UAA Planeterrella Device and Diagnostic DevelopmentHenrique Oliveira Miller,1 Isaac Hamlin,1 Monique Mojica,1 Amanda Bowman,1 & Nathaniel Hicks2

1College of Engineering and 2Dept. of Physics & Astronomy, University of Alaska Anchorage

Acknowledgments• UAA Innovate Program and

Office of Undergraduate Research

• Alaska Space Grant Program• The Institut de Planetologie et

d’Astrophysique de Grenoble

AbstractA "planeterrella"-type plasma discharge chamber has been constructed at the UAA Plasma Lab for student research projects and educational use. The device comprises an 18-inch diameter by 18-inch high Pyrex cylinder with aluminum end plates, with dry mechanical pumping to 50 mTorr. Argon and air can be admitted, with typical operating pressure 0.1 - 2.0 Torr. Two aluminum spherical electrodes with embedded permanent magnets act as anode and cathode for the DC glow discharge regime (e.g. 500 V, 10 mA), which can simulate aspects of planetary aurorae. Diagnostics are being added to the device, such as a Langmuir probe, UV-Visible spectrometer, and high speed camera, and integration of these with the discharge control software is presented along with time resolved measurements of the plasma environment.

Diagnostic Improvements:• Langmuir probe parts are being ordered and will be assembled.• National Instruments I/O modules will allow LabVIEW access to the system for control and

recording.• A High-speed camera (Kron Chronos 1.4) and Kodial glass viewport have been acquired. • A UV/Visible (200-900 nm) Ocean Optics HDX spectrometer has been purchased and will be

mounted to the chamber

Mechanical Improvements:• A custom ISO160-K feedthrough flange for the diagnostic equipment is under construction• New Teflon electrode arms with extra-vacuum access and two degrees of freedom (axial and

vertical) is being built for each electrode.

Planeterrella:Planeterrella was designed by Dr. Jean Lilensten at the Institut de Planetologie et d’Astrophysiquede Grenoble (1). The Plasma Physics Lab at UAA was allowed to use the design, and make functional modifications to better suit diagnostic equipment. As mentioned, it is a glow discharge plasma source, using two spherical, embedded-magnet electrodes and one needle electrode to produce plasma. There is a voltage controlled piezo-electric gas inlet that can either allow air or argon in order to control pressure and change the dynamics and emission spectra. A convection gauge is used to monitor pressure in the chamber, and can output to a control system. The device is mounted in a mobile rack for transport to classrooms and demonstrations.

Diagnostic Equipment and Upgrades:Langmuir Probe:A probe has been designed and modeled extensively. The alumina insulator has four bores so it can later be upgraded from a single probe if needed. KF16 feedthrough flanges will be used for connections. In addition, a compression coupling allows the probe to be shifted vertically. With this probe, data on plasma density, temperature, and potential will be gathered through LabVIEW analysis (2).

LabVIEW and Control Systems:Through the use of National Instruments I/O modules, control systems will be implemented to allow for automated pressure regulation, electrode voltage settings, and possibly electrode arm positioning in the near future. With new diagnostics, along with existing systems (a voltage controlled gas feed and pressure sensor) these types of controls systems will be easily constructed. This will be invaluable for the understanding and study of the many modes that Planeterrella exhibits. Aside from this, automation would allow for easy demonstrations, increasing interest in plasma physics.

High Speed Camera:A new Kron Chronos 1.4 high-speed camera was purchased recently, able to capture 1.3 megapixel 1280x1024 images at 1057 fps or up to 38,500 fps at reduced quality. and when placed in tandem with the Kodial glass viewport it will allow for a more rigorous study of the time dependent properties of plasma discharges in this device.

As mentioned, Planeterrella has many different characteristics that vary greatly with even slight setting and environment changes. Some of the most interesting dynamics are striations (both static and slowly time-variant), ring currents, arcing/strobing discharge, and slow time-dependent discharges (rotating, fluctuating brightness, etc.). However, these properties were only observed qualitatively, so diagnostics like a high speed camera would likely reveal many more dynamics and deepen our understanding of each phenomenon.

SpectrometerNot only does Planeterrella exhibit interesting time dependence, it also has various discharge spectra which relate to its different modes of operation. With the newly purchased Ocean Optics HDX UV/Visible spectrometer and new fiber optic cable and collimating lens, these spectra can be studied analytically.

On the right we see two different spectra, one for a “strobing discharge” and the other for a static spherical discharge on the smaller electrode. It is abundantly clear that the excitation lines are very similar, yet this is impossible to notice with the naked eye. Below is an example of a typical magenta discharge from the larger electrode.

SolidWorks (CAD) renders of the Langmuir probe have been made. A parts list has been compiled, and is partially purchased. The probe is 3.25’ in length, and will include KF16 ports for both vacuum and electrical feedthroughs, and multi-bore alumina insulator.

Large Electrode Spherical Discharge Spectrum

Small Electrode Spherical Discharge Spectrum

Strobing Discharge Spectrum

Custom Feedthrough:A blank ISO160-K Aluminum flange was acquired in order to machine custom feedthrough ports for the Planeterrella. This will allow for more diagnostic and equipment access on the top plate of our device. The three feedthroughs to be added are a KF-40 for the camera viewport, a KF-25 for the pressure sensor, and a KF-16 for the Langmuir probe. This will make space on the top plate for electrode arm ports.

Conclusion:The addition of the listed equipment and diagnostics will drastically improve Planeterella’s usefulness for both research and educational purposes (and already has). As more diagnostic devices are used, the complex and visually intriguing phenomena will be explored and understood in greater detail.

Contact: UAA Planeterrella: hmiller12@alaska.edu; UAA Plasma Lab: nkhicks@alaska.edu, http://plasma.uaa.alaska.edu

A photo of current Planeterrella setup, with the power sources controlling both discharge (bottom) and gas input (top).

An example of discharge and “coronal hole” on the large

electrode, clearly demonstrating the location of the embedded magnet (500V,

100mTorr in Argon gas).

SolidWorks render of the Langmuir probe, with vacuum ports, a tungsten filament, and an alumina insulator

Block diagram showing the feedback control loop from diagnostics , through LabVIEW and to voltage and pressure controllers.

Planeterrella operating with negatively biased small sphere, illustrating a stellar ring current about the small sphere

Glow discharge exhibiting striations. Parameters: -190V, 55mA on large

electrode, 350mTorr, positively biased needle, grounded small electrode.

References1. Lilensten, J., Provan, G., Grimald, S., Brekke, A., Flückiger, E., Vanlommel, P., . . . Garnier, P.

(2013). The Planeterrella experiment: From individual initiative to networking. Journal of Space Weather and Space Climate, 3.

2. Gandhi, S., Binwal, S., Kabariya, H., & Karkari, S. (2016). LabVIEW software for analyzing Langmuir probe characteristics in magnetized plasma. Journal of Instrumentation, 11(03).

SolidWorks drawing of the custom ISO160-K flange with added KF ports.

Old Fiber SpectrumNew Fiber SpectrumPeaks (nm)

The Kron Chronos 1.4 high speed camera, with 38,500 frame per second recording capabilities.

Apparatus:Planeterrella is an excellent demonstration device, but would benefit from greater ability to make quantitative measurements. In addition, the device settings are not easily adjusted, as it must be opened to move electrodes. This is unfortunate, as the device displays numerous phenomena that can currently only be documented qualitatively. Therefore, equipment is being added to remedy these issues and allow Planeterrella to function as a learning and research tool for plasma science and diagnostics.