Cygnus dose symmetry
The Cygnus Dual Beam Radiographic Facility consists of two identical radiographic sources each with a dose rating of 4 Rad at 1 m, and a 1 mm diameter spot size. The development of the rod pinch diode was responsible for the ability to meet these criteria. The rod pinch diode in the Cygnus machines use a 0.75 mm diameter tungsten tapered anode rod extended through a 9 mm diameter cathode aperture. When properly configured, the electron beam born off the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small x-ray source. The Cygnus sources are utilized as the primary diagnostic on experiments which are single-shot, high value events. In such an application there is an emphasis on reliability and reproducibility. The azimuthal quality and reproducibility of the Cygnus sources will be analyzed using lithium fluoride thermoluminescent dosimeters. Photogrammetry will be used to quantify the precision of the rod pinch diode build (i.e. the centeredness of the anode rod). One goal of these tests will be investigation of the relationship of dose symmetry to anode rod position (i.e. the correlation of off-center dose to an off-center anode rod).
Magnetic insulation, power flow, and pulse power results on RITS-3
RTFS (Radiographic Integrated Test Stand) is an induction voltage adder designed by Sandia and PSD to provide 16-MV, 150-kA electron beams and other capabilities. Previous publications have reported on tests of a single pulse forming line and adder cell, including initial results of the effects of various degrees of non-uniform injection of current into the adder bore on magnetic insulation and power flow in the downstream MITL. Now RITS-3 has been constructed, consisting of three pfls driven by a common intermediate store; three induction cells, one driven by each pfl; a three-stage, 4-MV, 150-kA vacuum voltage adder; and an output MITL and diode. Here we report on (1) simulations of the three-stage adder using the MRC 3-D particle-in-cell code LSP that address the effects of injected current non-uniformities on magnetic insulation and power-flow both upstream and downstream in a multi-cell adder; (2) experimental results compared with simulations; and (3) initial performance of the RITS-3 pulse power.
Modeling Coherent Backscattering Errors in Fiber Optic Gyroscopes for Sources of Arbitrary Line Width
We present a new model of the noise and drift induced by coherent backscattering in a fiber optic gyroscope (FOG) interrogated with a light source of arbitrary temporal coherence. This study is critical to understand whether a FOG driven with a laser instead of a broadband source can attain high sensitivity and stability, which would have the overwhelming benefit of improving the FOG scale factor stability by at least ten-fold and would enable the use of FOGs for inertial navigation of aircrafts. Analytical and numerical solutions bring to light two significant new predictions. First, coherent-backscattering noise can be made negligibly small by utilizing a laser with a very narrow linewidth (less than ~ 20 kHz), although in this regime the drift is high. Second, by using a laser with a broad linewidth (greater than ~ 10 MHz), both the noise and the drift are low enough for aircraft inertial navigation. The dependencies of the noise and drift on fiber loss, loop coupling coefficient, and backscattering coefficient are also presented to define the optimum mode of operation of this new class of FOGs.