Fig. 1. Single heat-exchanger thermodynamic cycle for closed-cycle EDL operation. Substituting Eqs. (2) through (4) into Eq. (1) and rearranging yields Knowing t)ps and r)M, and inferring r)d from experimental or theoretical studies of EDLs, only the ratio of compressor power to electrical power deposited into the gas, PCIPE, is needed to calculate r)L. This ratio is calculated using a purely thermodynamic analysis which closely follows the treatments of Monson (5,6) and Bums (7). Two different closed-cycle laser systems are postulated, and the system efficiency is calculated over a range of realistic parameters. For a CO EDL, a low gas-kinetic temperature is required to achieve lasing on low vibrational quantum number bands and to maximize the discharge efficiency. For a CO2 EDL, a gas-kinetic temperature of approximately 200 °K results in improved discharge efficiency for transitions in the 00°l—>02°0 band. Operation on these CO and CO2 transitions is necessary to maximize the atmospheric transmission efficiency. Isentropic expansion through a supersonic nozzle is used to achieve the desired static temperature. In the first thermodynamic cycle shown in Figure 1, the gas has a stagnation temperature TOI, a stagnation pressure P01, and a Mach number M — 0 in the plenum. The gas is accelerated through a nozzle to a Mach number and a static temperature at the entrance to a constant-area laser channel. Excitation power that is not extracted from this region as laser power remains in the gas and eventually goes into
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