Large area multi-filamentary plasma source for large volume plasma device-upgrade.

This paper discusses the salient features and plasma performance of the newly installed Large Area Multi-Filamentary Plasma Source (LAMPS) in large volume plasma device-upgrade. The plasma source is designed to exhibit a plasma electron density of ∼1018 m-3, low electron temperature (∼eV), and a uniform plasma cross section of 2.54 m2. The directly heated LAMPS emits accelerated primary energetic electrons when it is biased with a negative discharge voltage with respect to the anode. The hairpin shaped tungsten (W) filaments, each of diameter 0.5 mm and length 180 mm, are heated to a temperature of 2700 K by feeding ∼19.5A to each filament. The LAMPS consists of 162 numbers of filaments, and it has been successfully operated with a total investment of 50 kW of electrical power. The LAMPS as a laboratory plasma source is characterized by large operational life, ease of handling, better compatibility to high pressure conditions, and advantages over other contemporary plasma sources, viz., oxide coated cathodes, RF based sources, and helicon sources, when producing plasma over large cross sections and fill volumes. Pulsed argon plasma is produced with quiescence (δnene≪1%) using LAMPS for the duration of 50 ms and a reasonably good radial uniformity (Ln = 210 cm) is achieved. Good axial uniformity is also observed over the entire length of the device. Initial measurements on plasma parameters have yielded plasma density of ∼2×1017m-3 with existing set of filaments. A plasma density of ∼1018 m-3 is envisaged for larger thickness of filaments, such as 0.75 and 1.0 mm, with the existing plasma source assembly setup.

Development of electronic record-keeping software for remote participation in Large Volume Plasma Device upgrade using Angular 2 and NodeJS web technologies.

In an era of digital transformation and collaborations, the Web Information System (WIS) becomes an essential requirement for the information and data sharing of large experimental facilities among users. With the enhancement in the capabilities and performance of web technologies, sharing of experimental data using a flexible, modular, secure, and robust mechanism is feasible. In this direction, the Large Volume Plasma Device (LVPD), an experimental device dedicated for carrying out investigations for unfolding physical phenomena of relevance to Earth's magnetosphere and fusion plasmas, also adopts web-based electronic record keeping for its operation. The nature of investigations is concerned with plasma turbulence of electron scale, induced anomalous plasma transport and mitigation of energetic electrons by excited whistler turbulence that requires large scale, and simultaneous multiple point measurements from different electrostatic and electro-magnetic diagnostics. This paper discusses the WIS implementation in LVPD for the experimental configuration, information logging, and preliminary data analysis. The architecture of the system is spread over three tiers covering application, data, and presentation layers. The presentation layer is developed using the Angular 2 framework on the progressive web application architecture. The application and data layers are developed using NodeJS and PostgreSQL, respectively. The novelty of this paper lies in the integrated application development approach and applicability of the latest web technologies in the scientific and experimental domains. This paper discusses the literature survey of similar developments at other places, requirements, scopes, development artifacts, adapted tools and technologies, obtained results from actual plasma discharges of LVPD, and future enhancements.

Electro-mechanical probe positioning system for large volume plasma device.

An automated electro-mechanical system for the positioning of plasma diagnostics has been designed and implemented in a Large Volume Plasma Device (LVPD). The system consists of 12 electro-mechanical assemblies, which are orchestrated using the Modbus communication protocol on 4-wire RS485 communications to meet the experimental requirements. Each assembly has a lead screw-based mechanical structure, Wilson feed-through-based vacuum interface, bipolar stepper motor, micro-controller-based stepper drive, and optical encoder for online positioning correction of probes. The novelty of the system lies in the orchestration of multiple drives on a single interface, fabrication and installation of the system for a large experimental device like the LVPD, in-house developed software, and adopted architectural practices. The paper discusses the design, description of hardware and software interfaces, and performance results in LVPD.

A 5 kA pulsed power supply for inductive and plasma loads in large volume plasma device.

