Plasma activities in Central Department of Physics Tribhuvan
Plasma activities in Central Department of Physics, Tribhuvan University, Kathmandu Raju Khanal rkhanal@tucdp. edu. np
Outline • Kinetic trajectory simulation model for bounded plasmas • Fluid analysis of multi-component plasma sheaths • Basic simulation using PIC codes • Plasma focus device: Numerical Experiments using Lee model code • Arc plasma experiments
Divertor region in ITER Magnetic field lines
Magnetic Presheath Collisional Presheath Fig. General structure of plasma-wall transition region in presence of magnetic field
The magnetized PWT, more physical view (Stangeby, 2000)
The magnetized plasma-wall transition is a crucial element in overall tokamak behaviour. Understanding it is of utmost importance to tokamak modelling and operation. Better understanding contributes to more accurate simulations, especially improved fluid boundary conditions. via
We have developed a Kinetic Trajectory Simulation (KTS) model to study bounded plasmas and used it to study plasma sheaths The Plasma-Wall transition model
Exact ion trajectories are followed, to calculate along them the ion distribution function, assuming an arbitrary injection distribution. The electrons, on the other hand, are assumed to have a cutoff Maxwellian velocity distribution at injection and their density distribution is obtained analytically. For given injection distribution functions, and starting with an initial guess of the potential profile, the final self - consistent results are obtained iteratively.
Developed the model for simple 1 d 1 v cases Developed a scheme for coupling a quasineutral fluid presheath to a non-neutral, collisionless kinetic sheath Studied various problems: sheath properties for various presheath conditions effect of particle-induced electrons
A. Mishra R. Khanal
The KTS model has an important advantage that it can, in principle, be applied to any sort of bounded plasma problems, including collisional ones. In addition, our sheath electrons have a cut-off Maxwellian VDF, leading to the density distribution
Fig. : Dependence of the wall potential on (effective) ion temperature (a) according to Wesson (1997) and (b) as obtained from our calculation
Preheath – Sheath coupling a) = λD / L small but finite; b) → 0, presheath scale x = z / L; c) sheath scale = z /λD (Riemann 1991)
Preheath – Sheath coupling The presheath-sheath interface is defined by the marginal kinetic Bohm criterion or equivalently, the sheath-edge singularity of the presheath solution. We developed a numerical scheme to couple Plasma sheath and Presheath Khanal et al. (2005)
Preheath – Sheath coupling Our presheath-sheath transition equations then have 4 free parameters. Hence, we need to choose any 4 parameters (in a consistent manner, though). If the necessary four parameters are chosen from the presheath / sheath side, the corresponding sheath / presheath parameters are obtained by solving those equations.
Particle-induced electron emission (PIEE)
Normalized floating potential comparison with theoretical values Sharma & Khanal (2008); 5 Schupfer et al (2006)
We extended our model to include magnetic cases.
Kinetic energy of ion at the wall for a given magnetic field (150 m. T) at different angles (Chalise and Khanal 2015)
We expect our model to work as a basis for studying all types of magnetized plasma sheaths using a kinetic approach. In future, we envisage extending our model to fully 3 dimensional cases of magnetized plasma sheath.
Production and Characterization of Arc Plasma for Different Materials of the Electrodes Thakur, Khanal and Narayan (2016, 2018)
Effect of plasma treatment
The Plasma Dynamics in Focus Radial Phase Axial Accelaration Phase Inverse Pinch Phase HV 30 m. F, 15 k. V
Computed Properties of the PF 1000
IEEE Transactions on Plasma Science 45 (8), 2292 (2017)
Expertise and skills • Simulation (using self-developed codes in MATLAB, PIC codes, Lee-Model code) • Fluid analysis of multi-component plasma sheaths • Basic plasma experiments (recently started)
Interests • Simulation of magnetized plasma-wall transition region: Multi-component plasma sheaths Instabilities in the sheath • Seeded-Arc plasma experiments Plasma treatment of agricultural products • Laser-plasma interaction experiments) - in plan (simulation and basic
Resources • 120 M. Sc. (Physics) students enrolled every year Plasma physics is offered as an elective subject • Interest in M. Sc. Dissertation and Ph. D. is very high (4 Ph. D and 11 M. Sc. Students are currently enrolled) • Basic computational facilities • Basic plasma experiments
Possibility of participation in AWAKE Project • Simulation of various phenomena related to WFA Interaction of long and short laser pulses Wave-breaking limit Evolution of energy spectrum Electron pulse and conversion efficiency Laser wake field excitation • Plasma characterisation and interaction with material and surfaces • Training of young graduates and outreach activities
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