Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session ET2: DPP/GEC Joint Session: Low Temperature Plasmas I |
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Chair: Amy Wendt, University of Wisconsin Room: Oregon Convention Center Ballroom 203 |
Tuesday, November 6, 2018 9:30AM - 10:00AM |
ET2.00001: Activation of stem cell identity by low temperature plasma in primary prostate cells Invited Speaker: Deborah O'Connell Low-temperature plasmas, at atmospheric pressure and temperature, are efficient sources for highly reactive particles. In this presentation the concentration of the plasma generated reactive species, their transport into liquids and subsequent action on primary prostate cancer cells, and matched normal tissue from the same patient, will be discussed. Prostate cancers are heterogeneous mixtures of cancer cells with differing properties. Our aim is to understand the response of these cellular sub-populations to plasma treatment in order to develop a therapy targeted at the cancer 'stem' cells, recognised as the resistance population responsible for reoccurrence. While overall significant cell death is observed post treatment, critically, a very small resistant population of viable cells remained after exposure. Understanding how these cells survive, including resistance mechanisms, and cell death signalling processes that are initiated following treatment, is required to optimise LTP-induced killing of prostate cancers. We report the precise molecular mechanisms triggered by LTP treatment in the near-patient models of prostate cancer. An immediate early and multifaceted anti-oxidative response was induced within 30 minutes of treatment, regardless of tissue origin. This was sufficient to protect a proportion of cells, with a more stem/progenitor phenotype, from toxic levels of reactive oxygen species. A number of stem cell maintenance programs were also activated, including Notch signalling, which have been implicated in tissue regeneration. Notch is fundamental to organism development, by acting as a master regulator of stem cell fate, and is activated by plasma treatment. To develop an effective therapy, with reduced likelihood of relapse, we propose specifically targeting this pathway using a combination of plasma treatment with Notch inhibitors. [Preview Abstract] |
Tuesday, November 6, 2018 10:00AM - 10:30AM |
ET2.00002: Magnetized plasmas for high-throughput mass separation Invited Speaker: Renaud Gueroult Rotation in magnetized plasmas holds great promise for a variety of applications. Under some conditions, rotation is for instance believed to mitigate or suppress turbulence. Recently, it has been suggested that rotation could be used to confine particles in toroidal geometry without the need for a poloidal magnetic field [1], and that this scheme could improve efficiency as compared to tokamaks. Yet another promising application of plasma rotation is separation. At its roots, plasma separation can be thought of as differential magnetic confinement, a generalization of magnetic confinement. Advancing plasma separation science hence shares many scientific issues with magnetic confinement. Foundational work on plasma mass separation, i. e. separation based on atomic mass in a plasma, was motivated by isotope separation. This typically involves separating elements with small mass difference at relatively low throughput. On the other hand, it has been shown in the last decade that separating elements based on mass at high throughput could prove particularly advantageous for a variety of high societal impact applications, including nuclear spent fuel reprocessing, nuclear waste cleanup and rare earth elements recycling. Yet, separation mechanisms which are efficient at low throughput often do not scale up to high throughput separation. For instance, many separation concepts rely on collisionless operation, which is not practical at high throughput. New separation mechanisms which are efficient at high throughput are therefore called for. One promising option is rotating plasma configurations, in which centrifugal effects can be supplemented by electric and magnetic forces to produce separation. In this talk I will review some of the fundamental physics challenges which remain to be addressed to enable mass separation in rotating plasma configurations at high throughput. [1] Rax, J. M., Gueroult, R. and Fisch, N. J., Phys. Plasmas, 2017, 24, 032504 [Preview Abstract] |
Tuesday, November 6, 2018 10:30AM - 11:00AM |
ET2.00003: Plasma Processing of Functionally Enhanced Complex Material Systems at the Atomic Scale Invited Speaker: Jane Chang Functionally improved materials are driving the technological advanced in silicon based integrated circuits to enable the continued down-scaling of circuit density and performance enhancement in analog, logic, and memory devices. Plasma processing can enable the synthesis and patterning of these functionally enhanced materials, especially at the nanoscale. This paper will address both atomic layer deposition and atomic layer etching by plasmas. For atomic layer deposition, complex materials can be synthesized not only with elemental precision to achieve the desired functionality but also with outstanding conformality, by leveraging the self-limiting surface reactions. In this talk, I will discuss current research advances in atomic layer deposition for synthesizing multifunction and complex metal oxides with tailored electronic, chemical, interfacial, thermal properties and microstructures. For atomic layer etching, based on the thermodynamic screening, viable chemistries are tested experimentally to corroborate the theoretical prediction. Some of the above mentioned material systems such as magnetic materials used in non-volatile memory devices are used as examples to demonstrate the broad applicability of this approach. [Preview Abstract] |
