2015/8/7
加速器学会

FROL10

レーザー駆動陽子加速のための水素クラスターターゲットの特性評価

神野智史#, A), 田中宏尭B), 金崎真聡C), 榊泰直C),近藤 公伯C),松井隆太郎D), 上坂充A), 岸本泰明D), 福田祐仁C)Satoshi Jinno A), Hirotaka Tanaka B), Masato Kanasaki C), Hironao Sakaki C), Kiminori Kondo C),
Ryutaro Matsui D), Mitsuru Uesaka A), Yasuaki Kishimoto D), Yuji Fukuda C)A) The University of TokyoB) Kyushu UniversityC) Japan Atomic Energy AgencyD) Kyoto University1

Laser driven ion acceleration using cluster targets
1017 - 1019 W/cm2Single shot large lasera few shot/day
X10High rep. rate small laser~Hz

CO2 cluster

Background gas
CO2 + HeY. Fukuda et al., Phys. Rev. Lett. 103, 165002 (2009)
Y. Fukuda, S. Jinno et al., Radiat. Meas. 50, 92 (2013)

Magnetic-field assisted ion acceleration

Tenfold enhancement ofacceleration ion energy
T. Nakamura, et al., Phys. Rev. Lett. 105, 135002 (2010)

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Coulomb explosion of clusters
K. Nishihara, et al., Nucl. Instrum. Meth. A 464 (2001) 98–102.

Maximum ion energy obtainable from “pure” Coulomb explosion:2Rn2200Emax = 300Z 2 × =276Z×R(μ m) MeV22-30 5×10 cm  1μ m Ex) H2 cluster
44 MeV (dia. 800 nm) <= good to trigger nuclear reaction
276 MeV (dia. 2000 nm) <= good for cancer therapy

Laser intensity required to remove all electrons from a cluster:
4.6 ×10 22 cm -3  R0 a0 = 34 2 ×
 = 46.11× R0 (μ m)22-3 
5 ×10 cm  1μ m Ex) H2 cluster
7x1020 W/cm2 (dia. 800 nm) <= good to trigger nuclear reaction
4x1021 W/cm2 (dia. 2000 nm) <= good for cancer therapy
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The “J-KAREN” : Intense Laser Facility at JAEA-KPSI
Under a major upgrading
1 PW mode (40 J, 30 fs, 0.1 Hz) coming soon…
1021 - 1022 W/cm2
H. Kiriyama et al., Opt. Lett. 37, 3363 (2012).
Submicron size H2 cluster
Maximum energy
by Coulomb explosion：e-eee-ee-e-e-

44 MeV (dia. 800 nm)+++ + +++ ++++ +++ ++Coulomb explosion

In the recent simulation study, it is expected thatthe protons have the directionality.
Y. Fukuda, R. Matsui, Y. Kishimoto et al., 15th APRS, Kyoto, (2014).
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Purpose
Formation of hydrogen cluster
Small van der Waals’ force
Cooling the pulse valve

Pulse valve cooled by theliquid helium

Previous study
Liquid nitrogen cooling
Cluster size ～10 nm
T. Ditmire, et al., Phys. Rev. Lett. 78, 3121 (1997)
S. Sakabe, et al., Phys. Rev. A 69, 023203 (2004)

Theoretical prediction of thehydrogen cluster size distribution
is difficult.

Coulomb explosion: about 10 keV

Target diagnosis
Size measurement using
Mie scattering Investigation of the cluster formation condition
 Development of the formation model
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Measurement principle of particle size
Applicable size: 0.1 µm ~ 10 µm

Apparatus for measuring cluster size

(For the size greater than wavelength order)
Incident lightLens(f = 750)

Nd:YAG laser
Wavelength: 532 nm
Energy: 100 μJ
Pulse width: 20 μs
Repetition rate: 1 HzPMT(θ = 3~108º)NozzleMie scattering

Band pass filter

Forward scattering increases with the size

Need to consider the anisotropy

Measurement of scattering angle
distribution to size evaluation

PMT(reference)

Iris
Lens

Specification
Vacuum: ~10-6 Pa
Measurement time: 30 sec./1 plot
Angular resolution: 0.5 deg.

6 / 15Size analysis algorithm
Solve the inverse
problemSize distribution,,

 Non-negative least square method
Scattering coefficient foreach size by Mie theory

Angular distribution
obtained from experiments

102

Scattering coefficient103

x=3101

 Phillips-Twomey method(to obtain a smooth solution)x = 2.5x=2100Size distribution:x = 1.510-1
x=110-2

1020204060Angle / degree

80100

04080120Angle / degree

160n(x)In te n s ity / a rb . u n tis

104

1.0

1.5

2.0x

2.5

3.0

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Summary Development of submicron-size H2 clusters
 Constructed the nozzle with the cryostat
 PIC simulation for H2 clusters @ 1022 W/cm2
 Several tens MeV “impurity free” protons from PW lasers

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