E. Paller

Air constituent plasmas produced by a radiofrequency plasma source

Summary form only given, as follows. A radiofrequency plasma source is used to study the creation and sustainment of a high density plasma of air constituents (N/sub 2/, Ar, and O/sub 2/). Various antenna configurations, including helical antennas, are used in conjunction with a capacitive matchbox system and a broad-band (2-200 MHz), high power (1 kW) amplifier to couple power to the plasma. A calibrated Bird meter at the matchbox allows for real-time monitoring and measurements of forward and reflected power. The role of antenna configuration, applied magnetic field (100-1400 G), operating frequency, and gas concentrations on the power coupled to the high density (10/sup 11/-10/sup 13/ cm/sup -3/) plasma have previously been examined at lower gas pressures (10-100 mTorr), and these results are extended to higher pressure regimes. Antenna configurations, including multiple turn coils and variations on helical antennas, are tested to maximize power coupling to the plasma at pressures in the Torr range. Initial experiments at pressures of 1 Torr indicate a mixture of argon and nitrogen produces a plasma which exhibits synergistic power coupling features different than the cases of pure N/sub 2/ or pure Ar plasmas at the same pressure and input power. This phenomenon is explored to determine if a seed gas is beneficial to the breakdown of air constituents. Plasma density is measured by interferometer methods, and the wave B-field is measured by a B-dot probe. Network analyzer measurements are made on the power coupling system to determine antenna impedance values. The experimental results are compared with simulation results from ANTENA2 and MAXEB codes. A photomultiplier tube and spectrometer is used to examine plasma lifetime and emission spectra, providing insight into the chemical and physical processes in air constituent plasmas.

Optical emission, electron energy, density, wave magnetic field and spectrum measurements in a helicon plasma source

Summary form only given. Measurements and analysis of optical emission, electron energy analyzer, Langmuir and magnetic probe and wave spectra are presented for a wide range of helicon plasma source conditions. Helicon plasma source characteristics at lower argon neutral pressures of 2-6 mTorr at both low (200 G) and high (1.2 kG) magnetic field strengths and at high pressures (100 mTorr) are presented for a wide range of radiofrequency input powers. Plasma densities in the range of 10/sup 11/-10/sup 13//cm/sup 3/ are obtained in the UW helicon facility which utilizes a double half-turn helix. Observations of Ar II emission, its modulation and correlation with the RF phase are presented in both time and spatial domains for a variety of plasma conditions. The emission spectrum measured by optical probes either internal or external to the 10 cm diameter Pyrex cylinder plasma is compared with wave magnetic and plasma density as well as miniaturized electron energy analyzer measurements. In addition, both low frequency, fundamental, sideband and harmonic components of the RF wave are measured and analyzed to obtain a comprehensive picture of the helicon source operation for a variety of conditions. Network analyzer measurements, Antenna II wave modeling and wave-particle ionization models are used to analyze the properties of the plasma source.

Radio frequency produced high-pressure air constituent plasmas

Summary form only given, as follows. A high-density large volume plasma of air constituent (N/sub 2/, O/sub 2/, Air and Argon mixtures) is created using a high power (1-25 kW) pulsed radio frequency source at high gas pressures. Such high-Pressure air plasmas are finding increasing application in plasma processing industry, as plasma reactors, as light source and as biological decontaminants. One of the major issues particular to such plasma is the high power required to initiate and sustain the discharge. The power requirement to create and sustain the discharge can be reduced by mixing noble gas with air constituents. Initial experiments reveal that noble gas mix of nitrogen, argon and oxygen improves the antenna loading and is beneficial for the break down of air constituents. It also leads to a lower recombination rate. A tangentially injected high-speed swirl gas flow improves the plasma confinement. It also keeps the plasma off the inside walls of the Pyrex chamber and reduces the excessive heating of the plasma chamber. Radio frequency power is coupled through a five turn helical antenna using a capacitive matching network.. A large volume plasma in argon at 20 Torr at moderate radio frequency power 1.5 kW has been produced. Recent results with high power pulsed unit in high-pressure range (100-200 Torr of argon, nitrogen, oxygen and their mixture) will be presented.

Radiofrequency initiation and radiofrequency sustainment of laser initiated seeded high pressure plasma

We examine radiofrequency initiation of high pressure(1–70 Torr) inductive plasma discharges in argon, nitrogen, air and organic seed gas mixtures. Millimeter wave interferometry, optical emission and antenna wave impedance measurements for double half-turn helix and helical inductive antennas are used to interpret the rf/plasma coupling, measure the densities in the range of 1012 cm−3 and analyze the ionization and excited states of the gas mixtures. We have also carried out 193 nm excimer laser initiation of an organic gas seed plasma which is sustained at higher pressures(150 Torr) by radiofrequency coupling at 2.8 kW power levels.

Optical measurements of fast electron effects in a helicon plasma

Wave magnetic field and Ar II optical emission measurements correlated with the wave phase are used to analyze thermal and fast electron processes in a helicon plasma source. It is found that under appropriate conditions, significant wave-correlated contributions to the fast electron distribution occur in helicon source operation.

