Susanne Michelsen

Fast-ion dynamics in the TEXTOR tokamak measured by collective Thomson scattering

Here we present the first measurements by collective Thomson scattering of the evolution of fast-ion populations in a magnetically confined fusion plasma. 150 kW and 110 Ghz radiation from a gyrotron were scattered in the TEXTOR tokamak plasma with energetic ions generated by neutral beam injection and ion cyclotron resonance heating. The temporal behavior of the spatially resolved fast-ion velocity distribution is inferred from the received scattered radiation. The fast-ion dynamics at sawteeth and the slowdown after switch off of auxiliary heating is resolved in time. The latter is shown to be in close agreement with modeling results.

Heterodyne detector for measuring the characteristic of elliptically polarized microwaves.

We present the design and results of an innovative device which is capable of determining the three characteristic parameters of elliptically polarized light (ellipticity, angle of ellipticity and direction of rotation) for microwave radiation at a frequency of 105 GHz. The device consists of two perpendicularly oriented rectangular pickup waveguides to measure the electrical field in two orthogonal directions. The microwave frequency is mixed down by a heterodyne technique to frequencies on the order of 200 MHz. An oscilloscope is used to determine the relative amplitudes of the electrical fields and the phase shift between them, from which the three characteristic parameters are calculated. As an essential part of the commissioning, the device was used to characterize the polarizers of the transmission line for the collective Thompson scattering (CTS) experiment at ASDEX Upgrade. The measurements were also used to benchmark the modeling of the microwave propagation through the transmission line. Comparison between measurements and calculated wave characteristics show good agreement and are presented.

Fast ion collective Thomson scattering diagnostic for ITER: Design elements

Abstract The proposed fast ion collective Thomson scattering (CTS) diagnostic system for ITER provides the unique capability of measuring the temporally and spatially resolved velocity distribution of the confined fast ions and fusion alpha particles in a burning ITER plasma. The present paper describes the status of the iteration toward the detailed design of the ITER fast ion CTS diagnostic and explains in detail a number of essential considerations and challenges. The diagnostic consists of two separate receiving systems. One system measures the fast ion velocity component in the direction near perpendicular, and the other measures the component near parallel to the magnetic field. Each system has a high-power probe beam at an operating frequency of 60 GHz and a receiver unit. In order to prevent neutron damage to moveable parts, the geometry of the probes and receivers is fixed. An array of receivers in each receiving unit ensures simultaneous measurements in multiple scattering volumes. The latter receiving system (resolving the parallel component) is located on the high field side (HFS) of the plasma, and this constitutes a significant challenge. This HFS receiving unit has been central in the studies, and new HFS receiver mock-up measurements are presented as well as neutron flux calculations of the influence of the increased slot height.

Fast Ion Collective Thomson Scattering Diagnostic for ITER - Progress of Design

An integrated detailed design of a Collective Thomson Scattering (CTS) diagnostic system for measuring the distribution of fast ions in ITER has been performed. The system is based on two high power probe beams with a frequency of 60 GHz and two receiver systems. This system is able to fulfill the requirements for measuring the fast ion distribution from 100 keV to 3.5 MeV with a time resolution of 100 ms and a spatial resolution of 1/10 of the minor radius. Email of P.K. Michelsen: poul.michelsen@risoe.dk