Photon Monitors
J.W. Flanagan, H. Ikeda, E. Mulyani, G.
Varner, G. Bonvicini, +others
SKB Review
2016.6.13

Photon Monitors• XRM: X-ray Monitor– Pinhole, Coded Aperture mask, etc.
• sy (sx)• SRM: Synchrotron Radiation Monitor– Visible light monitor. Interferometer, streak, gated camera,etc.
• sz, sx (sy)• 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.

XRM: Status• HER and LER beam lines commissioned, and taking data withscintillators.
• Template fits implemented for taking data with single-slit, multi-slit
and URA masks.
• Calibration studies undertaken:– Source-point measurement– Overall magnification studies••••

Emittance Knob studies
Mask movement studies
Source-point movement studies
Changing beta function at source point (HER)– Light-level dependence (HER)• Beam studies undertaken– Emittance measurements at LER and HER,
– Electron cloud (LER) and current-dependence (HER)XRM: Principles
Mask patterns

Calculated images fordifferent beam sizes

Coded aperture imaging (R. H.
Dicke, Astrophys. Journ., 153,
L101 (1968)), using template
reconstruction.

Single slit, 33 mm wide

Single-shot statisticalresolutions expected

Multi-slit mask (E. Mulyani)

URA mask (E. E. Fenimore, T. M. Cannon,
Appl. Optics, Vol 17, No.3, 337 (1978).

E. Mulyani and J. Flanagan,
TUPB025, Proc. IBIC2015,
MelbourneXRM: Hardware

Masks: ~20 mm Au on 600 mm
CVD diamond substrate

US-Japan Collaboration (U.
Hawaii, SLAC, Cornell U.)
High-speed readout electronics
for the X-ray monitor, being
developed by U of Hawaii.

X-ray beam line underconstruction at LER

Water-cooled mask
holderDeep Si pixel detector
and spectrometer chips
for the X-ray monitor,
being developed at SLAC.

XRM: control room display panel

Single-slit
maskMulti-slitmask

XRM: control room display panel

Single-slit
mask

URAmaskXRM: e-cloud blow-up study (LER)
Single-Slit Mask
Multi-slit mask
URA mask
Single-Slit maskmmVery good fill-to-fill
repeatability

Very good agreement
between different
masks, especiallybelow 150 mm.
mA

XRM: Calibration
1. Geometric scale factors check

By moving either beam, or mask, andmeasuring how single-slit peak moves, we
can measure M/m or (M+1)/m, where:
M = geometric magnification (d2/d1)
m = scintillator camera scale (mm/pixel)
Parameter

Estimate from designand handmeasurements (LER)

ds1/dsBeam-based
measurements (LER)

Schematic of XRM beam line (not to scale)

Estimate from design andhand measurements (HER)

0.4229 ± 0.0029(0.69%)

Beam-based
measurements (HER)0.4369 ± 0.0038(0.87%)

M/m

66.21 ± 0.002 (0.003%)

69.45 ± 0.488 (0.7%)

60.87 ± 0.002 (0.003%)

59.23 ± 0.511 (0.9%)(M+1)/m

85.52 ± 0.002 (0.002%)

86.08 ± 1.56 (1.8%)

79.96 ± 0.002 (0.002%)

79.31 ± 0.10 (0.13%)

Geometric magnification factors agree well with beam-based
measurements at both LER and HER
E. Mulyani

XRM: Calibration
2. Emittance Knob Ratio
Based on “SYNCHROTRON RADIATION INTERFEROMETER CALIBRATIONCHECK BY USE OF A SIZE CONTROL BUMP IN KEKB” (N. Iida, J. Flanagan, Y. Funakoshi and K. Oide,TUPAN042, Proc. PAC07, Albuquerque) the variation of the vertical beam size by changing thebump height can be represented as :σ y  true vertical beam size with bumpσ 2y  σ 2y0  A 2 (h  h0 ) 2(σ)  (c.σ y )meas 2yσ y0  true vertical beam size without bump2(σ meas) 2  (c.σ y0 ) 2  cA  h  h0 y22σ meas
 true vertical beam size that mesuredyA  linear coefficien t of the vertical beam size vs bump heightc  calibration factor

For LERThis method measures the overall scaling
factor between the reported beam size
measurements and the true beam size.

