SPOT: a New Monte Carlo Solver for Fast Alpha Particles

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)The predictive transport code CRONOS has been augmented by an orbit following Monte Carlo code, SPOT (Simulation of Particle Orbits in a Tokamak). The SPOT code simulates the dynamics of non-thermal particles, and takes into account effects of finite orbit width and collisional transport of fast ions. Recent developments indicate that it might be difficult to avoid, at least transiently, current holes in a reactor. They occur already on existing tokamaks during advanced tokamak scenarios. For this reason the SPOT code has been used to study the alpha particle behaviour in the presence of current holes for both JET and ITER relevant parameters

MHD stability of fully non inductive discharges in Tore Supra

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)During the 2003 experimental campaign, the aim of realizing reliable fully non inductive discharges has been successfully completed in Tore Supra. One the major difficulties in optimizing this scenario comes from MHD stability issues. Indeed, the current profile obtained with LH antennas in these experiments is prone to the triggering of single or double tearing modes. Under certain conditions, the discharges enters in a regime of permanent MHD activity. The present work investigates the MHD properties of these fully non-inductive discharges in the operational space defined by the toroidal magnetic field B, the total plasma current Ip, and the mean parallel index of LH waves . Linear MHD stability properties divide the operational space in regions separated by rational values of the minimum of the safety factor. We discuss in our work the localisation of the transition between benign MHD activity and the MHD regime

Lower hybrid counter-current drive experiment in JET

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)Lower hybrid current drive has been demonstrated to be an efficient tool to modify the current profile in order to access to high energy confinement regimes. Counter-current drive could be an alternative scenario provided the current drive efficiency is not too small when fast electrons flow in the opposite way to the DC electric field. By reversing the toroidal field (Bt=-3.1T) and the plasma current (Ip=-1.45MA), counter current drive with lower hybrid waves has been investigated for the first time in JET. The experiments were carried out at low plasma density ( =1.0 x1019m-3 , ne(0)=1.6 x 1019m-3) with 2.9MW of lower hybrid power. The CRONOS code[1], which couples the diffusion equations to a 2-D equilibrium code, has been used to estimate the RF driven current. Runs indicate that loop voltage and internal inductance are best simulated with a current drive efficiency of –1.0 x 1019 A.W-1.m-2 with a peaked central LH power deposition deduced from DELPHINE[2]. This efficiency is indeed very close to the one found for co-LHCD at similar plasma current and density. Current profile evolves from a hollow profile (with a minimum at r/a ~0) and a maximum at r/a~0.4-0.5) to a rather flat profile (up to r/a=0.3)

Self-consistent simulation of plasma scenarios for ITER using a combination of 1.5D transport codes and free-boundary equilibrium codes

Self-consistent transport simulation of ITER scenarios is a very important tool for the exploration of the operational space and for scenario optimisation. It also provides an assessment of the compatibility of developed scenarios (which include fast transient events) with machine constraints, in particular with the poloidal field (PF) coil system, heating and current drive (H&CD), fuelling and particle and energy exhaust systems. This paper discusses results of predictive modelling of all reference ITER scenarios and variants using two suite of linked transport and equilibrium codes. The first suite consisting of the 1.5D core/2D SOL code JINTRAC [1] and the free boundary equilibrium evolution code CREATE-NL [2,3], was mainly used to simulate the inductive D-T reference Scenario-2 with fusion gain Q=10 and its variants in H, D and He (including ITER scenarios with reduced current and toroidal field). The second suite of codes was used mainly for the modelling of hybrid and steady state ITER scenarios. It combines the 1.5D core transport code CRONOS [4] and the free boundary equilibrium evolution code DINA-CH [5].Comment: 23 pages, 18 figure

Electron heat transport in ASDEX Upgrade: experiment and modelling

The electron heat transport is investigated in ASDEX Upgrade using electron cyclotron heating (ECH) combining steady-state and power modulation schemes. Experiments in which the electron heat flux has been varied in the confinement region while the edge was kept constant were performed. They demonstrate that Te and Te/Te can be varied by a factor of 3 and 2, respectively. They allow a detailed determination of the transport characteristics by comparing steady-state and modulation data with modelling. The analyses clearly show the existence of a threshold ( Te/Te)crit above which transport increases. Both steady-state and modulation experiments agree with such a transport model. The experiments have been carried out at low density in the L-mode to ensure low electron–ion coupling and good conditions for studying electron heat transport. The experiments were carried out at two different values of plasma current and show that transport increases at low current, as well-known from global scaling laws for confinement time. In the pure off-axis cases the region inside the ECH deposition is just at the ( Te/Te)crit threshold, which allows it to be measured directly from the profile of Te/Te deduced from the experimental Te profile. Using this technique, it appears that the turbulence threshold agrees with that expected from the trapped electron mode driven turbulence. It has the correct absolute value and seems to have the correct radial dependence that is determined by the trapped electron fraction and by the density gradient. It almost does not vary with other plasma parameters. In contrast, the threshold calculated for electron temperature gradient modes is higher than the experimental values of Te/Te and this turbulence is therefore not expected to be excited under these experimental conditions