Commissioning of Electron BeamCommissioning of Electron Beamfor SuperKEKB Injector Linac

Masanori Satoh (KEK, Linac Control G.)
for the Linac Commissioning GroupThe 18th KEKB Accelerator Review Committee, Mar. 4-6, 2013

Commissioning of Electron BeamRequirement

Commissioning of Electron Beam

Electron Beam Parameters
SuperKEKB Linac

KEKB Linac

Energy (GeV)78

HER stored current (A)

2.6

1.2

HER beam lifetime (min.)

10200

Maximum beam repetition (Hz)5050

Max. # of bunch in a rf pulse

22Emittance (mm⋅mrad)

20100Charge (nC)51

Energy spread (%)

0.08

0.05

Bunch length σz (mm)

1.3

1.3

Simultaneous top-up injection

4 rings (SuperKEKBe-/e+, PF, PF-AR)

3 rings (KEKB e-/e+, PF)Commissioning of Electron Beam

Energy Spread

Commissioning of Electron Beam

Uniform shape of longitudinal beam distribution• Energy spread should be less than 0.08%• Mitigate longitudinal wakefield and reduce energy spread• Gaussian distribution in momentum space

Uniform!

Gaussian!tCommissioning of Electron Beam

Energy spread• For 10 ps bunch length,• 〜 0.3% for Gaussian distribution• < 0.08% for uniform distribution• Uniform distribution is necessary. (rf gun)0.08%
M. Yoshida

Commissioning of Electron Beam

Low EmittanceCommissioning of Electron Beam

Low emittance electron• Low emittance electron beam should be delivered
to MR w/o damping ring.
• Emittance preservation is key issue• RF gun (M. Yoshida, T. Natsui, X. Zhou)• Emittance growth simulation (H. Sugimoto)• SAD code, Elegant• Initial bunch charge: 5 nC
• Initial emittance: 6 mm⋅mrad• Initial bunch length: 10 ps (FWHM)• Initial energy spread : 0.4%
• Initial beam energy: 20 MeV• Uniform longitudinal beam distribution

Commissioning of Electron Beam

Bunch compression at Jarc

• Mitigate transverse wakefield and emittance growth• Initial bunch length 10 ps => 5 ps (bunch compression at Jarc)• Control R56 at Jarc

Jarc

Bunchcompression

Commissioning of Electron Beam

Sector Cto5: -10 deg rf phase
R56 =-0.20

Emittance growth due to component misalignment• Simulation results from 100 different seeds• Misalignment of Quadrupole magnets and Accelerating structure:• σ < 0.1 mm: ε 20 mm·mrad is almost satisfied.
• σ > 0.1 mm: emittance preservation is very difficult.
<Emittance growth>・quadratic curve as a functionof misalignment
・strongly depend on error seedrequirement

Commissioning of Electron Beam

Emittance (misalignment σ = 0.3 mm)• Bunch compression is effective. However, still not enough for 20 mm⋅mrad
R56 = 0 (w/o compression)

R56 = -0.20

20 mm⋅mrad

20 mm⋅mrad

R56 = -0.30

Energy spread

20 mm⋅mrad
0.08%

Commissioning of Electron Beam

Sector Cto5: -10 deg rf phase
R56 =-0.20

Offset injection for emittance preservation• Offset injection: intentional change of misalignment seed
• Kicks at the beginning of Sector CJarc

Bunch
compression

Offset injection

Commissioning of Electron Beam

Sector Cto5: -10 deg rf phase
R56 =-0.20

Offset injection (simulation)••

Average(mm·mrad)Standard Deviation(mm·mrad)

W/O
Offset Inj.

4328

W/
Offset Inj.

7.4

2.9

Kick angle is relatively small compared to the case of orbit correction.
Need a high-precision and stable orbit control.

