Time resolution

Short risetime
Hope for headtail separation
with analysis

Tail decays within 2 ns at 200 V bias
Bunch-by-bunch separation

J. Segal (SLAC)XRM: LER X-ray beamline(Fuji D8)

Sourcebend

Opticsbox

X-ray beamline

Be Window,
Detector

XRM: HER X-ray monitor beamline(Oho D4)

Be window,
Detector

X-ray beamline

Opticsbox

SourcebendXRM: Heat load on optics
CesrTA D Line

SuperKEKB LERSuperKEKB HER

E (GeV)

5.3

4

7

r (m)

31.65

31.74

106

Critical energy (keV)

10.3

4.4

7.1

Zero-degree PowerDensity (kW/mr^2/A)

2.36

0.56

2.8

Linear Power Density(kW/mr/A)

0.345

0.112

0.313

Distance from source tooptics box (m)

4.549

9.39

10.27

Aperture width (mm)

2.38

0.5

0.5

Current (A)

0.200

0.243

3.6

2.6

Zero-degree PowerDensity (W/mm^2)

23

28

23

69

Linear Power Density(W/mm)

15

18

43

79

Total Linear Power over
Aperture Width (W)

36

43

21

40

Si mask OK
Dia. mask OK

Si mask NG
Dia mask OK

Burn test results

CesrTA burn test sets safe limits on incident power.
Need to filter out 2/3 of HER power before it hits optics.
Extra 1.4 cm of Be upstream of optics will work.

XRM: Upstream beam line
HER

•
•

4-mm wide collimator located ~8(7) m from source point in HER(LER)
Water-cooled Be filters––•

Water cooled beam stopper–••

2 cm total in HER
1 mm total in LER
To protect gate valve

Gate Valve
Vacuum pumps upstream of gate valve:–––

2 NEG pumps
1 ion pumpControlled by vacuum group (common with ring vacuum regardless of GV state)XRM: Downstream beamline
Opticsbox

Detector• Optics box– Water-cooled copper heatsink plate,with two mounting spaces for optics– Optics (Au on diamond substrate):• 32 um slit
– Simpler analysis possible, but photon
statistics too low for single-shotmeasurements, esp. in optics correction
mode (low current).

• Coded aperture– For single-shot measurements• Vacuum pumps:– 4 ion pumps– 1 NEG pump
– Controlled by monitor group• Screen monitor• Extraction window– 200 um Be• Detector (in air)

XRM: Alignment• Need to align x-ray beamlines to within ~0.1 mrad (4 mm over 40m).
• Initial crude beam-line layout with laser leveler (V, H)– Mainly to make sure no obstacles remain in path
– Serves to alert other groups as to where beam line will be• Semi-final (pre-commissioning) mechanical alignment with help ofmagnet group (using laser tracker, etc.)• Final mechanical alignment will require use of x-ray beam itself.
– Upstream aperture determined by horizontal collimator position.
– Can adjust positions of collimator, optics box, extraction window.
– Screen monitor midway downstream of optics box to assist withbeam-based alignment.
– Detector mounted on movable (translational, rotational) stages,
attached by flexible cables to readout electronics box.

XRM: Heat load on detector
SuperKEKB LERSuperKEKB HER

Filtered HER (to protect
optics)E (GeV)

4

7

r (m)

31.74

106

Critical energy (keV)

4.4

7.1

Zero-degree Power Density(kW/mr^2/A)

0.56

2.8

Linear Power Density (kW/mr/A)

0.112

0.313

Distance from source to detector
(m)

40.70

42.55

Detector width (mm)

0.1

0.1

Beam Current (A)

3.6

2.6

Air path length (cm)1010

Be window+filter thickness (cm)

0.02

0.02

1.42

Peak Power Density absorbed in
detector (W/mm^2)

0.7

2.8

1.0

Linear Power Density absorbed in
detector (W/mm) (Horizontal axis)

6

13

5

Integrated absorbed linear powerover 0.1 mm detector width (W)

0.6

1.3

0.5

Should design to be able to absorb a watt total, with peak power density of 2 W/mm^2
Diamond heat sinks on detectors?

