Effect of tailored density profiles on the stability of imploding z-pinches at microsecond rise time megaampere currents

To study the effect of the radial density profile of the material of a metal-plasma Z-pinch load on the development of magneto-Rayleigh-Taylor (MRT) instabilities, experiments have been performed at the Institute of High Current Electronics with the GIT-12 generator produced microsecond rise time megaampere currents. The load was an aluminum plasma jet with an outer plasma shell. This configuration provides the formation of a uniform current sheath in a Z-pinch load upon application of a high voltage pulse. It was successfully used in experiments with hybrid deuterium gas-puffs [Klir et al. 2020 New J. Phys. 22 103036]. The initial density profiles of the Z-pinch loads were estimated from the pinch current and voltage waveforms using the zero-dimensional "snowplow" model, and they were verified by simulating the expansion of the plasma jet formed by a vacuum arc using a two-dimensional quasi-neutral hybrid model [Shmelev et al. 2020 Phys. Plasmas 27 092708]. Two Z-pinch load configurations were used in the experiments. The first configuration provided tailored load density profiles, which could be described as ρ(r) ≈ 1/r^s for s > 2. In this case, MRT instabilities were suppressed and thus a K-shell radiation yield of 11 kJ/cm and a peak power of 0.67 TW/cm could be attained at a current of about 3 MA. For the second configuration, the radial density profiles were intentionally changed using a reflector. This led to the appearance of a notch in the density profiles at radii of 1–3 cm from the pinch axis and to magnetohydrodynamic instabilities at the final implosion stage. As a result, the K-shell radiation yield more than halved and the power decreased to 0.15 TW/cm at a current of about 3.5 MA.

Shelf life of plasma focus chambers with deuterium-tritium filling

The paper presents the results of an experimental study of the shelf life of sealed plasma focus chambers with deuterium-tritium and deuterium fillings. Shelf life is defined as maintaining the level of neutron yield during operation of PF chambers as part of pulsed neutron generators after long storage intervals. The release of impurities from the inner surfaces of the PF chamber and the accumulation of he-lium He3 due to the decay of tritium in the volume of the sealed-off PF chambers leads to a significant decrease in the neutron radiation yield several years after the chamber is filled with the working mixture. The paper shows that the shelf life of the chambers is significantly increased when using a gas generator, in which hy-drogen isotopes are contained in a bound state, and are released into the inner volume of the chamber only for the duration of operation as part of neutron gen-erators. It has been shown experimentally that spherical chambers of the PF9 type provide a level of neutron radiation yield Y, close to the initial value in the manu-facture of chambers, after more than 10 years of storage.

PARAMETRIC X-RAY RADIATION IN THE BACKWARD GEOMETRY

Parametric X-ray Radiation registered in the backward geometry is analysed. The main properties of the radiation for such geometry are discussed. The advantages of the backward geometry over other configurations regarding the intensity, the spectral width and the possibility to discriminate the contributions form different radiation mechanisms to the total radiation yield are presented.

Research on Photo Neutron Dose to Patient by (n, p) Reaction from a 15 MV Linear Accelerator

Introduction: Photoneutron produced during radiotherapy treatment was measured and the possibility for the radiation yield by the (n, p) reaction within the body was calculated. Materials and Methods: Photoneutron spectrum was measured using Columbia Resin (CR 39) film from a Siemens Primus Plus Linear accelerator and the possibility for the radiation yield by the (n, p) reaction within the body was calculated during radiotherapy treatment. Results--- The photoneutron spectrum was measured with CR 39 SSNTD and automatic track counting software. The interaction cross section for the (n,p) reaction for each energy and element were determined and radiation yield was calculated.For hydrogen, there is no (n,p) reaction. The (n,p) reaction is absent in C12for neutron of energy below 13.5 MeV. Oxygen has (n,p) reaction above 10 MeV. Nitrogen has a low threshold and there is no threshold for potassium and calcium. Conclusion--- From the result, it is clear that (n, p) reactions are significant and even though the dose from these reactions is low, the impact will be severe due to the high LET nature of proton. The data can be used to minimize the photoneutron production during the radiotherapy treatment in the future. The outcome of the work indicates the importance of photoneutron transport and dose deposition to be included in the treatment planning algorithm

Effect of polyethylene cross-linking on properties of foams

The process of cross-linking of polyethylene using gamma radiation (γ) and electron beam (EB) was tested from the point of view of density of foam. Particular attention was paid to the postradiation oxidation effect of the polymers. The study used two types of radiation sources of varying dose rates: gamma radiation (4 kGy/h) and EB (14 000 kGy/h). Radiolysis studies of the polymers used the radiation yield of hydrogen evolved (GH2, approximately proportional to the number of radicals) and radiation yield of oxygen absorbed by the polymer (GO2). Oxidation of polymer due to radiation was also evaluated using diffuse reflectance spectroscopy.