Tokamak equilibria with reversed current density

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For describing the E-J relation of high-Tc superconductors (HTS) in power applications, where the applied current I is generally limited by Ic, the critical state model, a piecewise linear generalization, or a simple power-law of the type E=Ec(J/Jc)^n are most often used. The power-law cannot be used for modelling the E-J relation with I>>I_c due to the unbound exponential increase of the electric field for currents above Ic, while in reality the non-linear HTS resistivity is limited by its normal state val

The finite element method has been employed in order to simulate the behaviour of a HTS cable for transport current applications. The E-J model includes an anisotropic dependence of the critical current density Jc and power index n on the local magnetic field, whose magnitude is non-negligible and determines the effective critical current of the cable. The cable consists of four electrically insulated layers, each of them composed by 20 superconducting tapes, providing a total critical current of about 4 kA

The extreme shaping capabilities of the TCV tokamak have been used to investigate the effect of plasma geometry on the confinement of non-recycling trace impurities injected by means of the laser blow-off technique. The progression of the injected silicon in the core of TCV Ohmic limiter plasmas was followed by the 200-channel soft x-ray (SXR) photodiode array with good spatial and temporal resolution. The results show that the plasma triangularity and elongation play an important role in the impurity confi

For some time it has not been clear to what extent neutral injected beam ions have a stabilizing influence on sawteeth. To investigate this, the well known toroidal internal kink instability is generalized to account for weakly anisotropic and flowing equilibria. An analytical approach is proposed, which upon employing an appropriate model distribution function, accurately accounts for the hot ion response of neutral beam injection (NBI) to the internal kink mode. Large fluid contributions, which are expect

The internal electric field in multilayer organic light-emitting diodes (OLEDs) is investigated using a combination of experimental measurement and numerical device modeling. This approach results in a detailed understanding of the functioning of a multilayer OLED. The method is applied to a standard device structure that has received broad attention in literature. From the experimental part, we have demonstrated that the average electric field inside the hole transport layer is larger than or equal to the

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

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

Recent operation of JET with centrally strongly reversed magnetic shear, produced with the help of lower hybrid current drive, has extended the domain in which internal transport barriers (ITBs) can be formed in JET. Performance is frequently limited by magnetohydrodynamic (MHD) instabilities in these reversed shear regimes. The most severe limit is a pressure driven kink mode which leads to a disruption. This disruptive limit is essentially the same in ITB plasmas with low or strongly reversed shear. Uniqu

A small component of ECCD exists when heating off-axis with no toroidal injection due to the field helicity. The sign of the ECCD will change depending on the absorption location in a poloidal plane, the beam injection relative to delB(vac), and the direction of the toroidal magnetic field. The importance of the ECCD component can be confirmed by the behavior of the sawteeth when the ECH deposition crosses the q=1 surface. The sawtooth period is very sensitive to the local shear at q=1 and it is shown that

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

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

Tokamak equilibria with reversed current density

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Modelling the E-J relation of high-Tc superconductors in an arbitrary current range

Numerical Modelling of a HTS Cable

Effects of plasma shape on laser blow-off injected impurity transport in TCV

The internal kink mode in an anisotropic flowing plasma with application to modeling neutral beam injected sawtoothing discharges

Internal electric field and charge distribution in multilayer organic light-emitting diodes

Overview of recent Alcator C-Mod research

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

MHD stability with strongly reversed magnetic shear in JET

Poloidally asymmetric plasma response with ECH deposition near q=1 in TCV

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

The design of central column protection tiles for the TCV tokamak

Experimental and theoretical stability limits of highly elongated tokamak plasmas