Future Light Source Energy Recovery Linac (ERL)

The R&D of design study of 4th generation

light source energy recovery linac

Light source

Free Electron Laser

Energy Recovery Linac

3rd generation Light Source

3rd generation Light Source Future Light Source

Short Bunch Length

~1/100

x

x’

y

y’ z

x

x’

y

y’ Smaller emittance

~1/100

Necessity of Future Light Source

Wave length

(30 nm → 1 Å)

Pulse length

(ps→ fs) FEL, ERL

Why Energy Recovery Linac?

High average brilliance

High repetition rate

Short bunch length

Many beam line

ERL XFE-O SASE-FEL 3rd SR

Average

brilliance ~1023 ~1027 ~1022~24 ~1020~21

Peak

brilliance ~1026 ~1033 ~1033 ~1022

Repetition

rate (Hz) 1.3 G 1M 100~10k ~500M

Bunch

width (ps) 0.1~1 1 0.1 10~100

# of beam

lines ~30 few ~1 ~30

(Brilliance : photons/mm2/mrad2/0.1%/s @ 10 keV)

Energy Recovery Linac

Principle of Energy Recovery

Challenges:

1. Low emittance, high current creation

2. Emittance preservation

3. Beam stability at insertion devices

4. Accelerator design

5. Component properties, e.g. SRF

Advantages Reduced size

Reduced RF power

Reduced cost

Injector

Arc section

Merger

Electron gun

Injector system

Superconducting Main Linac

Main issues in ERL

1. Space charge effect

3.5 keV 5.6 keV

35 MeV, 8.54 m Drift space

Initial beam distribution

(Beer-can shape)

2

2

2

2

2

0 2

1

2

1

2

1

2

1

2)( A

L

zA

L

z

L

z

L

z

a

QzEz

Electron

Electric field Electric field Electric field induced by

Many electrons

The head and tail of bunch was

accelerated and decelerated, respectively

Energy spread growth

Main issues in ERL

2. Coherent Synchrotron Radiation

Time(ps)

d

E(k

eV

)

x

x’

CSR kick

Energy change in a bending

due to the CSR

Error in bending angle

due to the energy difference

Emittance growth

due to the CSR effect

x

x’

CSR kick

Method of minimization

of emittance growth

Match the beam orientation angle

with CSR kick angle

Main issues in ERL

-0.557 rad

Horizontal CS parameter scan

Vertical CS parameter scan

Horizontal emittance

~ 1 mm-mrad

3. Merger optimization

-0.53 rad

x

x’

Space charge kick

Electron

Electric field Electric field

x

x’

Space charge kick

Analytical Calculation

Numerical Calculation

Emittance minimization by Courant-Snyder parameter scan in energy recovery linac, KPS spring meeting, Daejeon, 2011

Main issues in ERL

J. Rosenzwig

formula

4. SRF Focusing effect

5 MeV 10 MeV

Analytical

Numerical

The result shows a good agreement between numerical and analytical calculation!

1.3 GHz Superconducting niobium 9 Cell Cavity

Cryomodule

Beam Dynamics in Superconducting Energy Recovery Linac accelerator, The 14th ICABU, Gyeonju, 2010

Main issues in ERL

5. Arc section

Preparation of start-to-end simulation for compact ERL, Proceeding of IPAC 10, kyoto, May 2010

z

ΔE/E

Principle of bunch compression

Optics distortion by SC effect

Back-up

Energy Recovery Linac in the world

Brookhaven National Laboratory, USA

Cornell University, USA

The Japan Atomic Energy Research Institute, Japan

Daresbury Laboratory, UK

Newspaper

1

4

R&D Efforts for Key Accelerator Components

High-brightness photocathode DC gun:

500 kV, 10-100 mA

Normalized emittance: 0.1 - 1 mm·mrad

Gun drive laser:

High average power: 15 W CW

Repetition: 1.3 GHz, l ~ 800 nm

SC cavities for injector

High input power: 170 kW/coupler

Medium gradient: 15 MV/m

High beam currents: 100 mA (CW)

SC cavities for main linac

Medium gradient: 15-20 MV/m (CW)

High average current: 200 mA

Higher-order-mode damping

Main Linac

Injector

Return Loop

Energy Recovery Linac

High-power RF source

1.3 GHz, 300 kW (CW) for injector

Development of Photocathode DC Gun

500kV, 10mA Gun #1 (JAEA) 500kV, 10mA Gun #2 (KEK)

ceramic

sup

po

rt rod

field emission

guard rings

0

100

200

300

400

500

600

0

50

100

150

200

250

300a

pp

lied

Vo

lta

ge

[-k

V]

cu

rren

t [A

]

Stable operation at 500 kV for 8 hours

Gun #2 has been assembled..

16

Fiber Laser

for 10mA: 530nm, 20ps pulse duration, 1.5W Laser is required

Second harmonic power of 100 mW has been achieved. sufficient for initial

target of 1mA

Y. Honda, S. Matuba, T. Miyajima

PF-AR south experimental hall

Evaluation of cathode, beam control and monitor system by 200kV gun system.

