arXiv subjects

Debaprasad Sahu

Publications and source records attributed to Debaprasad Sahu.

5 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↗

arXiv2022

Influence of pulse modulation frequency on helium RF atmospheric pressure plasma jet characteristics

This work investigates the influence of pulse modulation frequency ranging from 50 Hz- 10 kHz on the helium RF atmospheric pressure plasma jet's fundamental characteristics. The impact of modulation frequency on plasma jet discharge behavior, geometrical variation, reactive species emission, and plasma parameters (gas temperature Tg, electron excitation temperature Texc, and electron density (ne) are studied using various diagnostics such as optical imaging, emission spectra, and thermal diagnostics. From the experiments, it is observed that operating the plasma jet at low pulse modulation frequencies (around 50 Hz) provides enhanced plasma dimensions, higher electron densities and greater optical emission from reactive species (viz., He I, O, OH, N2+, etc.) as compared to the higher modulation frequencies. Besides the low power consumption, the three times less gas temperature of the modulated plasma jet than the continuous wave mode makes it more advantageous for the applications. Moreover, the influence of duty cycle (D) and applied RF power (P) on the plasma jet characteristics are also discussed. It is found that 10- 40% duty cycle operation provides the most favorable attributes. More importantly, the concern of shorter plasma length in RF plasma jets is overcome by operating at 10- 20% duty cycle with increased applied power. This work thoroughly characterizes helium atmospheric pressure RF plasma jet with a wide range of pulse mode operating parameters, which could help select appropriate operating conditions for various industrial and biomedical applications.

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↗

arXiv2022

A Joint Calibration Technique for Improving Measurement Accuracy of Voltage and Current Probes During Synchronous Operation for RF Based Plasma Devices

This paper presents a joint calibration scheme for voltage (V) and current (I) probes that helps resolve accurately voltage-current phase differences even when the difference is very close to $90^{\circ}$. The latter has been a major issue with V-I probes when used with miniature RF plasma devices like the atmospheric pressure plasma jet (APPJ). Since the impedance of such miniature devices is predominantly capacitive, the phase difference between the voltage and current signals is very nearly $90^{\circ}$. It turns out, however, that when V-I probes are used with such devices without joint calibration, these frequently yield phase shifts over $90^{\circ}$. Also, since power absorption is proportional to the resistive part of the impedance it becomes very sensitive to the phase difference when it is close to $\approx90^{\circ}$. Thus, it is important to be able to resolve the phases accurately. Post-calibration, V-I probes would be indispensable for the electrical characterization of APPJs for determining average RF power $P_{av}$, plasma impedance $Z_p$, etc.Typical post-calibration V-I data yields, $Zp \approx 93.6 - j 1139 Ω (81.5 - j 1173 Ω)$ at $P_{av} \approx 9.8 W$ $(\approx7.7 W)$ for helium (argon) gas.

physics.plasm-ph↗