D. Aguiam

Making ICRF power compatible with a high-Z wall in ASDEX Upgrade

A comparison of the ASDEX Upgrade 3-strap ICRF antenna data with the linear electro-magnetic TOPICA calculations is presented. The comparison substantiates a reduction of the local electric field at the radially protruding plasma-facing elements of the antenna as a relevant approach for minimizing tungsten (W) sputtering in conditions when the slow wave is strongly evanescent. The measured reaction of the time-averaged RF current at the antenna limiters to the antenna feeding variations is less sensitive than predicted by the calculations. This is likely to have been caused by temporal and spatial fluctuations in the 3D plasma density distribution affected by local non-linear interactions. The 3-strap antenna with the W-coated limiters produces drastically less W sputtering compared to the W-coated 2-strap antennas. This is consistent with the non-linear asymptotic SSWICH-SW calculations for RF sheaths.

Implementation of the new multichannel X-mode edge density profile reflectometer for the ICRF antenna on ASDEX Upgrade

A new multichannel frequency modulated continuous-wave reflectometry diagnostic has been successfully installed and commissioned on ASDEX Upgrade to measure the plasma edge electron density profile evolution in front of the Ion Cyclotron Range of Frequencies (ICRF) antenna. The design of the new three-strap ICRF antenna integrates ten pairs (sending and receiving) of microwave reflectometry antennas. The multichannel reflectometer can use three of these to measure the edge electron density profiles up to 2 × 1019 m-3, at different poloidal locations, allowing the direct study of the local plasma layers in front of the ICRF antenna. ICRF power coupling, operational effects, and poloidal variations of the plasma density profile can be consistently studied for the first time. In this work the diagnostic hardware architecture is described and the obtained density profile measurements were used to track outer radial plasma position and plasma shape.

Feasibility study of a control system based on PLC and EPICS for the ESTHER combustion gas injection

The ESTHER laboratory will simulate spacecraft atmosphere re-entry conditions by generating a shock wave through the deflagration of a hydrogen, oxygen and helium gas mixture. The gas injection sequence into the combustion chamber must be precisely and safely controlled in order to prescribe the initial pressure in the two-stage shock tube and to avoid accidental detonations in any part of the system. In this work, a prototype control system setup using a Siemens PLC in an EPICS and CSS software environment is presented. An example application was developed, where a simple control sequence implemented on the PLC was remotely monitored and controlled by an operator interface. This setup was able to meet the control system requirements and the prototype served as the starting point for the development of the complete ESTHER gas injection controller.

Portable instrument for eddy currents Non-Destructive Testing based on heterodyning techniques

In this work an eddy current testing instrument employing heterodyning based measurements is presented. The instrument is composed of a portable computer and a dedicated electronic measurement circuitry to operate a specific type of probe. A DDS waveform generator and a transconductance amplifier are used to drive the probe with high amplitude currents and frequency up to 10 MHz. The probe output voltage is amplified up to 60 dB and down-converted to a lower intermediary frequency. The signal is converted into the digital domain and processed to compute the real and imaginary parts of the probe output voltage. The developed dedicated electronics were installed inside a rugged laptop computer to form a standalone instrument with post-processing and visualization capabilities. Electrical characterization and application results using the instrument and a particular eddy current probe are presented.