JAEA Nobuyuki Nishimori
Review of experimental results from high brightness dc guns: Highlights in FEL applications
Outline • Introduction • The DC gun-based Cornell photoinjector • High voltage DC gun at JAEA • High gradient and high voltage DC guns at KEK and Cornell • Summary
N. Nishimori FEL15 at Daejeon 2 Aug. 24, 2015
High repetition rate FEL Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 3
10 kW FEL for EUV lithography
https://portal.slac.stanford.edu/sites/lcls_public/lcls_ii/Pages/design.aspx
MHz XFEL
N. Nakamura, “An ERL-based high-power free-electron laser for EUV lithography”, 2015 EUVL Workshop
LCLS-II injector specifications bunch charge 95 % en (mm) peak current (A) average current (mA) 20 pC 0.25 5 0.02 100 pC 0.40 10 0.1 300 pC 0.60 30 0.3
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 4
• The Cornell photoinjector demonstrated cathode thermal emittance dominated beam satisfying LCLS-II specifications in 2015.
• The Cornell photoinjector demonstrated average beam current of 75 mA much higher than LCLS-II specifications in 2013.
C. Gulliford et al., Appl. Phys. Lett. 106, 094101 (2015).
L. Cultrera et al., Appl. Phys. Lett. 103, 103504 (2013); B. Dunham et al., Appl. Phys. Lett. 102, 034105 (2013).
• Reliability (long-term operational experience) is important especially for industrial application such as 10 kW EUV FEL for lithography.
Cathode thermal emittance
bunch charge en,th (mm) 95 % en (mm) LCLS-II specifications
20 pC 0.11 0.25 100 pC 0.24 0.40 300 pC 0.41 0.60
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 5
I.V. Bazarov et al., Phys. Rev. Lett. 102, 104801 (2009).
𝜀𝑛,𝑡ℎ = 𝜎𝑥
𝑀𝑇𝐸
𝑚𝑐2
MTE: cathode mean transverse energy sx: initial rms beam size q: bunch charge E: applied cathode field
MTE = 140meV (corresponds to 0.5mrad) : NaKSb cathode E = 4.3 MV/m: 400 kV DC gun @Cornell
The applied cathode field E should be greater than image charge field . 𝑞 𝜀0 𝜋 2𝜎𝑥 2
q 𝐸 𝐸 −
𝑞
𝜀0𝜋 2𝜎𝑥 2
D. Nguyen et al., “RF Linac for High-Gain FEL Photoinjectors”, LA-UR 14-23995
≥ 1
2
𝑞
𝜋𝜀0𝐸
𝑀𝑇𝐸
𝑚𝑐2
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 6
Cornell photoinjector
Courtesy of Adam Bartnik
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 7
400 kV DC Gun + Bunching/Focusing
400 kV DC Gun
50 MHz 520 nm
Cornell photoinjector
Courtesy of Adam Bartnik
NaKSb: MTE = 140 meV, QE roughly 5%
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 8
400 kV DC Gun + Bunching/Focusing
Short SRF Linac 5 – 15 MeV
400 kV DC Gun
50 MHz 520 nm
Cornell photoinjector
Courtesy of Adam Bartnik
Superconducting RF Cavities (niobium)
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 9
400 kV DC Gun + Bunching/Focusing
Short SRF Linac 5 – 15 MeV
400 kV DC Gun
50 MHz 520 nm
Cornell photoinjector
Courtesy of Adam Bartnik
Superconducting RF Cavities (niobium)
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 10
400 kV DC Gun + Bunching/Focusing
Short SRF Linac 5 – 15 MeV
400 kV DC Gun
50 MHz 520 nm
Cornell photoinjector
Courtesy of Adam Bartnik
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 11
400 kV DC Gun + Bunching/Focusing
Short SRF Linac 5 – 15 MeV
6 Dimensional Phase Space Diagnostics + High Power Beam Dump
Viewscreen
Emittance Measurement System
1st Slit 2nd Slit Deflecting Cavity
Faraday Cup + Viewscreen
Faraday Cup
400 kV DC Gun
50 MHz 520 nm
Cornell photoinjector
Courtesy of Adam Bartnik
Beam based alignment with near-zero bunch charge
• Measured beam response of each injector component.
