ADITYA-U resumed operations from 24 November, 2020 and continued till 18 th December, 2020. Almost 227 discharges were obtained with varied toroidal magnetic field (B) from 0.9 Tesla to 1.07 Tesla. The extensive wall conditioning with Hydrogen GDC as well as combination of Argon + Hydrogen GDC showed substantial reduction in various impurities mass species like H2, 02 N2 etc.
The longest ever ADITYA-U discharge of ~ 386 ms with ~ 134 kA of peak plasma current (Shot #34009) has been achieved by using 70% of available Volt-Sec at ~ 19 V of peak loop voltage. The discharge was obtained at toroidal field of ~ 1.07 Tesla and in absence of any strong pre-ionization.
Aditya-Upgrade plasma discharge with divertor coil operation showing strike points
actual experimental photograph, showing ion recirculation across the cathode openings.
Cylindrical IEC fusion device
The spherical ICE fusion device
Kinetic simulations have been performed using particle-in-cell method to analyse the behaviour of ions inside a cylindrical inertial electrostatic confinement fusion (IECF) device which is being developed as a table top neutron source. The ion recirculation across the gridded cathode, ion density and potential well profiles are investigated in a discharge plasma using XOOPIC (X11- based object-oriented particle-in-cell) code. The simulated results are also compared with the experiment to benchmark the results. The recirculation of the ions can be visualised from the phase space during runtime.The simulation contour plot of ions during -1 kV cathode voltage clearly indicates the signature of recirculating ions across the cathode grid openings. This compares well with the photograph of the actual experiment. Ion spokes or channels can be observed to
be coming out from the central core region. Ion density profile was measured along with experimental profile using Langmuir probe, and a maximum ion density is found to be ~10 16 m-3 during -5 kV operation. The potential profile indicates the formation of multiple or double well structures during -5 kV cathode voltage operation
The BEAM experimental device
plasmas confined by toroidal magnetic field is a viable mechanism to achieve controlled thermonuclear
fusion in laboratories from which abundant electricity can be produced. As the ITER fusion device is reaching towards achieving its first plasma, the nation is concurrently building technologies that will be required to indigenize a fusion reactor.
From both physics and engineering perspective, the laboratory experiments are highly needed to perfect the underlying technologies, create the absolute knowhow and generate relevant experimental data for benchmarking the modelling results associated with these complex machines.
In the Magnetized Plasma Development Laboratory, a Basic Experimental setup with Axial Magnetic field (BEAM) has been developed in which rigorous experiments are carried out on positive and negative ion beams produced by diverse discharge configurations; with primary focus on their interactions with electrodes in magnetized plasma. The BEAM setup is equipped with a quadrupole mass and energy analyzer system for diagnostics. Using this setup, energy distribution of plasma ions, multi charge ionic species, energetic neutrals that may be generated using different types of plasma sources such as hall thruster, high voltage sputtering magnetron discharge, ion extraction using plasma grids etc. can be characterized. The device is also equipped with a suite of indigenously developed electric probe diagnostic system that provide accurate measurement of plasma parameters at various axial and radial location inside the BEAM setup.
Electrode assembly of Capacitive-Coupled RF discharge
Inside view of BEAM setup showing the cylindrical discharge electrodes
Ring-shape hot plasma produced by cylindrical RF discharge with axial magnetic field.
Recent experiments in the BEAM demonstrates a remarkable mechanism of controlling the radial electron temperature and plasma uniformity inside cylindrical plasma column by a combination of external
plate biasing and diverging magnetic field.
This effect is highly promising for applications in industries, where homogeneous plasma is required for the treatment of large area substrates. The uniform plasma is also required in plasma based ion sources to minimize the beam divergence and spatial energy distribution of ions extracted from the source. Controlling the electron temperature is also important for the production of negative ions. This has been achieved in the BEAM by a suitable combination of electrode geometry and axial magnetic field. Due to high neutralization efficiency, negative ions are used for the neutral beam generation for applications ranging from plasma thruster to neutral beam heating in fusion device, and also for weapons. Presently studies on charge particle transport across magnetic field lines, wake creation in a flowing/ non - flowing magnetized plasma, investigation of radio-frequency magnetized sheaths and plasma surface interactions are some of the work being carried out using this device. In the future, it is planned to install a new set of electro -magnets in the BEAM to achieve peak magnetic field of 300 Gauss. The facility will lay
emphasis on development indigenous ion beam sources.