Photocathode DC Gun Test Facility at KEK

18

Present Status : Photo

Cryogenic Systems

RF Sources

Cryogenic Systems

RF Source: 300kW Cｌystron

Injector system

Components in ERL injector ① Photo cathode DC gun

Gun, HV power supply, driving laser system

② Solenoid magnet

To compensate emittance

③ Bunching cavity

Normal conducting cavity for bunching

④ SRF cavities

2-cell, 3 modules

⑤ Quadrupole magnets

To adjust CS parameters before merger section

⑥ Merger section

To merge injected beam into return loops

⑥

⑤

④

① ②

③

500 keV 5 – 10 MeV Beam energy:

Space charge effect is dominant.

Cross sections and field maps

(a) Cross sections

DC gun Solenoid magnet Bunching cavity SRF cavity

(b) 1D field map

Physics in ERL injector

(1) Space charge effect （Coulomb force between electrons)

(2) Solenoid focusing （Emittance compensetion）

(3) RF kick in RF cavity

(4) Coherent Synchrotron Radiation (CSR) in merger section

(5) Response time of photo cathode（It generates tail of emission.）

These effects combine in

the ERL injector.

The simulation code have to include

(1) External electric and magnetic fie

ld,

(2) Space charge effect (3D space char

ge).

To obtain high quality beam at the

exit of merger, optimization of be

amline parameters is required.

Method to research the beam dyn

amics:

Macro particle tracking simulatio

n with space charge effect is used.

Beam Simulation

Particle tracking code：GPT(General Particle Tracer)[1]

Space charge calculation：3D mesh based method

Initial particle distribution：beer-can No CSR effect in merger section

d = 4 sx

Initial distribution on cathode：beer-can

Dt=sqrt(12)*st [1] Pulsar Physics, http://www.pulsar.nl/gpt/index.html

Beam energy 5 – 10 MeV

Beam current 10 – 100 mA

Normalized rms emittance

n = /(gb)

1 mm·mrad (77 pC/bunch)

0.1 mm·mrad (7.7 pC/bunch)

Rms bunch length (rms) 1 – 3 ps (0.3 – 0.9 mm)

Purpose of simulation

To find optimum beamline parameters, i.e. magnet strength, RF phase, etc., with lower emittance and shorter bunch length.

To calculate beam parameters, i.e. emittance, beam size, etc., to design components in ERL injector.

How to optimize the parameters?

Macro particle tracking simulation with space charge requires longer CPU time.

In the optimization, tracking simulation is repeated to search optimum parameter. Therefore, the calculation time to optimize the parameters is too long.

To save the calculation time, efficient optimization method is required.

In order to reduce the calculation time, we use

Multi objective method as an efficient method, and

Cluster linux computer, which have 80 CPUs. The parallel 80 jobs, which have different beamline parameters, can be executed on the cluster computer.

To minimize emittance and bunch length

Trade-off solutions

Two objects in the optimization

1. Emittance

2. Bunch length

Multi objective optimization To minimize both emittance and bunch length at 1 m from the exit of merger

Multi objective method is used[2]

Free parameters in the optimization ① Initial laser radius (mm)

② Initial laser pulse length (ps)

③ Magnetic field of 1st solenoid

④ Electric field of bunching cavity

⑤ Magnetic field of 2nd solenoid

⑥ Electric field and phase of SRF1

⑦ Electric field and phase of SRF2

⑧ Electric field and phase of SRF3

⑨ Magnetic fields of 5 quadrupoles

[2] Ivan V. Bazarov and Charles K. Sinclair ,

Phys. Rev. ST Accel. Beams 8, 034202 (2005).

Number of free parameters: 16

Minimize both emittance and bunch length. (2 objects optimization)

Layout of beamline

Beam parameters are calculated at 1 m from exit of merger.

Results of optimization

Bunch length vs. normalized rms emittance

For shorter bunch length, emittance is larger than the cas

e of longer bunch length.

Normalized rms emittance

0.4 ～ 0.5 mm mrad

Results of optimization (1) Sector type（bending angles：-19, 22, -19 degree)

(2) Rectangular type（bending angles：-16, 16, -16 degree)

Normalized rms emittance

0.4 ～ 0.5 mm mrad

Emittance growth caused by space charge dispersion. The rectangular type gives smaller emittance than the

sector type. It seems that stronger longitudinal space

charge dispersion in the sector type causes the differe

nce of emittance, because the bending angle of the b

ending magnet in the sector type (19◦ or 22◦) are larger than one in the rectangular type (16◦).

(a) Maximum emittance growth

(b) Minimum emittance growth

Emittance growth depends on space charge dispersion.

Dependence on number of particles

In the macro particle tracking simulation, we can not avoid the effect of number of macro particles, because we can not simulate actual number of electrons.

