Aachen PK 2003 – scientific programme

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P: Plasmaphysik

P 10: Poster II

P 10.17: Poster

Tuesday, March 18, 2003, 17:30–19:15, Foyer

Safety factor profile evolution during the current ramp phase — •Alexey Merkulov¹, G.M.D. Hogeweij¹, R.J.E. Jaspers¹, H.R. Koslowski², A. Krämer-Flecken², F.C. Schüller¹, and E. Westerhof¹ — ¹FOM ‘Rijnhuizen’, Associatie Euratom-FOM, PO Box 1207, 3430 BE Nieuwegein, Netherlands — ²IPP, Forschungszentrum Jülich, Euratom Association, D-52425 Jülich, Germany

In a series of TEXTOR discharges early heating through neutral beam injection (NBI) during the current ramp phase has been applied in order to try to achieve a negative central shear (NCS). Electron cyclotron resonant heating (ECRH) is then applied to test for the presence of transport barriers. As the ECRH perturbs the polarimeter, no data on the safety factor (q-)profile are available during ECRH. The 1-D transport code ASTRA is used to simulate the current profile evolution during the current ramp phase of these discharges. The experimental profiles for T_e, n_e, and Z_eff, are used. The current diffusion equation is solved using neoclassical conductivity and including the non-inductive current from NBI. The calculations show that the q-profile just before ECRH is almost flat or slightly reversed, in agreement with polarimetry. In discharges with central ECRH a fast current penetration is found leading to q(0) dropping below 1 near the end of ECRH. This is consistent with the start of sawtoothing around that time. The results appear to indicate that a true NCS regime was not achieved. A new 140 GHz, 1 MW ECRH system is now available at TEXTOR. Calculations will be presented exploring the current drive capabilities of this system with a view to achieving NCS. Also optimizations of NBI current drive and heating will be considered.