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A Projectile Probe for Measuring the Electric Field Inside a Spacecraft Plasma Sheath

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Final rept. 14 Feb 1984-3 Mar 1987

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A self contained electrically floating spherical electric field probe has been developed use in volume regions where spatial field variation occurs on a length scale larger than the sphere diameter. In plasma sheath, the sphere floats to the local plasma potential, minimizing field perturbation, and provides a value of field magnitude found from the Laplacian spherical harmonic field solution. The sphere is also capable of monitoring the amount of charge collected on its own surface--a quantity that can in principle be used to infer properties of the ambient plasma. The 15 cm battery operated aluminum sphere contains six miniature 800 Hz field mill sensors, a synchronous detection data acquisition system and AD converter, and 50 MHz digital fm transmitter. Data is sent at 1200 BAUD to a nearby receiver and computer for processing in real time. Fields as low as 50 Vm can be detected with a sampling time of about 1 second. At present the probe works well in air and vacuum, but has been only partially successful plasma. Keywords Electric field measurements Plasma Sheath Sensors Probe Surface Charge Sphere Projectile Floating.

Subject Categories:

  • Test Facilities, Equipment and Methods
  • Electricity and Magnetism
  • Plasma Physics and Magnetohydrodynamics

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