arXiv subjects

M. Dan

Publications and source records attributed to M. Dan.

11 recordsLinked to original sources

arXiv2024

Investigating the rate of $^{10}$Be(n,$\gamma$)$^{11}$Be radiative capture reaction within the FRDWBA framework

This study examines the radiative capture of a neutron by $^{10}$Be using the Coulomb dissociation approach within the FRDWBA theory. We analyze the elastic Coulomb breakup of $^{11}$Be on a $^{208}$Pb target at 72 MeV/A to determine the photodisintegration cross-section and radiative capture cross-section. Utilizing the Maxwell-averaged velocity distribution, we calculate the resulting radiative neutron capture reaction rate for the $^{10}$Be(n,$\gamma$)$^{11}$Be reaction. Comparative analyses are conducted with experimental data, theoretical results from direct radiative capture methods, and transfer reaction calculations. Additionally, we contrast our findings with the existing $^{10}$Be($\alpha$,$\gamma$)$^{14}$C reaction rate and conclude the dominance of neutron capture over $\alpha$ capture by $^{10}$Be.

nucl-th↗

arXiv2024

Radiative neutron capture rate of $^{11}$B$(n,\gamma)^{12}$B reaction from the Coulomb dissociation of $^{12}$B

We calculate the $^{11}$B$(n,\gamma)^{12}$B reaction rate, an important constituent in nucleosynthesis networks, contributed by resonant as well as non-resonant capture. For the resonant rate, we use the narrow resonance approximation whereas the non-resonant contribution is calculated with the Coulomb dissociation method for which we use finite-range distorted wave Born approximation theory. We then compare our calculated rate of $^{11}$B$(n,\gamma)^{12}$B reaction with those reported earlier and with other charged particle reactions on $^{11}$B.

nucl-th↗

arXiv2023

Spider Ion Source and Extraction Power Supplies -- An update of the design after four years of operation

SPIDER, the ion source prototype for ITER neutral beam injectors, has been in operation since 2018. The experiment includes a system of Ion Source and Extraction Power Supplies (ISEPS), whose design dates back to 2011. Since then the experience gained has led to substantial changes, the most dramatic modification being the complete replacement of the radiofrequency power supply, described elsewhere. This contribution details operating experience and calculations that have led to defining new requirements for a specific subset of power supplies, the bias power supplies. The bias power supplies perform the function of filtering out electrons extracted together with the negative ions and in the original 2011 ISEPS design are single quadrant resonant converters. For the two bias power supplies, the picture resulting from the review described in the paper is a substantial redesign, with the ability to operate in four quadrants and a twofold increase of the rated output voltage the most significant new specifications.

physics.plasm-ph↗

arXiv2023

Lessons learned after three years of SPIDER operation and the first MITICA integrated tests

ITER envisages the use of two heating neutral beam injectors plus an optional one as part of the auxiliary heating and current drive system. The 16.5 MW expected neutral beam power per injector is several notches higher than worldwide existing facilities. A Neutral Beam Test Facility (NBTF) was established at Consorzio RFX, exploiting the synergy of two test beds, SPIDER and MITICA. SPIDER is dedicated to developing and characterizing large efficient negative ion sources at relevant parameters in ITER-like conditions: source and accelerator located in the same vacuum where the beam propagates, immunity to electromagnetic interferences of multiple radio-frequency (RF) antennas, avoidance of RF-induced discharges on the outside of the source. Three years of experiments on SPIDER have addressed to the necessary design modifications to enable full performances. The source is presently under a long shut-down phase to incorporate learnings from the experimental campaign. Parallelly, developments on MITICA, the full-scale prototype of the ITER NBI featuring a 1 MV accelerator and ion neutralization, are underway including manufacturing of in-vessel components, while power supplies and auxiliary plants are already under final testing and commissioning. Integration, commissioning and tests of the 1MV power supplies are essential for this first-of-kind system, unparalleled both in research and industry field. The integrated test to confirm 1MV output by combining invertor systems, DC generators and transmission lines extracted errors/accidents in some components. To realize a concrete system for ITER, solutions for the repair and the improvement of the system were developed. Hence, NBTF is emerging as a necessary facility, due to the large gap with existing injectors, effectively dedicated to identify issues and find solutions to enable successful ITER NBI operations in a time bound fashion.

physics.plasm-ph↗

arXiv2023

The $^{19}$N($n$,$\gamma)^{20}$N capture rate in light of the probable bubble nature of $^{20}$N

We aim to explore the bubble nature of the exotic nucleus $^{20}$N within the microscopic antisymmetrized molecular dynamics (AMD) approach. Constraining its structural parameters, we analyse its static properties. Subsequently, we use the AMD infused finite-range distorted-wave Born approximation theory to calculate the Coulomb breakup of $^{20}$N as an indirect approach to estimate the $^{19}$N$(n,\gamma)^{20}$N radiative capture rate.

