Date: 17 May, 2023

Dataset Title: Wave and plasma measurements of an electron cyclotron resonance ion source

Dataset Creators: Shadrach Hepner and Benjamin Jorns

Dataset Contact: Shadrach Hepner shadrach.hepner@gmail.com

Funding: National Aeronautics and Space Administration (NASA)


Key Points:
- We analyze the presence and impact of drift-driven, electrostatic instabilities on electron dynamics in a magnetic nozzle
- Momentum transfer between electrons and ions resulting from waves enhances outward electron transport
- Heat transfer may be inhibited by the field-aligned propagation as well


Research Overview:
These data provide direct measurements of plasma density oscillations throughout the plume of an electron cyclotron resonance thruster used for propulsion purposes. Such waves are known to induce cross-field electron momentum transport and to inhibit field-aligned heat transport. The data contained herein is a series of Langmuir probe traces collected with 1 mm diameter, 5 mm lengh tungsten probes.

Methodology:
We first translated the probes through the plume in two dimensions and measured I-V characteristics at a varying spatial resolution. We applied Druyvesteyn theory as per best practices to understand the electron populaion in steady state (Lobbia, R. B., & Beal, B. E. (2017). Recommended practice for use of Langmuir probes in electric propulsion testing. J Propul Power, 33(3), 566–581. https://doi.org/10.2514/1.B35531). 

We then used sets of probes with known separation (7 mm in r-z and 5 mm in the azimuth) and biased them to ion saturation (-45 V). We took time-resolved measurements of the ion number density and converted them to the frequency domain to understand the presence of oscillations. Taking these measurements simultaneously with multple probes at known separation, we then take the phase difference between the probes to back out the wave number. This process is described in more detail in  Beall, J. M. … Powers, E. J. (1982). Estimation of wavenumber and frequency spectra using fixed probe pairs. J. Appl. Phys., 53(6). https://doi.org/10.1063/1.331279.


Files contained here:
The files in this dataset are organized into 4 base folders.
LP : Langmuir probe raw data
- shifted_data : folder containing each individual point. The naming convention is Z_XX_R_YY.txt, where XX and YY are the axial and radial positions, respectively, in mm. Each of these files contains a two column dataset, the first of which is voltage applied to the probe and the second of which is current drawn, in A
- HEADER.txt : text file containing various parameters for the test operation.
WP_RZ : folder containing the time-resolved probe results from the probes separated in the r-z plane.
- shifted_data : this folder contains the individual datapoints for the probe measurements. The first line contains the sample rate (in seconds). The second line and onwards contains the full data collection. The three columns correspond to the three probes.
WP_TH : This folder contains data organized in the same way as WP_RZ, but therere are only two columns corresponding to the azimuthal probe pairs. 

Related publication(s):
Hepner, S. T. … Jorns, B. A. (2018). Observation of Low Frequency Plasma Oscillations in the Plume of a Partially Magnetized Magnetic Nozzle. 2018 Joint Propulsion Conference. https://doi.org/10.2514/6.2018-4730

Use and Access: 
This data set is made available under a Creative Commons Public Domain license (CC0 1.0).


To Cite Data: 
Hepner, Shadrach and Jorns, Benjamin (2023). Wave and plasma measurements of an electron cyclotron resonance ion source [Data set]. University of Michigan - Deep Blue.