Wave trajectories propagating obliquely to the magnetic field in toroidal plasmas are studied theoretically. Results show that the ordinary wave at the appropriate incident angle is mode converted to the extraordinary wave at the first turning point and is further converted to the electron Bernstein wave while passing a loop or a folded curve near the second turning point and is cyclotron-damped away, resulting in local electron heating, before arriving at the cyclotron resonance layer.
Spontaneous formation of spherical tokamak is observed during a microwave discharge at the electron cyclotron resonance (ECR) under a steady vertical magnetic field. In the course of slow plasma current increase, a fast rise of current (usually within several ms) occurs and the magnetic field topology changes drastically from open field type to closed one. After this current jump, a steady plasma current is maintained. The plasma current in the steady stage is proportional to the strength of the vertical field which balances the outward hoop force of the plasma current and maintains the MHD equilibrium. When a 5GHz, 130kW, 60ms microwave power is injected at 85G vertical field, plasma current of 6.8kA is obtained.
Finite element analysis (FEA) and NURBS-based computer-aided design (CAD) had been developed independently until isogeometric analysis, was introduced by Hughes et al in 2005. Unlike FEA, in isogeometric analysis the CAD geometry represented by NURBS surfaces/solids are converted to NURBS elements exactly without any approximations In this paper we investigate methods to generate NURBS solids used for isogeometric analysis NURBS solids include swung solids, lofted solids, and swept solids. Examples with various solids are provided to demonstrate the effectiveness of the proposed algorithms.
Incident lower hybrid waves (LHW) propagate toward the center of the plasma in a spiral form in the poloidal and the toroidal sections, and finally are absorbed by the ion Landau damping (ILD) and/or the electron Landau damping (ELD) in accordance with the refractive index parallel to the magnetic field N‖, which is varied considerably along the trajectory because of the toroidicity and the rotational transform. We propose the scaling law of the wave trajectories on plasma parameters, which shows that the control of N‖ or the applied frequency is necessary during the lower hybrid heating (LHH).
Summary form only given. Recent progress on spherical tokamak (ST) experiments has verified its advantage of high beta capability, which provides attractive engineering benefits connected with a compact design to realize an economical fusion power plant. Because of a severely restricted space at the narrow center column of ST devices, removing the central ohmic solenoid is considered to be a crucial step for a future plant and is also a key requirement of CTF. It is therefore strongly desired to develop an alternative way to ohmic heating to initiate and ramp-up the plasma current to a level high enough for the second heating and current drive by NBI to reach ignition. The main objective of LATE (low aspect ratio torus experiment) is to demonstrate the formation of ST by electron cyclotron heating (ECH) alone without the center solenoid. By injecting a 2.45 GHz microwave pulse up to 30 kW for two seconds, a plasma current has been initiated and ramped-up slowly to 7.2 kA with a slow ramp-up of the vertical field to maintain the equilibrium of the plasma current loop. Firstly, a steady toroidal field and a steady vertical field (Bv = 15 Gauss at R = 27 cm) are applied and hydrogen gas is introduced. Microwaves from three magnetrons are injected from outboard side with the linearly polarized electric field on the equatorial plane. An initial plasma is instantly produced at the fundamental EC resonance layer, and quickly expands into the low field side. A plasma current is then generated and increased up to 2.0 kA spontaneously and an initial closed flux surface is formed under the steady vertical field. The current subsequently ramps up slowly by increasing the microwave power and the Bv field in order to keep the higher current in equilibrium, and finally reaches Ip = 7.2 kA at Bv = 78 Gauss. This value of the Ip amounts 12 percent of the toroidal field coil current. Magnetic analysis shows that an ST equilibrium, having the last closed flux surface with an aspect ratio of R 0 /a = 20.5 cm/15 cm ~ 1.4, an elongation of kappa = 1.6 and q edge = 34, has been formed and maintained at the final discharge stage. The plasma current center is kept near the 2nd EC resonance layer and the line averaged electron density significantly exceeds the plasma cutoff density, suggesting that the second harmonic ECH by the mode converted electron Bernstein wave could be responsible for heating in the present plasma
We have observed spectra of lithium-like oxygen and carbon ions from the WT-3 tokamak plasma with an XUV spectrometer. On the basis of the branching ratios to visible UV spectral lines and the collisional-radiative model calculation for excited level populations, we have determined the absolute sensitivity of the spectrometer from 11.5 through 31.2 nm. From the line intensities emitted from the scrape-off layer plasma, we have estimated the charge exchange recombination rate coefficients of helium-like oxygen ions colliding with neutral hydrogen atoms or molecules.
