Laser ionization and radio frequency sustainment of high-pressure seeded plasmas

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, tetrakis(dimethylamino)ethylene, 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)approximate to4x10(12) cm(-3) 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. (C) 2002 American Institute of Physics.