Stable Beam Operation in cERL for Medical and Industrial Application at KEK

Hiroshi Sakai (KEK)on behalf of Compact ERL Development Team

• Introduction of Compact ERL (cERL)

• Long-term operation of SRF cavities and efforts to keep stable beam operation in cERL• Medical and industrial application in cERL at KEK

• Beam operation for 99Mo production in cERL (Medical Application)

• Beam operation for IR-FEL production in cERL (Industrial Application)

• Summary

19 pages

High Energy Accelerator Research Organization (KEK)M. Adachi, D. Arakawa, S. Eguchi, M. Fukuda, T. Furuya, K. Haga, K. Harada, N. Higashi, T. Honda,Y. Honda, T. Honma, X. Jin, E. Kako, Y. Kamiya, R. Kato, H. Kawata, Y. Kobayashi, Y. Kojima,T. Konomi, H. Matsumura, S. Michizono, C. Mitsuda, T. Miura, T. Miyajima, H. Miyauchi, Y. Morikawa,S. Nagahashi, H. Nakajima, N. Nakamura, K. Nakanishi, K. Nigorikawa, T. Nogami, T. Obina, F. Qiu,H. Sagehashi, H. Sakai, M. Shimada, T. Shioya, M. Tadano, T. Tahara, T. Takahashi, R. Takai, H. Takaki,O. Tanaka, Y. Tanimoto, K. Tsuchiya, T. Uchiyama, A. Ueda, K. Umemori, M. Yamamoto

National Institutes for Quantum and Radiological Science and Technology (QST)R. Hajima, K. Kawase, R. Nagai, M. Sawamura, M. Mori, N. Nishimori

National Institute of Advanced Industrial Science and Technology (AIST)T. Sato, M. Kakehata, H. Yashiro

Hiroshima University M. Kuriki

National Institute of Technology, Akita College F. Sakamoto

SLAC N. P. Norvell

Institute of Modern Physics (IMP) CAS China Z. Yang

Compact ERL Development Team

(1) Introduction to cERL

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Compact ERL (cERL)

Compact ERL (cERL) has been constructed in 2013 at KEK to demonstrate energy recovery with low-emittance, high-current CW beams of more than 10 mA for future multi-GeV ERL [1]. 1mA ERL achieved in 2016 at cERL [2].

λ/2

Injector

FEL SR

Main linac

Beam dump

Principle of Energy recovery linac (ERL)

To demonstrate 100% energy recovery stably, stable SRF operation is important under high current beam operation

[1] M. Akemoto, et al., ”Construction and commissioning of the compact energy-recovery linac at KEK”, Nucl. Instrum. Meth. A, 877, 197-219 (2018)[2] T. Obina, et al., “1 mA Stable Energy Recovery Beam Operation with Small Beam Emittance”, Proc. of IPAC2019, (Melbourne, Australia ) p1482-1485, (2019)

Compact ERL (cERL) in KEK

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©Rey.Hori/KEK

Injector LINAC

Main LINACCircumference ~ 90m

Marger

Beam Dump

9-cell SC cavity2-cell SC cavity

Buncher

Photocathode DC gun(Not SRF gun)

RF frequency= 1.3 GHz

Nominal beam energy 35 MeV 17.5-19.5 MeVNominal Injector energy 5 MeV 2.9-5 MeVBeam current 10 mA (initial goal)

100mA (final)Normalized emittance 0.1 ‒ 1 mm⋅mradBunch length(bunch compressed)

1-3ps (usual)100fs (short bunch)

Design parameters of the cERLPink is present value

Injector & Main linacmade by MHI.

