Volume 93, Issue 11, 01 June 2003
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
93(2003); http://dx.doi.org/10.1063/1.1571967View Description Hide Description
Atmospheric pressure inductively coupled thermal plasmas with pulsing mode are generated for 104 slpm standard liters per minute total flow rate of and mixtures (Ar 94% molar concentration) inside a torch of 55 mm inner diameter. The inverter-type power source of 22 kW maximum output supplied coil current of 1 MHz fundamental frequency at 17.3 kW level, and the coil current is modulated by an external pulsed signal to produce the desired pulse modulated plasmas. Spectroscopic measurements are carried out for the temporal radiation intensity and coil current intensity. In addition, a time-dependent, two-dimensional model, which works with coil current input, is solved by using the same coil current profile measured in the experiment. Experimental and theoretical results for 67% duty factor with 10 ms on-time are compared. The theoretical predictions are found comparable with the experimental findings although the theoretical time-dependent response is seen slower, especially over the time just after on-pulsation. An estimation of electron temperature helps to describe this discrepancy fairly adequately. Experimentally the shimmer current level is found to vary with gas composition as well as with on- and off-time of pulsing signal. Both the experimental and theoretical findings suggest that plasma responds slowly at any axial positions below midcoil compared to that at midcoil level.
93(2003); http://dx.doi.org/10.1063/1.1565822View Description Hide Description
Experiments are reported in which two configurations for ablation-plasma-ion-implantation (APII) are characterized by diagnostics and compared. The first configuration oriented the target parallel to the deposition substrate. This orientation yielded ion-beam-assisted deposition of thin films. A delay between laser and high voltage was necessary for this geometry to avoid arcing between negatively biased substrate and target. The second experimental configuration oriented the target perpendicular to the deposition substrate, reducing arcing, even for zero/negative delay between the laser and the high voltage pulse. This orientation also reduced neutral atom, ballistic deposition on the substrate resulting in a pure ion implantation mode. Ion density measurements were made by resonant laser diagnostics and Langmuir probes, yielding total ion populations in the range of Implanted ion doses were estimated by electrical diagnostics, and materials analysis, including x-ray energy dispersive spectroscopy and x-ray photoelectron spectroscopy, yielding implanted doses in the range This yields an APII efficiency of order 10% for implantation of laser ablated ions. Scaling of ion dose with voltage agrees well with a theory assuming the Child–Langmuir law and that the ion current at the sheath edge is due to the uncovering of the ions by the movement of the sheath.Thin film analysis showed excellent adhesion with smoother films for an accelerating voltage of higher voltages roughened the film.
93(2003); http://dx.doi.org/10.1063/1.1572549View Description Hide Description
A series of time-dependent one-dimensional simulations has been carried out on the hydrodynamic behavior of argon and air plasmas in an explosively driven magnetohydrodynamic power generator. The thermodynamic properties of plasma gases are computed using equation-of-state data obtained from a detailed theoretical model. The plasmaconductivities are given by a mixture rule, which comprises the fully and weakly ionized plasma approximations. The effects of the initial pressure and the magnetic field strength on the plasma behavior in the flow channel are examined over a moderate range of operating conditions, and then the computed results are compared with the experimental measurements, showing good agreement for the case of low magnetic Reynolds number.
93(2003); http://dx.doi.org/10.1063/1.1570931View Description Hide Description
Curved magnetic filters are often used for the removal of macroparticles from cathodic arc plasmas. This study addresses the need to further reduce losses and improving plasma throughput. The central figure of merit is the system coefficient κ defined as a filtered ion current normalized by the plasma-producing arc current. The coefficient κ is investigated as a function of continuous and pulsed magnetic field operation, magnetic field strength, external electric bias, and arc amplitude. It increases with positive filter bias but saturates at about 15 V for relatively low magnetic field (∼10 mT), whereas stronger magnetic fields lead to higher κ with saturation at about 25 V. Further increase of positive bias reduces κ. These findings are true for both pulsed and continuous filters. Bias of pulsed filters has been realized using the voltage drop across a self-bias resistor, eliminating the need for a separate bias circuit. Almost 100 A of filtered copper ions have been obtained in pulsed mode, corresponding to The results are interpreted by a simplified potential trough model.