XRM: Readout system• High-speed readout
electronics being
developed by UH:– Custom digitizer ASICs(selectable by replacing
daughtercard) for multi-turnmeasurements:• High-speed for bunch-slicing
measurements of a few
bunches• Slower speed for single-bunchmeasurements over wholetrain• Data transferred via
raspberry-pi in tunnel• Raw data sent to 64-CPU
fitting/analysis computer inabove-ground hut• Fitting results sent to EPICS
IOC in control building forbeam tuning purposes

64-channel readout motherboard and digitizer
daughter cards

XRM: Schedule
•

Now:
–
–
–
–
–
–

•

March, April 2013:––•

Fabrication of upstream components, optics boxes/mounts and masks
Imaging test of diamond mask prototype at CesrTA
Beam testing of readout system at ATF
Beam testing of high-energy detector at SLAC

From September 2014, in preparation for Phase 1:––•

Finalize designs of Be filters, Optics boxes/mounts, mask patterns
Rough layout of beam line

From April 2014:
–
–
–
–

•

Downstream beam pipes in fabrication
Vacuum pumps purchased/acquired
High-energy detector in fabrication at SLAC
Design of beam stopper finalized
Design of upstream beam pipes (except for Be filters) finalized.
Design of Be filters and optics boxes/mounts under discussion with companies.

Installation and alignment of beamline vacuum components
Installation of detectors and 64-channel readout systems

From Phase 1:––

Beam-based alignment
Check-out, calibration, commissioning of x-ray monitor system for emittance tuning.

LABM: Large Angle Beamstrahlung
Monitor• The radiation of the particles of one beam due to the bending force of the
EM field of the other beam
• Beamstrahlung POLARIZATION at specific azimuthal points provides
information about the beam-beam geometry.

G. Bonvicini

LABM: Detector concept - I
Light is extracted out
the Beam Pipe (brown)
By a Vacuum mirror.
The light is thenTransported through an
Optical Channel (blue
Pipes, gray elbows) to
An Optics Box (black)
Where light is divided
In two polarizations and4 spectral bands
G. Bonvicini

31

LABM: Detector Concept - II•••

Two view ports per beam tocontrol systematics - 4 Optical
Channels
Each view port light is split into
two polarizations, 4 bands - 8 PMTs
or SiPMTs per Channel, 32
channels total
Each Optics Box has two optical
tables, each table counting one
Optical Channel - 2 Optics Boxes

G. Bonvicini

32

LABM: Optics box and optical path
Prototype optics box

Optics Box Concept (one of two Optical
Tables shown)
Wollaston prism separates
Polarizations. Two mirrors
Change optical plane toruled gratings, which divide
light In 4 bands

Light collimators

PMTs
Changing just the gratingallows observation of 2
different bands (300-600
or 450-900 nm)

G. Bonvicini

PMT mounts inside optics box

Movable mirror

Original design

LABM: Be mirror and extraction holes• RF fingers around mirror stem not shownOriginal design

LABM: HOM losses• Loss factor: 1.6e-3 V/pC
• 84 W
– Extraction holes: 40 W each
– Mirrors: 2.5 W each
• If no RF fingers, 40 W each in trapped modes• Note: mirrors also receive incident Beamstrahlung power of ~2 W

LABM:
Extraction
chamber• Extraction holes:• Diameter 16 mm -> 8 mm
• Cuts HOM losses due
to extraction hole to afew Watts• Center of extraction hole
shifted 1 mm to betteralign with optical axis
• Beam reflected at ~10
mrad• Extraction hole depth
reduced to minimize
excessive collimation risk

New designNew design

LABM: Extraction chamber•

Mirror shield:• 6 mm-high aroundmirror, with 30degree leading andtrailing edges• Mirror sits in 3mm wide slot
• Mirror is 2-mm
wide
• View of IP
unobstructed• Reflections fromside of slot should
be at large enoughangle to beeliminable bydownstream
collimation

