Analysis of the ion energy transport in ohmic discharges in the ASDEX tokamak

An analysis of the local ion energy transport is performed for more than one hundred well documented ohmic ASDEX discharges. These are characterized by three different confinement regimes: the linear ohmic confinement (LOC), the saturated ohmic confinement (SOC) and the improved ohmic confinement (IOC). All three are covered by this study. To identify the most important local transport mechanism of the ion heat, the ion power balance equation is analyzed. Two methods are used: straightforward calculation with experimental data only, and a comparison of measured and calculated profiles of the ion temperature and the ion heat conductivity, respectively. A discussion of the power balance shows that conductive losses dominate the ion energy transport in all ohmic discharges of ASDEX. Only inside the q=1-surface losses due to sawtooth activity play a role, while at the edge convective fluxes and CX-losses influence the ion energy transport. Both methods lead to the result that both the ion temperature and the ion heat conductivity are consistent with predictions of the neoclassical theory. Enhanced heat losses as suggested by theories eg. on the basis of #eta#_i modes can be excluded. (orig.)23 refs.Available from TIB Hannover: RA 71(III/215) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Final report on the scientific and engineering design of a soft X-ray diode array diagnostic system for JET (KJ 1)

Reprint of IPP-JET--6SIGLEDEGerman

Recovery of ion temperature profiles from the analysis of energy-resolved neutral-flux measurements

In this paper, results of two approaches to account for the neutral density are reported, which substitute the time-consuming Monte Carlo simulations. In the first approach, the neutral density is estimated by transport formulas applicable to a planar slab model. This model is a somewhat crude approximation to the real situation in ASDEX Upgrade. The second approach, consists in empirically estimating the neutral density profile simultaneously with the ion temperature profile, while imposing a low-order parametric class of neutral-density profiles (of the neutrals stemming from the wall) along the line of sight. The class of functions (a variant of exponential survival functions) has been selected by investigating various fits to results results of a Monte-Carlo based T_i evaluation program, for some ASDEX-Upgrade discharges. The procedure roughly captures global features of the 'survival profile' of the atomic neutral density due to the wall sources, from the central region of the plasma up to the region close to the separatrix. The neutrals from volume recombination, which are important in the center of the plasma, are calculated separately. (orig.)Available from TIB Hannover: RA 71(5/99) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Charge exchange fluxes of ripple trapped slowing-down ions during L-to-H transition and ELMs

Neutral fluxes from charge exchange with ripple-trapped particles show a remarkably different behaviour during L and H mode; their measurement provides a new diagnostic for the mode discrimination of the plasma. A possible reason for the changes of the fluxes is the action of a radial electric field. This seems to grow steadily after the L-to-H transition with a strong increase (jump in the ms range) at the transition to the quiescent H-mode. During ELMs the fluxes reduce to L-mode level. Measurements with 100 #mu# time resolution show no action in the fluxes piror to the change in the D_#alpha#-signal at the start of type 1 ELM. (orig.)17 refs.Available from TIB Hannover: RA 71(1/288) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Overview of ASDEX Upgrade results

The ASDEX Upgrade programme is directed towards physics input to critical elements of the ITER design and the preparation of ITER operation, as well as addressing physics issues for a future DEMO design. After the finalization of the tungsten coating of the plasma facing components, the re-availability of all flywheel-generators allowed high-power operation with up to 20 MW heating power at I(p) up to 1.2 MA. Implementation of alternative ECRH schemes (140 GHz O2- and X3-mode) facilitated central heating above n(e) = 1.2 x 10(20) m(-3) and low q(95) operation at B(t) = 1.8 T. Central O2-mode heating was successfully used in high P/R discharges with 20 MW total heating power and divertor load control with nitrogen seeding. Improved energy confinement is obtained with nitrogen seeding both for type-I and type-III ELMy conditions. The main contributor is increased plasma temperature, no significant changes in the density profile have been observed. This behaviour may be explained by higher pedestal temperatures caused by ion dilution in combination with a pressure limited pedestal and hollow nitrogen profiles. Core particle transport simulations with gyrokinetic calculations have been benchmarked by dedicated discharges using variations of the ECRH deposition location. The reaction of normalized electron density gradients to variations of temperature gradients and the T(e)/T(i) ratio could be well reproduced. Doppler reflectometry studies at the L-H transition allowed the disentanglement of the interplay between the oscillatory geodesic acoustic modes, turbulent fluctuations and the mean equilibrium E x B flow in the edge negative E(r) well region just inside the separatrix. Improved pedestal diagnostics revealed also a refined picture of the pedestal transport in the fully developed H-mode type-I ELM cycle. Impurity ion transport turned out to be neoclassical in between ELMs. Electron and energy transport remain anomalous, but exhibit different recovery time scales after an ELM. After recovery of the pre-ELM profiles, strong fluctuations develop in the gradients of n(e) and T(e). The occurrence of the next ELM cannot be explained by the local current diffusion time scale, since this turns out to be too short. Fast ion losses induced by shear Alfven eigenmodes have been investigated by time-resolved energy and pitch angle measurements. This allowed the separation of the convective and diffusive loss mechanisms