Title: Analytical study of plasma stream dynamics in Pulsed Plasma Accelerator .

Speaker: Dr. Suramoni Borthakur

Date, time and Venue: Aug 06 , 2020 Time: 12.30 pm CPP-IPR, Seminar Hall

The effect of gas puffing on plasma stream velocity and its influence on the plasma stream was analytically investigated for the pulsed plasma accelerator system. A transient supersonic gas injection, just before the plasma discharge is one of the requirements for operating the device. This gas puff is carried out by an electromagnetically operated gas injection valve that can be operated over a range of pressures between 0.4-60 bar. The variable pressure of the valve delivers different amount of gas during injection. The cases for Argon, Nitrogen, Helium and Hydrogen gases are evaluated analytically in this work. The mass flow rates of the gases and the Alfven velocities were determined. This Alfven speed stands as a reference to the actual plasma velocity while designing the plasma system. Further, the plasma stream velocity profiles are estimated in terms of unionized gas densities for a constant mass flow rate of injected gas. The Alfven velocity is compared to the plasma velocity which was experimentally measured in an earlier work. The gas distribution profile of the injected gas obtained experimentally using a piezo-resistive pressure probe, has been used in this analysis. A critical analysis for possible plasma velocities due to this distribution profile was carried out.

Title: Application of plasma surface wave in communication technology .

Speaker: Dr. Rinku Mishra

Date, time and Venue: Aug 07 , 2020 Time: 11.45 am CPP-IPR, Seminar Hall

The investigation of surface wave propagation in the bounded system has attracted much attention due to its vital role in different fields of plasma physics. In communication technology, the application of surface waves in the plasma antenna has increased a lot in recent times. Plasma antenna uses plasma in place of metal conductor for transmission and reception of signals. The conductive and dielectric properties of plasma help the researchers to use plasma as a radiating element and expand its application in several areas of plasmabased technologies. The present proposed work has aimed to study the unique features of plasma antenna and its optimization process. Investigation of the plasma characteristics is essential to understand the antenna environment, as it is completely dependent on plasma frequency and electron density. The work performed here has attempted to study the plasma characteristics in the antenna environment. The results indicate that even for a slight change in gas pressure or power, the plasma antenna characteristics get affected drastically. The various antenna profile like the electric field, potential, phase space, and many others has been considered in the investigation. In the next phase, the benchmarking of results with the experimental system and optimization of the antenna parameter will be incorporated into the study. The wave dispersion phenomena using the PIC method will also be investigated to understand the transmission and reception of the antenna properties in a better way.

Title: Study of Double layers in a multicomponent plasma .

Speaker: Dr. Dharitree Dutta

Date, time and Venue: Aug 07 , 2020 Time: 11.00 am CPP-IPR, Seminar Hall

Current free double layers in an expanding plasma have been simulated with the 2D-3V XOOPIC code1 (Object Oriented Particle-in-Cell on X-windows). Earlier, Charles and Boswell2 have observed a strong, current-free, electric double layer with 𝜙 ~ 25𝑉, and a thickness of less than 1 𝑐𝑚, in an expanding, high density helicon sustained rf discharged plasma. A supersonic ion beam at about twice the Bohm velocity has been observed to be generated in the downstream region of the double layer3. By adopting the values of the physical parameters such as, chamber dimension, pressure, electron and ion density, and temperature etc. from the experimental work2, equivalent results have been obtained from this numerical simulation. A potential drop of 24 V within a thickness of 14 cm has been observed at a region around the joining of the source and expansion chamber. This potential drop is assumed to be associated with the acceleration of the ions within the double layer, which results in the generation of ion beam at that region. The average velocity of the energetic ions within the double layer is 1.516×104 m/sec, which is approximately twice the Bohm velocity. This work can be extended further to study the generation of current free double layers and their properties in a multi-component plasma in the Helicon Plasma Source (HeliPS) of CPP-IPR.

Title: Inertial Electrostatic Confinement device and its application .

