High Power Laser Science and Engineering, (2014), Vol. 2, e19, 6 pages.
© Author(s) 2014. The online version of this article is published within an Open Access environment subject to the conditions of the
Creative Commons Attribution licence <http://creativecommons.org/licences/by/3.0>.
doi:10.1017/hpl.2014.25
Generation of high-energy neutrons with the
300-ps-laser system PALS
J. Kr
´
asa
1
,D.Klír
2
,A.Velyhan
1
,E.Krousk
´
y
1
,M.Pfeifer
1
,K.
ˇ
Rez
´
a
ˇ
c
2
,J.Cikhardt
2
,K.Turek
4
,
J.
Ullschmied
3
, and K. Jungwirth
1
1
Institute of Physics, AS CR, 182 21 Prague 8, Czech Republic
2
Czech Technical University in Prague, FEE, 166 27 Prague, Czech Republic
3
Institute of Plasma Physics, AS CR, 182 00 Prague 8, Czech Republic
4
Nuclear Physics Institute, AS CR, 180 00 Prague 8, Czech Republic
(Received 22 February 2014; revised 20 May 2014; accepted 5 June 2014)
Abstract
The laser system PALS, as a driver of a broad-beam ion source, delivered deuterons which generated neutrons with
energies higher than 14 MeV through the
7
Li(d, n)
8
Be reaction. Deuterons with sub-MeV energy were accelerated from
the front surface of a massive CD
2
target in the backward direction with respect to the laser beam vector. Simultaneously,
neutrons were emitted from the primary CD
2
target and a secondary LiF catcher. The total maximum measured neutron
yield from
2
D(d, n)
3
He,
7
Li(d, n)
8
Be,
12
C(d, n)
13
N reactions was ∼3.5(±0.5) × 10
8
neutrons/shot.
Keywords: beam–target fusion; deuterons; laser ion sources; lithium; neutrons
1. Introduction
Recent rapid development of laser plasma accelerators
has made it possible to accelerate protons and deuterons
to high energies of approximately 70 and 170 MeV,
respectively
[1, 2]
. These beams hitting a secondary target
can create high-energy neutrons through, for example,
D(d, n)
3
He,
7
Li(p, n)
7
Be,
7
Li(d, xn)
8
Be,
9
Be(p, n)
5
9
B, and
9
Be(d, n)
5
10
B nuclear reactions
[2–15]
. Fast neutrons with en-
ergies in excess of 10 MeV resulting from the
7
Li(d, xn)
8
Be
reaction (Q = 15.03 MeV) have been reported by several
authors
[6–11]
. Acceleration of deuterons is mostly reported
in experiments using lasers with intensities of 10
19
Wcm
−2
.
The deuterons are accelerated in focal spots on thin-film
targets through either the target-normal sheath acceleration
(TNSA) mechanism or the newly recognized break-out
afterburner (BOA) mechanism
[2]
. There is another laser
ignition of fusion (LIF) scheme for applications, based on
the combination of ultra-high laser nonlinear force driven
plasma blocks and the relativistic acceleration of ion blocks,
which has shown how 70 MeV D
+
and T
+
ions can be
produced using of ps-laser pulses
[16]
. The laser-driven
bright sources of neutrons can be used in fusion material
research
[2, 11, 17]
and proton beams in medical disciplines as
hadron therapy for the treatment of cancer
[18]
.
Correspondence to: Email: krasa@fzu.cz
In contrast to ultra-short high-intensity lasers which allow
the generation of beams of protons and deuterons possessing
kinetic energies 1 MeV, sub-nanosecond lasers of the kJ-
class capable of delivering a moderate intensity onto a target
make it possible to accelerate ions up to MeV energies
per nucleon
[19–22]
. The clear-cut evidence that the fastest
protons accelerated by the laser system PALS (1.315 μm,
300 ps, 3×10
16
Wcm
−2
) have energies up to ∼4 MeV
[20, 21]
creates a way to accelerate a high number of deuterons from
the front side of a target and exploit them in the production
of high-energy (∼15 MeV) neutrons through the
7
Li(d, xn)
nuclear reaction even if the mean kinetic energy of the bunch
of deuterons is <1 MeV. In addition, under these conditions
up to 2 × 10
8
neutrons per laser shot have be generated
with the laser system PALS through the D(d, n)
3
He reaction,
which is scalable with energy of other laser systems
[22]
. This
scheme is applicable to newly developed high-energy-class
cryogenically cooled Yb
3+
:YAG multi-slab laser systems,
allowing the production of a plasma with intensity I λ
2
>
1 × 10
16
μm
2
cm
−2[23]
.
A common phenomenon observed in experiments is the
acceleration of protons coming from a contaminant layer on
the irradiated surface of the target. The protons accelerated
by the laser system PALS have a broad energy spectrum
around a mean value of ∼2.5 MeV. Although the total
cross section for neutron production through the
7
Li(p, n)
reaction is only about three times lower than that for the
1
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