Toroidal field ripple effects in TNS design

In the design of TNS, the choice of the number of TF coils has been made on the basis of trade-off studies among the plasma physics considerations and engineering design requirements. The theory of the magnetic field ripple effects has been studied to include the effects of noncircular cross sections such as those encountered in high-beta equilibria. A computer simulation model (RIPPLE) was developed to examine the field ripple effects on plasma transport and scaling. The magnetic field computer program BOVAL was used to calculate the magnetic field due to current flowing in a noncircular coil of finite rectangular cross section. The number of toroidal field (TF) coils is then determined by calculating the maximum magnetic field ripple that can be tolerated from plasma physics considerations

Kinetic simulations of X-B and O-X-B mode conversion and its deterioration at high input power

Spherical tokamak plasmas are typically overdense and thus inaccessible to externally-injected microwaves in the electron cyclotron range. The electrostatic electron Bernstein wave (EBW), however, provides a method to access the plasma core for heating and diagnostic purposes. Understanding the details of the coupling process to electromagnetic waves is thus important both for the interpretation of microwave diagnostic data and for assessing the feasibility of EBW heating and current drive. While the coupling is reasonably well-understood in the linear regime, nonlinear physics arising from high input power has not been previously quantified. To tackle this problem, we have performed one- and two-dimensional fully kinetic particle-in-cell simulations of the two possible coupling mechanisms, namely X-B and O-X-B mode conversion. We find that the ion dynamics has a profound effect on the field structure in the nonlinear regime, as high amplitude short-scale oscillations of the longitudinal electric field are excited in the region below the high-density cut-off prior to the arrival of the EBW. We identify this effect as the instability of the X wave with respect to resonant scattering into an EBW and a lower-hybrid wave. We calculate the instability rate analytically and find this basic theory to be in reasonable agreement with our simulation results

Compact DT fusion spherical tori at modest field

This paper is a compilation of viewgraphs on the Ignition Spherical Torus (IST). Topics addressed in the report are plasma and engineering aspects, toroidal field coil technology, attractive features of the compact torus, and the need for an additional physics data base. (WRF

Edge turbulence and transport: Text and ATF modeling

We present experimental results on edge turbulence and transport from the tokamak TEXT and the torsatron ATF. The measured electrostatic fluctuations can explain the edge transport of particles and energy. Certain drive (radiation) and stabilizing (velocity shear) terms are suggested by the results. The experimental fluctuation levels and spectral widths can be reproduced by considering the nonlinear evolution of the reduced MHD equations, incorporating a thermal drive from line radiation. In the tokamak limit (with toroidal electric field) the model corresponds to the resistivity gradient mode, while in the currentless torsatron or stellarator limit it corresponds to a thermally driven drift wave

Configuration control, fluctuations, and transport in low-collisionality plasmas in the ATF Torsatron

In low-collisionality plasmas confined in tokamaks and stellarators, instabilities driven by particles trapped in inhomogeneities of the magnetic fields could be important in increasing plasma transport coefficients. In the Advanced Toroidal Facility (ATF), an {ell} = 2, M = 12 field-period stellarator device with major radius R = 2.1 m, average plasma minor radius a = 0.27 m, central and edge rotational transforms {chi}{sub 0} {approx} 0.3, {chi}{sub a} {approx} 1, the effects of electron trapping in the helical stellarator field are expected to be important in plasmas with {bar n}{sub e} {approx} 5 {times} 10{sup 12} cm{sup {minus}3}, T{sub e0} {approx} 1 keV. Such plasmas have already been sustained for long-pulses (20 s) using 150--400 kW of 53.2-GHz ECH power at B = 0.95 T. Transport analysis shows that for {rho} = r/a {le} 1/3, the electron anomalous transport is {le}10 times the neoclassical value, while at {rho} = 2/3 it is 10--100 times neoclassical; this is compatible with expectations for transport enhancement due to dissipative trapped-electron modes. 4 refs., 3 figs

Synchrotron emission from the ring electrons in EBT

The energy spectrum of the synchrotron radiation emitted by the relativistic ring electrons in ELMP bumpy Torus (EBT) has been calculated for various classes of isotropic and anisotropic ring electron distribution functions. Calculations have been carried out for present (EBT-I/S) and planned (EBT-P) experiments. The ring temperatures in EBT-I and EBT-S are approx. 200 and approx. 500 keV, respectively. The projected ring temperature in EBT-P is approx. 1000 to 1500 keV. The calculations indicate that the radiation is predominantly in higher harmonics (l greater than or equal to ..gamma../sup 2//2) and the radiation spectrum monotonically decreases and becomes almost flat at high frequencies, as observed in the experiments. With increasing temperature and anisotropy, the total emission increases, the slope of the spectrum decreases, and the peak of the spectrum moves to higher frequency. Correlations of calculated intensity variations with temperature, density, beta, anisotropy, etc., are given that can be used as a useful tool for comparison of theory and experiment, as well as in the determination of ring properties and scaling of the radiation with ring parameters