A. Havranek

Status of the COMPASS tokamak and characterization of the first H-mode

This paper summarizes the status of the COMPASS tokamak, its comprehensive diagnostic equipment and plasma scenarios as a baseline for the future studies. The former COMPASS-D tokamak was in operation at UKAEA Culham, UK in 1992–2002. Later, the device was transferred to the Institute of Plasma Physics of the Academy of Sciences of the Czech Republic (IPP AS CR), where it was installed during 2006–2011. Since 2012 the device has been in a full operation with Type-I and Type-III ELMy H-modes as a base scenario. This enables together with the ITER-like plasma shape and flexible NBI heating system (two injectors enabling co- or balanced injection) to perform ITER relevant studies in different parameter range to the other tokamaks (ASDEX-Upgrade, DIII-D, JET) and to contribute to the ITER scallings. In addition to the description of the device, current status and the main diagnostic equipment, the paper focuses on the characterization of the Ohmic as well as NBI-assisted H-modes. Moreover, Edge Localized Modes (ELMs) are categorized based on their frequency dependence on power density flowing across separatrix. The filamentary structure of ELMs is studied and the parallel heat flux in individual filaments is measured by probes on the outer mid-plane and in the divertor. The measurements are supported by observation of ELM and inter-ELM filaments by an ultra-fast camera.

Measurements and modelling of plasma response field to RMP on the COMPASS tokamak

It has been shown on several tokamaks that application of a resonant magnetic perturbation (RMP) field to the plasma can lead to suppression or mitigation of edge-localized mode (ELM) instabilities. Due to the rotation of the plasma in the RMP field reference system, currents are induced on resonant surfaces within the plasma, consequently screening the original perturbation. In this work, the extensive set of 104 saddle loops installed on the COMPASS tokamak is utilized to measure the plasma response field for two n = 2 RMP configurations of different poloidal mode m spectra. It is shown that spatially the response field is in opposite phase to the original perturbation, and that the poloidal profile of the measured response field does not depend on the poloidal profile of the applied RMP. Simulations of the plasma response by the linear MHD code MARS-F (Liu et al 2000 Phys. Plasmas 7 3681) reveal that both of the studied RMP configurations are well screened by the plasma. Comparison of measured plasma response field with the simulated one shows a good agreement across the majority of poloidal angles, with the exception of the midplane low-field side area, where discrepancy is seen.

A compact, smart Langmuir Probe control module for MAST-Upgrade

A new control module for the MAST-Upgrade Langmuir Probe system has been developed. It is based on a Xilinx Zynq FPGA, which allows for excellent configurability and ease of retrieving data. The module is capable of arbitrary bias voltage waveform generation, and digitises current and voltage readings from 16 probes. The probes are biased and measured one at a time in a time multiplexed fashion, with the multiplexing sequence completely configurable. In addition, simultaneous digitisation of the floating potential of all unbiased probes is possible. A suite of these modules, each coupled with a high voltage amplifier, enables biasing and digitisation of 640 Langmuir Probes in the MAST-Upgrade Super-X divertor. The system has been successfully tested on the York Linear Plasma Device and on the COMPASS tokamak. It will be installed on MAST-Upgrade ready for operations in 2018.