1. 1/12 Dielectric Breakdown in Air Components at Microwave Frequencies under Stratospheric Conditions S.K. Remillard, A. Hardaway*, Hope College, Department of Physics Brian Mork, Jake Gilliland*, Hope College, Department of Chemistry *students This work is funded by the Michigan Space Grant Consortium Michigan Space Grant Consortium Conference, Oct 18, 2008, Ann Arbor

2. 2/12 Motivation To understand the response of “thin” air to intense microwave fields To study the electrodynamic mechanism involved in Ozone formation

3. 3/12 The Microwave Plasma Generator Swept Signal Generator Power Amplifier transmission frequency Microwave Resonant Cavity Network Analyzer 1.8 GHz Quarter wave resonator Frequency tuner ~1W

4. 4/12 Resonance and Perturbation Analysis Intense electric field in a resonator: E=10,000 V/m for P in =700 mW Perturbation measurement of the electric field in the gap using a PTFE insert: /4 Uniform Electric Field Region Total EM energy 0

5. 5/12 Network Analyzer Amplifier Pirani Gauge Vacuum Chamber Cryo Refrig Temperature Controller Compressor Jake Three Modules in this Experiment: Microwave Vacuum Cryogenic

6. 6/12 at breakdown Transmission of power through the resonator… below breakdown

7. 7/12 Air and its Principal Components 1.8 GHz and 290 K Paschen minimum

8. 8/12 Ambient Temperature Effects Water vapor makes breakdown more difficult at low pressure.

9. 9/12 Phenomenological Model #1 Mean Electron Energy ℓ=Mean Free Path P=pressure ℓ (A.U.)  U  (A.U.) Nitrogen at 294 K and 1.8 GHz Breakdown

10. 10/12 Phenomenological Model #2 What should be the breakdown E field? Effective field for energy transfer Collision Rate  P Number density  P Free fit parameter Does this fit the data? At breakdown

11. 11/12 Phenomenological Model #2 For a plasma in free space, m=1. (Gurevich, 1997) m=0.43 m=1 High  R 2 =7: Model doesn’t account for very low pressure Underestimated uncertainties dotted line: force m to be one

12. 12/12 Conclusion and Follow-up Next two variables: 1. Microwave frequency 2. Characteristic Diffusion Length Another goal is to relate ozone production in air discharge to the electromagnetic wave properties: 1. A residual gas analyzer gas sampler has been constructed 2. Currently designing a resonator that mounts directly to the gas sampler. Follow-up This work is funded by the Michigan Space Grant Consortium