Optics Correction
andLow Emittance Tuning
Hiroshi Sugimotofor SuperKEKB Optics&Commissioning Group

2016/06/13

The 21th KEKB Accelerator Review Committee

This Talk( ⌘y )rms [mm]History of residual vertical dispersion (LER)~30mm!

4mm!
"y ⇠ 12 pmDate• Optics correction and hardware calibration are iteratively repeated.#• Some details of optics correction are reported in this talk.
2016/06/13

The 21th KEKB Accelerator Review Committee2

Mission
Establish optics measurement and correction tools-Optics and orbit servers to control the magnet system.
Continuous Closed orbit correction
Tune Changer
Optics measurement and correction
Local-bump control
etc…

Hardware calibration and bug hunt
-Polarity check of the magnet using beam measurement.
Check BPM system (e.g. cabling, aging effect)
Beam based alignment (BBA)
etc…

Others-Check validity of the model lattice and correct the model if needed.

Low emittance tuning (LET)
Target vertical emittance is < 5-10 pm.
2016/06/13

The 21th KEKB Accelerator Review Committee

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Measurement Method• Optics measurement with orbit response analysis- Horizontal-vertical (XY) coupling:Vertical leakage orbits induced by horizontal kicks.
- Dispersion:
Response with RF frequency change.
- Beta function:
Orbit response analysis with steering kicks.

• ~60 BPMs (per ring) can be used with turn by turn (TBT) mode.

- Results are preliminary and not presented this report.
2016/06/13

The 21th KEKB Accelerator Review Committee

4Orthogonal Correctors• Skew quadrupole(SkewQ) coil of sextupole magnet
Symmetric / asymmetric excitation of skew-corrector pare can be used asorthogonal correctors for coupling and vertical dispersion.
The orthogonality allows us to reduce size of the problem.
Symmetric Excitation(XY-coupling corrector)#

Asymmetric Excitation(Vertical-dispersion corrector)#

Couplingparameters

VerticaldispersionSkewQ

SD#SD#π
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The 21th KEKB Accelerator Review Committee

5

Beam Based Alignment (BBA)
Steering

Quadrupole• All quadrupole magnets have BPM.

BPM(~ 450 BPMs per ring) #• Calibrate BPM offset so that the beam passes through the magnetic center of thenearby magnet#• The measurement is carried out in spare moments from vacuum scrubbing.##Benefit from BBA#⌘y [mm]HER• Before BBA: Hit hardware limit ofcorrector strength.#• After BBA: Required corrector
strength is remarkably reduced andallows us to further correction.

2016/06/13

Corrector strength# K1 [1/m]

The 21th KEKB Accelerator Review Committee

6Beta-Beat before Correction• Beta and phase functions are extracted from orbit response.
12 orbit responses are used.(6 per each direction)#LERx / x [%]y / y [%]

measxmodelx[rad]
measy

model
y[rad]((2016/06/13x / x )rms ⇠ 19.5 %y / y )rms ⇠ 20.5 %The 21th KEKB Accelerator Review Committee

⌫x ⇠

⌫y ⇠

0.074

0.141
7

Beta-Beat after Correction• Use quadrupole families distributed over the ring. #LERx / x [%]y / y [%]

meas
x

model
x[rad]
meas
y

model
y[rad]((2016/06/13x / x )rms ⇠ 2.0 %y / y )rms ⇠ 2.9 %The 21th KEKB Accelerator Review Committee⌫x ⇠ 0.004⌫y ⇠ 0.001

8

Horizontal Dispersion• Correction with horizontal orbital bumps at sextupoles.
Found that uncorrectable dispersion remains.
The error source seems to be located in the Tsukuba straight section.#• Quadrupoles in the Tsukuba section is additionally used.
A magnet name QLA2RP somehow shows the strongest corrector strength.#
Before Correction#( ⌘x )rms = 49 [mm]After Correction#( ⌘x )rms = 16 [mm]LER⌘x [mm]Tsukuba#

Horizontal bump[mm]#Quadrupole[1/m]#

2016/06/13

QLA2RP#The 21th KEKB Accelerator Review Committee

9Horizontal Dispersion
The mostregion in the tunnel.
• Correction with horizontal orbital bumps
at crowdedsextupoles.
Found that uncorrectable dispersion remains.Suspect Interference between magnets.#
The error source seems to be located in the Tsukuba straight section.#• Quadrupoles in the Tsukuba section is additionally used.
A magnet name QLA2RP somehow shows the strongest corrector strength.# HER!
Before Correction#

HER Bend! ( ⌘x )rms = 49 [mm]LER⌘x [mm]After Correction#
Tsukuba#

Horizontal bump[mm]#

Quadrupole[1/m]#

2016/06/13( ⌘x )rms = 16 [mm]LER!

