Future perspectives in solar hot plasma observations in the soft X-rays

TL;DR

This paper reviews advancements in multilayer coatings for soft X-ray solar observations, exploring multiband spectrometer designs to improve hot plasma diagnostics up to 15 MK.

Contribution

It investigates the use of M-fold and aperiodic multilayer stacks for multiband SXR spectrometers, proposing feasible designs for future solar missions.

Findings

Recent multilayer technology enables broad-range SXR mirrors.

Trade-off studies suggest viable eight-band spectrometer configurations.

Potential for enhanced solar hot plasma diagnostics in future missions.

Abstract

The soft X-rays (SXRs: 90--150 $\r{A}$) are among the most interesting spectral ranges to be investigated in the next generation of solar missions due to their unique capability of diagnosing phenomena involving hot plasma with temperatures up to 15~MK. Multilayer (ML) coatings are crucial for developing SXR instrumentation, as so far they represent the only viable option for the development of high-efficiency mirrors in this spectral range. However, the current standard MLs are characterized by a very narrow spectral band which is incompatible with the science requirements expected for a SXR spectrometer. Nevertheless, recent advancement in the ML technology has made the development of non-periodic stacks repeatable and reliable, enabling the manufacturing of SXR mirrors with a valuable efficiency over a large range of wavelengths. In this work, after reviewing the state-of-the-art ML coatings for the SXR range, we investigate the possibility of using M-fold and aperiodic stacks for the development of multiband SXR spectrometers. After selecting a possible choice of key spectral lines, some trade-off studies for an eight-bands spectrometer are also presented and discussed, giving an evaluation of their feasibility and potential performance.