Speaker: Dr. Neelanjan Buzarbaruah

Date, time and Venue: Aug 06 , 2020 Time: 11.45 am CPP-IPR, Seminar Hall

The Inertial electrostatic confinement (IEC) fusion is a competent source for studies relevant to basic plasma and applied fusion research in a portable geometry. The basic concept of IEC fusion relies on delivering fusion composites like neutrons, protons, and X-rays from a compact source in an electrostatic manner. Researchers across the world have worked efficiently to study its basic characteristics and many have utilized it for various societal applications. CPP-IPR has developed table-top IEC fusion devices (spherical and cylindrical) that demonstrate the 2.45 MeV neutrons by fusing deuterons (D-D) in a high electrostatic field (~ tens of kV). During my postdoctoral tenure, I have divided my work into four objectives that are being discussed hereafter. In my first work, I have used a kinetic particle-in-cell code (XOOPIC) to model the plasma characteristics in the cylindrical IEC device. The study has analyzed the potential and density profile of the ions that take part in fusion reactions during HV applications to the cathode of the device. The simulated profiles were compared with the experimental ones and further optimization on the computational results are done. The second part of my work discusses about the development of two different diagnostics tools namely double probe and emissive probe. The probes are used for characterizing the produced deuterium and hydrogen plasmas and the obtained results are analyzed. In the third work, the neutrons (106 n/s) are used for activation analysis on urea, such fertilizer is basically used as an alternative for explosive composites. The gamma rays produced due to thermal neutron activation has been detected using a NaI scintillator detector. Moreover, the IEC device emits X-raysalong with neutrons, therefore experiments on radiography have been performed in the same work. Lastly, to increase the density of the ions and neutron production rate from the IEC device application of the magnetic field is an alternate approach. Therefore, a preliminary study for implementing theapproach has been calculated and simulated. The detailed analysis of the results obtained in this tenure will be discussed in the talk.

Title: Studies on the mode transition, negative ion formation in electronegative gases and gas mixture in helicon discharge .

Speaker: Dr. Narayan Sharma

Date, time and Venue: Aug 06 , 2020 Time: 11.00 am CPP-IPR, Seminar Hall

Helicon waves are the low frequency electromagnetic waves that propagate in the presence of magnetic fields [1]. The main advantage of helicon discharge over other RF discharges is thatit produces higher plasma density (1017-19 m-3) [2]. Although helicon discharge is widelystudied with electropositive gases like argon, helicon discharge with the electronegative gas is a less explored field of research [3]. Electronegative plasma has wide range of application in semiconductor industry, etching and deposition of thin films, negative ion sources, [4] etc.and the helicon discharge produces higher plasma density. Therefore, the study of modetransition and discharge properties with the electronegative gas like oxygen and hydrogen isperformed. Experiment is performed in the Helicon Plasma Source setup. The use of helicondischarge as negative ion source is studied by comparing the negative ion density in hydrogenand oxygen plasma in order to study the influence of electron affinity of working gas on thenegative ion density. The effect of addition of argon gas in oxygen plasma on the modetransition and negative ion formation is also studied. The observed variation of plasmadensity and temperature in argon-oxygen mixed plasma is explained in terms of particle andpower balance equation and that of negative ion density is explained in terms of theproduction and loss mechanism of negative ions. In RF discharges, RF field can penetrate beyond the magnetic filter and cause additionalionization in the expansion chamber creating high energy electrons thereby decreasing the negative ion density. Optimizing the position of the magnetic filter with respect to that of theantenna could influence the presence of the high energy electrons. Hence, the proposed future work plan is to study the influence of the position of magnetic filter on electron temperature and hence on the negative ion density in helicon discharge. This work will facilitate theimprovement of negative ion density in RF plasma source. Another proposed work plan is to perform experiments in argon and hydrogen mixture to understand the influence of helicon discharge properties and negative ion density when electropositive argon gas is added to electronegative hydrogen plasma.

Title: Study of nonlinear coherent structures in presence of superthermal plasma particles .

Speaker: Dharitree Dutta

Date, time and Venue: March 16 , 2020 (Monday) Time: 03.00 pm CPP-IPR, Seminar Hall

Superthermal particles are ubiquitous component of space and near Earth plasma. In any low density and high temperature plasma, superthermal particles generate through wave particle interaction. Due to the absence of collision, those particles cannot relax to thermal equilibrium and thus their distribution cannot be explained with Maxwell-Boltzmann distribution. The distribution is the most acceptable distribution function to describe the velocity distribution of these particles. It has been observed that the presence of superthermal particles significantly alter the nature of linear and nonlinear plasma waves. Among different nonlinear coherent structures observed in the plasma, the solitons and double layers are the most popular structures. Solitons are special kind of solitary structures which can maintain its shape and size even after the collision with other solitons. On the other hand, double layers have been considered as one of the major acceleration mechanism associated with different phenomena occurring in the nature. The study of the generation and propagation of these nonlinear structures in presence of superthermal particles brings some new insights. With the help of those results one can understand the dynamics of different phenomena occurred in space and atmospheric environment.