Laser initiation and radiofrequency sustainment of seeded air plasmas

Summary form only given. Seeded gas plasmas and air constituents have been created by a 193 nm laser and radiofrequency sources. We have obtained 10/sup 14//cm/sup 3/ plasma densities with initial electron temperatures of 0.3 eV in TMAE (tetrakis (dimethylamino) ethylene) by laser photoionization. We developed a fast Langmuir probe analysis of plasma decay independent of ion species mix. Langmuir probe and optical emission data illustrating the density and temperature decay with TMAE mixed with nitrogen is presented. Simulations of antenna coupling, wave frequencies, wave propagation, and power absorption are compared with experimental observations for radiofrequency plasma sources. The source produces plasma densities of 2/spl times/10/sub 13//cm/sup 3/ in an 8500 cm/sup 3/ volume at electron temperatures of 5 eV in 10 mTorr Ar in a nonuniform magnetic field. Radiofrequency plasma production at pressures from 2700 Torr using Ar and laser initiated TMAE plasmas as seeds will be discussed.

Argon and air mixture plasmas produced by a radiofrequency plasma source

Summary form only given. A radiofrequency helicon plasma source is used to study the creation and sustainment of a high density plasma of air constituents (N/sub 2/, Ar and O/sub 2/). Various antenna configurations including helical antennas are used in conjunction with with a capacitive matchbox system and a broad-band (2-200 MHz) high power (1 kW) amplifier to couple power to the plasma. A calibrated Bird meter at the matchbox allows for real time monitoring and measurements of forward and reflected power. The role of antenna configuration, applied magnetic field (100-1400 G) operating frequency and gas concentrations of the power coupled to the high-density (10/sup 11/-10/sup 13/ cm/sup -1/) plasma have previously been examined at lower gas pressure (10-100 mTorr) and these results will be extended to higher pressure regimes. Experiments at lower pressures (10-100 mTorr) with a working gas of argon exhibit an intense 4 cm diameter blue mode emission, indicative of the excitation of the Argon II state. This blue core emission will be further studied with the use of photomultiplier tube and spectrometer.

A laser-produced plasma sustained by a radiofrequency source

Summary form only given. The creation of a high-density plasma in a high pressure environment is studied. The plasma is generated by photoionization of the organic seed molecule tetrakis(dimethylamino)ethylene (TMAE) and is sustained by RF coupling through the use of an antenna. The coupled power is a function of antenna configuration, plasma density, working gas and applied magnetic field. Previous studies have utilized these antennas to couple power to the plasma through the inductive mode of operation. The inductive source operates by coupling power to the plasma through collisional ohmic heating of the wave energy. Helicon antennas have been shown to be very efficient sources in the low pressure argon regime with densities of the order of 4/spl times/10/sup 12/ cm/sup -3/ with only 600 W of power in a 5 cm radius tube. The VUV laser in this experiment has created plasmas of order 10/sup 14/ cm/sup -3/. The high density gives a high condition which allows higher radiation resistance of the antenna and more power to couple the plasmas. The use of different working gasses is explored and the results are compared and interpreted. The computer codes, ANTENNA2 and MAXEB are used to optimize the experiment and interpret results. The radiation resistance is measured using a network analyzer, and compared to code results. The plasma parameters are measured by Langmuir probes and optical emission spectra.

Laser and radiofrequency wave creation of seeded air plasmas

Summary form only given, as follows. We are examining 193 nm laser ionization of an organic seed gas TMAE (tetrakis-dimethyl-amino-ethylene) in air plasma constituents including nitrogen and oxygen. The peak plasma density n/spl ges/10/sup 13/ cm/sup -3/, temperature (T/sub e/=0.2 eV) and lifetimes are measured for pure TMAE and with the air constituents added at pressures from 100 mTorr to atmospheric. The role of superexcited states, metastable states and the seed gas character is discussed. The effect of the wave frequency, magnetic field and antenna design for radiofrequency created plasmas in seed gases (argon and TMAE) and added air constituents are discussed. We examine laser and high voltage spark initiated plasmas at higher pressures and their radiofrequency sustainment. Modelling utilizing the ANTENAII and MAXEB codes are used to describe the wave penetration and absorption for different antennas.

Radiofrequency sustainment of a laser-produced plasma

Summary form only given, as follows. The plasma is generated by photoionization of the organic seed molecule tetrakis(dimethylamino)ethylene (TMAE) and is sustained by RF coupling through the use of an antenna. Both highly collisional ohmic heating, and collisionless Landau wave absorption are studied as various neutral gas pressures are varied over several orders of magnitude. A multiple turn helical coil is utilized to maintain the discharge and a strong magnetic field is introduced to enhance field penetration. A strong magnetic field gradient is used to help initiate the discharge. Plasma densities of the order 10/sup 13/ cm/sup -3/ are obtained in a 2.5 cm radius tube. The computer codes ANTENA2 and MAXEB are used to help model the results. Non linear effects of collisionless damping and plasma creation are investigated. TMAE gas is being investigated as a possible seed gas for initiating atmospheric air plasmas because the plasma can be initiated with such a high initial condition.