Main linac cryomodule9-cell cavity (named as ERL-model2)× 2HOM damped (for 100mA BBU suppression)

(main linac design) Input power : 20kW CW Eacc: 15 MV/mUnloaded-Q: Q0 > 1×1010

(Injector design) Input power : 180kW/coupler (10mA, max 10MeV) now 10kW/coupler Eacc: 15 MV/m（max 10MeV）

Unloaded-Q: Q0 > 1×1010

Injector linac cryomodule2-cell cavity × 3Double input coupler

Energy recovery done in main linac

H. Sakai, E. Cenni, K. Enami, T. Furuya, M. Sawamura, K. Shinoe and K. Umemori, Phys. Rev. Accel. and Beams 22 022002-1 – 022002-22 (2019)

K. Watanabe, S. Noguchi, E. Kako, K. Umemori, and T. Shishido, Nucl. Instrum. Methods Phys. Res. A 714, 67 (2013)

cERL beam operation for Applications • Superconducting accelerator with ERL scheme gives us high current linac-

based electron beam (~10mA) with high quality of the electron beam such as small emittance, Short pulses.

• The unique performance (high current, low emittance, short bunch with ERL) gives us several important industrial applications as follows.

• High resolution X-ray imaging device for medical use • Nuclear security system (gamma-ray by LCS)• (1) RI manufacturing facility for nuclear medical examination• (2) IR-FEL experiment with high current ERL beam• (3) Intense THz light generation with ERL

Already achieved these application by using Laser Compton Scattering (LCS) Exp. In 2015

Our targets in a few year (2018-2020)

Plan of cERL beam operation (2018~2020)• New beam line for 99Mo RI production & material

irradiation in cERL. (from 2019) • We will produce FEL with this high current beam in the IR-

FEL regime. (POC of EUV-FEL plan) Including high charge beam operation (~60pC).

• < 200fs bunch operation with THz generation (RCDRexperiment)

New beam line for 99Mo& material irradiation

cERL beam line

IR-FEL undulatorNew THz beam line

This talk

Y.Honda, et. al., “High-efficiency broadband THz emission via diffraction-radiation cavity”, Phys. Rev. Accel. Beams 22, 040703 (2019)

See detail for THz operation

T. Akagi, et., al. “Narrow-band photon beam via laser Compton scattering in an energy recovery linac” Phys. Rev. Accel. Beams 19, 114701 (2016)

(2) Long-term operation of SRF cavities and efforts to keep stable beam operation in cERL

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Basically we applied the pulse processing at the beginning of each period [3].

We briefly show 3-years operation status (8 periods) for medical and industrial application from FY 2018-2020.Period(operation

time)

Energy[MeV]

Current[mA] (Burst

,CW)

Comments

2018/38th phase(2 weeks)

17.5(Inj

3MeV)

Burst 60 pC/ bunch

• High charge beam study• THz radiation experiment

2018/69th phase(4 weeks)

17.5 Burst 60 pC/ bunch

&1 mA (CW)

• High charge beam study• THz radiation experiment• 1mA CW ERL beam

operation again2019/4

10th phase(4 weeks)

17.5 Burst 60 pC/ bunch

• High charge beam study• THz radiation • test of RI beam line

2019/611th phase(4 weeks)

17.519.5

Burst 60 pC/ bunch&

CW beam (<10μA)

• High charge beam study• THz radiation • start RI production and

irradiation experiment at RI beam line

Period(operation

time)

Energy[MeV]

Current[mA]

(Burst ,CW)

Comments

2019/1012th phase(4 weeks)

17.5 19(Inj 4MeV)

Burst 60 pC/ bunch & CW

beam (<10μA)

• High charge beam study• RI production and

irradiation experiment at RI beam line

2020/313th phase(5 weeks)

17.5(Inj 5MeV)

Burst 60 pC/ bunch

• IR-FEL operation by U1 undulator

2020/613th phase(5 weeks)

17.5(Inj 5MeV)

Burst 60 pC/ bunch &CW beam (<10μA)

• FEL operation by 2 undulaors

• RI production at RI beam line.

