The influence of the magnetic ergodization on edge turbulence and turbulence-induced transport has been investigated by Langmuir probes in TEXTOR under three different static DED configurations. Common features are observed. With DED, the edge equilibrium profiles are altered and the resultant positive Er is in agreement with modelling. In the ergodic zone, the potential fluctuations are strongly reduced and the local turbulent flux changes direction from radially outwards to inwards. In the same zone, the turbulence properties are profoundly modified by energy redistribution in frequency spectra, suppression of large-scale structures and reduction of the radial and poloidal correlation lengths for all frequencies. Meanwhile, the fluctuation poloidal phase velocity changes sign from the electron to ion diamagnetic drift, consistent with the change of the Er × B flow, whereas the slight radially outward propagation of fluctuations is hindered by the DED. In the laminar region, the turbulence correlation is found to react to the observed reduced flow shear. Before the DED the Reynolds stress displays a radial gradient at the plasma edge while during DED the profile is suppressed, suggesting a rearrangement by the DED on the flow momentum profile.

Systematic measurements on the edge turbulence and turbulent transport have been made by Langmuir probe arrays on TEXTOR under various static Dynamic Ergodic Divertor (DED) configurations. Common features are observed. With the DED, in the ergodic zone the local turbulent flux reverses sign from radially outwards to inwards. The turbulence properties are profoundly modified by energy redistribution in frequency spectra and suppression of large scale eddies. The fluctuation poloidal phase velocity changes direction from electron to ion diamagnetic drift, consistent with the observed reversal of the E r B flow. In the laminar region, the turbulence is found to react to an observed reduced flow shear. [4] have demonstrated that an ergodized magnetic boundary can be effective to optimize the plasma-wall interaction. Meanwhile, the local effects of the magnetic ergodization on edge turbulence and turbulent cross-field transport have also been studied both experimentally [1,5,6] and theoretically [7,8]. It has been observed on TEXT [1] and Tore Supra [2,5,6] that in the ergodic divertor (ED) configuration the edge density fluctuations are decreased whereas the turbulent cross-field diffusivity is less affected. However, a systematic investigation of the turbulence properties, such as frequency and wave-number spectra and the fluctuation propagations, has not been made or was done for a reduced set of wavenumber values [5]. A distinct description in the ergodic and laminar zones was also not given.Recently, on the tokamak TEXTOR the Dynamic Ergodic Divertor (DED) [4] has been installed at the high-field side of the torus (R=a 1:75=0:47 m), contrary to other machines where the ED coils were mounted at the low-field side [1][2][3]. The DED consists of 16 perturbation coils oriented parallel to the field lines on the magnetic flux surface with a safety factor q 3. With different current distributions in the coils, the base poloidal/toroidal modes, m=n, can be adjusted as 12=4, 6=2, and 3=1. The penetration depth into the plasma depends on m: In 12=4 the influence is restricted to the plasma boundary, while in 3=1 it can reach much deeper. In the outer plasma layer, DED induces stochastization of the magnetic field lines, including an ergodic zone with long and a laminar zone with short connection lengths to the wall [9]. In this Letter, we present the first systematic measurements by Langmuir probe arrays on the edge turbulence properties and fluctuation-driven transport in the presence of various static DED configurations (dc current on the coils).To get effective impacts of the DED at the plasma boundary, the discharge conditions have been optimized as follows: For m=n 12=4, I p 250 kA, B T 1:4 T, R=a 1:73=0:46 m, dc DED current I DED 12 kA; for 6=2, I p 270 kA, B T 1:9 T, R=a 1:73=0:46 m, I DED 6 kA; and for 3=1, I p 250 kA, B T 1:9 T, R=a 1:75=0:48 m, I DED 1 kA. The I DED is applied during the stationary phase of the Ohmic discharge. In all cases, no external tearing modes are excited, the lineaveraged plasma densit...

In this work the influence of external Resonant Magnetic Perturbations (RMPs) on the radial electric field E r in magnetically confined plasmas is investigated by Charge Exchange Recombination Spectroscopy (CXRS) at the Tokamak TEXTOR. For this purpose, an optical diagnostic was developed to perform CXRS with C 6+ ions utilizing a neutral hydrogen diagnostic beam. Two systems are used to measure the poloidal rotation as well as the ion pressure and the toroidal rotation, respectively. The setup allows measurements with 1-2 cm radial resolution and a velocity resolution of typically 1 km/s for v θ and 5 km/s for v φ . For the radial calibration active beam emission spectra (Doppler shift) are used. The wavelength reference is determined via differential Doppler shift spectroscopy and a neon reference line for the poloidal and toroidal system, respectively. The radial electric field, E r , is then deduced from the radial force balance of C 6+ ions. The experiments have been performed at the Tokamak TEXTOR. Here, the RMPs are produced with the Dynamic Ergodic Divertor (DED), a set of 16 helical perturbation coils located at the high field side of TEXTOR. Within this work, the base mode number of perturbations has been m/n = 6/2. With these new observation systems, we have first investigated the influence of external torque from neutral heating beams on plasma rotation and E r . The toroidal rotation in the center is proportional to the net beam torque with an offset counter-current rotation at zero net torque. At the plasma edge, the toroidal rotation is dampened by friction with neutrals and coupled to the counter-current Scrape-Off layer flow by perpendicular viscosity. The poloidal rotation follows the poloidal component of the beam torque in the plasma center (ranging from 3 ± 3 km/s), at the plasma edge it is dominated by drift effects and loss of fast particles of the counter beam. Under influence of the DED, a spin-up of rotation with the rise of the perturbation amplitude causes the E r to become more positive. An increase of +10 kV/m is observed. The toroidal contribution increases all across the minor radius because of the large perpendicular viscosity, while the poloidal contribution increases only locally inside the ergodic zone caused by the RMPs. The ergodic zone causes an electron loss, and subsequently a j × B force driven by the compensating ion return current. In addition, the DED changes the global confinement properties. Depending on the edge safety factor ("field line twist") q a , either increased or decreased particle confinement is observed. In case of the increased particle confinement (IPC) the increase in density (40%) and particle confinement time τ p (30%) is correlated to the connection of field lines at the q=5/2 surface to the DED target, locally changing the transport properties and the E r . Transport is reduced and the E r shear is increased locally at q=5/2 up to 1.5 · 10 5 s −1 , while the E r becomes more positive. The changes in magnetic topology calculated in the vacu...

During the static 6/2 Dynamic Ergodic Divertor experiments in TEXTOR, a significant influence of the edge resonant magnetic perturbation (RMP) on the turbulent blob transport in the scrape-off layer (SOL) has been observed. In ohmic discharges without the RMP, the blobs extend 4-5 cm deep into the SOL with a radially-outward moving speed of about 1 km/s, and hence, are constituting a strong outflow of mass. With the application of the RMP, the blob amplitudes and their radially moving velocity are both reduced, resulting in a significant reduction of the blob transport in the SOL. The reduction effect of the RMP on blobs is found to be robust to changes in the operational regime and to phasing variations of the RMP as well. The blob dynamics appears to be consistent with the paradigm of the radial motions of the blob structures driven by the interchange instability.

The design and main characteristics of fourteen-channel dispersion interferometer for plasma profile measurement and control in TEXTOR tokamak are presented. The diagnostic is engineered on the basis of modular concept, the 10.6 µm CO 2 laser source and all optical and mechanical elements of each module are arranged in a compact housing. A set of mirrors and retro-reflectors inside the TEXTOR vacuum vessel provides full coverage of the torus cross-section with twelve vertical and two diagonal