Δε y  73.2(pm) (knob)2Δε y  73.2(pm) (h - h0 ) 2
σ 2y  εy  β y  A 2 with β y  67.1721m
For HER(σ)  c σ y0  c 7.63647 59.287(h h0 )meas 2y2222

Not just geometric factors, measures
performance of overall system
Analysis: E. Mulyani

XRM: Emittance Knob Calibration
For LERΔε y  73.2(pm) (knob)2

True beam size upperbound (includes possible
smearing factors)

Δε y  73.2(pm) (h - h0 ) 2

Reported/truebeam size
scaling factor

σ 2y  εy  β y  A 2 with β y  67.1721m
LER_ mask

σy0Calibration factor cSingle slit

ss1

25.89 ± 2.14 (8.2%)

1.3 ± 0.03 (2.54%)

Multi-slit

ms1

27.89 ± 2.59 (9.11%)

1.16 ± 0.037 (3.19%)

URA

ura1

26.5 ± 2.8 (10.58%)

1.26 ± 0.04 (3.36%)

Single slit

Analysis: E. Mulyani

Multi-slitURA

XRM: Emittance Knob Calibration
HER @ Low Current (30 mA)

a = 1027.49 +/- 17.34 (1.688%)
h = 1.29558 +/- 0.007475 (0.5769%)
k = 1544.04 +/- 18.64 (1.207%)

a = 1626.04 +/- 63.09 (3.88%)
H = 1.25835 +/- 0.01907 (1.516%)
k = 1812.84 +/- 66.81 (3.685%)

a = 1279.44 +/- 17.35 (1.356%)
h = 1.28822 +/- 0.006045 (0.4693%)
k = 2148.23 +/- 18.64 (0.8675%)

LCA^2C (cal fac)

σy0h0SS

452.741.5 ± 0.02

26.1 ± 0.02

1.29 ± 0.007

ms452.74

1.7 ± 0.02

27.6 ± 0.01

1.29 ± 0.006

ura452.74

1.89 ± 0.04

22.5 ± 0.04

1.26 ± 0.02

Reported/truebeam size scaling
factorTrue beam size upperbound (includes possible Analysis:smearing factors)
E. Mulyani

XRM: Emittance Knob Calibration
HER @ High Current (740-700 mA)
a = 1528.86 +/- 56.23 (3.678%)
h = 1.91931 +/- 0.02169 (1.13%)
k = 5355.42 +/- 61.87 (1.155%)

a = 5413.02 +/- 760.9 (14.06%)
h = 1.64591 +/- 0.06178 (3.754%)
k = 7296.73 +/- 882.4 (12.09%)

a = 1881.9 +/- 202.4 (10.76%)
h = 1.85493 +/- 0.0587 (3.164%)k = 7451.76 +/- 226.2 (3.035%)

HCA^2SS

452.741.8 ± 0.04 39.8 ± 0.01 1.9 ± 0.02

ms

452.742.0 ± 0.1

ura

452.743.4 ± 0.14 24.7 ± 0.01 1.6 ± 0.06

Reported/truebeam size scaling
factorcσy0h042.3 ± 0.03 1.8 ± 0.06

True beam size upperbound (includes possible Analysis:smearing factors)
E. MulyaniXRM: Calibration Summary• Geometric factors seem to be well understood, towithin a few percent, for both LER and HER.
• Overall performance seems reasonable for LER, andin agreement with optics.
• Issues with overall performance of HER:
– Large reported/true scaling factors– Light-level dependence seen
• Due to diffuse reflection from wall behind scintillator?
– Wall much closer in HER than in LER– Changing background affecting fits in HER much more than inLER?

– Nevertheless, from overall pattern blurriness, the beam
does not seem all that small, so perhaps not just a fitting
problem if beam really is close to design emittance.
• Beam tilt at source point?
• …Scattering from walls of rotated holder?

XRM: Single-slit 2-D image

LER

HERx-y tilt at sourcepoint?

Images taken mid-March

Width:
Horizontal clipping due tomask holder rotation?

XRM: YAG:Ce scintillators after use
ＬＥＲＨＥＲXRM: YAG:Ce scintillators after abuse
Broken while cleaning

Heat shock?

