Kamran Akhtar

Plasma interferometry at high pressures

A general formulation for the measurement of plasma density and effective collision frequency for lowly as well as highly, collisional plasmas using millimeter wave interferometry is presented. In the presence of high density and collisionality at high gas pressures where the collision frequency (ν) is of the order of both the plasma (ωp) and the wave frequency of the millimeter wave (ω) (ν∼ω,ωp), the measured line-average plasma density has a complex dependence on phase shift as well as the amplitude change of the millimeter wave signal. The measurement scheme and analysis presented in this article show that for collisional plasmas, simultaneous measurement of the phase change and the amplitude change data is required to uniquely determine the plasma density and collision frequency. The treatment allows the application of millimeter wave interferometry to a wide range of relative collision frequency, wave frequency and plasma frequency since it uniquely determines the line-average plasma density and effe...

Optical, wave measurements, and modeling of helicon plasmas for a wide range of magnetic fields

Helicon waves are excited in a plasma wave facility by a half-turn double-helix antenna operating at 13.56 MHz for static magnetic fields ranging from 200 to 1000 G. A non-perturbing optical probe located outside the Pyrex™ plasma chamber is used to observe 443 nm Ar II emission that is spatially and temporally correlated with the helicon wave. The Ar II emission is measured along with wave magnetic and Langmuir probe density measurements at various axial and radial positions. 105 GHz interferometry is used to verify the bulk temperature corrected Langmuir probe measurements. The measured peak Ar II emission phase velocity is compared to the measured wave magnetic field phase velocity and code predicted wave phase velocity for the transition and blue mode regimes. Very different properties of the optical emission peak phase and wave characteristics for the transition and helicon modes of operation are observed. Comparison of the experimental results with the ANTENAII code [Y. Mouzouris and J. E. Scharer, ...

Substantial Doppler broadening of atomic-hydrogen lines in dc and capacitively coupled RF plasmas

The mechanism of extraordinary broadening of the Balmer lines of hydrogen admixed with noble gases in a dc glow discharge and a capacitively coupled rf discharge is studied over a wide range of pressure and gas compositions to test the field acceleration model (Cvetanovic et al 2005 J. Appl. Phys. 97 033302). High-resolution optical emission spectroscopy is performed parallel to the electrode axis (end-on) and perpendicular to the electrode axis (side-on) along with Langmuir probe measurements of plasma density and electron temperature for the parallel plate rf capacitive discharge case. Sharp pin-shaped tungsten dc electrodes are also used to minimize the backscattering of ions that are theorized by a field acceleration model to be heated in the sheath region. An excessively broad and symmetric (Gaussian) Balmer emission line corresponding to 20?60?eV of hydrogen atom energy is observed in Ar/H2 and He/H2 plasmas when compared with the majority species atom temperatures. Energy is transferred selectively to hydrogen atoms whereas the atoms of admixed He and Ar gases remain cold (<0.5?eV). Since there is neither a preferred ion nor atom in the field acceleration model, one should also observe enhanced temperature hydrogen and helium atoms in He/H2 discharges where the atomic mass is more comparable (4?:?1).

Spectroscopic observation of helium-ion- and hydrogen-catalyzed hydrino transitions

Four predictions of Mills’ Grand Unified Theory of Classical Physics (GUTCP) regarding atomic hydrogen undergoing a catalytic reaction with certain atomized elements and ions which resonantly, nonradiatively accept integer multiples of the potential energy of atomic hydrogen, m · 27.2 eV wherein m is an integer, have been confirmed experimentally. Specifically, a catalyst comprises a chemical or physical process with an enthalpy change equal to an integer multiple m of the potential energy of atomic hydrogen, 27.2 eV. For He+m = 2, due to its ionization reaction to He2+, and two H atoms formed from H2 by collision with a third, hot H can also act as a catalyst with m = 2 for this third H. The product is H(1/p), fractional Rydberg states of atomic hydrogen called “hydrino atoms” wherein n = 1/2, 1/3, 1/4, …, 1/p(p≤137 is an integer) replaces the well-known parameter n = integer in the Rydberg equation for hydrogen excited states. The predictions for the hydrino reaction of (1) pumping of the catalyst excited states, (2) characteristic EUV continuum radiation, (3) fast H, and (4) hydrino products were observed in multiple catalyst-hydrogen plasma systems.

Characterization of laser produced tetrakis (dimethylamino) ethylene plasma in a high-pressure background gas

We present an interferometric and spectroscopic characterization of ultraviolet (UV) laser photoionization of a low ionization potential organic vapor, tetrakis (dimethylamino) ethylene (TMAE), seeded in high-pressure air component gases. These experiments are performed to explore the feasibility of using an electrodeless UV laser preionization of TMAE to initiate a plasma seeded in atmospheric pressure gases that can later be sustained by radiofrequency (RF) power by inductive wave coupling, thereby reducing the initiation RF power budget. A large volume (500 cc), high-density (/spl sim/10/sup 13/cm/sup -3/), electrodeless plasma is created by single-photon, 193 nm excimer laser ionization. 105 GHz millimeter-wave interferometry along with optical spectroscopy is employed to investigate the plasma formation and decay characteristics. The TMAE plasma decay mechanisms including two-body and three-body recombination with and without high pressure gases are examined and the dominant loss processes discussed and evaluated. Both density and optical emission measurements show a delay of 140 /spl plusmn/ 10 ns in the peak plasma density and emission indicating that the dominant ionization process is delayed ionization via excitation of super-excited states. The experiment also shows that TMAE remains a viable seed gas for UV ionization in the presence of air for t/spl les/10 min.

