Energy loss of argon in a laser-generated carbon plasma
A. Frank,
1
A. Blažević,
2
P. L. Grande,
3
K. Harres,
1
T. Heßling,
2
D. H. H. Hoffmann,
1
R. Knobloch-Maas,
1
P. G. Kuznetsov,
4
F. Nürnberg,
1
A. Pelka,
1
G. Schaumann,
1
G. Schiwietz,
5
A. Schökel,
1
M. Schollmeier,
1
D. Schumacher,
1
J. Schütrumpf,
1
V. V. Vatulin,
4
O. A. Vinokurov,
4
and M. Roth
1
1
Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstraße 9, 64289 Darmstadt, Germany
2
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64291 Darmstadt, Germany
3
Universidade Federal do Rio Grande do Sul, Avenida Bento Goncalves 9500, Porto Alegre 91501-970, RS, Brazil
4
RFNC-VNIIEF, Sarov, Nizhny Novgorod Region 607190, Russia
5
Helmholtz-Zentrum Berlin für Materialien und Energie, Glienicker Strasse 100, D-14109 Berlin, Germany
Received 16 December 2008; revised manuscript received 4 November 2009; published 4 February 2010
The experimental data presented in this paper address the energy loss determination for argon at 4 MeV/u
projectile energy in laser-generated carbon plasma covering a huge parameter range in density and temperature.
Furthermore, a consistent theoretical description of the projectile charge state evolution via a Monte Carlo code
is combined with an improved version of the CasP code that allows us to calculate the contributions to the
stopping power of bound and free electrons for each projectile charge state. This approach gets rid of any
effective charge description of the stopping power. Comparison of experimental data and theoretical results
allows us to judge the influence of different plasma parameters.
DOI: 10.1103/PhysRevE.81.026401 PACS numbers: 52.20.Hv, 34.50.Bw, 52.40.Mj, 52.58.Hm
I. INTRODUCTION
The stopping power of heavy ions in matter is a field of
research that has been addressed for about a century. From
the pioneering works of Bohr 1, Bethe 2, and Bloch 3 to
a lot more advanced and complete treatments such as in
4 –6 the understanding of the interaction of charged par-
ticles with cold matter has continuously evolved and agrees
rather well with experimental data 7 by now. However, the
interaction of charged particles with ionized matter is not yet
fully understood and there are only few experimental data to
survey existing stopping power theories. The understanding
of this stopping regime is of crucial importance to a variety
of fields in physics, e.g., the realization of an ion-driven fast
ignition concept 8,9 or the target response in modern accel-
erators such as the large hadron collider LHC or the facility
for antiproton and ion research FAIR project. In the last
two decades several experiments concerning the energy loss
in plasma have been conducted covering the field of low-
density plasma with an intermediate temperature of several
eV produced by a gas discharge 10,11 to laser-generated
plasma 12 with temperatures up to 60 eV as well as access-
ing the warm dense matter regime via heavy-ion heating 13
or shock waves 14.
The unique combination of the universal linear accelera-
tor UNILAC with the high-energy laser for ion-beam ex-
periments nhelix15 allows the investigation of the inter-
action of heavy-ion beams with hot laser-generated plasma.
This paper hence addresses experimental data of heavy-ion
energy loss in carbon at higher temperatures and densities
than in former experiments 11,12, reaching temperatures of
up to 250 eV and densities covering the regime of a cold gas
of several mbar up to a pressure of 70 bar. Very accurate
results for the energy loss of argon at an energy of 4 MeV/u
in carbon plasma are presented. At this projectile energy both
projectile screening effects as well as changes in the excita-
tion energies of bound and free electrons of the target play an
important role. To quantify these effects the changes in the
former parameter are calculated via a specially developed
Monte Carlo MC code which determines the changes in the
projectile charge state distribution in the carbon plasma. The
stopping cross section for each argon charge state is calcu-
lated by a modified version of the CASP code 16, which
allows us to calculate the contributions to the stopping power
of free and bound electrons of the ionized carbon target as
well. This approach does not use any effective charge de-
scription of the projectile in the plasma as, for example, the
commonly used modification of the Bethe formula.
II. EXPERIMENTAL SETUPAND DATA
The energy loss is measured via the time-of-flight ToF
method as shown in Fig. 1. Laser and ion beam—in this case
36
Ar
16+
at 4 MeV/u—penetrate the target from opposite
sides. The UNILAC accelerator delivers an ion beam with a
length of 40 s. This beam includes a substructure of 108
MHz, which permits us to probe the target every 9.224 ns.
Each of these ion bunches has a Gaussian shape with a pulse
width of 2–3 ns full width at half-maximum FWHM. As
the ToF detector a chemical-vapor deposition CVD dia-
mond detector has been developed which offers an increased
FIG. 1. Color online Experimental setup of the energy-loss
measurements.
PHYSICAL REVIEW E 81, 026401 2010
1539-3755/2010/812/0264016 ©2010 The American Physical Society 026401-1