Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

delivers 60% of the x-ray flux from the rotating anode system. Additional ways to improve our microfocus x-ray system, and thus
increase the x-ray flux will be discussed.
Author
X Ray Diffraction; X Ray Sources; X Rays; Crystals; Proteins
20000067679 Jet Propulsion Lab., California Inst. of Tech., Pasadena, CA USA
Recent Trends in the Analysis of Quasioptical Systems
Hoppe, D. J., Jet Propulsion Lab., California Inst. of Tech., USA; Imbriale, W. A., Jet Propulsion Lab., California Inst. of Tech.,
USA; [2000]; 1p; In English; No Copyright; Avail: Issuing Activity; Abstract Only
The recent trend in microwave instruments is the use of multiple millimeter and submillimeter wavelength bands. These systems
are typically analyzed by using physical optics, Gaussian beams or ray tracing techniques. Physical optics offers high accuracy
at the expense of computation time. This trade-off becomes particularly apparent in the analysis of multiple reflector
antennas, such as beam waveguide antennas, where physical optics is used to compute the current on each reflector from the current
on the previous reflector. At the other end of the spectrum is ray tracing approaches that ignore diffraction effects entirely.
These methods are fast but sacrifice the ability to predict some effects accurately. An intermediate approach is to use an appropriate
set of expansion functions to model the field between the reflectors. If the set is chosen wisely only a few coefficients need to be
determined from each reflector current. The field is then computed at the next reflector through the use of the expansion functions
and their coefficients rather than by using the previous reflector current. For a beam waveguide system with no enclosing tubes
an excellent set of expansion functions is the Gaussian beam mode set. In many cases a preliminary design which includes the
effects on diffraction may be obtained by considering only the fundamental mode and a thin lens model for the reflectors. Higherorder
modes are included to model the effects of the curved reflector, which include asymmetric distortion of the beam, cross polarization,
and beam truncation. This paper describes a computer code implementing higher-order Gaussian beam scattering by
multiple reflector systems. There are four essential steps in the algorithm. (1) Compute the current on the first reflector using physical
optics using either a feed model or by an incident set of Gaussian beam modes. (2) Find the direction of propagation for the
reflected Gaussian beam-set using ray tracing. (3) Determine the waist size and location for the output beam set by examining
the amplitude and phase distribution of the current on the reflector. (4) Compute the amplitudes of the individual modes in the
output mode set. These steps are then repeated for each addition reflector in the chain. In each of these cases the previous Gaussian
beam set provides the input field for the current calculation. Details of the four steps discussed above will be discussed. Examples
will compare results from the Gaussian beam approach to pure physical optics, illustrating both its merits and limitations. Hybrid
approaches capable of eliminating some of the limitations will also be discussed.
Author
Microwave Sensors; Submillimeter Waves; Beam Waveguides; Ray Tracing; Physical Optics
75
PLASMA PHYSICS
�������� �������������������� ��� ������ ������� ��� ����������� ������� ��� �� ����������� ��� ����� ������� ��� �� ������
��������
20000062453 Wisconsin Univ., Dept. of Physics, Madison, WI USA
Dynamo and anomalous transport in the reversed field pinch
Prager, S. C.; Aug. 31, 1998; 31p; In English; 25th; controlled fusion and plasma physics; Sponsored by European Physical Society,
Switzerland
Report No.(s): DE99-000800; No Copyright; Avail: Department of Energy Information Bridge
The reversed field pinch is an effective tool to study the macroscopic consequences of magnetic fluctuations, such as the
dynamo effect and anomalous transport. Several explanations exist for the dynamo (the self-generation of plasma current)--the
MHD dynamo, the kinetic dynamo, and the diamagnetic dynamo. There is some experimental evidence for each, particularly from
measurements of ion velocity and electron pressure fluctuations. Magnetic fluctuations are known to produce energy and particle
flux in the RFP core. Current profile control is able to decrease fluctuation-induced transport by a factor of five. Improved confinement
regimes are also obtained at deep reversal and, possibly, with flow shear.
NTIS
Plasma Physics; Reverse Field Pinch; Radiation Transport
201