Bunch compression at the SPring-8 linac for successive generation - - PowerPoint PPT Presentation

Bunch compression at the SPring-8 linac for successive generation of THz pulse train in the isochronous ring

• T. Asaka, H. Hanaki,
• H. Dewa, T. Kobayashi,
• A. Mizuno, T. Taniuchi,
• S. Suzuki, H. Tomizawa,
• K. Yanagida

SPring-8, JASRI

• Y. Shoji,
• T. Matsubara,
• Y. Hisaoka,
• T. Mitsui,

NewSUBARU, LASTI, University of Hyogo

Contents

・ Introduction to CSR ・ Basic Idea ・ Demonstration Experiment ・ Upgrading plan

Introduction

Applications of Short Electron Bunch ・Coheremt synchrotron radiation (CSR) ・Short Pulsed X-Ray

For time resolving experiments → Sub-ps (femto-second) pulse → Intense ps pulse is still valuable → extremely strong THz radiation → stable radiation

z beam Bunch length

Coherent Synchrotron Radiation (CSR)

P

tot(ω) = p(ω) N +( N 2 − N ) f(ω) 2

[ ]

f(ω) = ρ(z)exp(iωz /c)dz ∫

p(ω) : power from an electron f(ω) : form factor

ρ(z)dz = 1 ∫ Form factor

( ρ(z) : charge density, )

Radiation power from N electrons in a bunch

• 1. Make short and intense bunch in a linac
• 2. Let the bunch circulate in an isochronous ring
• 3. Use short pulsed X-ray train or THz CSR

The Concept

P u l s e d X

• r

a y t r a i n T H z C S R

N

• s

t

• r

a g e ! !

Merits

(iii) Existing acceleratiors are enough for a few ps pulse.

• -> No special expense is required

(i) Short and intense pulse is obtained at ring BL.

• -> Light for many BLs at the same time

(ii) Short pulse train with fixed period

• -> It helps to confirm the synchronization.

Demonstration Experiment

1. ECS cavity --> energy gradient 2. Linac-NS BT--> magnetic compression 3. Streak camera --> measure bunch length

NewSUBARU

Linac-NS BT

Energy Compression System (ECS)

Booster synchrotron SPring-8 Linac

Electron Gun

20 40 (m)

Simulation of bunch compression

• 1

1 2 3 4 5

• 5

5 10 15 20 25 20 40 60 80 100 120

Dispersion η(m) Bunch length (ps) Location in Linac-NS transport line (m) (a) normal; ∆E/E=+0.3% (b) our choice; ∆E/E=+0.5% (c) too much compression; ∆E/E=+1.2%

Magnetic compression along the Li-NS transport

Bunch Length Measurement

10 20 30 40 50

Intensity (arb. unit) Time (ps) σ = 5.1 ps Data Gaussian fit

1σ = 5.1 ps

10 20 30 40 50 50 100 150 200 250 300

Intensity (arb. unit) Time (ps) σ = 2.2 ps Data Gaussian fit

BW < 10ps

1σ = 2.2 ps

Normal Operation Parameters ECS parameters Optimized

• 0.4
• 0.2

0.2 0.4

Intensity(arb. unit) ∆E/E (%)

Time profile at the initial turn in the ring

BW = 0.75%

Multi-turn Circulation

∆L/L = α1δ + α2δ2 + α3δ3 + ...

δ = ∆E E

(here )

αn : n-th momentum compaction factor

Energy dependence of path-length NewSUBARU storage ring Invert Bend →control α1 Modified DBA BM IB ・α1 =1.3×10-3 → ≈ 0 ・α2 = 0 (setting accuracy ≈ 10-3) ・α3 no control knob (α3 ≈ 0.5 ) Modified DBA

Tracking simulation in the non-linear rf bucket

Initial state; just after injection ∆E/E = ±0.5% ∆τ = ± 4ps

∆τ (ps) ∆E/E (%)

Tracking simulation in the non-linear rf bucket

Initial state; just after injection ∆E/E = ±0.5% ∆τ = ± 4ps

∆τ (ps) ∆E/E (%)

