Hope College Physics Department
Research Experiences for Undergraduates
Summer 2009
Project Summary


Project Title: Collisional-to-Collisionless Transition of a Microwave Induced Plasma
Student Name: Cameron Recknagel
Student's Home Institution: Hope College
Research Advisor: Dr. Stephen Remillard
Source of Support: This material is based upon work supported by the National Science Foundation under NSF-REU Grant No. PHY-0452206, by a seed grant from the Michigan Space Grant Consortium, by an R&D contract from Mesaplexx, pty ltd., and by the Hope College Division of Natural and Applied Science.

The microwave electric field required to induce dielectric breakdown of a gas exhibits a minimum at the boundary between pressure regions of plasma dynamics. The plasma produced by breakdown is separated into two regimes by this Paschen minimum: collisional plasma, which contains particles having frequent low-energy collisions resulting from the short mean free path of a high pressure gas, and collisionless plasma, which contains particles having infrequent high-energy collisions resulting from the long mean free path of a low pressure gas. The breakdown electric field was measured for several gases, revealing the minimum point and allowing the breakdown kinetics to be examined by relating the average electron kinetic energy to the mean free path. A change in mean free path dependence at the minimum indicates that a transition between plasma conditions indeed occurs at this minimum. Spectroscopic measurements of a helium plasma glow reveal a rise in relative intensity of the lower energy (1s2p1s3s) emission line and a sudden drop in the higher energy (1s2p1s3d) line at pressures above the minimum, indicating that at lower pressures the low frequency of collisions sends electrons into higher orbital states.

Publications and Presentations:
"Collisional-to-Collisionless Transition of a Microwave Induced Plasma", Christopher Ploch and Cameron Recknagel, West Michigan Undergraduate research Conference, Grand Rapids, Oct 31, 2009.
"Collisional-to-Collisionless Transition of a Microwave Induced Plasma", Christopher Ploch and Cameron Recknagel,Regional Summer Undergraduate Research Symposium, University of Notre Dame, July 31, 2009.