LABM: Extraction chamber
Shield ramp, no RF contacts• Loss factor: 12.3e-3 V/pC
• 645 W– But very little field leakage into mirror area, even without RF contact between mirror
and shielding ramp

LABM: Extraction chamber
Shield ramp,
with RF contacts (posts) toground mirror to undersideof shield

Essentially unchanged
Go with no RF contacts

•Wayne State:
–
–
–
–

–
–

Optics boxes have been redesigned and fabricatedOptical components calibrated
Part of optical transfer lines fabricatedReadout electronics for Phase 1 systematic checks designed
and in preparation
Final read-out system for Phase 2 operation being designed
Prior to Phase 1:•–

Install optical transfer lines, optical tables, Phase 1 electronics
Initial commissioning and systematic checks
NOTE: If possible, would like to try collisions without QCS––

Low-luminosity, but zero background

From Phase 2:••

Re-commissioning after re-configuration of IR, wth final
electronics
Final commissioning for physics running

KEK:
–
–
–
–

Wedge-shaped prism and lensFrom Phase 1:•••

LABM: Schedule

Mirrors in fabrication
Extraction chamber design finalized, to be ordered in April
2014 (vacuum group)
Racks purchased for LABM use
Installation of vacuum components by start of Phase 1.

Optical transfer line mirror

DR SRM: Components• Extraction mirror, transport line, streak camera, gatedcamera and optical elements: ready• Extraction mirror chamber : prepared by vacuum group• Painting of SRM hut will be done this month.
– Matte black interior• Set-up inside the hut will start soon.
• Installation of extraction mirror and transport line
depends on the progress of other groups.

DR SRM: Hut

DR SRM hut

Loss Monitor：MR• Ready for re-cabling and installation.
– Re-use detectors (ion chamber and PIN PD)
from KEKB.
– We use the same read-out system as KEKB• Satisfies specifications for SuperKEKB.

– Extra read-out modules for IC and PD channels
have been produced.
– New ADC modules (18K14 DIGITEX) developed
and produced.
• Old ones no longer being manufactured.

Loss Monitor：DR• Almost all components areready• Detectors: Reuse linac ion
chambers• Electronics– Integrator (gain of read-out
is changed from MR readout.)→ready– ADC, digital I/O: ready– I/O divider, H.V. filter, H.V.
divider: order in FY2014• H.V.: ready• Cables, Plate: ready• Installation starts in April.

Summary• At SuperKEKB Phase 1 turn-on (non-collision):– SRM & XRM:
• Alignment, commissioning and beam size measurements– LABM commissioning and background studies• Initial systematics checks.
• No final-focus quadrupole, so no SR background.
• If it is possible to collide in that condition, would provide a
valuable, background-free systematic check.

• At DR turn-on, DR SRM commissioning– DR BLM to be used for tuning• After Belle II completion, Beamstrahlung monitor
commissioning begins in earnest.
– Eventually aim to provide feedback for luminosity tuning.

SparesXRM: Single-shot resolution estimation• Want to know, what is chance that a beam of a certain size
is misfit as one of a different size?
• Tend to be photon statistics limited. (Thus coded aperture.)• So:– Calculate simulated detector images for beams of different sizes– “Fit” images pairwise against each other:• One image represents true beam size, one the measured beam size
• Calculate c2/n residuals differences between images:
N = # pixels/channels
n = # fit parameters (=1, normalization)
Si = expected number of photons in channel i• Weighting function for channel i:N[ si  si ]2
c2
1

,

2
 N  n  1 i 1 s i

s i  si .

– Value of c2/n that corresponds to a confidence interval of 68%
is chosen to represent the 1-s confidence intervalXRM: Summary• Source bends upstream of SRM source bends– LER bend is reused KEKB LER bend magnet (at half strength)– HER uses same current arc bend magnet– Some modifications to magnets downstream of source point have beenrequested of magnet group, to accommodate x-ray extraction line.

• sy: Coded Aperture Mask

– Single-shot (single-bunch, single turn) resolution expected to be sufficient.
– Single-shot mode probably be needed for low-emittance tuning, based on
experience at CesrTA.

