United States of America

bêçä=lâí~ó=EalbF=~åÇ=açå=iK=eáääáë=ElokiF erol.oktay@science.doe.gov

Microwave Imaging

(Collaboration of the Netherlands TEC partner FOM-Institute for Plasma Physics with Prof. N.C. Luhmann, Jr., Dr. C. Domier, Univ. California Davis; Dr. E. Mazzucato, Dr. H. Park, PPPL; Dr. T. Munsat, Univ. of Colorado, Prof. A. Mase, Kyushu University and Dr. K. Kawahata, NIFS)

A combined Microwave Imaging Reflectometry (MIR) and Electron Cyclotron Emission Imaging (ECEI) system, capable of measuring density and temperature fluctuations is installed and operating on TEXTOR. The MIR system is still in the commissioning phase. Experiments conducted in 2005 have revealed that the system is very sensitive to the angular alignment of the launch beam, with misalignments of ±0.5° generating runaway phases of > 10000 rad in 16 ms, corresponding to Dop-pler shifts of more than100 kHz. Experiments in 2006 will fix the angular alignment to within ±0.1°

via minimization of the runaway phase, after which the system will be employed in the study of mi-cro-turbulence.

The 2D ECE imaging system on TEXTOR consists of 128 channels, arranged in a matrix of 8 (horizontal) × 16 (vertical) sample volumes covering a poloidal cross-sectional area of 6×16 cm². The radial position of the sample area can be shifted through the plasma by tuning the local oscilla-tor frequency (frequency range 95–130 GHz). The system has already been used to make beautiful movies of the sawtooth oscillation and magnetic reconnection process and have resulted in both in-vited talks and publications. Comparisons have been made with a number of theoretical models (see figure below) and are motivating the development of refined theoretical models. These studies will be augmented in Fall, 2006 after a planned upgrade in the ECE Imaging electronics which will in-crease the instantaneous plasma coverage to 13–17 cm² and improve the temperature resolution by a factor of two.

GA-UCSD Collaboration on Stochastic Boundary Effects in Tokamaks

The General Atomics-UCSD collaboration with TEXTOR is focused on developing a fundamental understanding of stochastic layer physics in tokamaks by combining the unique experimental, theo-retical and numerical tools available within each group. The goal is to develop stochastic boundary layer control techniques that can be applied to burning plasma experiments such as ITER. Research at DIII-D is focused heavily on understanding the relationship between edge stability and the struc-ture of the pedestal in poloidally diverted plasmas while the TEXTOR Dynamic Ergodic Divertor program is carrying out basic research on transport and stability using stochastic layers in pumped limiter tokamak plasmas. Specific collaboration activities completed during 2005 include:

- B. Unterberg presented an experimental proposal on the “Influence of magnetic topology on transport in the stochastic loss layer during ELM suppression” at the DIII-D Research Op-portunities Forum, Nov. 15-17, 2005.

- T. Evans, R. Moyer and M. Schaffer made presentation on: “Configurational Effects of Magnetic Perturbation on Edge and Core MHD in DIII-D”, “Prospects for ELM Control at Lower Pedestal Collisionality with an Edge Resonant Magnetic Perturbation in DIII-D” and

“Preliminary Study of ITER Correction Coils for ELM Suppression” at the 2005 SFP Work-shop in Jülich, between March 15 and March 17, 2005.

- M. Lehnen participated in stochastic ELM control experiments at DIII-D from March 8 through March 11, 2005.

Future collaborations in this area will include scientists from TEXTOR and DIII-D participating jointly in the planning and execution of experiments on both devices and in modeling these experi-ments with transport and stability codes developed specifically for understanding the plasma re-sponse to stochastic boundary layers.

Fig. 1: Results from the 2D ECE imaging system on TEXTOR and comparison with a number of theoretical models.

Fast Ion Collective Thomson Scattering (CTS) Diagnostics (Collaboration between P. Woskov/MIT, H. Bindslev/Risø, and the TEC partners)

Progress in 2005-2006 consisted of recommissioning the fast ion CTS system and starting physics studies of fast ions in TEXTOR plasmas with neutral beam injection. Commissioning activities in-cluded optimizing the 110 GHz gyrotron for high power operation with a clean frequency spectrum

necessary to observe the Doppler broadened fast ion scattered signals. A new receiver transmission line with a rapid scanning launch mirror was aligned and tested. Studies of gyrotron and receiver beam overlap in refractive plasmas were started. Observations of neutral beam fast ions were achieved showing the asymmetric difference in the ion velocity distribution between perpendicular and parallel orientations relative to the magnetic field. Plans for 2007 to 2008 include continued studies of fast ions in both neutral beam and ICRH heated plasmas. Fast ion redistributions during SAW teeth will be one topic of study. Another topic of study will be ICRH fast ion relaxation rele-vant fusion α particle absorption physics. Potential interference of the ICRH on the performance of the gyrotron will also be studied for the first time in a tokamak environment. CTS results at TEX-TOR will be used as input for the design of a confined α particle diagnostic for ITER.

ORNL-TEXTOR Collaborations

Work with the TEXTOR group at JET has involved modeling JET trace tritium particle transport experiments. A paper with TEXTOR co-authors D. Reiter, S. Brezinsek and A. Pospieszczyk will be presented at the 17th PSI in Hefei. A multi-species (D, T, D2, DT, T2) version of the Eirene code was used for part of the analysis and molecular spectroscopic results (for HD) were used to confirm key modeling conclusions concerning preferential T enrichment near the outer midplane gas port. A visit by J. Hogan to Jülich was carried out in October 2005.

A collaboration with A. Kirschner on use of the Jülich ERO code has begun. This work will enable a treatment of carbon erosion from intra-tile gaps (~ 1 mm) in Tore Supra CIEL. The gyro-orbit ERO code is best suited for analysis of such relatively small areas near the generation zone, while the ORNL BBQ guiding center is optimized for treatment of the full SOL, as is required for core/edge coupling. The collaboration was kicked off during the October 2005 Jülich visit noted above, and was followed up with a visit by A. Kirschner to Cadarache to discuss the ERO/BBQ project in March 2006.