QLA2RP#The 21th KEKB Accelerator Review Committee

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XY-Coupling Measurement• Not so easy to extract optical coupling parameters R1-4 from closed orbit response.!

• Measure vertical leakage orbits induced by 6 steering kicks.#
LER

V. orbit by H. steering
#1
#2
#3
#4
#5

#6

2016/06/13

The 21th KEKB Accelerator Review Committee

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XY-Coupling Correction• Use the orthogonal correctors.#• The presented correction scheme effectively works, but…#LER

V. orbit by H. steering
#1
#2
#3
#4
#5

#6

2016/06/13

The 21th KEKB Accelerator Review Committee

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XY-Coupling Correction• Use the orthogonal correctors.#• The presented correction scheme effectively works, but…#LER

V. orbit by H. steering
#1
#2
#3
#4
#5

#6

Uncorrectable XY-coupling remains.!
2016/06/13

The 21th KEKB Accelerator Review Committee

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Leakage Field from Lambertson Septum• A Lambertson septum is used to deliver aborted beam to a beam dump.#• This magnet creates unexpected leakage field to stored beam line.##Lambertson septum

Stored beam

Beam dump

2016/06/13

Aborted beam

The 21th KEKB Accelerator Review Committee

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Historical Background• The problem was founded at the previous KEKB commissioning already.

- They installed permanent magnets to cure this problem (04/2000)#• The leakage field gets stronger in SuperKEKB.
- The vacuum chamber is replaced by an anti-chamber.
- A magnetic shielding system gets less effective due to clearance problem of the wider
aperture.
Mimashi-san’s talk?
A note from the previous KEKB commissioing

Tunnel survey@03/17/2016

Series of permanent magnets
2016/06/13

The 21th KEKB Accelerator Review Committee

15Cure to the Leakage Field• Activate two SkewQ coils installed in SF magnets using standby PS.

SextupoleLambertson septum
Activate those two SkewQ coils

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The 21th KEKB Accelerator Review Committee

Beam dump

16

Correction with the Additional SkewQ• The vertical leakage orbit is reduced.#

Before#After#

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For Further Improvement• A hardware group proposes a permanent SkewQ using Ferrite magnets.#• Installed it last Wednesday (June 8). #Ferrite magnets

B ~ 0.07 [T]2016/06/13

Ferrite magnets installed with supporting system

The 21th KEKB Accelerator Review Committee

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Measurement before&after Installation• Further improvement in the vertical leakage orbit.#

Before Installation#

After Installation#

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The 21th KEKB Accelerator Review Committee

19Vertical Dispersion after Installation• A sharp peak of vertical dispersion is vanished.#• As a result RMS residual is reduced from 6 mm to 4 mm.##

Residual V. dispersion#

Before Installation#

After Installation#( ⌘y )rms 6 [mm]( ⌘y )rms 4 [mm]⌘y [mm]Corrector strength#K1 [1/m]

2016/06/13

Strong corrector field is vanishedowing to the permanent SkewQ.#

The 21th KEKB Accelerator Review Committee

20Vertical EmittanceLER!
y = 67 m"y ⇠ 12 pm

HER!
Estimation with beam size measurement

Estimation with measured optics"y ⇠ 120 pm"y ⇠ 10 pm

Flanagan-san’s talk?

The exact value is still under discussion.
2016/06/13

The 21th KEKB Accelerator Review Committee

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Tune Chromaticity - HER • Measure Betatron tune with changing RF frequency.

Horizontal#⌫x

Vertical#⌫yModel#⇠y ⇠ 9.6⇠x ⇠ 10.6
Measurement#⇠x ⇠ 9.8
p/p0 [%]⇠y ⇠ 9.5
p/p0 [%]• Good agreement between the real and model lattice.!

