23P178-B
Ion Post Acceleration in Laser-Plasma Interaction
レーザー・プラズマ相互作用によるイオンの追加速D. Satoh1, K. Takahashi1, T. Izumiyama1, D. Barada1, S. Shigeo1, Y. Y. Ma2, W. M. Wang3, Z. M.
Sheng3
佐藤大, 高橋孝紀, 泉山豪, 茨田大輔, 川田重夫, Y. Y. Ma, W. M. Wang, Z. M. Sheng
1

Utsunomiya University
7-1-2, Yotoh, Utsunomiya 321-8585, Japan
宇都宮大学 〒321-8585 宇都宮市陽東7-1-22
National University of Defense Technology, Changsha 410073, China
3
Fudan University, Shanghai 200433, China
A remarkable ion energy increase is demonstrated for a post acceleration by a Laser-plasma booster.
Intense short-pulse laser generates a strong current by high-energy electrons accelerated, when an intense
short-pulse laser illuminates a plasma target. The strong electric current creates a strong magnetic fieldalong the high-energy electron current in plasma. During the increase phase in the magnetic field, thelongitudinal inductive electric field is induced for the forward ion acceleration by the Faraday law. Our
2.5-dimensional particle-in-cell simulations demonstrate a remarkable increase in ion energy by severaltens of MeV.

1. Introduction
By chirped pulse amplification, a higher laser
intensity has been realized, and high intensity
short pulse lasers are now available forexperiments and applications. On the other hand,
ion beams are useful for basic particle physics,
medical ion therapy, controlled nuclear fusion,
high-energy sources, and so on [1-3]. The energyof ions, which are accelerated in an interaction
between an intense laser pulse and thenear-critical density target, are over a few tens of
MeV [4]. The issues in the laser ion acceleration
include an ion beam collimation, ion energy
spectrum control, ion production efficiency, etc[1-5]. Depending on ion beam applications, theion particle energy should be controlled. Forexample, ion beam cancer therapy needs
100~150MeV for proton energy. Therefore, inthis paper we focus on a boost of ion beam energy
by post-acceleration in laser plasma interaction.
In this paper we propose a Laser-plasma booster
as ion post acceleration. In our study, we employ
an intense short-pulse laser and the near-criticaldensity plasma target, which consists of hydrogen.
Figures 1 shows the conceptual diagram of theLaser-plasma booster.

target has the flat-top. The edge region has a linear
density gradient from 0nc to the maximum densityof 0.5nc, and has a linear density gradient in 2λ inthe X and Y directions at the target edges. The laser
intensity is I=1.0×1020 W/cm2, the laser spot
diameter is 4.0λ, and the pulse duration is 40fs. Thelaser transverse profile is in the Gaussian
distribution, and the laser temporal profile is also
Gaussian. The laser wavelength is λ=1.053µm. The
near-critical density plasma target density is 0.5nc
and the ion beam density is 1016cm-3. The
pre-accelerated beam protons here the initial energyof 110MeV and is located at the left of the plasma
target initially. The initial proton beam size is 2λ in
X and 5λ in Y.

2. The Near-Critical Density Plasma Target
Simulation
We perform 2.5-dimensional particle-in-cellsimulations. The target model is shown in Fig.1.
The near-critical density plasma target is located in9.5λ< x <49.5λ and 19.0λ< y < 31.0λ. The plasma

Fig.1. Ion post acceleration scheme and thenear-critical density hydrogen plasma target. The
near-critical density plasma booster target provides astable inductive acceleration field, as a post accelerationof laser produced ions.

3. Post-Acceleration of The Ion Beam
Figures 2 show the distributions of accelerationelectric field Ex in MV/µm at (a) t=110fs and thedistributions of magnetic field Bz in T at (b) t=110fs.
The laser generates the high-energy electron insideof the target. A magnetic field is also formed along
the channel in the laser plasma interaction [6-8].
When the intense laser pulse propagates through theplasma, it accelerates a part of electrons. The
electrons form a high current and generate themagnetic field. In the laser plasma interaction, theion dynamics is affected directly by the electricfield and the behavior of the electrons. The
electrons form a strong magnetic field, and during
the increase in the azimuthal magnetic field theinductive strong electric field is generated [3]. The
ions are accelerated by the inductive electric field.
The inductive acceleration field moves with a speedis less than c, depending on the plasma density. At
this target density of 0.5nc, the speed of theinductive electric field is about 0.66c. Therefore,
the inductive acceleration field is appropriate forthe ion post acceleration and is rather stable.
Figures 3 shows the ion beam energy distribution at
t=50fs, 230fs and 450fs for the near-critical density
plasma target. At t=50fs shown in Fig.3 is theinitial energy of the ion beams which is not yet
accelerated. The maximum ion beam energy
reaches 171.2MeV from the initial energy of110MeV.

Fig.3. The ion beam energy distributions at t=50fs,230fs and 450fs for the near-critical density plasma
target. At t=50fs, the ion beam is not yet accelerated.
to increase the energy of the ion beam by theinductive acceleration field in the near-criticaldensity plasma target illuminated by an intense
short-pulse laser. The post-accelerated ion
maxmum energy increases from 110MeV to171.2MeV by the strong inductive accelerationelectric field. The work in this paper presents animportant method for an ion energy control in laser
plasma acceleration.
Acknowledgement
This work is partly supported by MEXT, JSPS
ILE/Osaka Univ. and CORE (Center for Optical
Research and Education, Utsunomiya Univ., Japan).
J.L. and O.K. gratefully acknowledge partial
supportbyCzech
ScienceFoundation(P205/11/1165) and Czech Ministry of Education(MSM6840770022).

References[1] K. Takahashi, S. Kawata, D. Satoh, Y. Y. Ma, D.
Barada, Q. Kong, and P. X. Wang: Phys. Plasmas
10 (2010) 093102.
[2] Y. Nodera and S. Kawata: Phys. Rev. E 78 (2008)046401.
[3] I. Velchev, E.Fourkal, and C. M. Ma: Phys. Plasmas14 (2007) 033106.
[4] T. Nakamura, S. Kawata: Phy. Rev. E 67 (2003)

026403.

Fig.2. The distributions of acceleration electric field
Ex in MV/µm at (a) t=110fs and the distributions ofmagnetic field Bz in T at (b) t=110fs.

4. Conclusions
In this paper we have proposed a laser-plasma
booster as an ion post-acceleration. We succeeded[5] Y. Nodera and S. Kawata: Phys. Rev. E 78 (2008)046401.
[6] Y. Y. Ma, Z. M. Sheng, J. Zhang, Y. T. Li, W. W.
Chang, X. H. Yuan, M. Chen, and J. Zheng: Phys.
Plasmas 13 (2006) 110702.
[7] T. Nakamura, S. V. Bulanov, T. Z. Esirkepov, and M.
Kando: Phys. Rev. Lett. 105 (2010) 135002.
[8] Y. J. Gu, Q. Kong, Y. Y. Li, H. Y. Ban, Z. Zhu, and S.
Kawata: Phys. Rev. Lett. 18 (2011) 030704.
[9] S. V. Bulanov, T. Zh. Esirkepov, J. Koga, T. Tajim,and D. Farina: Plasma Phys. Rep. 30 (2004) 18.