Igor I. Sobelman

CORONAS-F observations of active phenomena on the sun

Abstract Complex observations in the framework of the CORONAS-F Mission aimed at the study of active phenomena inthe solar corona are described. The main features are given for the following experiments: (1) XUV-imaging spectroscopy with high temporal and spatial resolution, (2) X-ray spectroscopy, (3) X-ray and gamma-ray photometer/spectrometer, and (4) solar cosmic rays. Some new observational data on the structure and dynamics of flares and transient events are discussed along with their analysis.

Diagnostics of the inner corona by XUV-imaging of the sun

Results of solar observations in the XUV-region by means of the telescope TEREK aboard the “Phobos-1” spacecraft are presented. Images of the Sun in the HeII 30,4 nm and FeIX-FeXI 17–18 nm lines were obtained with new types of optical elements — multilayer normal incidence XUV-mirrors and CCD-detectors. About 140 images were obtained with an angular resolution up to 15″ and with exposure times 0.1 to 40 s. In the images one sees the structures in the transition layer from corona to chromosphere which has temperatures in the range 5×104 – 1×106 K as well as in the polar and equatorial coronal holes. Besides, a unique phenomenon — a “blob” in outer corona at a distance about 2 solar radii has been observed. Processing of the data revealed a complex correlation between the XUV-images and the magnetic field structure in the photosphere.

X-ray telescopes aboard Fobos-I and Coronas

The TEREK imaging telescope installed on the Phobos-I spacecraft, and the TEREK-C telescope and spectroheliometer, designed for use in the Coronas project, are examined. In comparison with the TEREK instrument, the TEREK-C has an improved spatial resolution in the MX channel of up to 2 arcsec. The main parameters of the TEREK-C and the spectroheliometer are presented in tabular form, and an optical scheme of the TEREK instrument is given.

Normal-incidence multilayer mirrors for the 120-450 å wavelength region.

An electron-beam deposition method is used to fabricate spherical and flat mirrors with a peak reflectivity of 20% for wavelengths between 120 and 450 A. It is experimentally shown that the fabricated mirrors can be employed to form an image with a resolution of 1 μm for ultrasoft x rays. The possibility of producing intense directional high-temperature plasma radiation by spherical multilayer mirrors is demonstrated. A radiation intensity of 107 W/cm2 around 182 A has been experimentally obtained in the laser plasma image plane.

High-resolution neutron tomography

A neutron tomography technique with a coordinate resolution of several tens of micrometers has been developed. Our results indicate that the technique resolves details with dimensions less than 100μm and measures a linear attenuation of less than similar 0.1 cm−1. Tomograms can be reconstructed using incomplete data. Limits on the resolution of the restored pattern are analyzed, and ways to improve the sensitivity of the technique are discussed.

X-ray spectroheliographs with the Bragg focusing optics for the CORONAS project: design, fabrication, and optical testing

Two x-ray spectroheliographs have been designed for obtaining solar images in about 8.42 angstrom and in 1.86 angstrom spectral regions with high spatial and spectral resolution. In both devices unique optical elements-focusing Bragg crystal mirrors are used. Technologies of their production are described here. These mirrors were tested in the x-ray region for their iamging and dispersive properties. These calibration results are presented.

High-power Ti:sapphire lasers for optical polarization of 3He

A current status and perspectives of the work on a high density polarized 3He target are reported. The problems of high-power laser design for optical pumping are discussed. A general formulation for the analysis of an arbitrary linear resonator with internal lens of variable focal length, which represents the rod of a solid-state laser is presented. It is shown that mode spot size is stable with respect to lens optical power fluctuations in one part of resonator when it reaches a minimum on a laser rod. The rules for the design of stable resonators with two or more variable lenses are proposed.