Influence of B_t on the magnetic turbulence and on the runaway transport in low-density discharges
The analysis of small-scale magnetic fluctuations has been performed in the TEXTOR tokamak. Runaway electrons are used as test particles for studying the turbulent transport at different toroidal magnetic fields. The flux of runaways from the plasma increases with decreasing magnetic field strength. The comparison with a model of magnetic braiding provides insight into the basic properties of the turbulence. A substantial growth of the diffusion coefficients of runaways at the plasma edge with an increase in the width of the turbulent spectrum is demonstrated. The diffusion coefficients of runaways and their flux at the plasma edge are derived from measurements by an IR camera and runaway probe. The level of the magnetic fluctuations and the poloidal spectrum of the magnetic turbulence vary between 10−5 and 5 × 10−5 T and decrease with the magnetic field strength. In addition, the width of the spectrum can be derived to a poloidal mode spectrum of wn ≥ 20.