Title: Deposition of bimetallic nano-films on carbon based material for improved hydrogen generation in energy production using DC planar magnetron sputtering .

Speaker: Dr. Partha Saikia

Date, time and Venue: February 06 , 2020 (Thursday) Time: 03.00 pm CPP-IPR, Seminar Hall

Magnetron sputter deposition [1-3] is a versatile technique for the deposition of metallic as well as the compound thin films. The anomalous behaviour of plasma parameters in unbalanced DC magnetron discharge is still a topic of research for many researchers. In reactive sputtering,in addition to the sputtering gas (generally argon), reactive molecular gas such as nitrogen, oxygen etc. are added. The complex discharge behaviour of the molecular gases and the complexities, generated by the various plasma species in reactive sputtering makes the basic study of physical mechanism of the discharge much more challenging for the researchers.Therefore during my Ph. D tenure, the studies on DC planar magnetron glow discharge plasma was aimed to understand the variation of plasma parameters as a function ofthin film deposition conditions. Depending on those plasma parameters, the optimization of the growth of the deposited thin film can be obtained. We measured the plasma density and temperature as a function of the reactive gas partial pressures using the Langmuir probediagnostics. A study correlating the plasma parameters with the growth (orientation) of the depositing coatings (titanium nitride) was also carried out. However, as the magnetron discharge plasma contains sputtered material species also, the tip of the probe used to get coated by material deposition and thus, can lead to erroneous results. In this regard, ion acoustic wave diagnostic was used to probe magnetron discharge. Based on the expertise during the Ph. D tenure, we propose to deposit bimetallic nano-films on carbon based material for improved hydrogen generation, using DC planar magnetron sputtering in this project. In this regard, we plan to synthesis porous NiMoNx nano-crystallites films on the Carbon Clothes (CC) electrodes by DC planar magnetron sputtering on a pre-nitrogen plasma treated substrate [4]. The motivation behind it, is to use the deposits as electrocatalyst during the electrochemical water splitting into hydrogen (Hydrogen Evaluation Reaction) via solar irradiation. The mechanism of HER includes the adsorption and removal of adsorbed hydrogen atoms on the electrode surface. These are competitive processes, and a good catalyst should have an ideal balance between binding and releasing of adsorbed reaction intermediates. At present, Platinum is the state-of-the-art catalyst for HER. But owing to its very high price, numerous efforts are being devoted to develop alternative electrocatalysts. The nitrogen pre-plasma treatment is supposed to form 3D hierarchical porous structure that should facilitate transfer of reactants and provide larger contact area between carbon based electrode and catalyst, thus improving hydrogen evolution in water splitting .

Title: Bulk synthesis of tungsten-oxide nanomaterial for photocatalytic degradation of harmful dyes and studies on exposure behavior of Indian RAFM steel.

Speaker: Dr. Trinayan Sarmah,

Date, time and Venue: December 20, 2019 (Friday) Time: 12.00 pm CPP-IPR, Seminar Hall

