ルミノシティ調整

Y. Funakoshi
Accelerator Laboratory, KEK
2017.9.8@SuperKEKB国内レビュー

Contents• Phase 2 commissioning• 衝突調整• Dithering system（水平方向の衝突調整用システム）の最近の進展と立ち上げ• 垂直方向の衝突調整• ルミノシティ調整

SuperKEKB commissioning phases
Feb. 2016 ~ June 2016

Feb. 2018 ~ July 2018

~ autumn 2018

Phase 1w/o QCS and Belle II

Phase 2
w/QCS and Belle II

Phase 3
Physics Run

BKG study
Luminosity tuning
Target luminosity:
1~2 x 1034 cm-2 s-1

Luminosity tuning

w/o Vertex detector

vacuum scrubbing
basic machine tuning
No beam collision
Already done!

Damping ring commissioning: ~ Dec. 2017

Tasks in Phase 2• Basic tuning– Beam injection of the beam from DR, vacuum scrubbing…

• Performance check of QCS magnets• Squeezing IP beta functions at IP– Optics corrections• Beam collision tuning with “Nano beam scheme”• Belle II beam BG study and tuning• Other studies: electron clouds, other instabilities…
• Luminosity tuning• Physics Run

衝突調整• 衝突状態のサーチ• ビーム衝突フィードバック（軌道フィードバック）システムの立ち上げ• ビームアボート後の衝突の確立の手法

ビーム衝突のサーチ• Closed orbit correction of each beam
• Bunch timing adjustment– Rough adjustment: search for collision bucket• BPM measurement, luminosity monitor?

– Fine adjustment: RF phase scan
• Observer horizontal beam-beam deflection• Orbit adjustment– Scan orbits• beam-beam deflections• Luminosity• beam lifetime

軌道フィードバックシステム• アルゴリズム– Vertical• Beam-beam deflection (like KEKB)• Based on COD measurements using BPMs

– Horizontal• Dithering system (like PEP-II)

Orbit feedback at IP :Algorism• Beam-beam deflection (SLC, KEKB vertical)
Dy at IP=~5nm ~1/10sy*
IPBPM
Dy at BPM= ~1.3µm
SupeKEKB caseBPMLuminosity• Luminosity feedback (dithering)(PEP-II)
When we shake the beam at around the peak of theluminosity (dithering), the dithering frequency in theluminosity is minimized and there appears twice of they the dithering frequency.

• Beam size feedback (KEKB horizontal)
Luminosity
Beam sizesy (LER)x

At KEKB before installation of crab cavities,
the vertical beam of LER was used for thehorizontal orbit feedback at IP.

Horizontal orbit feedback• Difficulty to develop based on the beam-beam defection like thevertical case– Small xx• xx ~ 0.0028(e+), 0.0017(e-)– Two sources of horizontal beam-beam kick
• Horizontal offset and shift of collision timing• We need a different method for the Hor. feedback.

– Luminosity feedback (dithering) (like PEP-II)– Beam size feedback (like KEKB Hor. feedback before crab)• Effect of horizontal offset– Due to Hor. offset, the two beams collide at the position which is shiftedfrom the waist point.
– The crab waist seems to compensate this shift of waist.
– However, actually the situation becomes worse with the crab waist, since
we have to keep the both beams at the design collision point with thisscheme.

• Feedback speed– Fast vibration of IR quads is tolerable. We do not need very fast feedback( slower than ~ 1 Hz).

Fast luminosity monitoring - Plan for 2018 (and beyond... ) (1)
01/2018-06/2018: tests during phase II of SuperKEKB commissioning- Bhabha acquisition and first luminosity measurement tests- Single beam background characterization- Luminosity DAQ output provided to the SuperKEKB monitoring system and dithering system tests:

8 locations for the dithering coils in LER around IP.

11Belle 2
Electronics
Hut

1kHz b/w
Luminosity

EPICS control

B4
Control room

Lock-In-Amps (1~3)(x; y, y’ optional)

EPICS control
Lumi inNetworkEPICS
controlnetwork

Luminosity monitor
Detection system

Dithering System
Block Diagram

EPICS
control

EPICS control (< 1Hz)

Bump magnet
controller

SuperKEKB
TunnelOffset signals (phase, amplitude; 2x1)

ADC

ADC

ADC: 27 channels
12ch/module
PLC: Feedback process control-> need 3 modules
DAC
ADC
DAC: 12 channels
Amplitude readback
12x1
8ch/module
12x1, 12x1
Amplitude control-> need 2 modules
Programmable Amplifier(1~3)(BNC) CPU: 1 module
Dither waveform (sine wave)(x; y, y’ optional)
need 6 slots
Readback

