Studies of cERL injector

Studies of cERL injectorThursday, March 4, 2010

SLAC National Accelerator LaboratoryMenlo Park, California

Tsukasa Miyajima7th division, Accelerator Laboratory,

KEK, High Energy Accelerator Research Organization

48th ICFA Advanced Beam Dynamics Workshop on Future Light Sources

Contents1.Outline of compact ERL injector2.Beam Simulation to optimize beamline parameters3.Test beamline for cERL injector4.Future issues5.Summary

ERL collaboration team• High Energy Accelerator Research Organization (KEK)

– M. Akemoto, T. Aoto, D. Arakawa, S. Asaoka, A. Enomoto, S. Fukuda, K. Furukawa, T. Furuya, K. Haga, K. Hara, K. Harada, T. Honda, Y. Honda, T. Honma, T. Honma, K. Hosoyama, M. Isawa, E. Kako, T. Kasuga, H. Katagiri, H. Kawata, Y. Kobayashi, Y. Kojima, T. Matsumoto, H. Matsushita, S. Michizono, T. Mitsuhashi, T. Miura, T. Miyajima, H. Miyauchi, S. Nagahashi, H. Nakai, H. Nakajima, E. Nakamura, K. Nakanishi, K. Nakao, T. Nogami, S. Noguchi, S. Nozawa, T. Obina, S. Ohsawa, T. Ozaki, C. Pak, H. Sakai, S. Sakanaka, H. Sasaki, Y. Sato, K. Satoh, M. Satoh, T. Shidara, M. Shimada, T. Shioya, T. Shishido, T. Suwada, T. Takahashi, R. Takai, T. Takenaka, Y. Tanimoto, M. Tobiyama, K. Tsuchiya, T. Uchiyama, A. Ueda, K. Umemori, K. Watanabe, M. Yamamoto, Y. Yamamoto, S. Yamamoto, Y. Yano, M. Yoshida

• Japan Atomic Energy Agency (JAEA)– R. Hajima, R. Nagai, N. Nishimori, M. Sawamura

• Institute for Solid State Physics (ISSP), University of Tokyo– N. Nakamura, I Itoh, H. Kudoh, T. Shibuya, K. Shinoe, H. Takaki

• UVSOR, Institute for Molecular Science– M. Katoh, M. Adachi

• Hiroshima University– M. Kuriki, H. Iijima, S. Matsuba

• Nagoya University– Y. Takeda, T. Nakanishi, M. Kuwahara, T. Ujihara, M. Okumi

• National Institute of Advanced Industrial Science and Technology (AIST)– D. Yoshitomi, K. Torizuka

• JASRI/SPring-8– H. Hanaki

Tsukasa MiyajimaFLS2010, March 1-5, 2010,

SLAC National Accelerator Laboratory 2

The Compact ERL for demonstrating ERL technologies



Parameters

Beam energy 35 - 245 MeV

Injection energy 5 MeV

Average current 10 - 100 mA

Acc. gradient (main linac)

15 MV/m

Normalized emittance

0.1 - 1 mm·mrad

Bunch length(rms)

1 - 3 ps (usual)~ 100 fs (with B.C.)

RF frequency 1.3 GHz

Parameters of the Compact ERL

Before constructing large-scale ERL facility, we need to demonstrate the generation of ultra-low emittance beams using key devices.

Compact ERL

East Counter Hall

100 m



cERL injector• cERL injector: to generate electron beam with lower emittance and

shorter bunch length

Compact ERL

Parameters of the Compact ERL Injector

Photo cathode DC gun

Super conducting cavity(2 cell, 3 modules)

Merger section

ERL Injector



Components in ERL injector① Photo cathode DC gun

Gun, HV power supply, driving laser system② Solenoid magnet

To compensate emittance③ Bunching cavity

Normal conducting cavity for bunching④ SRF cavities

2-cell, 3 modules⑤ Quadrupole magnets

To adjust CS parameters before merger section⑥ Merger section

To merge injected beam into return loops

⑥

⑤

④

①

②

③

500 keV 5 – 10 MeVBeam 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) Higher order dispersion in merger section(5) Coherent Synchrotron Radiation (CSR) in merger section(6) Response time of photo cathode （ It generates tail of emissio

n. ）

These effects combine in the ERL injector.

The simulation code have to include(1)External electric and magnetic field, (2)Space charge effect (3D space charge).

To obtain high quality beam at the exit of merger, optimization of beamline parameters is required.

Method to research the beam dynamics: Macro particle tracking simulation with space charge effect is used.



Beam Simulation

Particle tracking code ： GPT(General Particle Tracer)[1]Space charge calculation ： 3D mesh based methodInitial particle distribution ： beer-canNo CSR effect in merger section

d = 4 x

Initial distribution on cathode ： beer-can

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

• 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.



