Laser ionization and radiofrequency sustainment of high-pressure seeded plasmas

Abstract

The feasibility of using a photoionized, low-ionization potential organic seed gas to initiate a high pressure plasma discharge is examined and compared to radio frequency breakdown of high pressure argon alone. The seed gas, tetrakis͑dimethylamino͒ethylene, which has an ionization potential of 6.1 eV is ionized by an ultraviolet laser through 6.4 eV photon absorption, and forms a plasma column inside a vacuum chamber. The plasma absorbs additional power through inductive coupling of 13.56 MHz helical antenna radio frequency wave fields to the plasma through electron acceleration, ionization, and collisional damping. Laser initiation of 2-6 mTorr of the seed gas in 1-150 Torr of argon is accomplished and produces steady-state line-average plasma densities of n e Ϸ4ϫ10 12 cm Ϫ3 in a volume of 300 cm 3 . The two-body recombination coefficient of the organic seed gas and its optimum partial pressure when mixed with argon are experimentally determined and analyzed. Particle loss and power requirements for maintaining the discharge are evaluated by examining ionization, diffusion, and recombination processes.

Laser initiation and radiofrequency sustainment of seeded air plasmas

“…MHz, sufficient to create the plasma at lower pressure and sustain it up to atmospheric pressure with a volume of about 2500 cubic centimeters (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) Watts / cm 3 ). The time scale for creating the high-pressure plasma from the initial low-pressure discharge was several minutes.…”

“…v=cr(TI)nO°v (18) in which a(Te) is the total collision cross-section of the collision processes between electrons and neutrals, no is the neutral density, and v is the average magnitude of the velocity of the electrons. Note that the total cross section ou is a function of Te.…”

“…The total cross section curves generalized by Zecca et al are used. We used 4 th order polynomial functions to fit these experimental cross section data curves and obtain r(Te) for use in (18).…”

“…The 5 cm line-average electron density, effective electron collision rate and electron temperature is diagnosable using the interferometer after the second stage of plasma (steadystate plasma) is formed. The two signals (in-phase and quadrature-phase) from the interferometer are acquired by two channels of the oscilloscope, which are used to extract the phase shift and attenuation of the wave after it penetrates the plasma [18], [19]. A raw interferometer trace in X-Y mode is presented in Fig.…”