• sx: Possible, if single-shot measurements are needed– SRM should work for this in slow integration mode

• Being developed in collaboration with Cornell U., U. Hawaii and SLAC
– Testing different components at CesrTA and ATF2

• Development work continuing on detector and readout

XRM:Tests at ATF2 beam line
Location
Source of SR: BH3X
X-ray line

Visible line

T. MitsuhashiHER, 59x10 um URA mask
Single width detectors:
100 um pixels

50 um pixels

25 um pixels

12.5 um pixels(taking root of sum of squares of sigmas)

Double width detectors (twice the photon flux):
100 um pixels

50 um pixels

25 um pixels

12.5 um pixels

LER, modified fibonacci patternSingle width detectors:
100 um pixels

50 um pixels

25 um pixels

12.5 um pixels

Double width detectors (twice the photon flux):
100 um pixels

50 um pixels

25 um pixels

12.5 um pixels

•Both rings:

Simulation parameters– 20 um Au on 500 um CVD diamond optics element– 200 um Be extraction window, 10 cm air– 2 mm deep x 75 um wide Si detector pixels••

Vertical size ranges from 12.5 um to 800 um microns/pixel.
Total vertical area = 4000 um.

– Simulate single-wafer detector seeing range of beam currents from full current down to 1/128
current (around the level that will be used for machine optics tuning).

•

LER:– At full current (3.6 A over 2500 bunches), expect per 25 um high pixel:••

Hole regions: 3967 photons/turn/bunchGold regions: 32 photons/turn/bunch– Patterns tested:
•
•
•
•

•

35 um “pinhole” (slit) = size which gives minimum PSF at detector plane
59x10 um URA mask
“13151 pattern”: 6 35-um pinholes with varying spacings between them“modified fibonacci pattern”: 8 35-um pinholes with varying spacings between them

HER:
– Additional 2 cm be filter placed upstream of optics element– At full current (2.6 A over 2500 bunches), expect per 25 um high pixel:••

Hole regions: 1655 photons/turn/bunchGold regions: 104 photons/turn/bunch– Pattern tested:•

59x10 um URA mask

Single-shot resolution estimation• Want to know, what is chance that a beam of a certain size
is misfit as one of a different size?
• Tend to be photon statistics limited.
• So:– Calculate simulated detector images for beams of different sizes– “Fit” images pair-wise against each other:• One image represents true beam size, one the measured beam size
• Calculate c2/n residuals differences between images:
N = # pixels/channels
n = # fit parameters (=0 here)
Si = expected number of photons in channel i• Weighting function for channel i:N[ si  si ]2
c2
1

,

2
 N  n  1 i 1 s i

s i  si .

– Draw contours at c2/n =1 to represent ~50% confidence
intervals.

Modified approach:• Draw contours at chisq = 80, instead ofchisq/dof = 1– This corresponds to chisq/dof = 1 for 50-um pixels• There are 80 50-um pixels in 4000 um simulated
detector– Should cancel out change in degrees of freedom
due to change in pitch

XRM:
Digitizer
STURM2ASIC
STURM ASIC for high-speed
readout (G. Varner).
Ver. 1 tested at KEK PF,
March 2009.
Ver. 2 fabricated.
Ver. 2 specs:
8 channels/STURM sampling
1 monitor channel
4 TSA sample buffers
8 samples/TSA buffer (32x channel)
288 Wilkinson conversion cells
1-200 GSa/s effective (5ps - 1ns Tstep)
1 word (RAM) sample readout
1+n*0.02 us to read n samples
100 kHz sustained readout (orbit)

XRM: SuperKEKB estimated single-shot resolutions(SuperKEKB full current)
Beam to mask: 12 m
Mask to detector: 36 m

•Red points: using 64-pixel
detector of same type as at CesrTA(Fermionics)•Green points: using detector withimproved photon detection
efficiency at higher x-ray energies(being developed)
Detected spectrum(Fermionics detector)

HER

Beam to mask: 8 m
Mask to detector: 32 m

LER