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 12
C. Gulliford et al., Phys. Rev. STAB 16, 073401 (2013).
Bunch charge εn,x(100%) εn,y(100%) 19 pC 0.33 mm 0.20 mm 77 pC 0.69 mm 0.40 mm 300 pC 1.36 mm 0.79 mm
Courtesy of Adam Bartnik
• Performed beam based alignment of gun, buncher, SRF cavities, and solenoids within 50 mm accuracy.
• Confirmed the emittance and beam sizes are reproduced by GPT simulations.
• Loaded optimum parameter set for each bunch charge and measured emittance and longitudinal profile.
Increasing solenoid current
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 13
Origin of asymmetry • Found a beam asymmetry after the first solenoid. • Likely culprit: stray quad field in the solenoid.
Courtesy of Adam Bartnik
Increasing solenoid current
Quad wiring
• Mitigated with a correcting quadrupole coil.
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 14
Q (pC) Ipeak Target (A) Ipeak (A) εn Target (95%, mm) εn (95%, mm) εn,th /εn 20 5 5 0.25 H: 0.18, V: 0.19 60%
100 10 11.5 0.40 H: 0.32, V: 0.30 80% 300 30 32 0.60 H: 0.62, V: 0.60 70%
C. Gulliford et al., Appl. Phys. Lett. 106, 094101 (2015).
Courtesy of Adam Bartnik
Emittance and longitudinal profile measurements
Aug. 24, 2015 15
Effects of the Laser Shape N. Nishimori FEL15 at Daejeon
C. Gulliford et al., Appl. Phys. Lett. 106, 094101 (2015).
Courtesy of Adam Bartnik
Effects of the laser shape
Aug. 24, 2015 16
Effects of the Laser Shape N. Nishimori FEL15 at Daejeon
Ideal Shape
C. Gulliford et al., Appl. Phys. Lett. 106, 094101 (2015).
Courtesy of Adam Bartnik
Effects of the laser shape
Aug. 24, 2015 17
Effects of the Laser Shape N. Nishimori FEL15 at Daejeon
Ideal Shape
C. Gulliford et al., Appl. Phys. Lett. 106, 094101 (2015).
Courtesy of Adam Bartnik
Effects of the laser shape
Aug. 24, 2015 18
Effects of the Laser Shape N. Nishimori FEL15 at Daejeon
Ideal Shape Measured Shape
C. Gulliford et al., Appl. Phys. Lett. 106, 094101 (2015).
Courtesy of Adam Bartnik
Effects of the laser shape
Development of a 500 kV gun at JAEA
Field emission seg
men
ted
cera
mic
s
guar
d rin
gs
R. Nagai et al., RSI 81, 033304 (2010). N. Nishimori et al., PRSTAB 17, 053401 (2014).
• a segmented insulator • 160 mm acceleration gap
stal
k
N. Nishimori FEL15 at Daejeon 19
acceleration gap
Time (hours) 0 50 200 100 150
0
100
300
500
600
Hig
h vo
ltage
(kV
) 200
400
Aug. 24, 2015
1.8mA@500keV
0
100
300
500
Hig
h vo
ltage
(kV
)
Bea
m c
urre
nt (m
A)
0.0
0.5
1.0
1.5
2.0
2.5
200
400
0 2 6 1 5
600
Time (min.)
500keV beam generation N. Nishimori et al., APL 102, 234103 (2013)
N. Nishimori FEL15 at Daejeon 20
500-kV gun
beam dump radiation shield
bending magnet
solenoid
1.2
0 20 10 30 40 50
1mA@440keV
Time (min.)
Bea
m c
urre
nt (m
A)
0.0
0.4
0.8
30 min.