During this post-doctoral tenure, I have worked on rapid, controlled synthesis of tungsten-oxide nanomaterials up to two hundred grams per hour, by a thermal plasm assisted novel experimental configuration. For few tens of mbar pressure in the vacuum chamber, an expanded argon/oxygen plasma beam is produced with collimated, frozen structure that interacts with a remote tungsten target in a controlled manner, to produce WO3 nanomaterials through oxidation of the bulk metal and subsequent sublimation of the tungsten-oxide. We confirmed the deposition of non-stoichiometric WO2.92 (average size 6 nm) in blue colour and stoichiometric WO3 in yellow (37 nm), which had specific surface area of 70.1 m2/g and 16.7 m2/g respectively. Pure WO3 demonstrated modest photo-catalytic properties, but a nanocomposite made with mixing graphitic carbon nitride (g-C3N4) demonstrated outstanding properties for degradation of Rhodamine B solutions. Compared to heating under a neutral oxygen environment, the present experiment demonstrated much-enhanced oxidation and sublimation reactions that may be attributed to the superior reactive properties of the oxygen ions and meta-stables in the plasma jet. Additionally, I have also studied Helium plasma exposure behaviour of India specific RAFM (IN-RAFM) as such plasma exposure of IN-RAFM has never been studied previously. Mainly experiments were carried out to investigate the effect of long fluence helium plasma exposure on the IN-RAFM steel, with the variation of ion-flux by almost an order (~3×1022-23 m-2s-1) and target temperatures in between 316-830 K, in the CIMPLE-PSI device. Modification of the surface morphologies, ranging between nanometer-sized needles to micrometer level pyramid-like structures with foam-like spongy surfaces and thick hollow fibers were observed, the precise type of which was controlled by the temperature of the plasma exposed steel substrate. Measurements by Energy Dispersive X-ray Spectroscopy (EDS) and Rutherford Backscattering Spectroscopy (RBS) confirmed surface enrichment of the exposed samples with high-Z element tungsten because mid-Z elements like Iron and Chromium are preferentially sputtered out by the low-temperature helium plasma ions. However, under high ion flux and temperature, the surface lateral inhomogeneity critically influenced the shape of the RBS spectrum, which make an incorrect impression as if tungsten had diffused into the bulk of the steel and subsequently necessitated a new way of understanding the measured data. Through optical emission spectroscopic observations, it was confirmed that the sputtering yield of the steel reduces with exposure time, because of the W enrichment and also due to the formation of the porous microstructures on the exposed sample surface. In the next post-doctoral extension tenure, optimization of the photocatalytic dye degradation process for two different dyes (cationic and anionic) using the plasma synthesized tungsten oxide catalyst, as well as tungsten oxide/g-C3N4 nanocomposite, shall be carried out. Additionally, scavenging analysis to formulate the role of radicals and other charged species, reusability test of the catalyst material, and detection of degraded by-products and its biocompatibility tests will be performed. Moreover, exposure behaviour of IN-RAFM under deuterium plasma shall be carried out in CIMPLE-PSI device.

Title: Study of double layers in a multi-component plasma

Speaker: Ms. Dharitree Dutta, Doctoral Candidate, Gauhati University

Date, time and Venue: June 24, 2019 (Monday) Time: 3.00 pm CPP-IPR, Seminar Hall

Double layers have been found in a wide variety of plasmas from laboratory to space and have been considered as one of the major acceleration mechanism associated with different phenomena occurring in nature. It consists of two thin adjacent regions of excess space charge, which give rise to a potential drop across the layers. The planetary magnetosphere, heliosphere, the Van Allen Radiation belt, and the ionosphere are few examples of the hosts of double layers in the space. Because of its growing interests, theoretical and numerical works on the formation and the properties of double layers in the presence of suprathermal particles have been done earlier. On the other hand, plasma in general, may contain additional positive and (or) negative ions as well as dust particles besides the electron and positive ion and thus forms the multicomponent plasma. The aim of the proposed work is to study the formation, and characteristics of double layers in a Helicon Plasma Device in the presence of different electronegative gas mixtures (i.e., O₂,Ar;  Ar,H₂) through numerical simulation. The work has scope of applications in the designing of space propulsion engines such as helicon double layer thrusters.

Title: Role of Sheath in Communication Blackout of Space Vehicle Re-entry

Speaker: Dr. Sayan Adhikari, Post Doctoral Fellow

Date, time and Venue: May 24, 2019 (Friday) Time: 3.00 pm CPP-IPR, VC Room

Communication blackout refers to the scenario when a spacecraft or module loses all of its communication with the Earth while reentering the Earth’s atmosphere at hypersonic speed. The blackout occurs due to the envelope of ionized air (plasma) around the spacecraft, created by the heat from the compression of the atmosphere. During the blackout, the radio waves used for communication between ground stations and satellites are attenuated and/or reflected by the plasma layer. The population of electrons near the antenna is the main reason behind this blackout. The plasma layer usually has an electron number density of 1017 to 1020 m-3. If the frequency at which the electrons oscillate is greater than the frequency of radio wave transmission, it results in reflection of the radio waves. The plasma frequency is directly proportional to the square root of the electron density of the plasma layer. Therefore, reducing electron density will certainly help in bringing down the plasma frequency. Eventually, it will help to reduce the blackout period. There are electrostatic and magnetized mitigation schemes, which provide a possibility for communication during radio blackout. The present study has attempted to explore the possibility of such mitigation schemes. The results suggest that magnetized mitigation schemes have more control over electron dynamics and capable of more power optimization.

In the next phase, exact environmental factors will be incorporated in the modeling to provide optimized parameters for different configurations of mitigation.

