Plenarvorträge - DPG-Tagungen

Plasmaphysik Mittwoch
die Veränderungen zeigen und wie man ihnen begegnet. Molybdän-
Spiegel wurden am Plasmarand von TEXTOR exponiert und spektroskopisch
beobachtet. Deponierung und Implantation von C als auch lokaler
Transport von Mo wurden durch SIMS Tiefenprofilierung nachgewiesen
und mittels Ionenstrahlanalysen quantifiziert. Reflektivität und Streuung
wurden im Bereich 250-2500nm in Abhängigkeit von Einfallswinkel und
Polarisation vor und nach Exposition gemessen. Dabei zeigte sich der
starke Einfluß der Veränderungen auf die optischen Eigenschaften, aus
denen sich Schlußfolgerungen für das Vorgehen bei ITER ergeben.
P 17.10 Mi 17:45 Foyer
Hyper-Thermic Atomic Hydrogen Beam Source for Surface
Studies — •Tatiana Babkina, Timo Gans, and Uwe Czarnetzki
— Institut für Plasma- und Atomphysik, Ruhr-Universität Bochum,
Germany
The present report is concentrated on the design of and first investigations
on a novel atomic hydrogen beam source. The source is based
on neutralisation and reflection of hydrogen ions at surfaces. Ions are
produced in a pulsed hydrogen RF discharge with magnetic confinement
at pressures in the Pascal range. A voltage pulse is applied to a small
electrode inside the discharge volume. Ions are accelerated in the sheath
potential in front of the electrode. A hydrogen atom beam is produced by
neutralisation and reflection of impinging ions at the electrode surface.
The atom beam traverses the plasma collisionless and can be applied for
detailed investigations of exothermic chemical reactions of hyper-thermic
hydrogen atoms at metal surfaces. The atomic hydrogen beam is investigated
by optical emission spectroscopy and an energy resolved mass
spectrometer opposite to the electrode. Influences of ion species, ion energy,
surface materials and threshold for neutralisation on the atomic
beam characteristics can be studied. The project is funded by the DPG
in the frame of the SFB 616.
P 17.11 Mi 17:45 Foyer
Mitigating Disorder-Induced Heating in Ultracold Plasmas ∗
— •D.O. Gericke and M.S. Murillo — Theoretical Division, Los
Alamos National Laboratory, Los Alamos, NM 87545, USA
Recent experiments demonstrated the creation of ultracold plasmas by
ionization of trapped atoms with temperatures in the µK range [1,2]. The
initial ion properties correspond to a very strongly coupled state; therefore,
ultracold plasmas could provide a new avenue to investigate strong
coupling effects with relatively long lived samples.
Unfortunately, the build up of correlations strongly heats the ions [3].
We show how this process is related to the establishment of Coulomb
structure in the final plasma state and give results for the amount of
disorder-induced heating for a wide variety of initial conditions. Since
the ions gain a large amount of kinetic energy while building up negative
potential energy, plasmas are usually heated to a moderately coupled
state that is almost independent of the initial temperature [4]. Two possibilities
for reducing the heating by the introduction of structure in the
initial state, i.e., the gas before ionization, are then discussed: the ionization
of a highly degenerate gas of fermionic atoms and the ionization
of highly excited atoms in Rydberg states.
[1] T.C. Killian et al., Phys. Rev. Lett. 83, 4776 (1999).
[2] M.P. Robinson et al.; Phys. Rev. Lett. 85, 4466 (2000).
[3] M.S. Murillo, Phys. Rev. Lett. 87, 1150031 (2001).
[4] D.O. Gericke & M.S. Murillo, Contrib. Plasma Phys. 43, 298 (2003).
∗ funded by the U.S. Department of Energy (contract W-7405-ENG-36)
P 17.12 Mi 17:45 Foyer
A SELF-CONSISTENT MODEL FOR A NONLINEARLY MODULATED
PLASMA BOUNDARY SHEATH : FOURIER ANALYSIS AND IMPLE-
MENTATION OF NEWTON’S METHOD
— •Mustafa Bayrak und Ralf Peter Brinkmann —
Lehrstuhl für Theoretische Elektrotechnik, Ruhr Universität Bochum,
Universitätsstrasse 150, 44780 Bochum
In the last years, in-situ diagnostic methods were successfully introduced
into the control of industrial plasma processes. In microelectronics,
these methods are known as AEC/APC, for advanced equipment
control/advanced process control. Self-excited electron resonance spectroscopy
(SEERS) is a particularly successful such methods, owing to its
robustness and the fact that is strictly passive and contamination free.