12

To HER iBump magnets

In phase 2, only x direction-> can be switched to y or y’12(BNC)

Drive voltage

Power supply (12)ー＞prepare basemodule with 9 slots

12x2

Dithering coils (12)Luminosity monitor

Orbit Feedback collaborators• Horizontal orbit feedback system– Organizer• M. Masuzawa, Y. Funakoshi– Dithering coils, programmable amp (designed and fabricated at SLAC)• U. Wienands, A. Fisher and others (SLAC)– Fast luminosity monitor• S. Uehara (Belle-II group)• P. Bambade, C. Rimbault, D. EL Khechen, D. Jehanno, S. D. Carlo, C. Pang (LAL Group)– Other hardware preparation (Lock-in Amp, Power supplies, PLC, DAC,cabling…)• T. Oki, S. Nakamura, T. Kawamoto (Magnet Group) + Control group– Software, Simulations• U. Wienands, T. Oki, T. Kawamoto, Y. Funakoshi + Control group• Vertical orbit feedback system– H. Fukuma and beam monitor group• BPMs, feedback circuits….

– N. Ohuchi, H. Yamaoka (QCS group)• QCS supports and vibration measurement, Simulation on QCS vibrations

Dithering system components (TB4 control room, old)
ü Components for the dithering system has been installed.
Takasago BWS60-5
Power amps. for

SLAC
Programmable amp.

iBump(HER)

Dithering (LER)

Signal Recovery Model 7230
DSP Lock-in amp.

Yokogawa FA-M3
Programmable logic controller

Tsukuba B4 control room (new)PLC, DAC, ADC

Lock-in Amp

ProgrammableAmp

Fast Luminosity Monitoring at LAL « KEKC. Rimbault•

Goal: Realization of a fast luminosity monitor based on radiative Bhabha scattering measurements
for SuperKEKB luminosity feedback, tuning and backgrounds studies (BEAST).
– Aimed precision for Train Integrated Luminosity (TIL): dL/L ~ 10 -2 to 10-3 in 1 to 10ms
– Fast signal from each bunch crossing for Bunch Integrated Luminosity (BIL),
2500 bunches/train, collisions every 4 ns•

Measure the radiative Bhabha process at vanishing photon scattering angle– Rate proportional to Luminosity– Large cross section ~ 0.2 barn•

Two complementary techniques developed at LAL and KEK:Ø ~ 5x5x0.5 mm3 single crystal CVD diamond sensors (CVD DS)
pairs coupled to fast charge / current amplifiers (LAL)Ø Cerenkov detector + scintillator (ZDLM group @ KEK)
positioned together outside of the beam pipe•

Two optimized locations fixed in 2014 and 2015:- In High Energy Electron Ring : 30m downstream the Interaction Point for Bhabha photon detection- In Low Energy Positron Ring : 11.9m from IP for Bhabha scattered positron detection
18

July 2016 à December 2017 : Prepare phase 2 commissioning (1)•Development of FPGA based DAQ for the phase II :èLuminosity firmware development:
signal pulse reconstruction algorithm: A1-A4
ètest on Train Integrated Lumi (TIL) & Bunch
Integrated Lumi (BIL) reconstruction: almost validated•Installation of a window in LER (confirmed for spring 2017)
è Adaptation of existing pillar for phase 2
è radiator design study: trapezoid shape Tungsten radiatorwith thickness of 6*RL will be used.

Fraction of detected Bhabha which can be achieved in
140𝝁𝒎 DS with different thickness radiator

Recent progress in preparation ofthe dithering system• Hardware– Network connection in TB4 control room: done
– Cabling among devices: almost done
– Installation and setup of PLC in TB4 control room: done
– Fast luminosity monitor: to be ready by the start of Phase 2• Software– Soft IOC on PLC: setup done
– EPICS records for Lock-in-am, DAC, ADC: prepared– Feedback control software written in Maple (U. Wienands)• Transferring to SAD script is going on. Simulation will be done on SAD.
• In the actual operation, it will work in soft IOC on PLC in the present plan.

• System tests in TB4 control room
– System test of Lock-in Amp was done.
– System test of programmable amp was done.
•U. Wienands stayed at KEK for a week for the test at the end of August.

iBump LER (Phase 3)

Bump Height: 10 µm
Bumpがない時：8.18E-13 m

iBump LER (Phase 2 4x8)

Horizontal kick < 44.4µrad

Bumpがない時：1.96E-13 m

Parameters for dither simulation
Luminosity

Ibeam [A]initialnominal

ultimate

1 x 1034 cm-2 s-1

1 x 1035 cm-2 s-1

8 x 1035 cm-2 s-1

LERHERLER

HERLER

HER

1.0

0.8

2.7

1.95

3.6

2.6

# of bunches25002500

2500

ex/ey (nm/pm)

2.2/445.2/104

3.2/51.84

4.6/77.28

3.2/8.64

4.6/12.88

bx*/by* (mm)128/2.16

100/2.4

128/1.08

100/1.2

32/0.27

25/0.30sx*/sy*(µm/nm)

16.8/308

22.8/500

20.2/237

21.4/305

10.1/48

10.7/59sx*eff (µm)

249

208

249

208

249

208

0.0033/0.024

0.0013/0.0257

0.0083/0.049

0.0052/0.046

0.0028/0.0881

0.0012/0.0807

xx/xy
Dx (lumi:20%drop)~110µm

~55µm

~10µm

Lumi. meas.

