Plasma transport across magnetic field lines in low-temperature plasma sources

Abstract

Plasma transport across magnetic field lines plays a key role not only in hot fusion plasmas but also in low-temperature plasma sources operating at low pressure, which often rely on external magnetic fields for their operation. Transport in these sources involves different physics than that in fusion plasmas: the ions are not (completely) magnetized, the plasma is sensitive to wall effects because the magnetic field lines intercept the chamber walls, and the neutral gas density is often much larger than the plasma density. This paper gives an overview of the main principles of magnetized low-temperature plasma transport as they are currently understood, including recent insights on the role of magnetic drift. Three important forms of magnetized low-temperature plasma transport are discussed: magnetized plasma diffusion, transport in E × B fields and magnetic drift. These phenomena are illustrated with recent numerical modeling results on a dipolar microwave source, an End-Hall ion source, and simplified version of the ITER negative ion source. For the latter source it is shown that obstructed magnetic drift can lead to plasma asymmetry and increased cross-field transport.

Spatial distribution of the plasma parameters in the RF negative ion source prototype for fusion

“…Such a pattern of the spatial distribution of n e is also shown in Refs. [9,10], but without the secondary maximum, which could be attributed to differences in the values of the magnetic induction and in the location of the MF. Here (Fig.…”

“…This result is in agreement with Refs. [8][9][10]. It is caused by the fluxes forming the total electron energy flux (6) -given by arrows in Fig.…”

“…Previously applied models (fluid [8,9] and PIC [10] models) showed that transport processes are in the basis of the electron cooling and of the spatial distribution of the electron density. Moreover, due to the E×B and diamagnetic drifts, as well as to the electron energy fluxes related to them, the spatial symmetry of the plasma parameters is broken.…”

“…The specific geometry of the IPP prototype RF source (cylindrical driver and rectangular expansion plasma volume) in combination with the three-dimensional topology of the magnetic filter field, calls for a 3D model description. However, this is a complex and time-consuming task, and the problem is, usually, treated as a 2D one [8][9][10].…”

Study on Anomalous Electron Diffusion in the Hall Effect Thruster

“…These efforts indicate that while the anomalous electron cross field transport is not yet conclusively understood, Bohm-type diffusion is likely a major contributing factor. Research on anomalous electron diffusion continues with deeper physical investigations of the two mechanisms [6][7][8][9][10].…”