The overall goal of this experiment is to show the mechanisms that cause regolith dust particles in space or laboratory conditions to gain enough charge to become lofted or mobilized. This method can help answer a key question about the role of electricity dust transport in shaping the surface of airless bodies in the solar system. This method paves the way for future studies including both experiment and computer modeling to ultimately explain the existing space observations and provide guidance for future mission investigations.
This method demonstrate how to move dust particles in a controlled manner which can help other researchers to develop their own experiments. Demonstrating the procedure will be Noah Hood, an undergrad student from our laboratory. The experiments require a vacuum chamber.
This one is 50 centimeters in diameter and 28 centimeters tall and connected to an argon tank and a pump system. Inside is a metal plate that is electrically isolated. At this point, prepare to load dust particles.
Use an insulating plate 20 centimeters in diameter and two centimeters thick, and place on top of it an insulting rubber sheet with a central hole. Next, load insulating irregularly-shaped dust particles in the hole. Move the insulating plate to the vacuum chamber.
There, place it on the metal plate inside. Next, set up a video camera to record dust movement. For illumination, use an LED light equivalent to at least a 500-watt incandescent source.
This image is of the dust particles before any beams have interacted with them. This electron beam experiment requires two filaments. As with this example, install a thoriated tungsten filament on each of the two electrode feed-throughs.
Install one of the feed-throughs on the top of the vacuum chamber. Connect this filament to filament power supplies. Then, install the second feed-through with a filament on the bottom of the chamber.
Continue by pumping the chamber to the desired base pressure. Next, use the argon gas feed to fill the chamber to about one half millitorr. When ready, turn on the filament power supplies and set the bias voltage to negative 120 volts.
Turn on the camera to record. At the power supply, increase the heating voltage. Stop when the emission current is a few milliamps.
Record the response of the dust particles. Expose two energetic and thermal electrons that begin to move. Turn off the filament power supplies and connect them to the bottom filament.
With the power supplies on, set the bias voltage to negative 40 volts. Increase the heating voltage to reach an emission current above 200 milliamps. Record the motion of the dust particles.
Exposed to only thermal electrons, they do not move. Begin with the vacuum chamber with the bottom sealed. Have the dust particles loaded onto the insulating plate supported by the metal plate.
Use only one feed-through. Install one thoriated tungsten filament onto it. Install the feed-through on the top of the chamber and connect the filament power supplies.
In the first sequence, set the bias voltage to negative 120 volts. Then, increase the heating voltage. Stop when the emission current is a few milliamps.
Record the response of the dust particles in the chamber. In this case, they move. The second sequence uses the same setup as the first.
In the second sequence, set the bias voltage to zero. Increase the heating voltage to reach a heating current of about two amps. Then, gradually change the bias voltage from zero to negative 120 volts.
Record the response of the dust particles in the chamber. In this case, they do not move. For this experiment, remove the electrode feed-through from the chamber.
Install a 172-nanometer UV lamp on the feed-through. Reinstall the feed-through and connect the lamp's power supply. With the chamber at base pressure, turn on the lamp to irradiate the dust particles.
Record the response of the particles under these conditions. In this experiment, 10 to 50-micrometer-diameter dust particles are exposed to plasma, and 120-electron-volt beam electrons. No particles are lofted when the electron beam is absent.
This is consistent with secondary electrons contributing to dust charging. The lofted particles are induced by an electron beam created by first setting a bias voltage and then increasing the heating voltage, a process that creates secondary electrons. In contrast, no dust movement is seen when the heating voltage is first set followed by increasing the bias voltage, a process with no secondary electrons.
Dust particles exposed to 172-nanometer UV lamp show dust hopping as indicated in this photo. When the dust is exposed to UV radiation for an extended time, the dust surface changes. This is captured in a series of photos in which the surface becomes smoother and eventually flattens out.
After watching this video, you should have a good understanding of how to move dust particles in a controlled manner. The key point is to create full electrons and/or secondary electrons from dusty surfaces. Based on this methods, new experiments, as well as computer modeling, can be developed to better categorize the nature of dust charging and transport.
This technique paves the way for researchers in space and planetary science, as well dusty plasmas, to explore the role of electrostatic dust transport in surface processing on airless planetary bodies and a near-surface dust environment around these bodies as well. Don't forget to wear gloves when handling thoriated tungsten wires because of thorium's low radioactivity. Also, cover the windows of the vacuum chamber to avoid any possible UV exposure.