Development of compact electron cyclotron resonance plasma source

Although it is well known that electron cyclotron resonance (ECR) produced plasmas are efficient, high-density sources and have potential applications in industry, a compact ECR plasma source still remains to be developed. This paper discusses the development of a novel, compact ECR plasma source (CEPS) that is both portable and easily mountable on a chamber of any size. The design of the CEPS is based on our detailed investigations of microwave coupling into a plasma loaded conducting waveguide and its subsequent absorption by the ECR process. It treats the plasma source section of the CEPS like a plasma loaded waveguide which can support a number of guided plasma waves that are both resonant (resonating at ωce ≈ ω), and non-resonant (propagating through the ωce ≈ ω layer). Also, these modes suffer a reversal of polarization along the radius (from right hand polarized to left and vice versa) so that both azimuthal modes m = + 1 (RCP on axis) and m = - 1 (LCP on axis) are absorbed with equal ease. The design of the CEPS uses a fully integrated microwave line (including a quartz, microwave window) for operation at 2.45 GHz, 800 Watts, cw. The required magnetic field is produced by a set of suitably designed NdFeB ring magnets. The paper discusses the development of the CEPS in light of the above physics issues and presents characterization results using a single CEPS. These CEPS were developed for very large volume plasma production and up to twelve such sources have also been used for producing plasma in a large volume plasma system (diameter ≈ 1m, height 1.55 m).

Absorption of high-frequency guided waves in a plasma-loaded waveguide

A kinetic theory model for the absorption of high-frequency guided plasma waves is presented for a warm, inhomogeneous, magnetized plasma column loaded inside a waveguide. Electron cyclotron resonance (ECR) absorption and Landau damping terms, derived as the anti-Hermitian part of the susceptibility tensor, are included in the model for a loss-free plasma-loaded waveguide developed earlier [A. Ganguli et al., Phys. Plasmas 5, 1178, (1998)]. In this formulation, the imaginary part of the complex propagation constant (in the presence of absorption) is obtained using a perturbation technique treating the anti-Hermitian part of the dielectric tensor as small in comparison to the Hermitian part, for the loss-free plasma. In this paper, we present the formulation for the inclusion of ECR absorption and Landau damping along with numerical results describing the role of a small population of warm electrons in wave damping in such a discharge. Numerical results are presented in the form of dispersion curves (plots...

Radio-Frequency Sustainment of Laser Initiated, High-Pressure Air Constituent Plasmas

In this paper we investigate the feasibility of creating a high‐density ∼ 1012−1014 cm−3, large volume seed plasma in air constituents by laser (300 mJ, 20(±2) ns) preionization of an organic gas seeded in high‐pressure gas mixtures and then sustained by efficient absorption of rf power (1–25 kW pulsed) through inductive coupling of the wave fields. A multi‐turn helical antenna is used to couple radio‐frequency power through a capacitive matching network. A 105 GHz interferometer is employed to obtain the plasma density in the presence of high collisionality utilizing phase shift and amplitude attenuation data. TMAE Plasma decay mechanisms with and without the background gas are examined.

Efficient Creation of Laser Initiated, RF Sustained Atmospheric Pressure Range Plasmas

Summary form only given. We examine 193 nm (6.4 eV) UV photon ionization of low ionization level (6.1 eV) seed (15 mtorr) gas to reduce the power levels for radio frequency (RF) sustainment of large volume (500-2500 cc), high density (1012-13/cc), atmospheric pressure range (50-760 torr) plasmas. These plasmas have potential applications in the areas of biological decontamination, radar absorption, thin films and processing of industrial materials. We have demonstrated the use of UV seeded plasma as a load for efficient inductive coupling at lower RF powers in argon. The tetrakis (dimethylamino) ethylene (TMAE), laser-initiated seed plasma recombination rates and observation of substantial delay in addition to direct ionization processes have been characterized in air and other gases. Current research is focused on the temporal measurement and matching of the laser and RF plasma load to the inductive helical antenna to produce high density, large volume plasmas. Time resolved antenna impedance and RF power measurements are performed to improve matching and determine the characteristics of the laser-ionized and radio frequency sustained plasma. In addition, millimeter-wave interferometry and optical emission spectroscopy diagnostics are used to determine the spatial and temporal plasma constituents. The addition of small concentrations (~2%) of hydrogen and measurements of line broadening are used together with the other diagnostics to determine the spatial and temporal plasma temperature, density, and recombination rates immediately after the rapid shut off of RF power

RF Matchings Time Resolved Impedance, Power and Interferometer Measurements of Laser Initiated, RF Sustained Atmospheric Pressure Plasmas

Summary form only given. The feasibility of laser ionization and radio frequency sustainment of high-pressure seeded plasmas in argon has been demonstrated by our group in previous work. The tetrakis (dimethylamino) ethylene (TMAE) laser-initiated seed plasma recombination rates have also been characterized. Time resolved impedance and RF power measurements are performed on the plasma system in order to optimize and further characterize this laser-ionized and radio frequency sustained plasma. An atmospheric pressure range (40-760 torr), large volume (~2000 cc) air and air constituent (N2 and O2) plasma of high density (>1012 cm-3 ) is initiated by a 193 nm excimer UV laser and sustained by 13.56 MHz RF power through a helix coil antenna and matching system. The plasma loading impedance in the steady-state regime was characterized using high voltage probes and found to be of order 4.0 + j100.0 Omega, which varies dependent on the gas pressure and flow rate. The temporal variation of the plasma impedance and net coupled RF power are measured. Interferometer and spectroscopic analysis of plasma density, temperature, collision rate and recombination rates are discussed