Particle simulation of lower hybrid wave propagation in fusion plasmas

Global particle simulations of the lower hybrid (LH) waves have been carried out using fully kinetic ions and drift kinetic electrons with a realistic electron-to-ion mass ratio. The LH wave frequency, mode structure, and electron Landau damping from the electrostatic simulations agree very well with the analytic theory. Linear simulation of the propagation of a LH wave-packet in the toroidal geometry shows that the wave propagates faster in the high field side than the low field side, in agreement with a ray tracing calculation. This poloidal asymmetry arises from the non-conservation of the poloidal mode number due to the non-uniform magnetic field. In contrast, the poloidal mode number is conserved in the cylindrical geometry with the uniform magnetic field.Physics, Fluids & PlasmasPhysics, NuclearSCI(E)[email protected]

ELM mitigation by supersonic molecular beam injection: KSTAR and HL-2A experiments and theory

We report recent experimental results from HL-2A and KSTAR on ELM mitigation by supersonic molecular beam injection (SMBI). Cold particle deposition within the pedestal by SMBI is verified in both machines. The signatures of ELM mitigation by SMBI are an ELM frequency increase and ELM amplitude decrease. These persist for an SMBI influence time τI. Here, τI is the time for the SMBI influenced pedestal profile to refill. An increase in fELMSMBI/fELM0 and a decrease in the energy loss per ELM ΔWELM were achieved in both machines. Physical insight was gleaned from studies of density and vΦ (toroidal rotation velocity) evolution, particle flux and turbulence spectra, divertor heat load. The characteristic gradients of the pedestal density soften and a change in vΦ was observed during a τI time. The spectra of the edge particle flux Γ ∼ 〈ṽrñe〉 and density fluctuation with and without SMBI were measured in HL-2A and in KSTAR, respectively. A clear phenomenon observed is the decrease in divertor heat load during the τI time in HL-2A. Similar results are the profiles of saturation current density Jsat with and without SMBI in KSTAR. We note that τI/τp (particle confinement time) is close to ∼1, although there is a large difference in individual τI between the two machines. This suggests that τI is strongly related to particle-transport events. Experiments and analysis of a simple phenomenological model support the important conclusion that ELM mitigation by SMBI results from an increase in higher frequency fluctuations and transport events in the pedestal. © 2014 IAEA, Vienna

Effects in CVD diamond exposed to fusion plasmas

Micro and nanocrystalline diamond layers have been deposited on molybdenum substrates by hot-filament CVD, and tested in the Mega Amp Spherical Tokamak as a protective coating of fusion plasma-facing materials. The modification of surface properties induced by high density plasma was investigated by SEM, X-ray photoelectron spectroscopy and Raman spectroscopy. Although some modifications of the coating, amorphization and some traces of arcing, diamond proved to be a viable protection as most of the samples were still coated after the plasma exposure. Fuel retention measurements, evaluated by nuclear reaction analysis, showed that a small amount of deuterium was trapped in the surface of the coatings. The chemical erosion of the layers was 50% lower than graphite, as evaluated by dedicated experiments in Pilot-PSI, a linear plasma simulator device. © 2009 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.</p