FIRST POLOIDAL ROTATION MEASUREMENTS IN THE TJ-II FLEXIBLE HELIAC

Introduction. The main motivation in obtaining poloidal rotation measurements in present fusion devices is to obtain information about the radial electric field. Neoclassical theory suggests that in stellarators the electric field reduces helical ripple loss and consequently improving plasma confinement. Poloidal rotation measurements have been reported in ECR heated plasmas in stellarator devices but as they were made using passive emission spectroscopy of ions that emit in the visible most of the results obtained are from the plasma periphery. For example, in the Heliotron-E device, the radial electric field at r ≈ 0.7-0.9 was found to be positive (the electron root) in low density plasmas (n e 2x10 13 cm -3 ) [1]. In electron cyclotron heated (ECH) plasmas (ne ≈ 5x10 13 cm -3 ) in the Weldelstein VII-A stellarator, the negative electric field observed was consistent with theoretical predictions [2]. In the Advanced Toroidal Facility, a positive electric field was observed in ECH low density plasmas (n e ≈ 5x10 12 cm -3 ) in measurements made using a heavy-ion beam probe technique [3]. Here, we report on the first measurements of poloidal rotation of impurity ions in the TJ-II flexible Heliac from which we estimate the sign and magnitude of the radial electric field. In addition, we describe the experimental set up used and finally we discuss the results obtained in TJ-II in the context of results from other stellarator devices. Experimental. TJ-II is a low magnetic shear stellarator of the Heliac type with an average major radius of 1.5 m and average minor radius of ≤ 0.22 m. The plasma is created and heated by 250 kW of ECR power at 53.2 GHz perpendicularly injected and tuned at the second harmonic. This experiment was carried out using standard TJ-II configurations (1): 100_50_65 with an iota of 1.61 at the centre and 1.73 at the edge; and 100_40_63 with slightly lower iota values.