Experimental Measurements of Soft X-Ray Emissivity Distribution and Electron Temperature Profile in Reversed Field Pinch Plasmas

This thesis reports the work performed during the three years of my Ph.D. course at the Physics Department of the University of Padova. Most of my research activity has been performed in Consorzio RFX (Padova) where the RFX experiment is located. RFX (Reversed Field eXperiment) is the largest toroidal device to study magnetically confined plasmas of thermonuclear interest in the so-called reversed field pinch (RFP) configuration. The RFP is one of the main configurations used to confine plasmas in toroidal devices with the purpose of studying controlled thermonuclear fusion as an energy source. The energy production by fusion in magnetically confined plasmas is an ambitious and important goal, which could contribute to solve the problem of a sustainable energy source for mankind. To be an efficient energy source, a sufficiently dense and hot plasma must be confined for a sufficiently long time. In order to fulfill this goal, energy and particle losses need to be understood and eventually controlled. In RFPs, transport is at present dominated by magnetic chaos, even if, under some circumstances that will be presented in this thesis, it can decrease to lower levels. The RFX experiment has been modified in order to investigate in a controlled way the effect of the magnetic boundary on plasma performances. In order to obtain such these information, my research activity has been focused on performing spatially resolved measurements of the plasma emissivity in the soft x-ray (SXR) energy range. In particular, I was involved in experimental and laboratory activities, in diagnostic operation and optimization, along with the design and realization of a new SXR diagnostic. I also analyzed SXR data, allowing a characterization of the plasma column and of the MHD plasma activity. The tomographic algorithms applied to the SXR signals allow for the reconstruction of the SXR emissivity distribution 2, which reflects the plasma magnetic topology. Such information can be completed by the estimation of the electron temperature (Te) profile, calculated with the two-foil technique. During my Ph.D., I was also involved in the collaboration between RFX and the University of Wisconsin, Madison, where the Madison Symmetric Torus (MST) experiment is located. My activity has been part of the collaboration between RFP groups for experimental studies on MHD processes and was focused on operating the SXR tomographic diagnostic installed in MST and realized by the RFX group. Data analysis was aimed at obtaining 2D profiles of the plasma electron temperature. My personal contribution has concerned the optimization of the geometry of the detection system and the electronic system, as well as the diagnostic operation. Moreover, I was directly involved in dedicated experimental campaigns and in the data analysis: the results are presented in this thesis