Effective collecting area of a cylindrical Langmuir probe in magnetized plasma

International audienceLangmuir probe diagnostic on magnetic plasma devices often encounters more challenges in data processing than in non-magnetized plasmas, the latest itself being far from simple. In this paper, a theory of particle collection by a probe at the plasma potential in collisionless weakly ionized plasmas is constructed, accounting for velocities distributed according to the Maxwell equation and different mechanisms of particle collection depending on their speed. Experimental validation of the presented theory has been done with 2 cylindrical probes (rpr = 75 mum and Lpr = 1 cm and rpr = 0.5 mm and Lpr = 1 cm) parallel to B --> on a linear plasma device Aline, with magnetic fields of 0.0024-0.1 T and plasma densities of 1015-1017 m-3 in helium. Cylindrical probe measurements are compared to data from a planar probe perpendicular to the magnetic field, and the results for electron density, temperature, and plasma potential are presented. The introduced theory is initially constructed for a cylindrical probe but is applicable to various probe sizes, shapes, and orientations. Alongside the main subject, a number of associated issues are addressed with different details: a probe design issue relative to the magnetized environment, the "intersection" method of plasma potential evaluation, and the robustness of the conventional "1st derivative" method, a current bump near the plasma potential, lower limit for electron temperature estimation, and self-consistent calculation of electron temperature and density

Theory of a cylindrical Langmuir probe parallel to the magnetic field and its calibration with interferometry

International audienceA theory for data interpretation is presented for a cylindrical Langmuir probe in plasma parallel to the magnetic field direction. The theory is tested in a linear low-temperature plasma device Aline, in a capacitive radio-frequency (RF) discharge. The probe is placed on a 3D manipulator and a position scan is performed. To exclude strong RF perturbations the probe is RF compensated. Using the theory electron densities are obtained from the current at the plasma potential, where no sheath is present. Results are calibrated by line-integrated density measurements of a 26.5 GHz microwave interferometer. Reasonable agreement is observed for probe and interferometer measurements. Furthermore, preceding, more general probe theory is compared to the one developed in the current work and the application limits are discussed

Development of pre-conceptual ITER-type ICRF antenna design for DEMO

ICRF antenna development for DEMO for the pre-conceptual phase is carried out by merging the existing knowledge about multi-strap ITER, JET and ASDEX Upgrade antennas. Many aspects are taken over and adapted to DEMO, including the mechanical design and RF performance optimization strategies. The minimization of ICRF-specific plasma-wall interactions is aimed at by optimizing the feeding power balance, a technique already proven in practice. Technological limits elaborated for the components of ITER ICRF system serve as a guideline in the current design process. Several distinctive aspects, like antenna mounting, integration with the neighbouring components or adaptation for neutron environment, are tackled individually for DEMO

Discharge initiation by ICRF antenna in IShTAR

IShTAR is a linear magnetized plasma test facility dedicated to the investigation of RF wave/plasma interaction. The IShTAR ICRF system consists of a single strap RF antenna. When using the antenna for plasma production without an external plasma source, it is shown that the plasma is either produced in front of the antenna strap or inside the antenna box depending on the antenna parameters. Here, we present experimental and numerical investigation of the plasma initiation parametric dependencies. Detailed pressure and RF power scans were performed in helium at f = 5.22 MHz and f = 42.06 MHz. The experiment shows the parameter ranges for which the plasma is produced in front of the strap, or inside the antenna box. These ranges are validated by simulations with the RFdinity model, and by theoretical predictions

IShTAR: a test facility to study the interaction between RF wave and edge plasmas

International audienceExistence of high electric fields near an RF antenna launcher causes a number of parasitic phenomena, such as arcing and impurity release, which seriously deteriorate the performance of an ICRF heating scheme in fusion devices. Limited accessibility of the near antenna region in large-scale fusion experiments significantly complicates the associated experimental studies. The IShTAR (Ion Sheath Test Arrangement) test facility has been developed with the requirement to provide a better accessibility and diagnosability of plasmas in the direct vicinity of an ICRF antenna. The purpose of this work is to give a detailed description on the experimental setup and the available diagnostics. Furthermore the paper will demonstrate the capability of the experiment to study phenomena near an ICRF antenna launcher which are relevant for large-scale fusion ICRH systems