Langmuir Spatial Probe Publications

Electron flow properties in the far-field plume of a Hall thruster

K Dannenmayer and Stéphane Mazouffre

Published 29 April 2013

Abstract

The plasma properties were investigated in the far-field plume of a 1.5 kW class Hall thruster using a single, cylindrical Langmuir probe. The plasma potential, the electron temperature and the electron density were measured at 191 positions, providing a detailed map of the plume pattern. This map shows that the plasma plume of a Hall thruster is an expanding jet that is symmetric about the thruster axis. The large data set was also used for a detailed analysis of the electron flow properties. This analysis reveals that the plasma plume of a Hall thruster is an isentropic expansion. In addition, the momentum conservation equation shows there is a polytropic relationship between the plasma potential and the electron density with a γ smaller than that for an atomic gas due to ionization.

Online at Plasma Sources Sci. Technol. 22 035004


Plasma parameters and electron energy distribution functions in a magnetically focused plasma

C. M. Samuell, B. D. Blackwell, J. Howard and C. S. Corr

Published 12 March 2013

Abstract

Spatially resolved measurements of ion density, electron temperature, floating potential, and the electron energy distribution function (EEDF) are presented for a magnetically focused plasma. The measurements identify a central plasma column displaying Maxwellian EEDFs at an electron temperature of about 5 eV indicating the presence of a significant fraction of electrons in the inelastic energy range (energies above 15 eV). It is observed that the EEDF remains Maxwellian along the axis of the discharge with an increase in density, at constant electron temperature, observed in the region of highest magnetic field strength. Both electron density and temperature decrease at the plasma radial edge. Electron temperature isotherms measured in the downstream region are found to coincide with the magnetic field lines.

Online at Phys. Plasmas 20, 034502 (2013)


Plasma drift in a low-pressure magnetized radio frequency discharge

D Gerst, S Cuynet, M Cirisan and S Mazouffre

Published 25 January 2013

Abstract

A bright strip-like structure is observed in a low-pressure capacitively coupled radio frequency discharge with a magnetic field perpendicular to the plasma flow. The structure forms for a broad set of operating conditions in different gases. Measurements indicate that the strip acts as a path for the electrons to cross the magnetic field, which makes the discharge inhomogeneous and non-symmetrical. The strip intensity is strongly reduced when switching from a capacitive to an inductive discharge. A theoretical analysis shows that the strip results from a drift of the magnetized electrons perpendicular to the magnetic and electric fields, which is intercepted by the dielectric walls of the discharge tube. In capacitive mode, the drift is mostly governed by the electric field whereas the pressure dominates in inductive mode.

Online at D Gerst et al 2013 Plasma Sources Sci. Technol. 22 015024 doi:10.1088/0963-0252/22/1/015024


Time-Resolved Measurements of Plasma Properties Using Electrostatic Probes in the Cross-Field Discharge of a Hall Effect Thruster

K. Dannenmayer, P. Kudrna, M. Tichý, S. Mazouffre

Published 9 Jan 2013

Abstract

Time-resolved measurements of the plasma parameters are performed in the plume of a cross-field discharge. The plasma potential is measured with a cylindrical Langmuir probe and an emissive probe. The electron temperature and density are measured with a cylindrical Langmuir probe. The cross-field discharge is maintained in a harmonic oscillation regime to guarantee reproducible conditions for all measurements

Online at DOI: 10.1002/ctpp.201310011


Plasma characterization of the superconducting proton linear accelerator plasma generator using a 2MHz compensated Langmuir probe

C. Schmitzer, M. Kronberger, J. Lettry, J. Sanchez-Arias and H. Störi

Published 16 February 2012

Abstract

The CERN study for a superconducting proton Linac (SPL) investigates the design of a pulsed 5 GeV Linac operating at 50 Hz. As a first step towards a future SPL H− volume ion source, a plasma generator capable of operating at Linac4 or nominal SPL settings has been developed and operated at a dedicated test stand. The hydrogen plasma is heated by an inductively coupled RF discharge e− and ions are confined by a magnetic multipole cusp field similar to the currently commissioned Linac4 H−ion source. Time-resolved measurements of the plasma potential, temperature, and electron energy distribution function obtained by means of a RF compensated Langmuir probe along the axis of the plasma generator are presented. The influence of the main tuning parameters, such as RF power and frequency and the timing scheme is discussed with the aim to correlate them to optimum H− ion beam parameters measured on an ion source test stand. The effects of hydrogen injection settings which allow operation at 50 Hz repetition rate are discussed.

Online at Rev. Sci. Instrum. 83, 02A715 (2012)