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 optimization①Initial laser radius (mm)②Initial laser pulse length (ps)③Magnetic field of 1st solenoid④Electric field of bunching cavity⑤Magnetic field of 2nd solenoid⑥Electric field and phase of SRF1⑦Electric field and phase of SRF2⑧Electric field and phase of SRF3⑨Magnetic 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 optimizationBunch length vs. normalized rms emittanceFor shorter bunch length, emittance is larger than the case of longer bunch length.

Normalized rms emittance0.4 ～ 0.5 mm mrad



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 for high current mode with 80 pC/bunch, 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 mradBunch length ： 0.63 mmKinetic energy ： 8.2 MeVRelated rms energy spread: 0.23 %



Time evolution of phase space distributioncathode

1st solenoid

2nd solenoidBunching cavity Exit of SRF 5 quadrupoles

Exit of merger

Bunch charge: -80 pC/bunchNormalized rms emittance ：　　 0.56 mm mradBunch length ： 0.63 mmKinetic energy ： 8.2 MeV



Summary of optimization• We have designed the injector for the cERL and carried out beam

dynamics simulation using the particle tracking code with 3D space charge effect.

• To optimize the beamline parameters, we are using multi objective method and cluster linux machine.

• At the end of the injector, we have obtained the emittance of 0.56 mm·mrad with the bunch length of 0.63 mm for the high current operation mode (80 pC/bunch).



Gun test beamline for cERL injector

NPES3, 200 kV guntransferred from Nagoya university at May 2009.

Gun Test beamline

Test area for 500 kV gun

Laser system

• Purpose of test beam line– To gain operation experience of the low energy beam.– To evaluate performance of the DC guns by an additional diagnostic line to measure

emittance and bunch length– To develop a new 500 kV gun, diagnostic system and the injector line used at cERL.

2010- middle of 2011: 200 kV gun2011 - : new 500 kV gun



Layout of gun test beamline

1st solenoid2nd solenoid

3rd solenoid 4th solenoid

1st view screen2nd view screen

1st slit(vertical)

1st slit(horizontal)

2nd slit(vertical)

2nd slit(horizontal)

The same layout as cERL injector Beam diagnostic line (emittance, Bunch length measurements)

Beam dump line

3rd view screen 4th view screen

5th view screen

deflectorBending magnet

Beam dump

Components for gun test facility• We are constructing gun test facility with 200 kV photo cathode DC gun in AR south experimental

hall, KEK. From this spring, we are going to start beam running.



Two solenoid magnets

Laser chamber

1st solenoid

2nd solenoid

Laser chamber

1st view screen monitor

2nd view screen monitorBunching cavity

From Gun

To SRF cavity

e-

e-

The layout of the cERL injector before SRF cavity.In the first test, the bunching cavity is not installed.



Beam dynamics of gun test beamline Initial parameters at point A:① Radius of initial particle

distribution ：　　 1.91 mm② Laser pulse full width ： 41.5 ps③ 1st Solenoid ： 0.039 T④ Bunching cavity ： 0 kV⑤ 2nd Solenoid ： 0.026 T

Gun 1st view screen 2nd view screen

1st slit 3rd view screen

A

Result of optimization

At 1st slit, Emittance: 0.42 mm mradBunch length: 6.7 mm



Future issues• Beamline parameter optimization for XFEL-O with 20 pC, 0.1 mm mrad.

– To obtain lower emittance, can we increase the voltage of the photo cathode gun over 500 kV?

• Beam optics matching with return loop• Establish the beam tuning method in the commissioning. • Beam simulation with CSR and Space charge effect in the merger section.

We developed CSR routine, which is effective in lower energy beam.

cf. K.-J. Kim et al., PRL 100, 244802 (2008).

R. Hajima and N. Nishimori (JAEA), Proc. FEL2008, pp. 87-89.

Beam simulation for XFEL-O• Target values for XFEL-O: < 0.1 mm mrad, 20 pC/bunch, 2 ps bunch length



Layout of beamline

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

Preliminary results

Preliminary resultsBunch charge: 20 pC/bunchGun voltage: 500 kV or 600 kV

(1) 0.6 mm (2 ps) bunch length enx = 0.14 mm mrad with 500 kV enx = 0.13 mm mrad with 600 kV


It is not so far from target value for XFEL-O. We are going to investigate the effect of gun voltage.



Summary• Beam dynamics simulation for the cERL has been carried out using 3D space

charge macro-particle tracking code. • To find the optimum parameters, which give minimum emittance and bunch

length, the parameter optimization has been carried. • For high current mode with 80 pC/bunch, we obtained the minimum emittance of

0.56 mm mrad with the bunch length of 0.63 mm.

• To design ERL components (Gun, Buncher, SRF cavities, solenoid, alignment, etc.), we have studied tolerances of errors in ERL injector.

• To evaluate performance of the DC guns, we are developing the gun test beamline in the PF-AR south experimental hall.

• From the early part of March, we are going to start beam running in the gun test beamline using NPES3 200kV DC photo cathode gun.

