arXiv subjects

D. Nath

Publications and source records attributed to D. Nath.

7 recordsLinked to original sources

arXiv2026

Understanding Carbon Sourcing and Transport Originating from the Helicon Antenna Surfaces During High-Power Helicon Discharge in DIII-D Tokamak

The high-power helicon wave system in the DIII-D tokamak introduces new plasma--material interaction (PMI) challenges due to rectified RF sheath potentials forming near antenna structures and surrounding tiles. Using the STRIPE modeling framework-which integrates SOLPS-ITER, COMSOL, RustBCA, and GITR/GITRm-we simulate carbon erosion, re-deposition, and global impurity transport in two H-mode discharges with varying antenna--plasma gaps and RF powers. COMSOL predicts rectified sheath potentials of 1-5 kV, localized near the bottom of the antenna where magnetic field lines intersect at grazing angles. Erosion is dominated by carbon self-sputtering, with RF-accelerated D+ ions contributing up to 1 % of the total erosion flux. GITRm simulations show that in the small-gap case, only ~ 13 % of eroded carbon is re-deposited locally, with 58 % transported into the core. In contrast, the large-gap case exhibits lower total erosion, along with reduced core penetration (~ 35 %) and weaker re-deposition (~ 4 %), consistent with lower collisionality and limited plasma contact. The simulation trends are consistent with experimental observations, which have not shown elevated core impurity levels during helicon operation in the present graphite-wall configuration. However, under certain plasma conditions and magnetic configurations, the helicon antenna may still act as a finite source of net erosion and core-directed impurity transport, potentially influencing the overall core impurity balance. These findings emphasize the need for sheath-aware antenna designs and predictive impurity transport modeling to support future high-power RF systems with high-Z first wall materials in fusion devices.

physics.plasm-ph↗

arXiv2020

Time dependent rationally extended Poschl-Teller potential and some of its properties

We examine time dependent Schrodinger equation with oscillating boundary condition. More specifically, we use separation of variable technique to construct time dependent rationally extended Poschl-Teller potential (whose solutions are given by in terms of X1 Jacobi exceptional orthogonal polynomials) and its supersymmetric partner, namely the Poschl-Teller potential. We have obtained exact solutions of the Schrodinger equation with the above mentioned potentials subjected to some boundary conditions of the oscillating type. A number of physical quantities like the average energy, probability density, expectation values etc. have also been computed for both the systems and compared with each other.

math-ph↗

arXiv2020

Quantum test of the Universality of Free Fall using rubidium and potassium

We report on an improved test of the Universality of Free Fall using a rubidium-potassium dual-species matter wave interferometer. We describe our apparatus and detail challenges and solutions relevant when operating a potassium interferometer, as well as systematic effects affecting our measurement. Our determination of the E\"otv\"os ratio yields $\eta_{\,\text{Rb,K}}=-1.9\times10^{-7}$ with a combined standard uncertainty of $\sigma_\eta=3.2\times10^{-7}$.

physics.atom-ph↗

arXiv2019

Optomechanical resonator-enhanced atom interferometry

Matter-wave interferometry and spectroscopy of optomechanical resonators offer complementary advantages. Interferometry with cold atoms is employed for accurate and long-term stable measurements, yet it is challenged by its dynamic range and cyclic acquisition. Spectroscopy of optomechanical resonators features continuous signals with large dynamic range, however it is generally subject to drifts. In this work, we combine the advantages of both devices. Measuring the motion of a mirror and matter waves interferometrically with respect to a joint reference allows us to operate an atomic gravimeter in a seismically noisy environment otherwise inhibiting readout of its phase. Our method is applicable to a variety of quantum sensors and shows large potential for improvements of both elements by quantum engineering.

physics.optics↗

arXiv2018

Non-Commutativity effects in the Dirac equation in crossed electric and magnetic fields

In this paper we present exact solutions of the Dirac equation on the non-commutative plane in the presence of crossed electric and magnetic fields. In the standard commutative plane such a system is known to exhibit contraction of Landau levels when the electric field approaches a critical value. In the present case we find exact solutions in terms of the non-commutative parameters $\eta$ (momentum non-commutativity) and $\theta$ (coordinate non-commutativity) and provide an explicit expression for the Landau levels. We show that non-commutativity preserves the collapse of the spectrum. We provide a dual description of the system: (i) one in which at a given electric field the magnetic field is varied and the other (ii) in which at a given magnetic field the electric field is varied. In the former case we find that momentum non-commutativity ($\eta$) splits the critical magnetic field into two critical fields while coordinates non-commutativity ($\theta$) gives rise to two additional critical points not at all present in the commutative scenario.

hep-th↗

arXiv2017

k deformed Dirac equation in crossed magnetic and electric fields

We obtain solutions of the (2 + 1) dimensional k deformed Dirac equation in the presence of crossed magnetic and electric fields. It is shown that the k deformed Landau levels are modified in the presence of the electric field. Contraction of Landau levels has also been examined and it has been shown that the contraction depends on a critical magnetic field which is independent of the deformation parameter in first order approximation.

physics.gen-ph↗

arXiv2015

Ground Tests of Einstein's Equivalence Principle: From Lab-based to 10-m Atomic Fountains

To date, no framework combining quantum field theory and general relativity and hence unifying all four fundamental interactions, exists. Violations of the Einstein's equivalence principle (EEP), being the foundation of general relativity, may hold the key to a theory of quantum gravity. The universality of free fall (UFF), which is one of the three pillars of the EEP, has been extensively tested with classical bodies. Quantum tests of the UFF, e.g. by exploiting matter wave interferometry, allow for complementary sets of test masses, orders of magnitude larger test mass coherence lengths and investigation of spin-gravity coupling. We review our recent work towards highly sensitive matter wave tests of the UFF on ground. In this scope, the first quantum test of the UFF utilizing two different chemical elements, Rb-87 and K-39, yielding an Eötvös ratio $η_{\,\text{Rb,K}}=(0.3\pm 5.4)\times 10^{-7}$ has been performed. We assess systematic effects currently limiting the measurement at a level of parts in $10^8$ and finally present our strategies to improve the current state-of-the-art with a test comparing the free fall of rubidium and ytterbium in a very long baseline atom interferometry setup. Here, a 10 m baseline combined with a precise control of systematic effects will enable a determination of the Eötvös ratio at a level of parts in $10^{13}$ and beyond, thus reaching and overcoming the performance limit of the best classical tests.