Tuesday, November 6, 2018 11:00AM - 11:30AM |
ET2.00004: Separating divertor closure effects in the SOL and pedestal Invited Speaker: Auna Moser Comparison between an open divertor and a more-closed divertor in DIII-D demonstrates detachment at a 20ā30% lower pedestal density (ne,ped) in the closed divertor, due to a combination of decreased fueling of the pedestal and increased dissipation in the scrape off layer (SOL) in the closed divertor, both resulting from increased neutral trapping in the divertor. Predicting whether the relationship between divertor closure and detachment will hold for an opaque SOL, in which the contribution of ionizing neutrals to fueling the pedestal is lessened, requires separating out the different mechanisms contributing to the density difference at detachment. A series of experiments on DIII-D characterizes matched discharges using various divertor configurations to isolate the effects of divertor closure. We identify detachment onset as the rollover in peak ion saturation current as a function of ne,ped, and support interpretation with DIII-Dās diagnostic suite. We use high resolution edge Thomson scattering measurements and power balance to determine density profiles and to find separatrix location and density, ne,sep. These experiments show detachment at 10ā20% lower ne,sep in the closed divertor than the open, supported by SOLPS simulations showing increased neutral trapping, and hence increased dissipation, in the closed divertor. We also find a difference in ne,ped/ne,sep: for matched ne,sep, the closed divertor has 10ā20% lower ne,ped, consistent with modeling showing a smaller ionization fraction inside the separatrix in this case. Changing the ionization profile by changing closure also allows us to investigate the relative contributions of ionization and radial transport to the density pedestal profile. Understanding how these pieces fit together will help us develop predictive models of pedestal density and detached divertors compatible with a high performance core. [Preview Abstract] |
Tuesday, November 6, 2018 11:30AM - 12:00PM |
ET2.00005: Electron kinetics at the plasma-solid interface Invited Speaker: Franz Xaver Bronold The most fundamental manifestation of the interaction of a plasma with a solid surface is the formation of an electric double layer consisting of an electron-depleted region on the plasma side of the interface and an electron-rich region on the solid side. It arises because electrons, outrunning the heavy species of the plasma, are deposited more efficiently onto or inside the solid than they are extracted from it by the neutralization of ions and Auger de-excitation of radicals. In my talk I will present the main results of our continuing effort, recently summarized in [1], to understand the electron kinetics across the plasma-solid interface from a microscopic point of view. Motivated by the prospects of solid-based opto-electronic plasma-devices and the charging of grains in dusty plasmas we set up schemes, based--respectively--on an invariant embedding approach and a semi-empirical Anderson-Newns model, for calculating electron sticking/backscattering and secondary electron emission probabilities. Besides presenting new results for these quantities, I will describe in this talk also first steps towards a kinetic modeling of the electron kinetics at the plasma-solid interface which treats electron transport across the interface self-consistently with the charge dynamics inside the plasma and the solid. We expect this type of integral modeling to open up new vistas for controlling miniaturized discharges on semiconducting substrates [2]. For the diagnostics of the solid-based space-charge regions in these devices, finally, we propose IR-ATR and EELS spectroscopy. [1] F.X. Bronold et al., Eur. Phys. J. D (2018) 72:88. [2] J.G. Eden et al., IEEE Trans. Plasma Sci. {\bf 41}, 661 (2013). Support from the Deutsche Forschungsgemeinschaft through project B10 of the SFB/TRR24 is greatly acknowledged. [Preview Abstract] |
Tuesday, November 6, 2018 12:00PM - 12:30PM |
ET2.00006: Three regimes of high voltage breakdown in a high current plasma switch for modern electric grid Invited Speaker: LIang Xu The high voltage breakdown of gases is important for many applications, e.g., for electric insulation, high-power switches, and tokamak start-up. However, low pressure and high voltage breakdown mechanism is poorly understood, because of necessity to include into consideration kinetic effects and complex particle-surface interactions. We studied the left branch of Paschen curve experimentally, analytically and by means of particle-in-cell/Monte Carlo collision (PIC/MCC) simulations for helium. A multi-valued Paschen curve in low voltage range ~1kV and also in high voltage range ~200kV was observed by experiments and predicted by PIC/MCC and analytical model [1, 2]. Three regimes of the breakdown have been identified according to contribution of impact ionization by electrons, by ions, and by fast neutrals to the total plasma generation. In the fast neutral and ion regime, the ionization avalanche is growing from the anode toward the cathode. Particles backscattering from the electrodes contribute the most to ionization near the anode and are responsible for initiating the ionization avalanche: fast neutrals backscattering from the cathode and fast electrons backscattering from the anode. [1] L. Xu et al. Phys. Plasmas 24, 093511 (2017). [2] L. Xu et al. Plasma Sources Sci. Technol. https://doi.org/10.1088/1361-6595/aace19 (2018). [Preview Abstract] |
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