Title: Wave Propagation in Dusty Plasma System

Speaker: Ms. Rinku Mishra, Doctoral Candidate

Date, time and Venue: May 15, 2019 (Wednesday) Time: 3.00 pm CPP-IPR, VC Room

Study of plasma waves is prevalent to understand different types of linear and non-linear plasma instabilities and energy transport. The collective behavior of plasma is very complex in nature, since it depends on the interaction of electrons and ions. Addition of dust into the plasma makes it more difficult to comprehend. The dust particles act as a source or sink for the electrons and ions making them non-neutral in nature. The coupling of charged particles with the electric or magnetic field in electron-ion plasma often leads to excitation of the various wave in a given plasma system. The presence of dust particles as an additional species introduces new wave modes and also modifies the existing ones. Considering dusty plasma to be infinitely continuous, several studies have been carried out to analyze the wave phenomena in a dusty plasma. Although, it is obvious that bounded or finite plasma always gives the realistic information. In case of bounded plasmas, apart from the electrostatic and electromagnetic plasma waves, surface wave also plays an important role. The surface wave is defined as the wave whose maximum energy is concentrated at the interface separating two media of different dielectric permittivity and shows the evanescent behavior on both sides of the interface. The dispersive property of plasma surface waves is mainly defined by the boundary conditions such as continuity of electric and magnetic field components along the sharp interface. However, the existence of plasma surface wave necessitates a sharp boundary. It has wide range of applications in industrial and laboratory environment which attracts various researchers to this field. Some of the important applications of plasma surface wave include plasma electronics, plasma antenna, plasma production, plasmonics devices, and particle heating by surface wave propagation in fusion.

The present topic of talk aimed to discuss the propagation of electrostatic waves namely the surface wave and volume waves in bounded and unbounded media respectively in dusty plasma. The dust charge fluctuation has been incorporated to study wave properties of the volume waves in both linear and non-linear regimes. The significant findings obtained through the studies are also highlighted.

Title: Development and studies of a coaxial pulsed plasma accelerator

Speaker: Mr. Suramoni Borthakur, Doctoral Candidate

Date, time and Venue: May 15, 2019 (Wednesday) Time: 4.00 pm CPP-IPR, VC Room

A Pulsed Plasma Accelerator (PPA) system is a pulsed plasma device that produces a high density-high energy plasma stream with a very high velocity. The pulsed nature of the plasma has the advantage of achieving a very high energy density for a short duration, practically which is difficult to be produced in a continuous plasma device. When a pulsed power is applied across the two coaxial electrode assembly of the plasma system, the high voltage pulse forms plasma of the existing gas. The impulse high current produces a high magnetic field that interacts with the plasma sheath current density to provide the Lorentz thrust. This thrust gives the necessary acceleration to the plasma stream which can be used for many fruitful purposes, including matters relevant to fusion science. Such a device essentially has two main segments, one is a dedicated pulsed power source and the other is the plasma system. In general, the conventional pulsed plasma device has a discharge duration in the range of few tens of microseconds. But a modified form called the quasi-steady type plasma accelerators can have a much longer plasma life in the range of few hundreds of microseconds [1]. The difference in the time and energy factors greatly modifies the subsequent plasma characteristic, flow dynamics and plasma material interaction effects. Such a longer duration pulse demands some considerations in designing the circuit as well as in the selection of the components of Pulsed Power System [2]. Along with it, the plasma system also requires some pre-estimation and analysis of the plasma flow in the coaxial electrode system. All these things were brought into consideration while developing the PPA. Once installed, the next important activity was to ascertain the important parameters of the plasma like, plasma density, electron temperature, beam structure, stream velocity and energy density of the plasma [3]. Finally, an attempt was made to study plasma matter interaction using the plasma stream on material targets. The above mentioned development work will be presented in the presentation. Further, this device has the scope for exploring its performance for deposition purpose. Also, the theoretical work carried for understanding the plasma flow can be studied under the influence of magnetic field.

