Focused excimer laser initiated, radio frequency sustained high pressure air plasmas

Journal Article · Tue Nov 15 00:00:00 EST 2011 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3660690· OSTI ID:22036773

Giar, Ryan; Scharer, John ^[1]

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1. Department of Electrical Engineering, University of Wisconsin-Madison, 506 Engineering Research Building, 1500 Engineering Drive, Madison, Wisconsin 53706 (United States)

Measurements and analysis of air breakdown processes and plasma production by focusing 193 nm, 300 mJ, 15 MW high power laser radiation inside a 6 cm diameter helical radio frequency (RF) coil are presented. Quantum resonant multi-photon ionization (REMPI) and collisional cascade laser ionization processes are exploited that have been shown to produce high-density (n{sub e} {approx} 7 x 10{sup 16}/cm{sup 3}) cylindrical seed plasmas at 760 Torr. Air breakdown in lower pressures (from 7-22 Torr), where REMPI is the dominant laser ionization process, is investigated using an UV 18 cm focal length lens, resulting in a laser flux of 5.5 GW/cm{sup 2} at the focal spot. The focused laser power absorption and associated shock wave produce seed plasmas for sustainment by the RF (5 kW incident power, 1.5 s) pulse. Measurements of the helical RF antenna load impedance in the inductive and capacitive coupling regimes are obtained by measuring the loaded antenna reflection coefficient. A 105 GHz interferometer is used to measure the plasma electron density and collision frequency. Spectroscopic measurements of the plasma and comparison with the SPECAIR code are made to determine translational, rotational, and vibrational neutral temperatures and the associated neutral gas temperature. From this and the associated measurement of the gas pressure the electron temperature is obtained. Experiments show that the laser-formed seed plasma allows RF sustainment at higher initial air pressures (up to 22 Torr) than that obtained via RF-only initiation (<18 Torr) by means of a 0.3 J UV laser pulse.

• OSTI ID: 22036773
• Journal Information: Journal of Applied Physics, Vol. 110, Issue 10; Other Information: (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AIR
ANTENNAS
BEAM-PLASMA SYSTEMS
COMPARATIVE EVALUATIONS
COUPLING
ELECTRON DENSITY
ELECTRON TEMPERATURE
EXCIMER LASERS
GHZ RANGE
IMPEDANCE
ION TEMPERATURE
IONIZATION
LASER RADIATION
MULTI-PHOTON PROCESSES
PLASMA DENSITY
PLASMA DIAGNOSTICS
PLASMA PRODUCTION
PLASMA SEEDING
RADIOWAVE RADIATION
SHOCK WAVES