Measurements of Thermal Ion Drift Velocity and Temperature Using Planar Sensors

  1. Robert F. Pfaff,
  2. Joseph.E Borovsky and
  3. David T. Young
  1. R. A. Heelis and
  2. W. B. Hanson

Published Online: 18 MAR 2013

DOI: 10.1029/GM102p0061

Measurement Techniques in Space Plasmas: Particles

Measurement Techniques in Space Plasmas: Particles

How to Cite

Heelis, R. A. and Hanson, W. B. (1998) Measurements of Thermal Ion Drift Velocity and Temperature Using Planar Sensors, in Measurement Techniques in Space Plasmas: Particles (eds R. F. Pfaff, Joseph.E. Borovsky and D. T. Young), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM102p0061

Author Information

  1. William B. Hanson Center for Space Sciences, University of Texas at Dallas, Richardson, 75080

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1998

ISBN Information

Print ISBN: 9780875900858

Online ISBN: 9781118664384



  • Space plasmas—Measurement;
  • Plasma diagnostics


Satellite measurements of the ion temperature, velocity, and concentration may be obtained by measuring incident variations in the ion flux using a retarding potential analyzer (RPA). A retarding voltage inside the sensor can be used to control the energy of ions having access to the detector. By examining the variations in this flux as a function of energy, the temperature can be determine. The thermal velocity of low energy ions is frequently much less than satellite orbital velocities, in which case the direction of arrival of the ions is approximately aligned along the satellite velocity vector and does not change greatly. In this case the precise arrival angle of the ions can be obtained by a device called an ion drift meter (IDM), which measures the current asymmetry on a detector surface caused by deviations of the ion beam from normal incidence. There is a simple trigonometrical relationship between the ion arrival angles, the normally incident ion velocity, and the transverse velocity. Here we describe the operating principles embedded in the required measurements and the limitations that are inherent in the various measurement techniques. In the presence of a magnetic field where the ion gyrofrequency exceeds the ion-neutral collision frequency, the ion velocity perpendicular to the magnetic field can be derived from a measurement of the electric field vector and knowledge of the magnetic field vector. These conditions apply in the Earth's ionosphere above about 250 km altitude and the relative merits of electric field and ion drift measurements are discussed for this case.