Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session KW2: Magnetically Enhanced Plasmas |
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Chair: Tim Gans, York University Room: 308 AB |
Wednesday, October 14, 2015 1:30PM - 2:00PM |
KW2.00001: Fundamental Study on Filter Effect of Confronting Divergent Magnetic Fields Applied to a Low-Pressure Inductively Coupled Plasma Invited Speaker: Hirotake Sugawara Function of confronting divergent magnetic fields (CDMFs) applied to an inductively coupled plasma called the X-point plasma\footnote{T. Tsankov and U. Czarnetzki 2011 IEEE Trans. Plasma Sci. {\bf 39}, 2538.} was investigated. The plasma is driven by a planar spiral rf antenna on the top of a cylindrical chamber. The CDMFs are induced by two coaxial coils with dc currents of opposite directions, and have cusps on their separatrix plane and a magnetic null point at its center. Electron motion in H$_2$ at 1~Pa under the CDMFs was simulated using a Monte Carlo method. Electrons released form the chamber ceiling were captured in the upper region of the chamber by magnetic flux lines running between the ceiling and side wall. However, some of them diffused downward across the separatrix in two ways: passage through the weak magnetic field around the center, and displacement of electron gyrocenters from the upper region to the lower region due to scattering by gas molecules near the outer part of the separatrix. While the former was unselective about electron energy, the latter tended to occur for high-energy electrons with long gyroradii. This position-dependent selectivity in electron passage across the separatrix indicates applicability of the CDMFs as a magnetic filter or shutter. [Preview Abstract] |
Wednesday, October 14, 2015 2:00PM - 2:15PM |
KW2.00002: Microwave Assisted Helicon Plasmas Earl Scime, Umair Siddiqui, John McKee, Zach Short, Julianne McIlvain Up to 1.2 kW of pulsed 2.45 GHz microwaves are injected into argon and helium helicon plasmas at 6 to 20 mTorr neutral pressure, at 500 W of continuous rf power, and up to 1 kG magnetic field strengths. The objective is to heat the tail of the electron energy distribution function (EEDF) and populate ion metastable states for investigation with laser-induced-fluorescence. Langmuir probes are used to measure the EEDF and optical emission spectroscopy is used to monitor ion emission from excited states populated by the additional microwave power. The injection of microwave power in argon helicon plasmas is shown to heat the high energy tail of the EEDF without increasing the plasma density. Argon ion emission is shown to increase by a factor of 4. Injection of microwaves into a helium helicon plasma is shown to cool the bulk of the EEDF and increase the plasma density. Previously absent helium ion emission lines are observed with the injection of microwaves. [Preview Abstract] |
Wednesday, October 14, 2015 2:15PM - 2:30PM |
KW2.00003: Negative hydrogen ions in a linear helicon plasma device Cormac Corr, Jesse Santoso, Cameron Samuell, Hannah Willett, Rounak Manoharan, Sean O'Byrne Low-pressure negative ion sources are of crucial importance to the development of high-energy (\textgreater 1 MeV) neutral beam injection systems for the ITER experimental tokamak device. Due to their high power coupling efficiency and high plasma densities, helicon devices may be able to reduce power requirements and potentially remove the need for caesium. In helicon sources, the RF power can be coupled efficiently into the plasma and it has been previously observed that the application of a small magnetic field can lead to a significant increase in the plasma density. In this work, we investigate negative ion dynamics in a high-power (20kW) helicon plasma source. The negative ion fraction is measured by probe-based laser photodetachment, electron density and temperature are determined by a Langmuir probe and tuneable diode laser absorption spectroscopy is used to determine the density of the H(n $=$ 2) excited atomic state and the gas temperature. The negative ion density and excited atomic hydrogen density display a maximum at a low applied magnetic field of 3 mT, while the electron temperature displays a minimum. The negative ion density can be increased by a factor of 8 with the application of the magnetic field. Spatial and temporal measurements will also be presented. [Preview Abstract] |
Wednesday, October 14, 2015 2:30PM - 2:45PM |