1kHz

1kHz

1kHz

accuracy~5 x 10-3(w/ radiator)

1.3 x 10-3(w/o radiator)< 1 x 10-3sx*eff = szsinf

Field measurements andprogrammable amp calibration data

Measured on Aug. 31st 2017

T. OkiDamping and phase delay of a magnetic field
Bout = B0 sin (wt )Bin =11+ (wt )2

B0 sin éëwt - arctan (wt ) ùû

Damping ratio

Phase delay

where,
Phase difference: ~ 5 degrees@77Hz among coils

µ0 bt
t=2 r
: ramping time for step response,b: outer radius (m),t : thickness (m),r: resistivity (W × m)

Red: outer radius = 51mm, thickness = 6mm
Green: outer radius = 48mm, thickness = 3mm
Blue: outer radius = 42mm, thickness = 2mm

A.W. Chao and M. Tigner, Editors,Handbook ofAccelerator Physics and Engineering,
World Scientific, Singapore (1999), p. 268

Conceptual drawing for 3 type of beam pipes
ZDS1{L, R}P
Inner diameter: 80 mm
Thickness: 2 mm

ZDS2{L, R}P
Inner diameter: 90 mm
Thickness: 3 mm
10 µm Cu coating inside.

ZDS{3, 4}{L, R}P
Inner diameter: 90 mm
Thickness: 6 mm
10 µm Cu coating inside.

All pipes are made of SS316L.

Y. Suetsugu

Effect of phase difference among coils

Phase 2 4x8

Damping of magnetic field due to eddy current

T. Oki

Damping ratio
Bin
1=2Bout
1+ (wt )µ0 bt
where: t =,2 rSS316L
Copper(KEKBLER pipe)

b: outer radius (m),t : thickness (m),r: resistivity (W × m)
A.W. Chao and M. Tigner, Editors,
Handbook ofAccelerator Physics and Engineering,
World Scientific, Singapore (1999), p. 268

Ditheringfreq. range
1k 10k 100k

Resistive and thinner pipe suppresses the damping effect.

K. Ohmi

by*~300µm
Swaist:1/10 by* (~30µm)-> Lum. Loss ~ 3.5%
Dx = Tan[2f]*Ds
Ds=30µm -> Dx = =2.5µm

Luminosity degradation due tohorizontal orbit shift at IPby*841

Estimation of QCS vibration and luminosity degradation(vertical)

100
10

Measuredground motion(input data)
125 nm@25 Hz

Phase (deg.)

Integral amplitude (nm)1000

H. Yamaoka

0.1

QC1RP and QC1RE vibrate with same phase,but the amplitude difference still arises: 25 nm at 25 Hz…
Phase 3
Luminosity degradation (based on beam-beam simulation by K. Ohmi)
15 (recent meas.)
Frequency (Hz)24.85 38.93 69.34 99.60
DyIP*rms (nm)

18.63

1.72

8.29

3.14

40

L/L0average (%)

95.4

99.8

99.7

99.7

84

Feedback rejection gain

-16.7dB (19 nm -> 2.8 nm)-23dB (40nm -> 2.8 nm)

QCSLとQCSRクライオスタットの振動測定（山岡さん）
・2017/3/6の電磁⽯打合せの資料より…。

鉛直⽅向
QCSL: 45nm@20Hz
QCSR: 300nm@15Hz
注意：前⾴のはコイルの振動で、こっちはクライオスタット

Beam-Beam simulation results
K. OhmiJust 20 nm offset leads to 6 % degradation of luminosity.

Commissioning of orbit feedbacksystems• Tuning of iBump orbit– iBump in HER: COD measurements -> correction so that the bumps areclosed.
– iBump in LER (dither orbit):• Response of bpm signal (phase) to coil excitation by using LIM• observe the 77 Hz component at two BPMs outside of the bump with 90
degree phase difference in each horizontal and vertical directions ->correction so that the 77 Hz components are minimized• correction using turn-by-turn BPMs?
• Prior to those corrections, should we do corrections by using a DC bump?

