Faculty Advisor

Michael Demetriou

Faculty Advisor

John Blandino

Faculty Advisor

Nikolaos A. Gatsonis

Faculty Advisor

David Cooke

Faculty Advisor

William Durgin


The Turning Point Method (TPM) for the evaluation of ion scattering in a sheath of a biased probe immersed in an unmagnetized plasma is reviewed. The TPM implemented originally in a computer program for spherical probes is expanded to include cylindrical probes as well as the evaluation of the turning angle of the charged particle (repelled or attracted) around the probe. TPM results have the potential to provide a standard against which to compare more complicated current collection simulations. TPM results are validated by comparing with Laframboise's earlier work for current collection in the Orbital Motion Limited regime. Calculations of the turning angle of a charged particle with specific energy and angular momentum revealed that higher plasma shielding limits the range of impact parameters that experience significant scattering, and that attracted particles entering tangent to the sheath experience increased scattering. The TPM results also show that there are significant changes in orbital trajectories between different space charges within the Orbital Motion Limited limit.


Worcester Polytechnic Institute

Degree Name



Mechanical Engineering

Project Type


Date Accepted





orbital trajectory, ion collection, turning point method, spherical probes, turning angle, ion scattering, cylindrical probes, Ions, Scattering, Probes (Electronic instruments), Orbital mechanics, Space plasmas