KW2.00004: Analysis of Electron Trajectories in Magnetized High Power Plasmas Dennis Krueger, Sara Gallian, Jan Trieschmann, Ralf Peter Brinkmann High Power Impulse Magnetron Sputtering (HiPIMS) is an important example of magnetized technological plasmas. With HiPIMS the focus lies on the generation of a high density plasma with a remarkably high degree of ionization [1]. It can be used for the deposition of thin films with superior density and quality. Theoretical approaches to the regime of magnetized low temperature plasmas encounter some fundamental difficulties, for example concerning the details of the magnetic field configuration, the strongly varying degree of magnetization, and the frequent wall interactions. A kinetic single particle model is used for the investigations. Single electron trajectories are analyzed with the widely used Boris algorithm [2] within the magnetized zone above the target (racetrack). We further examine a configuration where symmetry breaking occurs due to a potential bump, which is rotating azimuthally around the racetrack (spoke). Observing the effects of this structure on the single electron motion may allow us to obtain further insight into this phenomenon. \\[1ex] [1] J. T. Gudmundsson et al., J. Vac. Sci. Technol. A \textbf{30}, 030801 (2012)\\[0ex] [2] J. P. Boris, Proc. 4th Conf. Num. Sim. Plasmas, 3--67 (1970) [Preview Abstract] |
Wednesday, October 14, 2015 2:45PM - 3:00PM |
KW2.00005: Observation of helicon wave with m$=$0 antenna in a weakly magnetized inductively coupled plasma source Bert Ellingboe, Nishant Sirse, Rachel Moloney, John McCarthy Bounded whistler wave, called ``helicon wave,'' is known to produce high-density plasmas and has been exploited as a high density plasma source for many applications, including electric propulsion for spacecraft. In a helicon plasma source, an antenna wrapped around the magnetized plasma column launches a low frequency wave, $\omega_{\mathrm{ce}}$/2 \textgreater $\omega_{\mathrm{helicon}}$ \textgreater $\omega _{\mathrm{ce}}$/100, in the plasma which is responsible for maintaining high density plasma. Several antenna designs have been proposed in order to match efficiently the wave modes. In our experiment, helicon wave mode is observed using an m$=$0 antenna. A floating B dot probe, compensated to the capacitively coupled E field, is employed to measure axial-wave-field-profiles (z, r, and $\theta $ components) in the plasma at multiple radial positions as a function of rf power and pressure. The B$_{\mathrm{\theta }}$ component of the rf-field is observed to be unaffected as the wave propagates in the axial direction. Power coupling between the antenna and the plasma column is identified and agrees with the E, H, and wave coupling regimes previously seen in M$=$1 antenna systems. That is, the B$_{\mathrm{z}}$ component of the rf-field is observed at low plasma density as the B$_{\mathrm{z}}$ component from the antenna penetrates the plasma. The B$_{\mathrm{z}}$ component becomes very small at medium density due to shielding at the centre of the plasma column; however, with increasing density, a sudden ``jump'' occurs in the B$_{\mathrm{z}}$ component above which a standing wave under the antenna with a propagating wave away from the antenna are observed. [Preview Abstract] |
Wednesday, October 14, 2015 3:00PM - 3:15PM |
KW2.00006: Spatial and temporal evolution of negative ions in a pulsed inductively coupled hydrogen plasma source across a magnetic filter Stuart Nulty, Cormac Corr Low-temperature electronegative plasmas have important applications in high-energy sources for fusion energy, plasma thrusters~and materials processing. Neutral beam injection systems and space thruster technology such as the PEGASUS propulsion system rely on efficiently producing extractable negative ions. In this work we investigate the production of hydrogen negative ions in a pulsed inductively coupled plasma across a magnetic filter. The electron energy distribution function, plasma density and electron temperature are determined using an RF compensated Langmuir probe, and time-resolved laser photo-detachment is used to measure the negative ion fraction. The spatial and temporal evolution of these plasma parameters within the plasma source will be presented. Using a pulsed plasma and a magnetic filter, the electron temperature can be efficiently controlled and a higher density of negative ions compared to electrons can be obtained at certain locations within the source. [Preview Abstract] |
Wednesday, October 14, 2015 3:15PM - 3:30PM |
KW2.00007: Coupling modes in a dipolar microwave plasma source Ana Lacoste, Pierre Baele, Remy Maurau, Stephane Bechu, Alexandre Bes The multi-dipolar microwave plasma is a suitable technology for the scaling-up of high density plasma processing in the very low pressure range. Effectively, a large area or volume of plasma can be achieved by a mere distribution, over 2 or 3 dimensions, of a number of elementary plasma sources. To enhance the microwave coupling efficiency and optimize the spatial repartition of the elementary plasma sources, it could be helpful to localize the production regions and coupling modes that govern the energy transfer from the wave to the electrons. The main objective of this work is to identify the possible coupling modes as a function of operating parameters. Accordingly, the plasma parameters (electron temperature, density) were correlated together with the electromagnetic radiation, as well as with different coupling modes observed as a function of microwave power. High plasma densities, up to 10 times the critical density (for one source), can be achieved through an efficient transfer of the electrostatic wave energy to the electrons. [Preview Abstract] |
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