• Setup the orbit feedbacks– Vertical feedback– Horizontal feedback (dithering)• A. Fisher (SLAC) will stay at KEK in the commissioning of dithering system• U. Wienands will stay at KEK for about 1 month in the commissioning of ditheringsystem.

ビームアボート後の衝突の確立の手法• KEKBでは、二つのビームを衝突状態に持っていく途中（過渡現象）でビームロスするなどの現象が見られ、苦労する場合があった。
– Nano beam 衝突はでどうか？
• 実際にやって見ないとわからないことも多いが、予めシミュレーションをやっておきたいルミノシティ調整• 基本的なマシンパラメータの確立– IP beta functions– Betatron tunes– Beam currents, Number of bunches• Tuning items– Tuning knobs• X-Y coupling• waist points• IP dispersions• Target values of orbit feedback• Betatron tunes– Method of parameter search• Scan, scan, scan,,,,,

Strategy of Beta Squeezing in Phase-2PhaseLERHER

βx* [mm] βy* [mm] scale

βx* [mm] βy* [mm] scale

2.0*

384

81

12 x 300 400

81

16 x 270

2.1

384

5.4

12 x 20400

616 x 20

2.2

256

2.16

8x8

200

2.48x8

2.3

128

2.16

4x8100

2.4

4x8

2.4

128

1.08

4x4100

1.2

4x4

3.x

32

0.27

1x125

0.30

1x1
Y. Ohnishiadiabatic squeezing

We hope to squeeze the IP beta functions down to 4 x 8 in Phase 2.
If possible, 4 x 4 is desirable.

37

Issues• IR design and dynamic aperture• Optics corrections & Low emittance tuning• Beam-beam related issues• IP orbit control to maintain beam collision• Beam loss and beam injection• Electron clouds• Injector upgrade for low emittance & highintensity beams• Detector beam background
The items in red were partially studied in Phase 1.

SuperKEKB Luminosity Projection

A lot of difficult works should be done in Phase 2 and 3.

Spare slides

iBump LER (Phase 2 8x8)

Bump Height: 10 µm

Bumpがない時：1.96E-13 m

iBump steering kick angle
iBump FB

積分磁場（Tm） kick angle(mrad) @7GeV @5A

Commemnt

垂直ステアリング0.00335

0.143571429 江川・植木さんの磁場測定結果

水平ステアリング0.006110.261857143 江川・植木さんの磁場測定結果

Dithering

積分磁場（Tm） kick angle(microrad) @4GeV @5A

Horizontal

0.000451

33.825UliさんのIPAC論文

Vertical

0.000592

44.4UliさんのIPAC論文

Shift of collision timing makes ahorizontal kick• With the drift of collision timing ->noshift of collision point ->no waist
problem• However, the drift of collision timing
makes a beam-beam defection andinterferes with the detection of thetrue hor. offset.
• Hor. offset from shift of collision timing– offset：Dx=c Dt sinf
– Tolerance for true horizontal offset: Dx
corresponding Dt =0.20ps ->RF phaseof 0.07°

Lorentz boost

fprojection

Dt -> Dx=c Dt sinfLuminosity and beam-beam
parameter with superbunch
collision

Luminosity

Beam-beam parameterσxeffective = σz sinφcφc2.2mm
1.1mm
design, 0.3mm10.95
0.9
0.85

0204060∆ x (µm)

1.05

80

0.8

100

0.95

00.05

1.05

L/L0

0.9
0.85

0.85
0.8

0.75

0.75

0.7
0.2
ηy (mm)

0.2

0.9

0.8

0.1

0.15

2.2mm
1.1mm
design, 0.3mm

10.95

00.1
∆ y (µm)

2.2mm
1.1mm
design, 0.3mm

1L/L0

1.05

2.2mm
1.1mm
design, 0.3mm

L/L0

L/L0

1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
00.3

0.4

0.7
00.5

11.5
ηy’

2

2.5

1.05

2.2mm
1.1mm
design, 0.3mm

0.9

0.95

0.8
L/L0

L/L012.2mm
1.1mm
design, 0.3mm

10.9

0.7
0.6

0.85

051015r1 (mrad)

1.05
10.95
0.9
0.85
0.8
0.75
0.7
0.65
0.6
0.55

0.4

20

2.2mm
1.1mm
design, 0.3mm

L/L0

L/L0

0.8

0.5

0102030-1
r3 (m )

40

50

01.05
10.95
0.9
0.85
0.8
0.75
0.7
0.65
0.6
0.55

123r2 (mm)45452.2mm
1.1mm
design, 0.3mm

0123r4 (rad)Fabrication and field measurement

Fabrication and measurement of coils will be finished by this March.
U. Wienands, S.D. Anderson, MFD Metrology, SLAC