The specified calculation of wavelengths of resonance transitions in He-like ions (Z = 16-39) is compared with the results of the X-ray measurements in the spectra of low-inductance vacuum spark in the present paper. The calculation was made by Z-expansion method in the screening representation with the inclusion of relativistic and radiative effects. The experimental data have been obtained with compensation of the Doppler shift and taking into account the correction caused by the presence of adjoining satellites with n = 3. A slight difference between the theory and the experiment in the region Z = 38, 39 has been found.

We discuss the possibility of creating novel research tools by producing and storing highly relativistic beams of highly ionised atoms in the CERN accelerator complex, and by exciting their atomic degrees of freedom with lasers to produce high-energy photon beams. Intensity of such photon beams would be by several orders of magnitude higher than offered by the presently operating light sources, in the particularly interesting γ-ray energy domain of 0.1-400 MeV. In this energy range, the high-intensity photon beams can be used to produce secondary beams of polarised electrons, polarised positrons, polarised muons, neutrinos, neutrons and radioactive ions. New research opportunities in a wide domain of fundamental and applied physics can be opened by the Gamma Factory scientific programme based on the above primary and secondary beams.

The x-ray structure (λ<10 Å) of the DPF-78 discharge was investigated with different heavy-gas admixtures to a basic D2 filling. A possible classification of plasma features is proposed. Micropinches with an unusual high aspect ratio of about 10:1 were found. Soft x-ray spectra of single micropinches were registered on film. The use of x-ray spectroscopic methods by means of spectra simulation codes allowed us to estimate the parameters of particular types of pinches with axial size of 0.5 mm and full radial size of 0.05 mm. In the He-like ionization state we obtained ne≊3×1021 cm−3 and Te≊0.8 keV. The electron temperature determined in the H-like ionization stage was considerably higher, Te≊2 keV, indicating a strong ionizing plasma. Possible deviations from the Bennett condition are discussed in connection with the spectroscopic results.

An experimental and theoretical investigation of the micropinching process in a low-inductance vacuum spark is presented. The existence of the two types of micropinches which differ by their dimensions and emitted X-ray spectra of multicharged ions is explained from the point of view of a 'radiative collapse' model.

The work is devoted to the study of the plasma, created by a fast discharge in a spherical cavity. The discharge was driven by an inductive storage with plasma erosion opening switch (dI/dt $10 12 A/s). The plasma was produced in a spherical cavity (alumina, 11 mm diameter). Xe, Ar, and He at the pressure 80 Pa were used as working gases. The time evolution of the spatial structure and of extreme ultraviolet (EUV) spectra of the discharge plasma was studied by means of micro channel plate detector. The discharges with Xe and Ar resulted in the stable appearance of the spherically shaped plasma with the diameter about 1-3 mm. The plasma emission in the EUV region lasts $500 ns. The EUV spectrum of Ar discharge at the moment of maximum of the electron temperature T e contains the lines of Ar X (ionization potential 478.7 eV), that indicates a value of T e in the range 50-100 eV. The mechanism of plasma appearance can be the cumulation of the convergent spherical shock wave, generated by fast heat deposition and magnetic pressure in working media near the inner surface of the discharge volume. V C 2014 AIP Publishing LLC.