Dissipative collapse of a Karmarkar star

In this paper, we employ the Karmarkar condition to model a spherically symmetric radiating star undergoing dissipative gravitational collapse within the framework of classical general relativity. The collapse ensues from an initial static core satisfying the Karmarkar condition in isotropic coordinates and proceeds nonadiabatically by emitting energy in the form of a radial heat flux to the exterior Vaidya spacetime. We show that the dynamical nature of the collapse is sensitive to the initial static configuration that inherently links the embedding to the final remnant. Our model considered several physical tests on how an initially static stellar structure onset to a radiative collapse.

Testing of the SOLPS-ITER code at Globus-M2 spherical tokamak with detached divertor

In according to a present understanding of Scrape-Off Layer (SOL) physics, future thermonuclear devices like ITER, DEMO and beyond, require high radiation regimes in order to reduce heat loads on tokamak divertor. Recent experiments at ASDEX Upgrade, JET and other tokamaks demonstrated that such regimes might be achieved by the seeding of the radiative impurities. In the present paper the modeling of the high radiation regimes and the transition to the detachment at the Globus-M2 spherical tokamak is performed by the SOLPS-ITER transport code. The obtained modeling results for GLobus-M2 tokamak demonstrate the trend similar to what is observed at larger machines, e.g. AUG and JET. The significant reduction of peak power density at the outer target plate and transition to the detachment with High Field Side High Density (HFSHD) formation at the inner plate was achieved with impurity seeding rate almost equal to the deuterium puff (in el/sec). However, unlike AUG, further increasing of the seeding rate leads not to a formation of the radiative X-point, but to a radiative collapse. This is caused by smaller machine size, which allows the impurity neutrals to penetrate easier into the confined region. It was noticed that starting with attached divertor the inner target transits to the detachment earlier than the outer one.

Numerical experiments on the PF1000 plasma focus device operated with nitrogen and oxygen gases

The indicative values of reduced Pease–Braginskii (P–B) currents are estimated for a nitrogen and oxygen plasma focus. The values of depletion times indicate that in N2 and O2 with estimated 3–4% of pinch energy radiating away over the duration of the pinch, we may expect some cooling effects leading to small reductions in radius ratio. In other gases with higher atomic number, the pinch duration is much more than the depletion time, so radiative contraction may be anticipated. The Lee model was employed to study the soft X-ray from PF1000 operated with nitrogen and oxygen. We found nitrogen soft X-ray yield in the water window region of 3.13 kJ, with the corresponding efficiency of 0.9% of the stored energy [Formula: see text], while for the oxygen it was found to be [Formula: see text] = 4.9 kJ, with the efficiency of 1.4% [Formula: see text]. The very modest enhancement of compression (radius ratios around 0.1) in the pinches of these two gases gives rise to rather modest pinch energy densities (PEDs) under 109 Jm[Formula: see text]. This is in contrast to Kr or Xe where it had been shown that the radiative collapse leads to radius ratios of 0.007 and 0.003, respectively, with PEDs going to large values considerably exceeding 10[Formula: see text] Jm[Formula: see text].

The influence of an equation-of-state during radiative collapse

We study the role played by an equation-of-state during gravitational collapse of a radiating star. Starting from an initially static matter configuration obeying a linear equation-of-state, the star loses hydrostatic equilibrium and undergoes dissipative collapse in the form of a radial heat flux. We show that the equation-of-state parameter plays an important role in determining the temperature profiles of the collapsing body.