Microwave techniques for electron cyclotron resonance plasma diagnostics

Abstract

This paper reviews the main microwave diagnostic techniques and tools adopted in electron cyclotron resonance (ECR) (and others) ion source laboratories, with a special focus on techniques and instruments developed at INFN-LNS. Along with the tools used for optimization of microwave launching (power monitors, spectral analysis, and network analyzers), this paper deals, in particular, with more recent devices on-purpose developed to perform in-plasma analysis, such as absolute density measurements and density profiles retrieval. Among these, the first example of microwave interferometry for ECR compact machines (the VESPRI interferometer at INFN-LNS) will be briefly discussed, in combination with microwave polarimetric techniques based on Faraday rotation detection. More sophisticated microwave techniques are going to be designed and are now at a numerical study stage, e.g., profilometry and imaging via inverse scattering methods (this paper will offer short theoretical bases and first numerical results on 1D profilometry). In the end, the relevance about the implications and interplays of microwave techniques in multidiagnostic systems (microwave, optical, and x-ray domains) will be commented, with a special focus on time resolved microwave measurements and advanced signal processing via wavelet transform, useful for characterization of plasma instabilities.

Laboratory magnetoplasmas as an ideal experimental environment for nuclear astrophysics β-decay studies

“…The interferometric n e measurement is based on the phase-shift induced by the plasma refractive index. Results obtained by interferometry and polarimetry are in good agreement [24] (fig. 2.d-right), with errors respectively of 50% and 27%.…”

A high resolution γ-ray array for the pandora plasma trap

“…Such a value, while being apparently small compared to the typical values of the photopeak efficiency of the arrays used nowadays, is however sufficient, due to the high number of decaying ions present in the plasmoid, to measure the predicted variations in the decay rates. This critical aspect was verified, through simulations, for the first physic cases selected in PANDORA (see Table 1) for their relevance in s-process nucleosynthesis: 176 Lu, 134 Cs, 94 Nb [5]. All three nuclei are expected to undergo significant variations of their half-life in plasma environment.…”

“…In this last case the predicted increase of the decay rate due to in plasma ionization is one order of magnitude. Simulations of real experimental runs, assuming a plasma volume of 1500 cm 3 and a concentration of the radioactive isotope ranging from 10 11 ions/cm 3 for 176 Lu case to a much smaller value of about 10 6 ions/cm 3 for 134 Cs, show that to collect the statistics needed to achieve a 3σ-confidence level on the decay rate measurement, experimental runs should last from several days to about 3 months, depending on the isotope under investigation [5,7]. Such a result clearly indicates that the sensitivity of the setup depends not only on the total detection efficiency of the HPGe array but also on the concentration of decaying ions confined in the trap (a value that can be tuned in each experiment considering also the possible limits imposed by radioprotection issues to the maximum total activity achievable) and on the expected variation of the half-life of the radioactive ion species.…”

“…This new approach, based on the study of decays rates in a laboratory magneto-plasma confined in a compact plasma trap, aims to carry out measurements in which the decaying ions display a charge state distribution resembling the one present in the hot stellar environment (or that can be properly scaled to it). Plasma parameters will be inferred using dedicated noninvasive diagnostic tools [4] and the nuclear decay rates will be evaluated as a function of the charge state distribution of inplasma ions [5].…”

The PANDORA project: A setup for in-plasma β-decay studies in nuclei of astrophysical interest

“…Similar information can be extracted for the hot and cold components using an HPGe detector and an optical spectrometer, respectively [15]. The multi-diagnostic system includes also an interfero-polarimeter [16] to measure the line-integrated total density and a RF probe coupled to a spectrum analyzer or a scope for time resolved spectroscopy [16] and for monitoring and mastering the plasma stability. A pin-hole camera will be used for high resolution spatiallyresolved soft X-ray spectroscopy to investigate the plasma structure and the confinement dynamics in the range 2 -20 keV [17].…”