• Inj. Cavity became worse but recovered by processing

2021/2-314th phase(7 weeks)

17.5(Inj 5MeV)(480 keVGun)

Burst 60 pC/ bunch

• FEL production by 2 undulaors

• THz radiation • test of RI beam line with

high energy

We note that from 2017 (7th phase), one of the main linac cavity suffered from the thermal breakdown due to unknown burst event. Therefore, in 2018 beam energy reduced from 20MeV to 17.5 MeV [1]. How do we overcome field reduction and keep stable operation ?

[3] H.Sakai et. al., Proc. of LINAC18, THPO008, p695

Recovery by pulse processing of injector cavity under sudden FE increase

Once FE onset became worse

After pulse processing, field emission onset recovered to more than 8MV/m , higher than nominal value.

During 3 years operation, once we met sudden FE increase on 2020.June.18.-> It is difficult to operate when FE onset was decreased below 7 MV/m.

Before pulse processingNominal field of 5MeV operation(7MV/m)

7MV/m

Courtesy of E.Kako

Even though sudden FE increased, high peak pulse processing worked well for injector cryomodule. keep stable operation

FE created

final

After pulse processing

Pulse processing condition 0.5ms & 5ms with 10Hz >15 MV/m field

Nominal field of 5MeV operation(7MV/m)

7MV/m

Main linac Q-value history

Due to the low Q-value of ML1, first we need to reduce the field down to 17.5 MeV in 2018.

Cavity kept Q0 ~2 x 109

on ML1 after unknown burst event

Cavity kept Q0 ~6 x 109

on ML2 at 8.6 MV from 2015 to 2020

Burst event(2017)

This Q-value is not determined by RBCS but by Rres.

No.2 cavityNo.1 cavity

Total performance after changing He pressure

Total energy INj1(MV/m) INj2(MV/m) INJ3(MV/m) ML1(MV) ML2(MV) He pressure He flow

17.5 MeV 5.49 4.38 3.49 5.5 7.65 3.0 kPa 71.9 m^3/h

19.5 MeV 5.49 4.38 3.49 6 9.15 3.5 kPa 90.2 m^3/h

(17.5MeV operation)

19.5MeV operation, we could keep more than 1 hour by changing He pressure.Injector 4 MeV operation

3.5kPa

3.0kPa

3.0 kPa : 1.99 K3.5 kPa : 2.04 KIf Rs is dominated by Rres, we have little difference of Rs between 3.0 kPa and 3.5 kPa.

On the other hand, actual cryocapacity is linear to the pressure of the He pressure tank. In our case3.0 kPa : 85 m^3/h3.5 kPa: 99 m^3h

We tried to change the He pressure from 3.0 kPa to 3.5 kPa and tried higher energy operation.

From this test, we will operate under 3.5 kPa and can increase the beam energy 19.5 MeV again. obtain more margin for stable beam operation.

(2019/6/18)

(19.5MeV operation)

He flow

Inj1 (MV/m)

Inj2(MV/m)

Inj3(MV/m)

ML2(MV)

ML1(MV)

(3) Medical and industrial application in cERL at KEK

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(A) Beam operation for 99Mo production in cERL (Medical Application)(B) Beam operation for IR-FEL production in cERL (Industrial Application)

Concern about the stable supply of 99Mo / 99mTc• 99Mo is almost 100% imported, even though the

largest number of applications in nuclear medicine diagnosis

• Problem of the stable air transportation(Problem caused by volcanic eruption in the past)• Most 99 Mo is manufactured in nuclear reactor• Due to the aging of nuclear reactors, stable supply

in the future is a big issue

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A state of brain blood flow revealed by nuclear medicine diagnosis by 99 mTc

Development of RI manufacturing (99 Mo / 99

mTc) by using accelerator for stable supply

Required Specification for accelerator (final)

• 20 ~ 50 MeV electron beam• Several mA to 10 mA (final)A few 10MeV

Electron Beam Bremsstrahlung

99Mo

(A) RI manufacturing facility for nuclear medical examination (99Mo/99mTc)

• The test irradiation of electron beams to a multiple molybdenum target will be done from 2018 to 2020 produce 99Mo and check the yield of the production in order to realize a real machine with large electron beam power.