Note that some discoloration wherebeam hits remains even after cleaning.
Would helium help reduce surfacecontamination build-up?

After (too-rapid?) exposure to unmasked
beam at 890 mA. Needs care to expose
more gradually!

Visible x-ray path inair (LER, 100 mA):

XRM: To Do•

Reduce diffuse reflected background– Install black paper lining in optics boxes next Thursday maintenance•••

Extract horizontal profiles from scintillator image for knife-edge H. size measurements (nextThursday maintenance)
Tilt knob studies at source point (esp. HER)
Refine model of system using raw data taken during calibration runs
– Variations in Au depth over mask surface– Understanding of background sources (esp. HER)
– More precise beam line length surveys•

Examine masks after exposure to beam
– Especially single-slit patterns, with “dips” in measured images•

Some kind of build-up on mask surface?

– Evidence of holder rotation in HER?
••

If so, redesign holder to be less sensitive to rotation?

Improve vacuum pumping ability around optics box– Extra NEGs?

•Get fast pixel detector and read-out going– Goals:••••

Phase II: 64-channel readouts with InGaAs and/or deep Si detector
Phase III: 128-channel readouts with deep Si detector

Helium enclosure in detector box to minimize scattering and ozone production
Devise cooling for scintillator in addition to detector?

SRM: Status• Vertical and Horizontal interferometers set up
to measure vertical and horizontal beam sizes
at LER and HER• Calibration studies started• Streak cameras set up– Bunch-length measurements madeSR Source Bend Parameterex

S-LER1(BSWFRP)
3.20E-09

S-HER(BSWOLE)
4.54E-09

k0.27%

0.25%

ey

8.64E-12

1.14E-11mbx
by8.86
30.71

10.17
26.92

mmsxsyBeam Energy
Bend effective length
Bend angle
Bend radius r
Observation wavelength l

168.4
16.3

214.9
17.5mm
mm

40.89
5.04
179.0
4.00E-07
1.07
2.90
5.00
580.0
4.00E-07
0.7GeVm
mrad
mm
mrad

0.2
0.990%

mrad
mrad

Max. Visibility (H) gmax

0.2
0.890%

Max. Visibility (V) gmax

98%

98%

Min. measurable beam size sx min

164.1

157.4mm

Min. measurable beam size sy min

15.715.0mm

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

SRM: 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.

•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.

SRM: Extraction mirrors and chambers

Diamond extraction mirror for visible lightbeam size monitor in holder

Extraction chamber installed in tunnel.
(Vac. Group)

Mirror mounted in extraction chamber.

•Diamond mirrors for visible light monitors
have been installed in extraction chambers
and aligned.

SRM: Control room display panel

SRM: Calibration measurements
Pinhole slit scan examples: Move pinhole
just downstream of extraction mirror, see
where on the mirror the light comes fromthat hits each interferometer slit

Ratio of slit separations between
interferometer slit plane andextraction mirror plane:•Magnification of system shows no beam current dependence up to780 mA!
•This is exactly what we had hoped for by using the diamond mirrors.
•Will it persist up to full beam currents?

SRM: Calibration measurements• But, there is a mystery: Whyis the slit ratio so large?
– Measured ratio between slit
separation at interferometer
plane and mirror plane is ~6.9 at
HER, ~5.8 at LER.
– Geometrically, it should only beabout a factor of ~2.5-3…
• Source point -> mirror = ~24 m inboth LER and HER• Mirror -> interferometer = <~40m in both LER and HER– …if all mirrors and windows insystem are flat
– …and if distances are correct• Are we conceivably not looking at
the correct source point? Seems
hard to believe…

Projection of pinhole atinterferometer plane as it is scanned
across surface of mirror:

Slope = 6.2

SRM: Bunch Length Measurement with Streak Camera

Pilot bunch
LER: 200-shot integration
HER: 10-shot integration(2016/6/10, Ikeda)

SRM: To Do• Investigate higher-than-expected slit ratio of system:– Remove masking from pinhole plates next Thursday
maintenance, take images of whole mirror shape (and atdifferent beam currents)– Local bumps at all components between mirrors and source
bends to rule out incorrect source– Inject laser from source point to measure slit ratio? (Post-PhaseI)• Investigate shift of optical axis seen in HER, but not in LER.
• Consider possible solutions for low light intensity at streakcameras– Wider mirrors, plus full-beam mode might suffice at HER?
• Mirror width limited by technical capabilities of manufacturer• Don’t share with interferometers when using streak camera?

