NASA Scientific and Technical Aerospace Reports

distribution of ions) with given initial conditions will undergo chaotic motion.
NTIS
Ions; Magnetic Field Configurations
20040111127 Princeton Univ., NJ
Landau Damping and Anomalous Skin Effect in Low Pressure Gas Discharges: Self-Consistent Treatment of
Collisionless Heating
Kaganovich, I. D.; Polomarov, O. V.; Theodosiou, C. E.; Jan. 2004; 42 pp.; In English
Report No.(s): DE2004-821522; PPPL-3922; No Copyright; Avail: Department of Energy Information Bridge
In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the
electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably
from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the
nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying
assumptions: a uniform density pro.le and a Maxwellian EEDF. In the present study a self-consistent system of equations for
the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is reported. It consists
of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. This
system was applied to the calculation of collisionless heating in capacitively and inductively coupled plasmas. In particular,
the importance of accounting for the nonuniform plasma density pro.le for computing the current density pro.le and the EEDF
is demonstrated. The enhancement of collisionless heating due to the bounce resonance between the electron motion in the
potential well and the external rf electric .eld is investigated. It is shown that a nonlinear and self-consistent treatment is
necessary for the correct description of collisionless heating.
NTIS
Collisionless Plasmas; Gas Heating; Kinetic Equations; Landau Damping
20040111128 California Univ., Lawrence Berkeley National Lab., Berkeley, CA, USA, Deutsches Elektronen-Synchrotron,
Hamburg, Germany
Damping Ring Designs and Issues
Wolski, A.; Decking, W.; 2004; 10 pp.; In English
Report No.(s): DE2004-822803; LBNL-52580; No Copyright; Avail: Department of Energy Information Bridge
The luminosity performance of a future linear collider (LC) will depend critically on the performance of the damping
rings. The design luminosities of the current LC proposals require rings with very short damping times, large acceptance, low
equilibrium emittance and high beam intensity. We discuss the design strategies for lattices achieving the goals of dynamical
stability, examine the challenges for alignment and coupling correction, and consider a variety of collective effects that
threaten to limit beam quality. We put the design goals in context by referring to the experience of operating facilities, and
outline the further research and development that is needed.
NTIS
Damping; Accelerators; Stability
20040111129 Lawrence Livermore National Lab., Livermore, CA
Beam-Target Interaction Experiments for Multipulse Bremsstrahlung Converters Applications
Sampayan, S.; Buckles, R.; Caporaso, G.; Chambers, F. C.; Chen, Y. J.; 2004; In English
Report No.(s): DE2003-15005533; No Copyright; Avail: National Technical Information Service (NTIS)
As part of the Dual Axis Radiography Hydrotest Facility, Phase II (DARHT II) multipulse Bremsstrahlung target, we have
been performing an investigation of (1) the possible adverse effects of backstreaming ion emission from the Bremsstrahlung
converter target and (2) maintaining sufficient target density to ensure dose in latter pulses. Theory predictions show that the
first effect would primarily be manifested in the static focusing system as a rapidly varying x-ray spot. From experiments
performed on ETA-II, we have shown that the first effect is not strongly present when the beam initially interacts with the
target. Electron beam pulses delivered to the target after formation of a plasma are strongly affected, however. Secondly, we
have performed studies of the effect of the time varying target density on dose and seek to demonstrate various techniques for
maintaining that density. Measurements are presented of the target density as a function of time and are compared with our
hydrodynamic models.
NTIS
Accelerators; Bremsstrahlung; Radiography; X Rays
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