nucl-th↗

arXiv2021

Exploring the structure of $^{29}$Ne

We apply a fully quantum mechanical Coulomb breakup theory under the aegis of post form finite-range distorted wave Born approximation to analyze the elastic Coulomb breakup of $^{29}$Ne on $^{208}$Pb at $244$\,MeV/u. We calculate several reaction observables to quantify its structural parameters. One-neutron removal cross-section is calculated to check the consistency of the ground state configuration of $^{29}$Ne with the available experimental data. A scrutiny of the parallel momentum distribution of the charged fragment reveals a full width at half maximum of $82$\,MeV/c, which is in good agreement with the experimental value and indicates a moderate halo for a nearly spherical $^{29}$Ne in the $^{28}$Ne$(0^+) \otimes 2p_{3/2}\nu$ ground state. The energy-angular distributions and average momentum of the charged fragment point to the absence of post-acceleration effects in the breakup process, a desirable result for the elastic breakup.

nucl-th↗

arXiv2021

A unified description of the structure and electromagnetic breakup of $^{\bf 11}$Be

We study both the static properties of $^{11}$Be and its reaction dynamics during electromagnetic breakup under a unified framework. A many-body approach - the antisymmetrized molecular dynamics (AMD) is used to describe the structure of the neutron-halo nucleus, $^{11}$Be. The same AMD wave function is then adapted as an input to the fully quantum theory of Coulomb breakup under the aegis of the finite range distorted wave Born approximation theory. The calculated observables are also compared with those obtained with a phenomenological Woods-Saxon potential model wave function. The experimental core-valence neutron relative energy spectrum and dipole response along with other observables are well described by our calculations.

nucl-th↗

arXiv2013

The structure and fate of white dwarf merger remnants

We present a large parameter study where we investigate the structure of white dwarf (WD) merger remnants after the dynamical phase. A wide range of WD masses and compositions are explored and we also probe the effect of different initial conditions. We investigated the degree of mixing between the WDs, the conditions for detonations as well as the amount of gas ejected. We find that systems with lower mass ratios have more total angular momentum and as a result more mass is flung out in a tidal tail. Nuclear burning can affect the amount of mass ejected. Many WD binaries that contain a helium-rich WD achieve the conditions to trigger a detonation. In contrast, for carbon-oxygen transferring systems only the most massive mergers with a total mass above ~2.1 solar masses detonate. Even systems with lower mass may detonate long after the merger if the remnant remains above the Chandrasekhar mass and carbon is ignited at the centre. Finally, our findings are discussed in the context of several possible observed astrophysical events and stellar systems, such as hot subdwarfs, R Coronae Borealis stars, single massive white dwarfs, supernovae of type Ia and other transient events. A large database containing 225 white dwarf merger remnants is made available via a dedicated web page.

astro-ph.HE↗

arXiv2012

On the point mass approximation to calculate the gravitational wave signal from white dwarf binaries

Double white dwarf binaries in the Galaxy dominate the gravitational wave sky and would be detectable for an instrument such as LISA. Most studies have calculated the expected gravitational wave signal under the assumption that the binary white dwarf system can be represented by two point masses in orbit. We discuss the accuracy of this approximation for real astrophysical systems. For non-relativistic binaries in circular orbit the gravitational wave signal can easily be calculated. We show that for these systems the point mass approximation is completely justified when the individual stars are axisymmetric irrespective of their size. We find that the signal obtained from Smoothed-Particle Hydrodynamics simulations of tidally deformed, Roche-lobe filling white dwarfs, including one case when an accretion disc is present, is consistent with the point mass approximation. The difference is typically at the level of one per cent or less in realistic cases, yielding small errors in the inferred parameters of the binaries.

astro-ph.HE↗

arXiv2008

Mass transfer dynamics in double degenerate binary systems

We present a numerical study of the mass transfer dynamics prior to the gravitational wave-driven merger of a double white dwarf system. Recently, there has been some discussion about the dynamics of these last stages, different methods seemed to provide qualitatively different results. While earlier SPH simulations indicated a very quick disruption of the binary on roughly the orbital time scale, more recent grid-based calculations find long-lived mass transfer for many orbital periods. Here we demonstrate how sensitive the dynamics of this last stage is to the exact initial conditions. We show that, after a careful preparation of the initial conditions, the reportedly short-lived systems undergo mass transfer for many dozens of orbits. The reported numbers of orbits are resolution-biased and therefore represent only lower limits to what is realized in nature. Nevertheless, the study shows convincingly the convergence of different methods to very similar results.

astro-ph↗

arXiv2008

Simulating Black Hole White Dwarf Encounters

The existence of supermassive black holes lurking in the centers of galaxies and of stellar binary systems containing a black hole with a few solar masses has been established beyond reasonable doubt. The idea that black holes of intermediate masses ($\sim 1000$ \msun) may exist in globular star clusters has gained credence over recent years but no conclusive evidence has been established yet. An attractive feature of this hypothesis is the potential to not only disrupt solar-type stars but also compact white dwarf stars. In close encounters the white dwarfs can be sufficiently compressed to thermonuclearly explode. The detection of an underluminous thermonuclear explosion accompanied by a soft, transient X-ray signal would be compelling evidence for the presence of intermediate mass black holes in stellar clusters. In this paper we focus on the numerical techniques used to simulate the entire disruption process from the initial parabolic orbit, over the nuclear energy release during tidal compression, the subsequent ejection of freshly synthesized material and the formation process of an accretion disk around the black hole.

astro-ph↗