• For XFEL-O, the minimun emittance is calculating with 20 pC/bunch.• So far, we have obtained the minimum emittance of 0.13 mm mrad with the

bunch length of 0.6 mm (2 ps) and the gun voltage of 600 kV.



Backup slides

Effect of gun voltage





Preliminary resultsBunch charge: 20 pC/bunchGun voltage: 500 kV or 600 kVAt exit of merger

Results of Gun and solenoid beamline



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 [2] 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 optimization1.Emittance2.Bunch length

[2] Ivan V. Bazarov and Charles K. Sinclair , Phys. Rev. ST Accel. Beams 8, 034202 (2005).



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

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

Normalized rms emittance0.4 ～ 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 difference of emittance, because the bending angle of the bending magnet in the sector type (19◦ or 22◦) are larger than one in the rectangular type (16◦).

(a) Maximum emittance growth(b) Minimum emittance growthEmittance growth depends on space charge dispersion.

Beam parameter with 7.7 pC/bunch• Charge: 7.7 pC/bunch• Emittance: 0.097 mm mrad (horizontal), 0.090 mm mrad(vertical)• Bunch length: 1.3 ps

25 February, 2009 PF-ISAC Light Source Subcommittee 26

R. Hajima, et. al., “Design Study of the Compact ERL”

1D CSR routine in GPT


• We developed 1D CSR routine, which is effective in lower energy beam, e.g. beam energy of 10 MeV.

• Based on Sagan’s formula[4]

(1) Energy loss due to CSR

(2) Emittance growth caused by CSR

Layout of beamline

Using the CSR routine, we can calculate CSR effect in lower energy region, e.g. beam enegy of 10 MeV.

Tolerance of errors in ERL injector• Tolerances of errors in ERL linacs are important to design ERL components (Gun,

Buncher, SRF cavities, solenoid, alignment, etc.). • For example, to design LLRF system, tolerances of phase and amplitude error are

required.

• The tolerances were calculated using numerical space charge simulation code, GPT.

• In this presentation, we show variations of – Arrival time– Transverse emittance– Kinetic energy

at the end of merger, when gun voltage, RF amplitude or phase are varied.


Amplitude error in RF cavity

Phase error in RF cavity

Errors in ERL injector


⑥⑤

④

①

②

③

500 keV 5 – 10 MeV

• Misalignment– Emittance growth– Orbit distortion

• Laser timing jitter• Ripple of gun HV source

– Arrival time– Kinetic energy

• Amplitude error in RF cavities• Phase error in RF cavities

– Emittance growth– Arrival time– Kinetic energy– Bunch length

① Photo cathode DC gun Misalignment, laser timing jitter, ripple of gun HV

source② Solenoid magnet

Misalignment, field error③ Bunching cavity

Misalignment, amplitude and phase error④ SRF cavities

Misalignment, amplitude and phase error⑤ Quadrupole magnets

Misalignment, field error⑥ Merger section

Arrival time delay is occurred by varying kinetic energy and R56.

Example: Ripple of Gun HV source


• Arrival time• 0.1% error: -120 fs

• Normalized rms emittance• ±0.1% error: fluctuation of 3.5 %

• Kinetic energy• 0.1% error:

99.96%

Results of tolerance calculations


• Difference of arrival time at exit of merger becomes about 100 fs.• The arrival time includes the effect of R56 in the merger section.

• From the above results, we decided the requirement for design of components, as following;

• Gun HV ripple < 0.1 %• Error of RF amplitude < 0.1 %• Error of RF phase < 0.1 degree

Problem of space charge calculation in merger

• Merger section• Original routine (spacecharge3dmesh)　　　⇒　 calculated emittance is not correct.• It is clear for smaller number of particles.

• We checked the source code.

orbit（ in drift space ）

emittanceCalculated emittance depends on angle from z-axis.

Why?

Injected beam

Beam goes forward along the following orbit.

Enhanced space charge calculation in GPT• In original spacecharge3dmesh routine,　　　 direction of mesh box ： fixed to coordinate in GPT• When beam go forward along oblique line fro z-axis, 　　　 mesh size becomes coarse.

We made enhanced routine 　⇒ spacecharge3dmeshxz

Original

Enhanced routine

Spacecharge3dmeshxzThe enhanced routine can calculate the accurate emittance.

Misalignment of solenoid• Misalignment of solenoid position and angle

35

The beam parameters are calculated at exit of SRF cavities.

Result 1: Ripple of Gun HV source• Arrival time• 0.1% error: -120 fs

10 June, 2009 ERL09 36



99.96%

Timing in buncher

10 June, 2009 ERL09 37

Result 2: Amplitude error in RF cavities

10 June, 2009 ERL09 38


• Arrival time• 0.1% error: -100 fs• SCA02


100.05%• SCA03

Result 3: Phase error in RF cavities

10 June, 2009 ERL09 39

• Normalized rms emittance• ±0.1 deg. error: fluctuation of 2.5 %

• Arrival time• 0.1% error: -120 fs• SCA01


99.98%• BCA01

Studies of cERL injector

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