Title: Inertial Electrostatic Confinement device and its application

Speaker: Mr. Neelanjan Buzarbaruah

Date, time and Venue: March 1, 2019 (Friday) Time: 3.45 pm CPP-IPR, Seminar Hall

Inertial electrostatic confinement (IEC) is a fusion concept that delivers fusion composites like neutrons, protons, and X-rays from a compact, low cost, and simple device. Seeing such multiple characteristics this confinement approach has been utilized for various non-electrical near-term applications prominently for neutron activation analysis (NAA). The other areas where it has been extensively used include land mine detection, neutron radiography, clandestine material detection at air and seaports, plasma space propulsion, subcritical fusion-fission hybrid reactors, tunable X-ray sources, boron neutron capture therapy (BNCT), medical isotope production, positron emission tomography (PET), ion thrusters etc. Thus, such cost-effective portable sources based on the principle of IEC provides a wider dimension of fusion-based applications. In India, CPP-IPR is the first institute to develop table-top IEC fusion devices (spherical and cylindrical) that demonstrate the 2.45 MeV neutrons by fusing deuterons (D-D). In such a device an HV (~ tens of kV) is applied to the cathode grid for the gas breakdown, the ions produced in the discharge oscillates in the negative potential well and overcomes the Coulomb barrier to fuse and produce neutrons. The signature of the D-D fusion neutrons emitted from the IEC device has been sensed using a number of detectors and it has been reported that presently the device is able to produce 10⁶ n sec^-1.

In order to increase the neutron production rate (NPR) from the cylindrical IEC device a work plan has been proposed that addresses some of the governing issues in the device such as improvement/increase of ion density, improved diagnostics for studying the fusion reaction regimes, application of magnetic fields for studying the confinement of ions and study on ion material interaction. The details of the proposed plan and work will be discussed during the talk.

Title: Experimental Studies of Helicon Plasma in Electronegative Gases

Speaker: Mr. Narayan Sharma

Date, time and Venue: March 1, 2019 (Friday) Time: 3.00 pm CPP-IPR, Seminar Hall

The name Helicon Plasma Source (HeliPS) comes from the Helicon waves which are low frequency electromagnetic waves that propagate in the presence of magnetic fields. The ability of helicon discharge to produce higher plasma density and also less contamination due to the presence of antenna outside the chamber makes helicon plasma source more suitable for higher negative ion density. Considering these advantages of helicon discharge, a Helicon Plasma Source (HeliPS) is designed and developed for production and experiment of negative ions as well as the study of ion-ion plasma using electronegative gases such as hydrogen and oxygen. After design and development of the system, the characterization is done and the transition to helicon mode is established by various experiments. Experiments on negative ions in HeliPS are done by using hydrogen and oxygen gases. From the comparison of I-V curves at the different cases, the condition that favours the formation of ion-ion plasma in HeliPS is studied. Using uniform plasma model of propagation of electromagnetic waves in cylindrically bounded plasma, the collisional power deposition mechanism relevant to helicon discharge in HeliPS considering the realistic antenna structure is computed.

Although negative oxygen and hydrogen ions are produced successfully in HeliPS, there is scope for further improvement of negative ion density which at present is of the order of 10^9-10 cm^-3. Proposed future work plan is to increase the negative ion density by using a gas mixture of argon and hydrogen & also argon and oxygen. Another proposed experiment is the extraction of ions by using grid assembly in the region between the expansion and extraction chambers of HeliPS. The Faraday cup placed beyond the extractor grid assembly will measure the extracted ion currents.

Title: Studies on dust containing hydrogen plasma in a multidipole device

Speaker: Mrs. Deiji Kalita

Date, time and Venue: January 30, 2019 (Wednesday) Time: 11.00 am CPP-IPR, Seminar Hall

Abstract: Dust formation and its charging play a crucial role in plasma processing devices and in fusion devices where magnetic fields are often used. The behavior of plasmas in a magnetic field is one of the interesting and essential topics in plasma physics. The role of magnetic field in various sophisticated plasma fusion devices is to confine the plasma elements. The influence of charged dust particulates on the plasma environment alters the transport of ions and electrons due to Lorentz force. The experiments are performed in the dusty plasma device where plasma is created by the hot cathode filament discharge technique. The plasma is confined by a full lined cusp magnetic field cage. To observe the effect of magnetic field on plasma parameters and dust charge, a permanent magnet having magnetic field strength 1.2 kG is placed inside the plasma chamber. The plasma parameters are measured axially at different distance from the magnet with the help of a cylindrical Langmuir probe. To study the effect on dust charging in presence of magnetic field, tungsten dust particles having (4 – 6) micron are used. The experimental work presented in the thesis includes the studies of the effect of external magnetic field (in presence/absence of) on different plasma parameters and particle charging. The different plasma parameters like electron density, ion density, electron temperature; electron energy probability function (EEPF), plasma oscillations for various dust densities are mainly investigated. The basic understanding to the study of electron energy distribution function (EEDF) is important for examining the different plasma parameters to optimize the plasma processes used for various applications. For the formation of transport barriers, cross-field diffusion coefficients and plasma–substrate interactions at the magnetized plasma, a clear understanding of EEDF is very necessary. The detail study on electron energy probability function (EEPF) is explained for hydrogen plasma in presence of magnetic field and dust grains at different conditions. The cold and high energetic electron densities, temperatures at different dust densities are evaluated from EEPF under the influence of magnetic field. Additionally, plasma oscillations for different dust densities and their effect with change in magnetic field strength are summarized at the end.

