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首页> 美国政府科技报告 >Microwave cavity diagnostics of microwave breakdown plasmas. Final report.
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Microwave cavity diagnostics of microwave breakdown plasmas. Final report.

机译：微波击穿等离子体的微波腔诊断。总结报告。

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We have performed microwave cavity perturbation measurements in the LLNL AIM facility using a 329-MHz cavity that allow us to examine in detail the plasma formation and decay processes for electron densities between approximately 10(sup 5) and 10(sup 7)/cm(sup 3). We believe these to be the lowest density plasmas ever studied in microwave breakdown experiments, and as such they allow us to determine the power and energy required to produce plasmas suitable for HF radar reflection as well as the effective lifetimes of these plasmas before re-ionization is required. Analyses of these results leads to the following conclusions. (1) For microwave breakdown pulses varying from 0.6 to 2.4 (mu)s, the threshold power required to produce measurable plasmas is 30 to 12 MW/m(sup 2) at 0.01 torr, decreasing to 3.5 to 1.8 MW/m(sup 2) at 1 to 3 torr, and then increasing to 5 to 3.5 MW/m(sup 2) at 30 torr. The threshold power in each case decreases with increasing pulse length, but the required pulse energy increases with decreasing power or increasing pulse length. (2) The effective electron density decay rates are approximately 100/s for 0.1 to 1 torr, after which they increase linearly with pressure. Thus, the useful plasma lifetimes are in the range of 20 to 40 ms at the lower pressures and decrease to about 1 ms at 30 torr. These decay rates and lifetimes are comparable to those that would exist for artificially ionized regions in the upper atmosphere. (3) The collision frequencies measured at pressures of 1 torr and above correspond to electron temperatures of 800 K or less. In fact, the inferred temperatures for p > 3 torr are below room temperature. This may be due to a contribution to the measured conductivity by negative ions.

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