This paper describes 5 kA, 12 ms pulsed power supply for inductive load of Electron Energy Filter (EEF) in large volume plasma device. The power supply is based upon the principle of rapid sourcing of energy from the capacitor bank (2.8 F/200 V) by using a static switch, comprising of ten Insulated Gate Bipolar Transistors (IGBTs). A suitable mechanism is developed to ensure equal sharing of current and uniform power distribution during the operation of these IGBTs. Safe commutation of power to the EEF is ensured by the proper optimization of its components and by the introduction of over voltage protection (>6 kV) using an indigenously designed snubber circuit. Various time sequences relevant to different actions of power supply, viz., pulse width control and repetition rate, are realized through optically isolated computer controlled interface.

Performance of large electron energy filter in large volume plasma device.

This paper describes an in-house designed large Electron Energy Filter (EEF) utilized in the Large Volume Plasma Device (LVPD) [S. K. Mattoo, V. P. Anita, L. M. Awasthi, and G. Ravi, Rev. Sci. Instrum. 72, 3864 (2001)] to secure objectives of (a) removing the presence of remnant primary ionizing energetic electrons and the non-thermal electrons, (b) introducing a radial gradient in plasma electron temperature without greatly affecting the radial profile of plasma density, and (c) providing a control on the scale length of gradient in electron temperature. A set of 19 independent coils of EEF make a variable aspect ratio, rectangular solenoid producing a magnetic field (B(x)) of 100 G along its axis and transverse to the ambient axial field (B(z) ~ 6.2 G) of LVPD, when all its coils are used. Outside the EEF, magnetic field reduces rapidly to 1 G at a distance of 20 cm from the center of the solenoid on either side of target and source plasma. The EEF divides LVPD plasma into three distinct regions of source, EEF and target plasma. We report that the target plasma (n(e) ~ 2 × 10(11) cm(-3) and T(e) ~ 2 eV) has no detectable energetic electrons and the radial gradients in its electron temperature can be established with scale length between 50 and 600 cm by controlling EEF magnetic field. Our observations reveal that the role of the EEF magnetic field is manifested by the energy dependence of transverse electron transport and enhanced transport caused by the plasma turbulence in the EEF plasma.

Revisiting plasma hysteresis with an electronically compensated Langmuir probe.

The measurement of electron temperature in plasma by Langmuir probes, using ramped bias voltage, is seriously affected by the capacitive current of capacitance of the cable between the probe tip and data acquisition system. In earlier works a dummy cable was used to balance the capacitive currents. Under these conditions, the measured capacitive current was kept less than a few mA. Such probes are suitable for measurements in plasma where measured ion saturation current is of the order of hundreds of mA. This paper reports that controlled balancing of capacitive current can be minimized to less than 20 µA, allowing plasma measurements to be done with ion saturation current of the order of hundreds of µA. The electron temperature measurement made by using probe compensation technique becomes independent of sweep frequency. A correction of ≤45% is observed in measured electron temperature values when compared with uncompensated probe. This also enhances accuracy in the measurement of fluctuation in electron temperature as δT(pk-pk) changes by ~30%. The developed technique with swept rate ≤100 kHz is found accurate enough to measure both the electron temperature and its fluctuating counterpart. This shows its usefulness in measuring accurately the temperature fluctuations because of electron temperature gradient in large volume plasma device plasma with frequency ordering ≤50 kHz.

Experimental observation of electron-temperature-gradient turbulence in a laboratory plasma.

We report the observation of electron-temperature-gradient (ETG) driven turbulence in the laboratory plasma of a large volume plasma device. The removal of unutilized primary ionizing and nonthermal electrons from uniform density plasma and the imposition and control of the gradient in the electron temperature (T[Symbol: see text] T(e)) are all achieved by placing a large (2 m diameter) magnetic electron energy filter in the middle of the device. In the dressed plasma, the observed ETG turbulence in the lower hybrid range of frequencies ν = (1-80 kHz) is characterized by a broadband with a power law. The mean wave number k perpendicular ρ(e) = (0.1-0.2) satisfies the condition k perpendicular ρ(e) ≤ 1, where ρ(e) is the electron Larmor radius.