Title: Study on Plasma Surface Wave and Interaction of Dust Acoustic Mode with Dust Void

Speaker: Ms. Rinku Mishra

Date, time and Venue: 6th December 2018 (Thursday) Time: 3.00 pm CPP-IPR, Seminar Hall

Abstract: Plasma waves are very much prevalent to understand different types of linear and non-linear plasma instabilities and energy transport. Bounded or finite plasma medium is always known to give the realistic information about the wave properties of plasma. When we talk about bounded plasmas, apart from the electrostatic and electromagnetic plasma waves, plasma surface wave also plays an important role. However, the existence of plasma surface wave necessitates having a sharp boundary. Its wide range of applications in industrial and laboratory environment attracts various researchers to this field. Some of the important applications of plasma surface wave include plasma electronics, plasma antenna, plasma production, plasmonics devices, and particle heating by surface wave propagation in fusion. This thesis aims to investigate the propagation of both surface wave and volume waves with the inclusion of dust charge fluctuation under different situations in dusty plasma. A significant part of it has also discussed the interaction of dust acoustic wave with dust void mode. Theory and computation methodology propounded in this thesis is expected to have important industrial applications.

Title: DevelopMent Of A neutron source based on the inertial electrostatic confinement fusion scheme and its applications

Speaker: Mr. N. Buzarbaruah

Date, time and Venue: 26th November 2018 (Monday) Time: 3.00 pm CPP-IPR, Seminar Hall

Abstract: Compact and portable fusion neutron sources have high demand in the society compared for its use in various near-term applications. Some of the compact fusion sources are D-T accelerators, Z-pinch, Inertial Electrostatic Confinement (IEC) Fusion, Dense Plasma Focus (DPF) etc. Compared to other sources, IEC looks more attractive because of the operational simplicity, multifunctional usage, and cost-effectiveness. It is noteworthy to mention that by burning advanced fuels such as D-D (deuterium - deuterium) and D-T (deuterium - tritium), the device produces neutrons typically of the order of 107 - 108 n/sec and 109 - 1011 n/sec in steady state and pulsed modes, respectively. The produced neutrons can be exploited for different areas such as material science, biology, medicine, security, and industrial engineering. The IEC scheme relies on the trapping of deuterons within a purely electrostatic field that is appeared in between the central grid (cathode) and vacuum vessel (anode). On application of negative potential (-50 to -100 kV) to the cathode grid, the deuterons accelerate to the central region and, subsequently, oscillate across the grid to produce fusion at the core. This thesis work presents the design, fabrication, installation, and operation of the neutron source based on IEC Fusion scheme. The first chapter discusses its origin and principle of operation. The second chapter deals with the designing of the steady state volumetric neutron source that can produce neutrons of the order 106 to 108 D-D n/sec. The designing aspect considered some basic theoretical assumptions and computational tools to ascertain the ion trajectories inside the electrostatic field of the device. After fixing the device parameters and fabricating the same, the device has been installed with a host of supporting units and diagnostics that is presented in the third chapter. The fourth chapter highlights about the production of deuterium plasma inside the IEC device. The characteristic behaviour of the hot and cold cathode discharges using suitable diagnostics such as Langmuir probe and emission spectroscopy are also discussed in the chapter. On application of high negative voltage (~ 80 kV) to the cathode, the ions in the plasma are accelerated towards the cathode and recirculates. At optimum condition the deuterons fuse to produce neutrons that are detected by suitable neutron diagnostics discussed in chapter five. After the successful demonstration of neutrons, this maiden device at CPP-IPR successfully demonstrated the use of the neutrons for explosive detection. A detailed discussion on the design, fabrication and realization of the IEC device would be presented in the talk.