• start 10uA with 20 MeV (max) electron CW beam

• This project was done under research contract with “Accelerator Inc.”https://www.accelerator-inc.com/

Motivation: get several knowledges to design a target system for large irradiation power such as a practical technique for 99Mo production, target thermal design, extraction method of 99mTc

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DC GunSRF Injector linacSRF Main linacIrradiationsection

No energy recovery in irradiation operation

Electron Beam : Max Power 200W

Available beamBeam repetition Continuous Wave

Max energy (MeV) 21Max current (µA) 10Max power (W) 200Energy spread

(measured) 5×10-4

beam size atTarget (measured) σ ~1.5 mm

THOO02

Aluminum capsule target holder

Typical trend of beam current(faraday cup set on the same position of target)

9 μA(CW)

17.5MeV case

30min.

Beam current is very stable

cERL – irradiation beam line

Gun current

100Mo targets with 1mm disks and 9mm disks in target folder

e- beam

Courtesy of Y.Morikawa, N.Higashi, K.Harada, M. Yamamoto, H.Matsumura and A. Toyoda

Y. Morikawa, et al., “New Industrial Application Beamline for the cERL in KEK”, Proc. of IPAC2019, (Melbourne, Australia ) p3475-3477, (2019)

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Photon was created by bremsstrahlung of target.RI was created by gamma-n reaction by using these photons.

Longitudinal profile of measured IP image RI (99Mo) Simulation results of photon flux (< 8MeV)

・Calculated by FLUKA・Electron Energy : 17.5MeV・Transport Cut off : 8MeV

・Experiment at cERL・Sample : Plate of Metal MoSize : 35mm×L70×t1(mm)・Electron Energy : 17.5MeV

・Experiment at cERL・Sample : Disk of Metal MoSize : φ35mm×t1(mm)・Electron Energy : 19.5MeV

Depth 1cmOn the surface 0cm Depth 2cm

Depth 3cm Depth 4cm Depth 5cm Depth 6cm

Meaasured transvers profile of –IP image of different positionsIP-setup

THOO02

Clear beam profiles were obtained by using stable cERL beam.

By using stable cERL CW beam, we could clear RI image and this profile are almost consistent with our simulation.First data was summarized in Press release (2019.Oct.18) : https://www.kek.jp/ja/newsroom/2019/10/18/1400/and detailed analysis will be published in a peer review journal.

Profile was almost consistent with simulation

Irradiated targets in capsule under cERLbeam

Results of RI production of 99Mo Courtesy of Y.Morikawa, N.Higashi, K.Harada, M. Yamamoto, H.Matsumura and A. Toyoda

Main high-power laser in MIR range is CO2 laser only → Insufficient understanding of basic phenomena required for processing

[Target of this project]

Ave.

pow

er

0.1W

10W

1kW

InfraredVisibleUV

CO2Laser

FiberLaser

YAGLaser

DiodeLaser

Wavelength ranges of lasers

Project theme founded by NEDO (Ministry of Economy, Trade and Industry) “Development of high-power mid-infrared lasers for high-efficiency laser processing utilizing photo-absorption based on molecular vibrational transitions.”

KEK’s missionDevelopment of high-power IR-FEL (10 ~ 20 μm) & processing material

(B) IR-FEL production in cERLOrganic materials (Resin, Engineering plastic) : light-weight, low-cost, high-functional Recently, the use of organic materials has been increasing. Processing methods : Machining, Molding, Laser processing (CO2, Fiber)

KEKcERL

These organic materials have vibration absorption in the mid-infrared region

A tunable high-power laser is required to create a database for processing!