– …shorter bend radius source magnet at LER…?

LABM: Large-Angle Beamstrahlung Monitor for SuperKEKB(Wayne State U., Mexico City U., Tabuk U. (Saudi Arabia))• Beamstrahlung: Radiation emitted by the particles in one beam due tothe bending force of the EM field of the other colliding beam. Many
similarities with SR but also some substantial difference due to very
short “magnet”.
• Beamstrahlung polarization at specific azimuthal points provides
unique information about the beam-beam geometry.
TopView:
IPSideView:
Belle IIObserve polarization of thelarge angle beamstrahlung(visible light spectrum)

Vertical polarization component

LABM: Principle

Horizontal polarization component

Simulation studies:
Examples of beambeam patterns which
could be extracted
from the signal
reconstruction. Uxand Uy are the x- andy-components of thepolarizedBeamstrahlung
powers [beam 1(2):Solid (Dashed) line].
U0: Power of theperfect beam.
G. BonviciniLABM Status• LABM beam lines and optics boxes installed atIR.
• DAQ and EPICS records developed for Phase I– Stand-alone – not yet integrated into accelerator
operations.

• Measurements made with beam, usingsynchrotron light from far side of IP.
– Measurements being made to refine models ofbeam line.

LABM Beamlines

Left (Nikko) side

Right (Oho) side

Test fit of LABM
extraction mirror(left) and extraction
window (right) on IR
beam pipe.
Inside view of
LABM extraction
mirror inside HOMprotection slot in IR
beam pipe.

LABM
Schematics of the optical box

The constructed optical box

G. Bonvicini

LABM• LABM DAQ Structure
G. Bonvicini

PMT count rate (Hz)HER Beam Current (scaled)
PMT count rate (Hz)LABM

Time (hours)

HER Beam Current (mA)

• Rate versus current for one of the LABM PMTs.
G. Bonvicini

LABM: Data taking with SR from other side of IP
Nikko Down angular scan with “red“ PMT.

IP

Nikko Up angular scan with “red" PMT.

SR reflectionsSR

Oho Down angular scan with “red" PMT.

Oho Up angular scan with “red" PMT.

IPIP

G. Bonvicini

LABM: To Do• Dismantle beamline above tunnel-floor levelat conclusion of Phase I• Re-install beamline just before Phase II turn on• Modify some components based on
experience at Phase I– Wollaston prism alignment, beam pipe lengths, …
– Further development of readout system.

Summary• Photon monitors have undergone first round of commissioning.
• Basic functionalities demonstrated.
– LER XRM looks to be reasonably well-understood, and in agreementwith optics group’s estimates.
– Diamond SRM mirrors show excellent performance in terms of lack ofsensitivity to beam current.
– LABM measuring SR from other side of IP.

• Systematics issues undergoing further analysis– HER XRM:
• Excessive scattered light background on scintillator images?
• Beam tilt at source point?

– SRM higher than expected geometric magnification in system• Hardware issues identified to work on between Phase I and Phase II.

Sparesシンチレーターで見るシングルスリットのイメージ

LER

HER
傾き：
光原点でｘ－ｙ
カプリング？

幅：
マスクホルダーの回転（今日調整する予定）

ⅹ線モニターのパネル• ＬＥＲ：• ＨＥＲ：• βｙ＝６７ｍ• σｙ＝６５μｍ• εｙ＝６３ｐｍ– κｘｙ＝～３．３％（ゼロカレントのεｘ設計値を使う時）• βｙ＝１０ｍ• σｙ＝１２０μｍ• εｙ＝１４４０ｐｍ• κｘｙ＝～３３％（ゼロカレントのεｘ設計値を使う時）

Large-Angle Beamstrahlung Monitor(LABM)

Schematics of the Large Angle BeamMonitor to be installed at SuperKEKB.

Simulation studies: Examples of beam-beampatterns which could be extracted from the signal
reconstruction. Ux and Uy are the x- and ycomponents of the polarized Beamstrahlung
powers [beam 1(2): Solid (Dashed) line]. U0: Powerof the perfect beam.