Commissioning of Electron Beam

Offset injection (experiment at Sector A, B)
Effective for high-intensity bunch

Steering current (A)KEKB review2012, M. Yoshida

Commissioning of Electron Beam

Low emittance electron issue• Component alignment is important• σ < 0.1 mm: good for emittance (alignment is very difficult)• σ > 0.1 mm: Beam manipulation is necessary.
• σ 〜 0.3 mm• Jarc:Bunch compression• Sector C: Offset injection• Emittance can be preserved.
• Small energy spread is difficult.

• Alignment requirement• σ < 0.3 mm for global (whole Linac)• σ < 0.1 mm for local (one Sector ̴ 100-m-long)

Commissioning of Electron BeamHigh Precision
Beam Position
MeasurementCommissioning of Electron Beam

• Current system:– WindowsXP-based digital oscilloscope• 10 GSa/s, 8 bits, 1 GHz bandwidth, 4 channels• Acquisition speed: 50 Hz• Twenty four systems process 100 BPMs
• Position measurement precision: 50 µm (3-BPM)• More precise orbit measurement < 10 µm• New system based on band-pass sampling scheme is undertest and development.

Commissioning of Electron Beam

New system:
Oscilloscope（current）

LiberaBrilliance SP

Libera SPE（under test）

KEK-VMEbased（under development）

Signal generator(gain calibration)

N/A

N/AN/A〇

Band-pass filter

N/A

fc: 522 MHz
BW: 24 MHz

fc: 522 MHz
BW: 24 MHz

Fc: 300 MHz
BW: 30 MHz

A/DC

8 bits, 10 GSa/s

16 bits, 125 MSa/s

16 bits, 160 MSa/s

16 bits, 250 MSa/s

Software (EPICS)〇〇〇×(need development）

Event system

via network

via network

EVR inside(µ-TCA-like)

VME-EVR

Precision

50 µm (3BPM)

10 µm (test pulser)
20 µm (3BPM, 0.1 nC)

3.5 µm (test pupulser)? (3BM)?

Remarks

FY2015End of support

Discontinued

Candidate

Candidate18

Commissioning of Electron Beam

SimultaneousTop-Upfor 4 Rings

Commissioning of Electron Beam

Simultaneous Top-up Operation for three rings• Stored
Beam current
beam current
stabilitystabilityin Original
sinceOperation
Apr. 2009- KEKB: 1300
mAmA(~ 0.05%)(~ 50 %): e-: 12.5 Hz, e+: 25 Hz- PF: 0.05
240 mAmA (~(~ 530.01%)%) :0.5 Hz

KEKB e-PF

KEKB e+Luminosity
20

Commissioning of Electron Beam

PF-AR injection: 20 min., twice daily• Interrupt KEKB injection• Problem for SuperKEKB (beam life: 10 min.)Commissioning of Electron Beam

Simultaneous top-up including PF-AR injection• PF-AR and KEKB share the long part of beam transport line.
• Existing tunnel space is very tight.
• New beam transport line is required for PF-AR top-up injection.

New BT for PF-AR(H. Takaki)Commissioning of Electron Beam

Summary
Stable beam operation(simultaneous top-up for 4 rings)
Feedback loops (energy, orbit , energy spread)
Precise beam diagnostic and control
Commissioning tools

Low emittance(20 mm·mrad)

Small energy spread(0.08%)

rf gunAlignment
Bunch compression
Offset injection

Uniform longitudinalbeam distribution

High bunch charge (5 nC)

Commissioning of Electron Beam

Future plan
• Low Emittance Preservation– Simulation study• Including BPM reading, steering setting errors, and timing jitter– Beam study• Bunch compression at Jarc

– Streak camera required• Emittance preservation study– Wire scanner (Sector2) will be installed• Pulse-to-pulse beam stability• High precision BPM data processing system– Evaluation, 3-BPM (beam test)• Simultaneous top-up 4 rings (including PF-AR)

Commissioning of Electron Beam

Thank you foryour attention!