RF and microwave diagnostics for compact plasma traps and possible perspectives for fusion devices

Abstract

Plasma diagnostics is a topic having a great impact on R&D in compact ion sources as well as in large fusion reactors. Towards this aim, non-invasive microwave diagnostics approaches, such as interferometric, polarimetric and microwave imaging profilometric techniques can allow obtaining volumetric, line-integrated or even space-resolved information about plasma electron density. Special probes can be also designed and implemented in order to characterize external and/or self-generated radio-waves in the plasmas. In particular, the design, construction and operation of a K-band microwave interferometry/polarimetry setup based on the Frequency-Modulated Continuous-Wave (FMCW) method at INFN-LNS will be described: this tool provides reliable measurements of the plasma density even in the extreme unfavorable wavelength-to-plasma scale ratio in plasma-based ion sources. A “frequency sweep” and a post-processing filtering method (for interferometry and polarimetry, respectively) were used to filter out the multipath contributions or cavity induced depolarizations in the detected signals. Besides this, the use of the aforementioned RF plasma-immersed probes will also be discussed, which allow measuring local E-fields and fast temporal response in order to characterize turbulent (through kinetic instabilities, cyclotron maser emission, etc.) vs. stable plasma regimes. An analysis based on wavelet transform applied to measurements of plasma radio self-emission in B-minimum and simple mirror traps will be presented. These tools and methods have the potential to be applied to plasma machines both in compact traps and large-size reactors with a proper scaling.

A new approach to β-decays studies impacting nuclear physics and astrophysics: The PANDORA setup

“…Some other tools are under development to improve the performances of the setup. In particular, the collaboration is working on the implementation of the Microwave Imaging Profilometry (MIP), to achieve an online measurement of local values of the electron density that can be synergic with the microwave polarimeter already described [23], as well as on the Incoherent Thomson Scattering (ITS) [24], which is an alternative technique for investigating the absolute plasma density, the electron energy distribution functions, and even the electron global drift velocity.…”

Experimental and numerical investigation of magneto-plasma optical properties toward measurements of opacity relevant for compact binary objects

“…Injection of the aforementioned metallic elements in ECR plasmas requires specific vaporization techniques, both using resistive ovens (RO) to evaporate the metallic compound whose vapor pressure goes to 10 -2 mbar at temperature T ≤ 2000 K, or sputtering (Sp) techniques, usually used for refractory elements. The choice of methods also depends on the efficiency of injection (Mascali et al, 2022a;Mauro et al, 2022). On this basis, selenium and strontium are chosen as day-0 cases for the first measurements.…”

“…Generated plasmas are suitable for studies of astrophysics, nuclear, and multidisciplinary physics, especially on the basis of their stellar-like temperature conditions. In this context, a particular effort has been spent at the INFN-LNS to develop a multi-diagnostics system to allow both a full characterization of the plasma parameters for all electron and ion species involved and interdisciplinary studies (Mazzaglia et al, 2018;Naselli et al, 2019a;Mazzaglia et al, 2019;Naselli et al, 2022a;Mascali et al, 2022b;Torrisi et al, 2022). The FPT is therefore a valuable experimental facility operative at the INFN-LNS to benchmark monitoring diagnostics and experimental techniques to be employed in PANDORA, of course on a larger scale, which is precious for the future envisaged in-laboratory plasma measurements relevant for the KN study.…”