Displacement Determination of the Guard Electrode for the New Calculable Capacitor at NIM
We present our continuing work on the displacement determination of the guard electrode for the new vertical calculable capacitor. We describe a method for determining the displacement by actively locking the Fabry-Perot interferometer to a stabilized laser at two cavity lengths of interest. In order to lock the interferometer tightly, the modulation width of the laser is optimized for the full-width at half-maximum at the two different cavity lengths. For each of the cavity lengths, the Fabry-Perot interferometer is maintained at its resonance, and the cavity length is quantized with a space of λ/2. Then, its corresponding ratio between the fixed standard capacitor and the calculable capacitor is accurately measured by a capacitance bridge. The two main parameters for determining the displacement between the two cavity lengths-i.e., the difference in order number (AN) of the interferometer and the laser wavelength (λ)-are obtained from the capacitance bridge measurement based on a 1-pF standard capacitor with a priori value and the accurate wavelength measurement of an iodine laser, respectively. Evaluation of the displacement sensing system confirms a relative uncertainty of 5.2 × 10-9 over a range of 205 mm.
Diffraction Correction of Locking Fabry-Perot Interferometer in Calculable Capacitor at NIM
This paper describes a diffraction correction of the displacement measurement in calculable capacitor. A mathematical model of the locking interferometer based on Gaussian beam propagation is set up. The phase difference between the two cavities of interest is analyzed numerically. The simulation result demonstrates that the minimum value of the displacement correction can be obtained by actively detecting the laser light at a distance of 560 mm from output mirror.
Far-field dispersal modeling for fuel-air-explosive devices
A computer model for simulating the explosive dispersal of a fuel agent in the far-field regime is described and is applied to a wide variety of initial conditions to judge their effect upon the resulting fuel/air cloud. This work was directed toward modeling the dispersal process associated with Fuel-Air-Explosives devices. The far-field dispersal regime is taken to be that time after the initial burster charge detonation in which the shock forces no longer dominate the flow field and initial canister and fuel mass breakup has occurred. The model was applied to a low vapor pressure fuel, a high vapor pressure fuel and a solid fuel. A strong dependence of the final cloud characteristics upon the initial droplet size distribution was demonstrated. The predicted fuel-air clouds were highly non-uniform in concentration. 18 refs., 86 figs., 4 tabs.