60 0
100
300
500
Hig
h vo
ltage
(kV
)
200
400
600
Aug. 24, 2015
Injector acc.
compact ERL (cERL) at KEK N. Nishimori FEL15 at Daejeon 21
gun
Gun assembly at cERL
Oct. 2012 Transport of gun from JAEA to cERL at KEK Jun. 2013 Injector commissioning 5MeV-0.3μA Mar. 2014 ERL loop commissioning 20MeV-4.5μA Mar. 2015 Laser Compton Scattering (LCS) 20MeV-80mA
Gun voltage is limited to 390kV at cERL.
Aug. 24, 2015
bunch charge en (mm) peak current (A) average current (mA) 60 pC 0.60 30 10
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon 22
Reliability and high average current are important as well as brightness.
N. Nakamura et al., “Design work of the ERL-FEL as the high intense EUV light source”, Proc. of ERL2015 (2015).
10 kW EUV FEL injector specifications after merger
cERL prototype for future ERL light sources: LCS, THz, and EUV FEL
N. Nishimori FEL15 at Daejeon 23 Aug. 24, 2015
Gun operational status for two weeks Stable operation
Interruption to enter the acceleration hall
Pressure rise caused by gate valve open and close
500 kV
Gun HV
Vacuum pressure
10-10 Pa
0 kV
390 kV
10-8 Pa
0.7x10-9 Pa
10-7 Pa
N. Nishimori FEL15 at Daejeon
Gun operational status during LCS experiment 24
100
QE
(%)
GaA
s @
530n
m
0 2
time (hours)
6 B
eam
cur
rent
(μA
)
80
60
40
20
0
Aug. 24, 2015
1
5
4
3
2
1
0
10
8
6
4
2
0
12
14
5
4
3
2
1
0
6
7
Qua
ntum
effi
cien
cy (%
)
Cha
rge
extra
ced
(C)
Jan. 2015
Feb. Mar. Apr. May
1/e life=6,000 hours
July
N. Nishimori FEL15 at Daejeon 25 Aug. 24, 2015
laser position
June
QE during the cERL operation GaAs @ 530nm
a short
a short
A Plan to 500kV operation at the cERL 26 N. Nishimori FEL15 at Daejeon Aug. 24, 2015
a short
a short
A Plan to 500kV operation at the cERL 27 N. Nishimori FEL15 at Daejeon Aug. 24, 2015
addition
addition
stal
k
a short
a short
A Plan to 500kV operation at the cERL 28 N. Nishimori FEL15 at Daejeon
• Installed an additional ceramics in July 2015 • Performed HV test up to 550 kV without stalk
Aug. 24, 2015
• Install a stalk in Sep. 2015 • Perform HV test with cathode electrode • Perform beam generation in Nov. 2015
addition
addition
stal
k
Aug. 24, 2015
Time (hours)
0
100
200
300
400
500
600
Hig
h vo
ltage
(kV
)
10-9
10-8
10-7
vacu
um (P
a)
0 1 2 3 4 5 6 7
550kV for > 3hours
HV test with the additional insulator without stalk N. Nishimori FEL15 at Daejeon 29
N. Nishimori FEL15 at Daejeon 30
MOGA optimization for EUV FEL photoinjector Aug. 24, 2015
Courtesy of Tsukasa Miyajima
N. Nakamura et al., Proc. of ERL2015, MOPCTH010
bunch charge en (mm) peak current (A) 60 pC 0.60 30
10 kW EUV FEL injector specifications after merger
EUV FEL injector (merger not included)
500 kV Gun Two solenoid magnets Two injector cryomodule (Max. Eacc: 8 MV/m) Buncher
Beam Einj=10.5 MeV
1ps 2ps
en=0.30mm, 30A before merger
Q=60 pC、E=10.5 MeV 0.6
0.5
0.4
0.3
0.2
0.1
0.0
100%
em
ittan
ce(m
rad)
0 0.2 0.4 0.6 0.8 1 rms bunch length [mm]
Cathode Anode
e- beam
6.9 MV/m @ photocathode center (=E)
11.0 MV/m @ cathode ball surface
31
70 mm gap 500 kV gun at KEK
Courtesy of Masahiro Yamamoto
𝜀𝑛,𝑡ℎ ≥ 1
2
𝑞
𝜋𝜀0𝐸
𝑀𝑇𝐸
𝑚𝑐2
Vacuum pressure: ~4x10-10 Pa
32
HV conditioning test 1st day (~2.5 h)
2nd day (~4 h)
Reached 550kV in 48 trips / a short time (~7hs.)
