E. O. Baronova

Cauchois–Johansson x-ray spectrograph for 1.5–400 keV energy range

A Cauchois–Johansson optical scheme is proposed, based on a specially designed cylindrical quartz crystal. The corresponding x-ray spectrograph is manufactured, which provides high spectral resolution in transmission and reflection regimes and covers the wide energy range of 1.5–400 keV. The device is calibrated with an x-ray tube and is suggested to be used in high-temperature plasma diagnostics.

Impurity Radiation from a Tokamak Plasma

In tokamak operating modes, energy balance is often governed by impurity radiation. This is the case near the divertor plates, during impurity pellet injection, during controlled discharge disruptions, etc. The calculation of impurity radiation is a fairly involved task (it is sometimes the most difficult part of the general problem) because the radiation power is determined by the distribution of ions over the excited states and by the rate constants of elementary processes of radiation and absorption. The objective of this paper is to summarize in one place all the approximate formulas that would help investigators to describe radiation from the most often encountered impurities in a fairly simple way in their calculations accounting for plasma radiation, without reference to special literature. Simple approximating formulas describing ionization, recombination, and charge-exchange processes, as well as radiative losses from ions with a given charge, are presented for five impurity species: beryllium, carbon, oxygen, neon, and argon. Estimating formulas that allow one to take into account plasma opacity for resonant photons in line impurity radiation are also presented.

Study of a cumulative jet in a plasma focus discharge by the method of shearing interferometry

The dynamics of the cumulative jet formed in the course of plasma compression in a plasma focus discharge is investigated by the method of differential optical interferometry. The jet propagation velocity is found to be V = (2.3–3) × 107 cm/s, which coincides with the results of calculations performed in a 2D ideal MHD model. Ejection of matter from the anode in the late stage of the discharge due to the interaction of the cumulative jet and the electron beam with the anode surface is observed.

X-ray spectropolarimeter

We have constructed a novel single-crystal x-ray spectropolarimeter that separates spatially the two perpendicularly polarized components of an x-ray beam. We have tested this device by using an x-ray tube, and confirmed its performance to be satisfactory as expected from its design.

Study of X-ray polarization and e-beams generation during hot-spots formation in PF-discharges

Strong turbulence phenomena, as observed within dense magnetized plasmas, are of interest for theoretical and experimental studies. This paper concerns the filamentation and formation of “hot-spots” in high current PF-type discharges, as well as the emission of fast electron beams and X-ray pulses. The generation of oriented e-beams can induce the polarization of X-rays, as observed within the MAJA-PF facility at SINS.

Dynamics of axial plasma jets in neon and argon plasma focus discharges

Axial plasma jets at the final stage of plasma focus discharge filled by neon or argon were studied by the method of shearing interferometry. It was found that neon plasma is more stable than argon one and jets in neon are stronger than in argon. The velocity of current sheath, taken from experiment, is Vsh = (2-3) × 106 cm/s, while the velocity of cumulative jet is Vj = (3-4) × 107 cm/s. These features are supported by theoretical interpretation given in the frame of 2D MHD model.

Determination of the plasma parameters in the PF-3 facility by the methods of X-ray spectroscopy

NeIX and NeX spectra emitted by the PF-3 high-current (2 MA) plasma focus facility are measured. A numerical model describing the spectral intensities of the emission of helium- and hydrogen-like neon ions from an optically thick plasma is proposed. The electron temperature Te and electron density ne in the plasma of the PF-3 facility are determined by comparing the calculated and measured emission spectra of neon.

Polarized x-rays from a Z-pinch plasma

This paper presents the first experimental evidence for polarization of x-rays from He-like argon in a plasma focus, and for x-rays from He-like iron from a vacuum spark. The diagnostic needs two crystal spectrometers with mutually perpendicular dispersive planes parallel and perpendicular to the discharge axis. Resonance lines from He-like ions are always polarized, and this fact has implications for estimating plasma parameters. X-ray polarization also gives information about anisotropy in fast electrons with energy of a few keV.

Electron beam generation in the turbulent plasma of Z-pinch discharges

Numerical modeling of the process of electron beam generation in z-pinch discharges are presented. The proposed model represents the electron beam generation under turbulent plasma conditions. Strong current distribution inhomogeneity in the plasma column has been accounted for the adequate generation process investigation. Electron beam is generated near the maximum of compression due to run away mechanism and it is not related with the current break effect.

On evaluating x-ray imaging crystals with synchrotron radiation

Bent crystals used in diagnostics of plasmas combine x-rays diffracted from across the crystal. Therefore imperfections in the resulting 1-D spectrum or 2-D image are not the best way to find out why one particular crystal may differ in its performance from another and what, if anything, to do about it. Instead, here we want to measure the diffraction locally, with the necessary resolution. Nominally monochromatic and unidirectional radiation from the synchrotrons standard x-ray optics proved to be insufficient for the purpose. Here much better radiation comes from the x-ray topography setup at the x-ray optics testing beamline 1-BM at the Advanced Photon Source, thanks to a specially designed quartz conditioning crystal. Some worrisome features in a bent crystals diffraction have thereby disappeared, while minor fabrication flaws remain highly visible.