180 research outputs found
Electron cyclotron resonance near the axis of the gas-dynamic trap
Propagation of an extraordinary electromagnetic wave in the vicinity of
electron cyclotron resonance surface in an open linear trap is studied
analytically, taking into account inhomogeneity of the magnetic field in
paraxial approximation. Ray trajectories are derived from a reduced dispersion
equation that makes it possible to avoid the difficulty associated with a
transition from large propagation angles to the case of strictly longitudinal
propagation. Our approach is based on the theory, originally developed by the
Zvonkov and Timofeev [1], who used the paraxial approximation for the magnetic
field strength, but did not consider the slope of the magnetic field lines,
which led to considerable error, as has been recently noted by Gospodchikov and
Smolyakova [2]. We have found ray trajectories in analytic form and
demonstrated that the inhomogeneity of both the magnetic field strength and the
field direction can qualitatively change the picture of wave propagation and
significantly affect the efficiency of electron cyclotron heating of a plasma
in a linear magnetic trap. Analysis of the ray trajectories has revealed a
criterion for the resonance point on the axis of the trap to be an attractor
for the ray trajectories. It is also shown that a family of ray trajectories
can still reach the resonance point on the axis if the latter generally repels
the ray trajectories.
As an example, results of general theory are applied to the electron
cyclotron resonance heating experiment which is under preparation on the Gas
Dynamic Trap in the Budker Institute of Nuclear Physics [3]
Weak antilocalization in quantum wells in tilted magnetic fields
Weak antilocalization is studied in an InGaAs quantum well. Anomalous
magnetoresistance is measured and described theoretically in fields
perpendicular, tilted and parallel to the quantum well plane. Spin and phase
relaxation times are found as functions of temperature and parallel field. It
is demonstrated that spin dephasing is due to the Dresselhaus spin-orbit
interaction. The values of electron spin splittings and spin relaxation times
are found in the wide range of 2D density. Application of in-plane field is
shown to destroy weak antilocalization due to competition of Zeeman and
microroughness effects. Their relative contributions are separated, and the
values of the in-plane electron g-factor and characteristic size of interface
imperfections are found.Comment: 8 pages, 8 figure
Interference induced metallic-like behavior of a two-dimensional hole gas in asymmetric GaAs/InGaAs/GaAs quantum well
The temperature and magnetic field dependences of the conductivity of the
heterostructures with asymmetric InGaAs quantum well are studied.
It is shown that the metallic-like temperature dependence of the conductivity
observed in the structures investigated is quantitatively understandable within
the whole temperature range, K. It is caused by the interference
quantum correction at fast spin relaxation for 0.4 K K. At higher
temperatures, 1.5 K K, it is due to the interaction quantum correction.
Finally, at K, the metallic-like behavior is determined by the phonon
scattering.Comment: 4 pages, 4 figure
The environment effect on operation of in-vessel mirrors for plasma diagnostics in fusion devices
First mirrors will be the plasma facing components of optical diagnostic
systems in ITER. Mirror surfaces will undergo modification caused by erosion
and re-deposition processes [1,2]. As a consequence, the mirror performance may
be changed and may deteriorate [3,4]. In the divertor region it may also be
obscured by deposition [5-7]. The limited access to in-vessel components of
ITER calls for testing the mirror materials in present day devices in order to
gather information on the material damage and degradation of the mirror
performance, i.e. reflectivity. A dedicated experimental programme, First
Mirror Test (FMT), has been initiated at the JET tokamak within the framework
Tritium Retention Studies (TRS).Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France).Submitted by B. Schunke on behalf of V. Voytseny
Role of doped layers in dephasing of 2D electrons in quantum well structures
The temperature and gate voltage dependences of the phase breaking time are
studied experimentally in GaAs/InGaAs heterostructures with single quantum
well. It is shown that appearance of states at the Fermi energy in the doped
layers leads to a significant decrease of the phase breaking time of the
carriers in quantum well and to saturation of the phase breaking time at low
temperature.Comment: 4 pages, 6 figure
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