arXiv subjects

Ashish Ganguli

Publications and source records attributed to Ashish Ganguli.

4 recordsLinked to original sources

arXiv2026

Modelling of Flowing Plasma in the Magnetic Field of the Small Volume Plasma System Experiment

A flow model for a magnetized plasma has been developed to investigate the flow dynamics in the small volume plasma system (SVPS) experiment. The SVPS experimental conditions require the model to describe a stationary, collisional, quasineutral, axisymmetric plasma. Also, the ions are cold while the electrons are isothermal and in thermal equilibrium, obeying the Boltzmann relation. In a plasma flowing along a magnetic field, the velocity of ions along the magnetic field lines is much greater than the velocity perpendicular to the field. The latter feature permits a unique ordering of the relevant variables, when the flow equations are transformed to the magnetic coordinate system (MCS), where the coordinate axes are parallel and perpendicular to the field lines. The ordering of the flow variables in the MCS allows a further simplification of the flow equations, by permitting their splitting into set of reduced, simplified equations. The SVPS experimental data are used to provide the requisite boundary conditions for initializing and solving the reduced flow equations on a magnetic coordinate grid along the different lines of the MCS. An important aspect of the present work is the validation of the splitting scheme used to derive the simplified and reduced flow equations. This is achieved by an in-depth comparison of the predictions from the model equations with the experimental data. The obtained numerical results compare favourably with the SVPS observations and have been discussed rigorously. The model developed here provides a framework for exploring magnetized plasma dynamics in the given cylindrically symmetric magnetic field configuration and can be further extended to more complex configurations.

physics.plasm-ph↗

arXiv2026

Mass Spectrometry Studies of Hydrogen Ions Energy Distributions in an ECR- based Large Volume Plasma Source

Plasma is produced in a Large Volume Plasma Source (LVPS; dia. = 1 m, height = 1m) using CW microwaves (= 400 - 600 W, 2.45 GHz), in a compact ECR plasma source (CEPS) attached to LVPS, at hydrogen gas pressures = 1 - 3 mTorr. Plasma expands along the CEPS magnetic field into LVPS. A Hiden Analytical HPR 60 molecular beam mass spectrometer (MBMS) is used to measure the H^- ion energy distribution functions (IEDFs) in the downstream plasma. Previous plasma characterization studies in LVPS indicated favourable downstream plasma conditions for volume production of H^- ions. Measurements conducted with the MBMS probe aligned facing the plasma flow = 80 cm downstream, gave typical H^- count rates = 3 x 10^5 counts /s, at = 400 W, = 1 mTorr, along with a distinct high energy tail (<= 20 eV). These and other results are analyzed in detail. The positive ion spectrum showed the H_3^+ count to be consistently high in all cases (= 60-70 %); the counts for H_2^+ and H^+ were =30-35 % and a =few %. Combining the Langmuir probe (LP) and MBMS data it is possible to determine the approximate densities in front of the MBMS probe aperture. At = 500 W and = 2 mTorr, one finds: n_(H^+) = 9.6 x 10^9 cm^(-3), n_(H_2^+) = 1.7 x 10^10 cm^(-3) and n_(H_3^+) = 4.3 x 10^10 cm^(-3). The corresponding H^- density, = 80 cm downstream is n_(H^-) = 3.9 x 10^8 cm^(-3). Accounting for all H^- losses due to scattering and destruction, one finds the effective mean free path for H^- loss to be = 12.4 cm. Noting that H^- formation takes place about = 10 - 30 cm downstream of the source exit, the approximate average H^- density in the formation zone is determined as = 5.5 x 10^10 cm^(-3). This value is remarkably encouraging for H^- production in volume mode, considering the large chamber volume and area, as well as the very moderate power used for the experiments.

physics.plasm-ph↗

arXiv2026

Investigation of high pressure capacitively coupled plasmas produced by electrons energized in DC sheath at powered electrode

A 13.56 MHz, capacitively coupled plasma is investigated experimentally to determine the power absorption mechanism across a wide pressure range ({\approx} 5 - 600 mTorr) at {\approx} 10 W. Axial profiles of plasma parameters are measured along with V_{DC}, the DC self-bias voltage on the powered electrode (PE), from which the DC sheath voltage drop, V_{s} is determined. Axial profiles of electron ohmic power absorption reveal that power deposition is highest in low-density regions and lowest in high-density regions, indicating that plasma formation is not driven by Ohmic heating. Probability arguments were correlated with locations of the density peaks to determine the ionization mean free paths ({\lambda}_{iz}) at each pressure. Electron acceleration and average electron velocity acquired in the DC sheath voltage drop at PE were also calculated to determine {\lambda}_{iz} independently for comparing with those calculated from the density profiles. The agreement is good for all pressures, barring the lowest pressure ({\approx} 5 mTorr) for which there is significant deviation. The electron sheath transit times are a small fraction of the RF period, implying that the accelerated electrons experience the RF field as instantaneous "spot values" superimposed on V_{s}, the DC sheath drop. The negative self-bias on PE renders the RF swing asymmetric making it negative for most of the cycle. Since the RF accelerates electrons when it is negative and takes energy from them when it is positive, net power is transferred to the electrons during the course of steady-state measurements, averaged over many RF cycles. Except at {\approx} 5 mTorr where stochastic heating dominates, the RF field at higher pressures exhibits a novel role, not hitherto reported.

physics.plasm-ph↗

arXiv2022

Excitation of helical shape argon atmospheric pressure plasma jet using RF pulse modulation

The article reports the excitation of a helical argon atmospheric pressure plasma jet using a pulse modulated 13.56 MHz radiofrequency (RF) power source. This helical structure is observed in open ambient air which is far different from the conventional conical shape. This helical structure originates due to the periodic pressure variation in the discharge region caused by pulse modulated RF (2 kHz modulation frequency (fp)) and propagates downstream into the ambient air. The geometrical characteristics of the observed structure are explored using optical imaging. Moreover, the influence of various input parameters viz., duty cycle (D), gas flow rate (Q), and RF power (P) of the modulated pulse on the formation of helical structure are studied. These helical structures have an implication on the plasma jet chemical features (enhancement of reactive oxygen and nitrogen species (RONS)) as these are involved in increase in air entrainment into the ionization region desired for various plasma applications.

physics.plasm-ph↗