Electrostatic probe measurements have been performed in order to derive plasma parameters in a pulsed-power discharge. The experiment has been designed to produce plasma filled arc-shaped magnetic flux tubes. The plasma is sustained by high current densities along the tube axis, which drive the arc-shaped structure to expand via the magnetic hoop-force. The electrostatic probe is located at a fixed position in space and scans over the minor diameter (≈3 cm) of the discharge arc while it passes. The probe is designed as an asymmetric triple probe in order to get instantaneous information on electron temperatures and densities. Peak values of up to 10 eV and about 2 × 1021 m−3 respectively were found. Owing to the high reproducibility of the experiment it was possible to take double probe characteristics in subsequent shots for comparison. In addition, the measurements of the line integrated density were performed by means of a CO2 laser interferometer. The results of the electrostatic triple probe in the investigated plasma regime are compared with the results of the laser interferometer. While the shapes of the density distribution are in reasonable agreement, the peak values derived from the triple probe underestimate the electron density by up to a factor of 5.

The ITER Diagnostic Pressure Gauges (DPG)

The FlareLab experiment at Bochum University has been constructed to generate and investigate plasma-filled magnetic flux tubes similar to archshaped solar prominences, which often result in coronal mass ejections (CMEs). In its first version, the device has been used to reproduce and extend previous studies of Bellan et al (1998 Phys. Plasmas 5 1991. Here the plasma source consists of two electrodes, which can be connected to a 1.0 kJ capacitor bank, and of a horseshoe magnet, which provides an arch-shaped guiding field. The discharge is ignited in a cloud of hydrogen gas that has been puffed into the space above the electrodes. In the first few microseconds the plasma current rises at a rate of several kA µs −1 , causing the plasma column to pinch along the guiding B-field and to form an expanding loop structure. The observed dynamics of the magnetic flux tubes is analysed by means of three-dimensional MHD simulations in order to determine the influence of parameters like the initial magnetic field geometry on magnetic stability. At present, FlareLab is redesigned to mimic a model that was proposed by Titov and Démoulin (1999 Astron. Astrophys. 351 707) to investigate twisted magnetic configurations in solar flares.

No abstract

Hot cathode ionization gauges are intended to be the only in-situ diagnostic for neutral gas pressures in the vacuum vessel of ITER. The development bases on the well established ASDEX pressure gauge. The upper measuring limit for ITER is required to be at least 20 Pa in hydrogen at a magnetic flux density of up to 8 T. The objective of the presented study is to find parameter and design settings that allow to satisfy this specification. At the same time, the sensitivity shall be high and only weakly dependent on the magnetic field strength. Gauge parameters, specifically the electron emission current, the electrode potentials and the transparency of the acceleration grid, were varied consecutively to assess their impact on the calibration characteristics. The ratio of ion to electron current as a function of pressure and magnetic flux density was obtained for each parameter set.A monotonic progression of the signal in dependence of the pressure was proven even up to 30 Pa. This was achieved by a low grid transparency and high electric field strength at the cathode. While the former leads to a lower sensitivity, which is unfavorable for measurements in the low pressure range, this can be compensated by a higher electron current.