The Properties of the Frequency Splitting of the Axisymmetrical Magnetoacoustic Wave and an Application to Current Profile Diagnosis

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Research on the Alcator C-Mod tokamak [1] is focused on high particle- and power-density plasma regimes to understand particle and energy transport in the core, the dynamics of the H-mode pedestal, and scrape-off layer and divertor physics. The auxiliary heating is provided exclusively by RF waves, and both the physics and technology of RF heating and current drive are studied. The momentum which is manifested in strong toroidal rotation, in the absence of direct momentum input, has been shown to be transpo

A detailed study has been made of the onset and behaviour of (m = 3, n = 2) neoclassical tearing modes (NTMs) on JET, validating many of the underlying concepts in NTM physics. In particular, fitting onset thresholds in terms of the correctly motivated physics parameters produces scalings closer to theoretical expectations. The use of such locally measured parameters also removes previous inconsistencies in the data between different divertor configurations. The evolution of island size with beta confirms t

A pulse height analysis (PHA) x-ray system has been successfully implemented on the tokamak TCV, aiming at a low cost monitor system of the plasma electron temperature and impurity content. To meet the need for high throughput and fast acquisition, mandatory in tokamaks with relatively short pulse duration and high-energy fluxes, the original germanium detector is being replaced by a Silicon Drifted Detector and the traditional dedicated analog electronics for a Digital X-Ray Signal CAMAC compatible unit. A

We present a method to image Jones vector by use of digital holography. We show that with unique hologram acquisition, our method permits to image and to calculate Jones vector and therefore polarization parameters. The idea is to use two reference waves polarized perpendicularly that interfere with object wave and to reconstruct separately the two wave fronts. The precision and limitations of the method are evaluated here using a numerical model.

Sawtooth inversion radii and profile peaking factors of a large variety of ohmic and ECH heated L mode plasmas, including, elongations up to 2.6 and triangularities between -0.5 and 0.75, have been investigated in the TCV tokamak. In ohmic plasmas, normalized inversion radii and electron temperature profile peaking factors (corrected for sawtoothing effects) depend solely on the parameter (j)/q(0)j(0), irrespective of plasma shape. With ECH this parameter remains the main scaling parameter. Density profiles

Alfven eigenmodes and other magnetohydrodynamic phenomena have been studied in tokamak plasmas at the Joint European Torus (JET) using a new eight-channel, 4 s, 1 MHz, 12-bit data acquisition system (KC1F) in conjunction with the JET fast Mirnov magnetic fluctuation pickup coils. To this end, the JET magnetic pickup coils were calibrated in the range 30-460 kHz using a new remote calibration technique which accounts for the presence of the first few LRC circuit resonances. Signal processing software has bee

Growth rates of the axisymmetric instability of elongated plasmas in TCV are measured, in open loop configuration, for a wide variety of plasma shapes with elongations and triangularities in the ranges 1.3 < kappa < 2.2 and -0.3 < delta < 0.6, respectively, and for stability margins covering the range 1.03 < f < 1.60. In addition, the stability of the vertical position control system is investigated experimentally, under closed loop conditions, by varying the feedback gains and by measuring the oscillation

The large variety of plasma shapes produced in the TCV tokamak places unique demands on the plasma facing surfaces. In particular, the central column graphite armour tiles are solicited during the creation of all TCV plasmas and function as power handling surfaces for both limited and diverted discharges. The higher power flux densities accompanying the addition of electron cyclotron heating systems have necessitated a new, optimized, design for these tiles. The optimization process and the subsequent new t

There is not yet a straightforward method for determining the D-T ratio in the centre of a tokamak plasma. One of the simpler measurements put forward in the past is the interpretation of the MHD spectrum in the frequency range of the global Alfven eigenmodes (GAE). However, the frequencies of these modes do not depend on the plasma mass alone, but are also quite strongly dependent on the details of the current and density profiles; this creates a problem of deconvolution of the estimate of the plasma mass

Stability limits of highly elongated, D-shaped plasmas have been measured in the TCV (tokamak a configuration variable) tokamak. It is found that the plasma current is limited by kink-type disruptions, preceded by magnetohydrodynamic (MHD) mode activity. The mode structure has been analyzed using magnetic fluctuation and soft x-ray diagnostics. Mode numbers, growth rates, and experimental stability limits are consistent with ideal and resistive MHD models, based on measured plasma shapes and profiles. These

The influence of local equilibrium parameters on the Alfven spectrum is studied. The aim is to solve the inverse problem: identification of the plasma profiles, and especially the safety factor profile, using measurements of magnetohydrodynamic (MHD) waves. A study case is presented to determine what the possible uses of MHD spectroscopy are. The dependence of the TAE (Toroidicity induced Alfven Eigenmode) frequency on the safety factor at the edge is shown. The possible use of Alfven continuum modes near t

The TCV tokamak offers outstanding variability of the plasma shape. Using x-ray tomography, the shape of the inner flux surfaces of a poloidal cross section of the plasma can be reconstructed, including fast variations due to MHD activity. Both the hardware and the software of the 200 channel system developed for TCV are described. A new 'dynamical' calibration takes actual plasma parameters into account to determine the spectrum-dependent detector efficiency, resulting in an enhanced quality of reconstruct

The Properties of the Frequency Splitting of the Axisymmetrical Magnetoacoustic Wave and an Application to Current Profile Diagnosis

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Overview of recent Alcator C-Mod research

Onset of neoclassical tearing modes on JET

Real-time signal analysis on the TCV PHA diagnostic

Jones vector imaging by use of digital holography: Simulation results

Shape dependence of sawtooth inversion radii and profile peaking factors in TCV L mode plasmas

Fast magnetic fluctuation diagnostics for Alfven eigenmode and magnetohydrodynamics studies at the Joint European Torus

Vertical position control in TCV: Comparison of model predictions with experimental results

The design of central column protection tiles for the TCV tokamak

Measurement of the effective plasma ion mass in large tokamaks using global Alfven eigenmodes

Experimental and theoretical stability limits of highly elongated tokamak plasmas

Determination of local tokamak parameters by magnetohydrodynamic spectroscopy

X-ray tomography on the TCV tokamak