Current Research into Applications of Tomography for Fusion Diagnostics

Retrieving spatial distribution of plasma emissivity from line integrated measurements on tokamaks presents a challenging task due to ill-posedness of the tomography problem and limited number of the lines of sight. Modern methods of plasma tomography therefore implement a-priori information as well as constraints, in particular some form of penalisation of complexity. In this contribution, the current tomography methods under development (Tikhonov regularisation, Bayesian methods and neural networks) are briefly explained taking into account their potential for integration into the fusion reactor diagnostics. In particular, current development of the Minimum Fisher Regularisation method is exemplified with respect to real-time reconstruction capability, combination with spectral unfolding and other prospective tasks.Peer reviewe

Current Research into Applications of Tomography for Fusion Diagnostics

Retrieving spatial distribution of plasma emissivity from line integrated measurements on tokamaks presents a challenging task due to ill-posedness of the tomography problem and limited number of the lines of sight. Modern methods of plasma tomography therefore implement a-priori information as well as constraints, in particular some form of penalisation of complexity. In this contribution, the current tomography methods under development (Tikhonov regularisation, Bayesian methods and neural networks) are briefly explained taking into account their potential for integration into the fusion reactor diagnostics. In particular, current development of the Minimum Fisher Regularisation method is exemplified with respect to real-time reconstruction capability, combination with spectral unfolding and other prospective tasks.EURATOM 63305

Radiation distributions in TCV

Total radiative powers measured by foil bolometer and AXUV camera systems are compared to SOLPS5 simulations in low and high density deuterium and helium diverted discharges on the TCV tokamak. For low density the match between simulation and measurements is satisfactory, but at high density strongly radiating regions outside the SOLPS5 simulation grid are seen in measurements and this may indicate the presence of enhanced convective particle transport in the low field side midplane region. The chord coverage of the foil bolometer system does not, however, allow detailed resolution in this region. The comparison of foil and AXUV data also demonstrates that ageing of the AXUV diodes under plasma irradiation combined with the unevenness of the diode spectral response, strongly limits their application for total radiative power measurements. (c) 2007 Elsevier B.V. All rights reserved

Detection systems for measurements of high-temperature plasma radiation on the COMPASS tokamak by fast bolometers and soft X-ray detectors

Title: Detection systems for measurements of high-temperature plasma radiation on the COMPASS tokamak by fast bolometers and soft X-ray detectors Author: Miroslav Vácha Department: Institute of Particle and Nuclear Physics Supervisor: Mgr. Vladimír Weinzettl, Ph.D., Institute of Plasma Physics AS CR, v.v.i. Supervisor's e-mail address: [email protected] Abstract: Multi-channel spectroscopic diagnostics on the COMPASS tokamak com- prising AXUV-based bolometers, soft X-ray (SXR) and visible light detectors will cover a wide spectral range of the core and edge plasma emission, aiming to realize a fast tomography at microsecond time scales. This thesis reports on a development of the bolometric and SXR diagnostics. First, procedures of the detector selection and their tests are described. There the design and tests of the special complex port plug, com- bining both detection systems, taken into account a strongly limited available space, a heat protection and a shielding during a cleaning glow discharge, is also summarized. Development of new electronic amplifiers and their connection with the data acquisition system is documented. In the last chapters, basic methods for analysis of data collected using these diagnostic systems are introduced. Keywords: tokamak, plasma radiation, photodiode, tomographyNázev práce: Detekční systémy pro měření vyzařování vysokoteplotního plazmatu tokamaku COMPASS na bázi rychlých bolometrů a měkkých rentgenových detektorů Autor: Miroslav Vácha Katedra: Ústav částicové a jaderné fyziky Vedoucí práce: Mgr. Vladimír Weinzettl, Ph.D., Ústav fyziky plazmatu AV ČR v.v.i. e-mail vedoucího: [email protected] Abstrakt: Mnohokanálová spektroskopická diagnostika pro tokamak COMPASS na bázi AXUV bolometrů, měkkých rentgenových detektorů a detektorů viditelného světla pokrývá široké spektrum vyzařování tokamakového plazmatu a umožní rychlou tomo- grafii v mikrosekundových časových škálách. Práce shrnuje vývoj bolometrické a měkké rentgenové diagnostiky. Nejprve je diskutován výběr detektorů a jejich testy. Dále je shrnut návrh kombinované vložky do diagnostického portu, která umožňuje umístit oba systémy do velmi malého prostoru a zároveň jim poskytuje chlazení a stínění v průběhu procedur čištění komory. Rovněž je dokumentován vývoj nových zesilovačů signálu a jejich zapojení do systému sběru dat. V závěrečných kapitolách jsou prezen- továny základní metody analýzy dat z těchto diagnostických systémů. Klíčová slova: tokamak, vyzařování plazmatu, fotodioda, tomografieInstitute of Particle and Nuclear PhysicsÚstav částicové a jaderné fyzikyFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Development of Smart, Compact Fusion Diagnostics using Field-Programmable Gate Arrays

Abstract: Fusion research requires high quality diagnostics to understand the complex physical processes involved. Traditional analogue systems are complex, large and expensive, and expansion of diagnostic capabilities is often impossible without building a completely new system at considerable expense. Field-programmable gate array (FPGA) technology can provide a solution to this problem. By implementing complex functionality and digital signal processing on an FPGA chip, diagnostic hardware can be greatly simplified and compacted. In this thesis we describe the enhancements of two diagnostics for the MAST-Upgrade tokamak using FPGA technology. Firstly, the design of the back end electronics for the new divertor bolometer is described. Results of tests of the new electronics at a number of sites, including lab-based testing and tokamak installations, are also presented. We demonstrate the correct functionality of the electronics and illustrate a number of important effects which must be taken into account when interpreting bolometer data on MAST-U. Secondly, we describe the new control and acquisition electronics developed for the MAST-U divertor Langmuir probe diagnostic. Much of the analogue control circuitry of the previous system has been upgraded to a digital implementation on an FPGA, which results in a significantly more compact and cost effective design. Given that MAST-Upgrade will feature around 850 Langmuir probes, these improvements are extremely important to keep the diagnostic manageable. Again, results are presented from the testing of the system at several sites, which both demonstrate the correct functionality of the new system and provide information on the diagnostic behaviour which needs to be accounted for when interpreting the probe data during MAST-U experiments