Figure 1. The helicon plasma source that was developed at PEPL and that is being used in this project.
Partially ionized low temperature plasmas (LTPs) have a wide range of applications, from being the driving mechanism in Hall thrusters (HETs) to becoming an essential tool in the manufacturing of semiconductors and surgical instruments.
With the continued push for more efficient use of propellant in HETs along with the continued drive for smaller electronic components and higher energy efficiency in the production process, better control of the electron energy distribution functions (EEDFs) is needed.
In order to make a device that uses plasmas more efficient, electrons with energies that contribute to ionization need to be increased.
Those that are involved in transient processes, or that do not have enough energy to ionize need to be decreased.
However, the ability to predictably control the EEDFs of LTPs remains a challenging problem in plasma physics due to the complex electromagnetic interactions that take place in the actual system.
This project serves as a first step in addressing the issues involved since time-resolved EEDF data will be obtained and analyzed for various configurations of a simplified scenario.
The results of this test cell can be used as a guide for developing methods of EEDF control in more complex plasma systems.
A helicon source (that may also be run in ICP mode) will be used to generate a primary plasma plume with argon gas.
A secondary source will be used to inject gas/plasma into the primary plume such that collisional interaction between the two sources leads to changes in the electron energy distribution function (EEDF).
For example, injection of a neutral gas of the same species as the primary plasma may lead to depletion of the high-energy tail of the EEDF due to ionization.
Injection of a source containing electronically excited radicals may lead to enhancement of the EEDF tail due to de-excitation events.
The secondary source will be introduced through a small tube. In later experiments, this source will be injected through a ring with multiple injection points.
Initial studies will focus on steady state behavior, and later investigations will consider transient phenomena including pulsed operation of the two sources.
These processes will be studied experimentally at PEPL using various diagnostics such as a Langmuir probe, Mach probe, and high-speed imaging.
Computational analyses will be carried out by affiliated labs (Boyd & Kushner) using a hybrid particle-fluid model coupled to a plasma kinetics Boltzmann solver.
Figure 2. The experimental setup (in PEPL's Junior Test Facility
) during an initial run where data were being taken for characterization of the primary source.
Selected Relevant Publications
Lemmer, K. M., "Use of a Helicon Source for Development of a Re-Entry Blackout Amelioration System,"
Ph.D. Dissertation, University of Michigan, 2009.