ExB Probe
Wien Velocity Filter

An ExB probe is a plasma diagnostic tool useful for characterizing ion charge state. Singly, doubly, triply, etc. charged ions can be distinguished for argon, xenon, and other common working gas plasmas. The ExB probe can be combined with our electrostatic energy analyzer to provide energy-specific charge state data. Plasma Controls can provide custom cables, feed-thrus, and measurement equipment to meet specific needs.
Dimensions: 28.0 L x 7.6 W x 5.2 T cm

Theory of Operation
Ions enter the probe through a set of collimated apertures to limit the probe's field of view. The ions then enter a region that has both electric (E) and magnetic (B) fields, and experience forces according to the Lorentz equation F = q (E + v x B). For ions that have a particular velocity, the net force is zero, and those ions are able to pass through the crossed field region to a current detector.

Energy is related to velocity through E = 1/2 m v2, where kinetic energy often comes from changes in potential difference E = q ΔV. Particle velocity, then, is a function of charge-to-mass ratio. Sometimes, the signal from a singly-charged particle of one species will overlap with that of a doubly-charged particle of another species.

Typical Data

The ion current reaching the analyzer's detector can be plotted as a function of electric field. Downstream of an ion source, which has a relatively narrow beam voltage, ions of different mass and charge can be distinguished.

The area under each signal can be integrated and compared to determine double-to-single ratios. This can be important, for example, in cases where high energy ions can cause undesirable sputtering.