10.6μm

New Undulators for FEL

Beam Energy 17.5 - 19.0 MeVInjector Energy 3.0 - 5.0 MeVE-Gun Energy 500 keV (or 480 keV)Bunch repetition 1.3 GHz (or 81.25 MHz)Average current 1 mA (or 5 mA ) in CWOperation mode CW or Burst

Requirement of the wavelength range of IR-FEL(10〜20um)

cERL FEL layout & operation During FEL optimization, we operate Burst mode

Burst mode (FEL&e-beam tuning)Macro pulse of 0.1 ~1 μs at 1 - 5 Hz

12.3 ns (81.25MHz)0.77ns (1.3 GHz)

60-pC bunch

Bunch repetition: 1.3 GHz or 81.25 MHz

Our target:1W level IR-FEL(81.25 MHz)~12nJ/pulse

Beam parameter• Energy : 17.5 (– 19.0) MeV• Bunch charge : 60 pC• Repetition : 81.25 MHz• Bunch length : 0.5 – 2 ps (FWHM)• Energy spread : 0.1%• Norm. emittance : 3 π mm mrad

Undulator parameter• Type: APU (Planar)• Gap: 10 mm (Fixed)• K: 1.42• Period λu : 24 mm• Total length : 3 m• No. of Undulator : 2

Undulator #1 Undulator #2

FEL monitor port#1

FEL monitor port #2

Setup of cERL-FEL

Two 3m undulators

Only FEL was reflected and electron went through the hole

electron

FEL profile at mirror

FEL

Operation was done by burst mode

Bunch length compressed in this arc section

First IR-FEL production in cERL

Undulator #1(U1)

Undulator #2(U2)

FEL tuning (by using AI)

Detailed results will be submitted to NIM-A

Beam operation was done under burst mode1.3 GHz, 5Hz repetition, 100ns macropulse

20:0

0

17:0

0

MCT MCT

Both lights come from U1 and U2 were measured by HgCdTe detector (MCT).

7% r.m.s

By using FEL optimization by using AI under stable cERL beam condition, we successfully obtained 5~10 times higher light signal from U2 than that from U1.FEL was produced. And the light intensity almost satisfied our requirements.

30 min.

FEL light was very stable.We tuned the many components to get higher light at U2 end

In detail, please seehttp://arxiv.org/abs/2106.13247

Summary• Show our status of cERL at KEK . High current beam operation of 1mA was achieved at

cERL. plan to increase 10 mA.• We made efforts for keeping SRF cavities performance by processing and cryogenic

control in cERL to keep stable beam operation. Thanks to this efforts, we carried out stable beam operation as follows.

• cERL now move to use for the industrial application by using SCRF technology. 99Mo beam line was built for RI production with CW beam of 10uA and successfully produce 99Mo.

• In order to demonstrate ERL-SASE-FEL scheme, IR-FEL production started in cERL. High power IR-FEL with SASE scheme was produced by constructing 2 x 3 m undulators in cERLbeam line based on the budget of NEDO project in Japan.

Our SRF technology will promote high power irradiation beam production with high energy such as RI production. Furthermore, for more higher light source of EUV-lithography,10 kW class high power EUV light source is NOT just a dream from the experience of cERL in KEK with 10mA beam. EUV-SASE-FEL

under ERL scheme

10kW EUV light

cERL EUV-FEL

800MeV 10mA

Acknowledgements• The irradiation beamline, target system and extra shieldings are fully

supported by Accelerator Inc. and all these R&D are done under the consignment contract.

• The radioisotope generations are the joint research with Chiyoda TechnolCorporation

• FEL production work is based on results obtained from NEDO project "Development of advanced laser processing with intelligence based high-brightness and high-efficiency laser technologies (TACMI project).“

• Part of this work was supported by JSPS KAKENHI Grant Number 18H03473.• We would like to express our gratitude to all members of safety-shift under

cryo and beam operation.

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