To obtain more accurate results,

In early optimization : 5k particles （to save CPU time）

But, the accuracy is not so good for 5 k particles

In final optimization, we optimize beam line parameters with 200 k particles after the early optimization with 5k particles.

Normalized rms emittance Rms beam size

At lease Nps > 100 k

For 77 pC, actual number of electrons is 480 M particles.

Optimum beamline parameters

Beam line parameters, which give bunch length of 0.63 mm and normalized rms emittance of

0.56 mm mrad

*:RF phase from maximum acceleration.

Time evolution of beam parameters

(1) Normalized rms emittance (2) Rms beam size and bunch length

(3) Kinetic energy and energy spread

Normalized rms emittance： 0.56 mm mrad

Bunch length：0.63 mm

Kinetic energy：8.2 MeV

Time evolution of phase space distribution

cathode

1st solenoid

2nd solenoid Bunching cavity Entrance of SRF 5 quadrupoles

Exit of merger

Normalized rms emittance：

0.56 mm mrad

Bunch length：0.63 mm

Kinetic energy：8.2 MeV

Main SRF and injector SRF

35

Super conducting cavities

Injector Cavity ・ Frequency 1.3 GHz ・ Eacc = 14.5 MV/m ・ High current CW operation, 100mA

Input coupler should handle total of 1MW. ・ Double feed for each cavity ・ Input power : 167 kW/coupler

main linac cavity ・ Frequency 1.3 GHz ・ Eacc = 15 ～ 20 MV/m ・ Energy recovery ・ High current CW operation, >100mA

Due to CW high current operation, strong HOM damping is essential to avoid beam instabilities and large heat loads.

Cryomodule design for cERL injector

Input coupler

(double feed)

Cavity : 3 x 2-cell cavities

Slide-Jack tuner and piezo tuner

4 or 5 coaxial HOM coupler

s for one cavity

e-

Vacuum vessel

Cryomodule development for Main linac cavity

Input coupler ・ 20kW CW (total reflection) ・ High power tests are in progress

First module with two cavities for cERL project

HOM damper ・Handle 150W HOM power ・Operation at 80 K

37

3

8

Development of Superconducting Cavities

Injector Cavities

2-cell cavity design

Medium gradient: 7.5 - 15 MV/m

High input power: 85-170 kW/coupler

Improved HOM coupler design

Status:

Achieved field gradient of 40.9MV/m in pi-mode without HOM pick-up probes.

Prototype cavity. Result of vertical test.

K. Watanabe et al., SRF2009, pp. 359-363.

K. Watanabe et al., LINAC2010, to be published.

Main-Linac Cavities

9-cell cavity design

HOM damping with large beam pipes/absorbers

High beam current: 200 mA

CW operation with 15 - 20 MV/m

Status:

Although the large beam pipe size is not good for high gradient, the field gradient of 25 MV/m was achieved !!

Q0-Eacc curve of vertical test.

K. Umemori et al., SRF2009, pp. 355-358.

K. Umemori et al., LINAC2010, to be published

3

9

Development of 1.3 GHz High-Power Source

• Three 300-kW klystrons will be used in the injector.

• A 1.3-GHz, 300-kW klystron (E37750) was successfully develo

ped at Toshiba.

• Output rf power of 305 kW (efficiency: 63%) could be produce

d at Toshiba.

• We constructed a test bench for high-power input couplers at K

EK.

Gain curves of the klystron

Frequency 1300 MHz

Heater voltage 10.5 V

Heater current 14.5 A

Beam voltage 49.5 kV

Beam current 9.75 A

Output power 305 kW

Input power (at sat.) 34 W

Beam perveance 0.89 P

Efficiency 63.2%

Gain 39.5 dB

Operation parameters of the 300-kW klystron.

Testing at Toshiba. High-power test bench at KEK. S. Fukuda et al., 6th Conf. of Particle Acc.

Society of Japan, Aug. 2009 [in Japanese].

Arc section

41

Optical matching with the injector does not finish.

The bx function is set to 5 m to suppress the emittance growth due to CSR wake.

The dispersion function is non-zero at the end of the dump line to avoid the beta function becomes huge.

Quadrupoles for laser-ICS does not use.

Quad for laser-ICS

Dεnx due to CSR wake is huge at the low

electron energy, 35 MeV

Transverse beam size after the energy re

covery can be huge.

Preliminary 1 loop 35 MeV Optics

42

Results of Tracking 35MeV, 77pC, n = 0.3 mm-mrad, sz = 3 ps, particle = 1E6

8E-6 [m] 3E-3 [m] 6E-4 [m] Cavity

arc

arc

arc arc arc arc

nx sx sy

• Maximum beam rms size – In the SC Cavity ： sx=0.87mm

– In the Dump line： sx=3.1mm

• Maximum nx – Just after energy recovery：6E-7

– Dump line：7E-6

• Vertical rms beam size is smaller than 1mm.

Maximum beam size

at Dump line In the SC cavity

after energy recovery

4 mm 10 mm

1 mm 1 mm