A magnetically confined dc plasma discharge sustained by a thermionic source was investigated using a combined experimental and theoretical approach. The discharge originates in an arc plasma source and is expanded in a cylindrical chamber, where it is stabilized by an annular anode. The plasma expansion is contained by an axial magnetic field generated by coils positioned at the top and the bottom of the reactor. The plasma reactor design allows control of the energy of ions impinging on the substrate and thus a high electron density of about 1017 m−3 at 1 Pa can be reached. The plasma is studied using a model composed of the Poisson and of the charged species continuity equations, solved in the flow and temperature fields determined by solving the Navier–Stokes and Fourier equations. The model equations are integrated using the finite element method in a two-dimensional axial symmetric domain. Ionization rates are either assumed constant or determined by solving the Boltzmann transport equation in the local electric field with the Monte Carlo ͑MC͒ method. Electron and ion transport parameters are determined by accounting for magnetic confinement through a simplified solution of the ion and electron momentum conservation equations, which yielded parameters in good agreement with those determined with the MC simulations. Calculated electron densities and plasma potentials were satisfactorily compared to those measured using a Langmuir probe. The model demonstrates that the intensity of the magnetic field greatly influences the electron density, so that a decrease by a factor of 2 in its intensity corresponds to a decrease by almost an order of magnitude of the electron and ion concentrations.

An experimental and theoretical investigation of a magnetically confined dc plasma discharge

RONDANINI, MAURIZIO;CAVALLOTTI, CARLO ALESSANDRO;CHRASTINA, DANIEL;ISELLA, GIOVANNI;MOISEEV, TAMARA;VON KÄNEL, HANS
2008-01-01

Abstract

A magnetically confined dc plasma discharge sustained by a thermionic source was investigated using a combined experimental and theoretical approach. The discharge originates in an arc plasma source and is expanded in a cylindrical chamber, where it is stabilized by an annular anode. The plasma expansion is contained by an axial magnetic field generated by coils positioned at the top and the bottom of the reactor. The plasma reactor design allows control of the energy of ions impinging on the substrate and thus a high electron density of about 1017 m−3 at 1 Pa can be reached. The plasma is studied using a model composed of the Poisson and of the charged species continuity equations, solved in the flow and temperature fields determined by solving the Navier–Stokes and Fourier equations. The model equations are integrated using the finite element method in a two-dimensional axial symmetric domain. Ionization rates are either assumed constant or determined by solving the Boltzmann transport equation in the local electric field with the Monte Carlo ͑MC͒ method. Electron and ion transport parameters are determined by accounting for magnetic confinement through a simplified solution of the ion and electron momentum conservation equations, which yielded parameters in good agreement with those determined with the MC simulations. Calculated electron densities and plasma potentials were satisfactorily compared to those measured using a Langmuir probe. The model demonstrates that the intensity of the magnetic field greatly influences the electron density, so that a decrease by a factor of 2 in its intensity corresponds to a decrease by almost an order of magnitude of the electron and ion concentrations.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/544342
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