Title: DEVELOPMENT, STUDIES AND APPLICATION OF PULSED PLASMA ACCELERATOR

Speaker: Mr. S Borthakur

Date, time and Venue: 26th November 2018 (Monday) Time: 3.00 pm CPP-IPR, Seminar Hall

Abstract: A coaxial pulsed plasma accelerator is developed at CPP-IPR, powered by a 200 kJ Pulsed Power System with a peak discharge current of 100 kA for a pulse duration of 0.5 ms. The device can produce high density, high velocity plasma stream and can be utilised to study and simulate heat flux and Plasma Matter Interaction (PMI) related issues of tokamak plasma. Basically, the device consists of a coaxial electrode assembly housed inside a vacuum chamber. The basic design concept for relatively longer duration steady plasma stream production from plasma accelerator is taken from Morozov's theory. To sustain the plasma stream, a continuous supply of gas in between the electrodes is required during pulsing which is done by an electromagnetically actuated Gas Injection Valve (GIV). The plasma thus produced has been characterized using different diagnostics. Triple Langmuir probe (TLP) is used to measure the plasma density and electron temperature and found to be ~ 1021/m3 and ~ 24 eV respectively for nitrogen plasma. Double plate probe is used to measure the plasma stream velocity and found to be few tens of km/s. The energy density of the plasma during its impact on material surface is measured using a calorimeter and found to be of few hundreds of kJ/m2. As an initial test, nitrogen plasma beam is allowed to impact on SS304 surface and the effects are analysed. Further the observed properties of plasma beam show its potentiality for important results in the field of Plasma Matter Interaction (PMI). In this thesis, the development of a PPA along with a dedicated PPS, characterisation of the plasma produced and some preliminary PMI studies have been presented.

Title: A study on particle drifts across a magnetic filter and negative ions

Speaker: Parismita Hazarika

Date, time and Venue: 9th November 2018 (Friday); Time: 3.00 pm CPP-IPR, Seminar Hall

Abstract: The present thesis work mainly deals with the study of particle drift across a magnetic filter in different source and magnetic filter field configurations. This study has importance in volume negative ion sources, where optimization of the negative ion formation parameters require a proper study of the transverse magnetic filter field and the filter field region. The first objective of this thesis is to study the effect of electrostatic trapping of magnetized electrons in the filter region which is done by application of a negative potential to the TMF channels with reference to the ground. This study helps us to understand the role played by the trapped electrons in altering the plasma parameters in the source and target region and thereby on the plasma transport processes. The second objective of this thesis is to study the effect of density, temperature and magnetic field dependent charged particle drift on cross field plasma transport. To measure negative ion density, a proper diagnostic system is required. So, the third objective of the thesis deals with setting-up of the laser photo-detachment diagnostic and measurement of negative ion density. This diagnostic system consists of a pulsed laser having a diameter of a few mm of suitable wavelength and energy. Different filament materials are also used to study their influence on different plasma parameters such as density, temperature, plasma potential etc. and negative ion production.

Title: Development of Helicon Plasma Source and a Study of Ion-Ion Plasma

Speaker: Narayan Sharma

Date, time and Venue: 9th November 2018 (Friday); Time: 3.00 pm CPP-IPR, Seminar Hall

Abstract: The name Helicon Plasma Source (HeliPS) used for our experimental set-up is derived from Helicon waves. They are the low frequency electromagnetic waves that propagate in the presence of magnetic fields. Helicon waves are right handed circularly polarized electromagnetic waves which propagate in the presence of magnetic fields. The ability of helicon discharge to produce higher plasma density and less contamination makes helicon plasma source more suitable for higher negative ion density. Considering these advantages of helicon discharge, a Helicon Plasma Source (HeliPS) is designed and developed for production and experiment of negative ions as well as the study of ion-ion plasma using electro-negative gases such as Hydrogen and Oxygen. After design and development of the system, the characterization is done and the transition to helicon mode is established by various experiments. Experiments on negative ions in HeliPS are done by using Hydrogen and Oxygen gases. From the comparison of I-V curves at the different cases, the condition that favours the formation of ion-ion plasma in HeliPS is studied. Using uniform plasma model of propagation of electromagnetic waves in cylindrically bounded plasma, the collisional power deposition mechanism relevant to helicon discharge in HeliPS considering the realistic antenna structure is computed. The talk discusses on the design, development, and characterization of HeliPS as well as the production of negative ions using Hydrogen and Oxygen gases.