2016/06/13

The 21th KEKB Accelerator Review Committee

22Tune Chromaticity - LER • Measure Betatron tune with changing RF frequency.

Horizontal#⌫x

Vertical#⌫yMeasurement#⇠x ⇠ 5.2⇠y ⇠ 5.2
Model#⇠x ⇠ 3.1
p/p0 [%]⇠y ⇠ 9.6
p/p0 [%]• Large discrepancy compared with that of HER.!
• Off-momentum beta and phase are measured and analyzed.
No big error sources are founded so far.#• Need more study to clarify the source of the discrepancy.#
2016/06/13

The 21th KEKB Accelerator Review Committee

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Optics Correction SummaryLERHER[%]

2/3

3/4

⌘x /

⌘y [mm]13 / 417 / 5⇠x /⇠y2 / -4

<1/<1~12?

~10?

x/ x

/"y [pm]y/ y• Error of the linear chromaticity in LER is still mystery.#• The exact value of vertical emittance is still unknown.
2016/06/13

The 21th KEKB Accelerator Review Committee24

Mission
Establish optics measurement and correction tools.
-Optics and orbit servers to control the magnet system.
Continuous Closed orbit correction
Tune Changer
Optics measurement and correction
Local-bump control
etc…

Hardware calibration and bug hunt.
-Polarity check of the magnet using beam measurement.
Check BPM system (e.g. cabling, aging effect)
Beam based alignment (BBA)
etc…

Others-Check validity of the model lattice and correct the model if needed.

Low emittance tuning (LET)
Target vertical emittance is < 5-10 pm.
2016/06/13

The 21th KEKB Accelerator Review Committee

25

StatusEstablish optics measurement and correction tools.
-Optics and orbit servers to control the magnet system.
Continuous Closed orbit correction
Tune Changer
Optics measurement and correction
Local-bump control
etc…

Hardware calibration and bug hunt.
-Polarity check of the magnet using beam measurement.
Check BPM system (e.g. cabling, aging effect)
Beam based alignment (BBA)
etc…

Maybe related

Others-Check validityof the model
latticeand correct themodel if needed.
Mysteryof tune
chromaticity
in LER

Low emittance tuning (LET)
Reached~10pm?,
the exact
value is stillisunderdiscussion.
Targetverticalemittance< 5-10pm.
2016/06/13

The 21th KEKB Accelerator Review Committee

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Thank you for listening

2016/06/13

The 21th KEKB Accelerator Review Committee

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2016/06/13

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Machine Parameters in Phase I
LER

HER

Units

Beam energy

4.000

7.007

GeV

Beam current

910

830

mA

# of bunches

1576

1576

Bunch current

0.58

0.52

Hor. emittance

1.8

4.6

Momentumcompaction

2.45 x 10-4

4.44 x 10-4

Energy spread

7.5 x 10-4

6.3 x 10-4

Total Vc

7.56

12.45

MV

Bunch length

4.6

5.3

mm

-0.019-0.02544.59/44.63

45.57/43.61

U0

1.76

2.43

τx,y/τx

46/23

58/29

νs
Tune νx/νymAMachine Parameters in Phase III
Machine Parameters2013/July/29

LER

HER

unit

E

4.000

7.007

GeVI

3.6

2.6

A

1.04

mA

2,500

Number of bunches
Bunch Current

1.44
3,016.315

Circumferenceεx/εy3.2(1.9)/8.64(2.8)

4.6(4.4)/12.9(1.5)

Coupling

0.27

0.28

βx*/βy*32/0.27

25/0.30
83

Crossing angle

nm/pm():zero current
includes beam-beam

mm
mrad

αp

3.18x10-4

4.53x10-4σδ

8.10(7.73)x10-4

6.37(6.30)x10-4

Vc

9.4

15.0

MV

σz6.0(5.0)

5(4.9)mm

νs-0.0244-0.0280νx/νy44.53/46.57

45.53/43.57U01.86

2.43

MeV

τx,y/τs43.2/21.6

58.0/29.0

msec

ξx/ξy0.0028/0.0881

0.0012/0.0807

Luminosity

2016/06/13

m8x1035

The 21th KEKB Accelerator Review Committee():zero current():zero current

cm-2s-130