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DOE OSTI2011

RF-Plasma Source Commissioning in Indian Negative Ion Facility

The Indian program of the RF based negative ion source has started off with the commissioning of ROBIN, the inductively coupled RF based negative ion source facility under establishment at Institute for Plasma research (IPR), India. The facility is being developed under a technology transfer agreement with IPP Garching. It consists of a single RF driver based beam source (BATMAN replica) coupled to a 100 kW, 1 MHz RF generator with a self excited oscillator, through a matching network, for plasma production and ion extraction and acceleration. The delivery of the RF generator and the RF plasma source without the accelerator, has enabled initiation of plasma production experiments. The recent experimental campaign has established the matching circuit parameters that result in plasma production with density in the range of 0.5-1x10{sup 18}/m{sup 3}, at operational gas pressures ranging between 0.4-1 Pa. Various configurations of the matching network have been experimented upon to obtain a stable operation of the set up for RF powers ranging between 25-85 kW and pulse lengths ranging between 4-20 s. It has been observed that the range of the parameters of the matching circuit, over which the frequency of the power supply is stable, is narrow and further experiments with increased number of turns in the coil are in the pipeline to see if the range can be widened. In this paper, the description of the experimental system and the commissioning data related to the optimisation of the various parameters of the matching network, to obtain stable plasma of required density, are presented and discussed.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Phase composition and magnetic properties of niobium-iron codoped TiO{sub 2} nanoparticles synthesized in Ar/O{sub 2} radio-frequency thermal plasma

Nanoparticles of Nb{sup 5+}-Fe{sup 3+} codoped TiO{sub 2} with various Nb{sup 5+} concentrations (Nb/(Ti+Fe+Nb)=0-10.0 at%) and Fe{sup 3+} (Fe/(Ti+Fe+Nb)=0-2.0 at%) were synthesized using Ar/O{sub 2} thermal plasma. Dopant content, chemical valence, phase identification, morphology and magnetic properties were determined using several characterization techniques, including inductively coupled plasma-optical emission spectrometer, X-ray photoelectron spectroscopy, X-ray diffraction, UV-vis diffuse reflectance spectrometer, field-emission scanning electron microscopy, transmission electron microscopy and SQUID commercial instrument. The XRD revealed that all the plasma-synthesized powders were exclusively composed of anatase as major phase and rutile. The rutile weight fraction was increased by the substitution of Fe{sup 3+} for Ti{sup 4+} whereas it was reduced by the Nb{sup 5+} doping. The plasma-synthesized Nb{sup 5+}-Fe{sup 3+} codoped TiO{sub 2} powders had intrinsic magnetic properties of strongly paramagnetic and feebly ferromagnetic at room temperature. The ferromagnetic properties gradually deteriorated as the Fe{sup 3+} concentration was decreased, suggesting that the ferromagnetism was predominated by the phase composition as a carrier-mediated exchange. - Graphical Abstract: Spherical nanoparticles of Nb{sup 5+}-Fe{sup 3+} codoped TiO{sub 2} were synthesized using Ar/O{sub 2} thermal plasma. The plasma-synthesized powders were composed of anatase as major phase and rutile. Rutile weight fraction was increased by Fe{sup 3+} addition but was reduced by Nb{sup 5+} doping. Strongly paramagnetic and feebly ferromagnetic properties are of intrinsic nature. Ferromagnetic properties gradually deteriorated as Fe{sup 3+} concentration was increased. Highlights: > Nanoparticles of Nb{sup 5+}-Fe{sup 3+} codoped TiO{sub 2} were synthesized using Ar/O{sub 2} thermal plasma. > The plasma-synthesized powders were composed of anatase as major phase and rutile. > Rutile weight fraction was increased by Fe{sup 3+} addition but was reduced by Nb{sup 5+} doping. > Strongly paramagnetic and feebly ferromagnetic properties are of intrinsic nature. > Ferromagnetic properties gradually deteriorated as Fe{sup 3+} concentration was increased.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2011

HHFW Heating and Current Drive Studies of NSTX H-Mode Plasmas

30 MHz high-harmonic fast wave (HHFW) heating and current drive are being developed to assist fully non-inductive plasma current (I{sub p}) ramp-up in NSTX. The initial approach to achieving this goal has been to heat I{sub p} = 300 kA inductive plasmas with current drive antenna phasing in order to generate an HHFW H-mode with significant bootstrap and RF-driven current. Recent experiments, using only 1.4 MW of RF power (P{sub RF}), achieved a non-inductive current fraction, f{sub NI}{approx}0.65. Improved antenna conditioning resulted in the generation of I{sub p} = 650 kA HHFW H-mode plasmas, with f{sub NI}{approx}0.35, when P{sub RF}{>=}2.5 MW. These plasmas have little or no edge localized mode (ELM) activity during HHFW heating, a substantial increase in stored energy and a sustained central electron temperature of 5-6 keV. Another focus of NSTX HHFW research is to heat an H-mode generated by 90 keV neutral beam injection (NBI). Improved HHFW coupling to NBI-generated H-modes has resulted in a broad increase in electron temperature profile when HHFW heating is applied. Analysis of a closely matched pair of NBI and HHFW+NBI H-mode plasmas revealed that about half of the antenna power is deposited inside the last closed flux surface (LCFS). Of the power damped inside the LCFS about two-thirds is absorbed directly by electrons and one-third accelerates fast-ions that are mostly promptly lost from the plasma. At longer toroidal launch wavelengths, HHFW+NBI H-mode plasmas can have an RF power flow to the divertor outside the LCFS that significantly reduces RF power deposition to the core. ELMs can also reduce RF power deposition to the core and increase power deposition to the edge. Recent full wave modeling of NSTX HHFW+NBI H-mode plasmas, with the model extended to the vessel wall, predicts a coaxial standing mode between the LCFS and the wall that can have large amplitudes at longer launch wavelengths. These simulation results qualitatively agree with HHFW+NBI H-mode data that show decreasing core RF heating efficiency and increasing RF power flow to the lower divertor at longer launch wavelengths.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