α2 = 0 α3 = 0.5 α4 = -20 α1 = 0 After 100 turns α1 = -1 X10-5 After 100 turns

Quasi-isochronous ring 50 turns with σ < 3ps

2 3 4 5 6 7 10 20 30

Turn number Time(µs)

Bunch length : σ (ps)

25 50

α 1=0 α 1=-0.02×10

• 3

α 1=-0.06×10-3 α 1=1.3×10-3 α 1=-0.06×10-3 3 ps injection 2 ps injection

Optimum α1 was larger than the expected Bunch elongation was faster than the expected

CSR detection

Set-up of micro-wave detector (90-140GHz)

Signal waveform

• 0.05
• 0.025

0.025 0.05 0.075 0.1 0.05 0.1 0.15

Voltage (V)

Time (µs)

Revolution period=0.4µs

Turn by turn CSR power

24 pC/bunch 20 pC X 3 bunches

Stronger CSR at the injection It lasted longer than the normal condition

0.05 0.1 0.15 0.2 0.25 0.3 5 10 15 20 25 30

Power (mW)

Time from injection (µs) Turn number

25 50 75

Normal Operation Compressed, Single bunch, QI ring

Bunch length & CSR power

24 pC/bunch 20 pC X 3 bunches

0.05 0.1 0.15 0.2 0.25 0.3 5 10 15 20 25 30

Power (mW)

Time from injection (µs) Turn number

25 50 75

Normal Operation Compressed, Single bunch, QI ring 2 3 4 5 6 7 10 20 30

Turn number Time(µs)

Bunch length : σ (ps)

25 50

α 1=0 α 1=-0.02×10

• 3

α 1=-0.06×10-3 α 1=1.3×10-3 α 1=-0.06×10-3 3 ps injection 2 ps injection

0.01 0.1 1 10 100 1 10

f (ω)

2

Frequency (GHz)

90GHz 140GHz 3 cm-1

Wave number (cm

• 1)

10 20 30 40 50 10 15 20 25 30 35 Time from injection point ( µs)

Time (ps)

2.4ps (1σ) 2.3ps 2.9ps 4.1ps 5.3ps Data Gaussian fit

Reduction of CSR

Sensitive to a small change of the bunch length

Evolution of time profile after injection

Gaussian σ = 2.9ps Triangle L = 7.6ps

contribution of form factor f(ω)

1st 50th

Summary of Experiment

Short Bunch Circulation ・succeeded to keep 1σ < 3ps for 50 turns ・larger CSR lasted longer

Of course, still there are many problems …

Future Improvement

Ring (magnet system) ・improve stability ; temperature control ; magnetic field ; better tuning = improvements for the daily operation Linac (electron gun) ・thermionic gun --> photo-cathode RF gun

Photo-cathode RF gun

Thermionic Gun

20 40 (m)

RF gun R&D room

Rf gun Acceleration structure

Photo-cathode rf gun

Electron Gun Thermionic Photo-Cath Energy Spread + 0.5% + 0.1% Bunch Length 2.2 ps < 1 ps Bunch Charge < 0.1 nC > 1 nC

∆E/E (%) ∆τ (ps)

Initial state ∆E/E = ±0.5%; ∆τ = ± 2.2ps

α1 = -1.5 X10-6; after 500 turns

Initial state ∆E/E = ±0.1%; ∆τ = ± 1ps

α1 = -0.5 X10-6; after 500 turns

~ 50 >100 ? 1 quasi-dc Pulses per shot 24 1000 ~ 10 ~ 1 charge (pC/bunch) 3 (1σ) <1.0 0.16 (1σ) 1.0 (1σ) bunch length (ps) Short Bunch Circulation (SPring-8 Linac & NewSUBARU) Demonstration Photo-cathode gun Laser Slicing (ALS) QI operation (BESSY-II) Beam Parameters

Comparison with other methods

stable short strong

Beam physics study

• 1. Stable operation of quasi-isochronous ring
• 2. Circulation of an extreme beam

Similarity with ERL’s arc Problem would be enhanced with multi-turn circulation Ring parameter can be tuned using stored beam

• 3. Future project at Tohoku Univ.

Circulation of sub-mm pulse [ H. Hama, 27th International FEL Conference (2005)].