SEERS operates by observing the self-excitation of the so-called series
resonance that occurs in bounded plasmas. The mechanism of this
resonance involves a periodic exchange of energy between the electrostatic
field of the plasma boundary sheath and the kinetic motion of the
electrons in the bulk. A deeper understanding of the SEERS method
requires a detailed analysis of the mechanisms which excite this oscillation,
in particular the nonlinearities of the sheath. In this work, we
present a self-consistent model of a nonlinearly modulated plasma boundary
sheath. The non-linear dependence of the fourier coefficients of the
current density through the sheath and the voltage across the sheath are
related and their mutual dependence is characterized.
P 17.13 Mi 17:45 Foyer
THEORETICAL AND NUMERICAL ANALYSIS OF THE
ELECTRON MOTION NEAR THE NEUTRAL POINT OF
THE MAGNETIC FIELD — •Murat Vural und Ralf Peter
Brinkmann — Lehrstuhl für Theoretische Elektrotechnik, Ruhr Universität
Bochum
Electron heating, i.e. the conversion of directed field energy into thermal
electron energy, requires a randomization process which destroys the
coherence in the motion of the electrons accelerated by the field. The
standard Ohmic heating, i.e. the scattering of electrons at the neutrals
of the background becomes very inefficient at gas pressures below 1 Pa.
In this work, we investigate the efficiency of an alternative mechanism,
namely the “scattering“ of magnetized electrons at a neutral loop in the
magnetic field configuration.
In the neighborhood of neutral points (where the magnetic field vanishes),
however, the adiabatic invariance is destroyed and the electron
motion becomes strongly chaotic. We consider a simple but realistic model
of a stationary non-uniform and rotational invariant magnetic field
configuration with neutral loop superimposed with an electrical RF modulation,
similar to that of a neutral loop discharge (NLD). We find that
the randomization of the electron motion by the neutral point provides
a very efficient heating mechanism at low gas pressure.
P 17.14 Mi 17:45 Foyer
EUV spectra of light elements — • ˇ Zeljko Andreić 1 , Hans-
Joachim Kunze 2 und Ante Hečimović 3 — 1 Faculty of Mining, Geology
and Petroleum Engineering, University of Zagreb, Pijerottijeva 6,
10 000 Zagreb, Croatia — 2 Institute of Experimental Physics V, Ruhr-
University, 44780 Bochum, Germany — 3 Faculty of Science, University
of Zagreb, Bijenička 32, 10000 Zagreb, Croatia
Spectra of laser-produced plasmas of light elements (Be-Al) were systematically
obtained with the help of a flat-field spectrograph built around
a Hitachi 1200 l/mm grating. The primary detector was a gated MCP
whose output plane was imaged onto a CCD camera. The whole spectral
range of the instrument was covered and individal spectra were assembled
together. In experiments the experimental parmeters were kept the
same. In the case of gaseous elements (N, O, F) their simplest solid compounds
were used as ablation targets. The goal is to obtain single element
spectra that cover the whole spectral range of the instrument in question
(i. e. approximately 3-30nm. For each element the instrumental spectrum
and the ”true” spectrum, cleaned of higher order spectral lines will be
assembled and made available on our web site. Such spectra can be used
to simplify wavelength calibration of XUV instruments built arround the
same or a simmilar gratings, and line identification in this spectral range.
Work is still in progres, but the first results (complete spectra of several
elements) are available and will be presented.
This work is suported by the Croatian Ministry of Science and Technology
(research grant no. 0195052), and by the Alexander von Humboldt
Foundation.
P 17.15 Mi 17:45 Foyer
Selbstkonsistente kinetische Beschreibung einer gestörten
Neon-Glimmentladung — •F. Sigeneger 1 , S. Arndt 1 , H.
Testrich 2 und Ch. Brandt 2 — 1 INP Greifswald — 2 Institut für
Physik, Ernst-Moritz-Arndt-Universität, 17489 Greifswald
Theoretische Untersuchungen eines im Übergangsbereich zwischen
positiver Säule und Anode gestörten zylindrischen Neonplasmas werden
vorgestellt. Sie nehmen Bezug auf spektroskopische Messungen an
Gleichstrom-Glimmentladungen, die durch eine radial eingeführte
Langmuirsonde gestört wurden. Die selbstkonsistente Analyse des
Neonplasmas beruht auf einem iterativen Hybridverfahren, das eine
hydrodynamische Beschreibung von Ionen, Elektronen und angeregten
Atomen sowie die Lösung der Poissongleichung umfasst. Die erforderlichen
ortsabhängigen Transport- und Ratenkoeffizienten der Elektronen
werden durch die gekoppelte Lösung der axial inhomogenen Boltzmann-