Effect of finite analyzer size on the distribution functions measured in field-free plasmas.

Ideal, gridded, planar electrostatic retarding field analyzers correctly measure isotropic velocity distributions in field-free plasmas if the grid and collector are infinite. However, the finite apertures in practical analyzers block some particles that have sufficient momentum to be collected. We calculated the resulting error in the measured distribution function for a range of analyzer sizes when a Maxwellian distribution enters the analyzer.