Courtesy of Masahiro Yamamoto
10H 2H 4H 8H 8.7H 8H 8H
No breakdown happened during totally 50 hours of 500 kV-holding test.
33
HV holding test
Courtesy of Masahiro Yamamoto
Variable gap segmented insulator gun at Cornell
34
Stability test with various gaps:
Dis
char
ge R
ate
(per
min
)
50mm 30 mm 35 mm 40mm
J. Maxson et al., RSI 85, 093306 (2014)
50 mm gap
P. Slade, The Vacuum Interrupter, CRC Press, 2008
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon
Courtesy of Jared Maxson
Variable gap segmented insulator gun at Cornell
35
Stability test with various gaps:
Dis
char
ge R
ate
(per
min
)
50mm 30 mm 35 mm 40mm • Surprisingly good agreement between different HV systems.
• But what configuration is best for the beam emittance? –Turn to simulations.
J. Maxson et al., RSI 85, 093306 (2014)
50 mm gap
Recent Result from KEK
P. Slade, The Vacuum Interrupter, CRC Press, 2008
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon
Courtesy of Jared Maxson
MOGA optimizations with various gaps • Choose 3 Cornell style guns as the injector source use MOGA
• 500 kV: 70mm • 450 kV: 50 mm • 400 kV: 30 mm
36
P. Slade, The Vacuum Interrupter, CRC Press, 2008
larger field…
…smaller V
Z position within gun (mm)
𝐸𝑧 (
MV
/m
)
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon
Courtesy of Jared Maxson
Emittance vs. bunch charge with various gaps
37
Approaching thermal emittance!
Aug. 24, 2015 N. Nishimori FEL15 at Daejeon
Courtesy of Jared Maxson
100
% e
mit
tan
ce (𝜇𝑚
)
Co
re e
mit
tan
ce (𝜇𝑚
)
𝜖𝑐𝑛𝑥 =1
4 𝜋𝜌𝑚𝑎𝑥
Summary
N. Nishimori FEL15 at Daejeon 38 Aug. 24, 2015
• The DC gun-based Cornell photoinjector demonstrated cathode emittance dominated beam satisfying LCLS-II specifications with a 400 kV gun.
• Higher voltage and higher gradient gun developments with segmented insulators are in progress at JAEA/KEK and Cornell University to go beyond the Cornell photoinjector. • 500 keV beam generation from JAEA gun with 160 mm gap • 50 hours holding at 500kV with 70 mm gap at KEK gun • Experimental and numerical studies with 20-50 mm gaps at Cornell gun
• Gun operational experience for users is accumulated at the cERL.
Acknowledgements
N. Nishimori FEL15 at Daejeon 39 Aug. 24, 2015
We acknowledge Adam Bartnik, Colwyn Gulliford, Jared Maxson, Bruce Dunham, and Ivan Bazarov at Cornell University for useful discussion on the Cornell photoinjector developments. We thank Masahiro Yamamoto, Tsukasa Miyajima, Yosuke Honda at KEK, Masao Kuriki at Hiroshima University, Ryoji Nagai and Ryoichi Hajima at JAEA for helpful discussion on KEK/JAEA gun developments. This work is partially supported by JSPS Grants-in-Aid for Scientific Research in Japan (15H03594).