My internship project has been explained pretty extensively in several previous blog posts, but here's a brief summary. I encourage you, as the reader, to check out the links in this post or previous posts if you're curious to know more details.
For my internship project, I worked on the Lithium Granule Injector (LGI), which is exactly what it sounds like. The DIII-D reactor creates fusion inside of a controlled plasma, and the LGI shoots small (300-900 microns) granules of lithium - and potentially other materials - into the plasma. Its purpose is to induce small Edge Localized Modes (ELMs), which are disturbances in the plasma whereby it builds up pressure and ejects some mass from its magnetic confinement. Research is ongoing to learn about the nature of ELMs, but the concept is similar to solar flares. During normal reactor operations, ELMs occur naturally as the magnetic fields generated by the plasma interact with the magnetic confinement fields and produce disturbances. These ELMs are typically explosive and unpredictable, and although they don't damage DIII-D, they will damage ITER, a reactor under construction in France for which DIII-D is conducting experiments. The LGI induces small ELMs at extremely regular intervals with a frequency of around 200 per second in order to prevent larger disturbances from being able to form. The ELMs generated by the LGI will be harmless to ITER.
The entire concept hinges on the lithium granules being injected with extreme regularity, however, which the current design cannot accomplish. In my project, I ran experiments to test concepts and develop new ones, all with the goal of dropping granules into an impeller (which hits the granules into the plasma like a ping-pong paddle) with extreme regularity. All of the concepts I experimented with hinged on the idea of sorting the granules by size and then getting a group of granules of a single size to line up single-file to be dropped into the impeller. (Because lithium is a dangerous material, we used graphite granules for our tests.) The first two concepts involved stacking the granules in a tube and controlling the rate at which they fell. Unfortunately, this concept had too many issues with clogging inside the tube, so we had to change gears. Next, we tried using a linear vibratory feeder to move the granules along a track while employing various methods to narrow the granule flow down into a single stream. This was where, about a week and a half into the internship, we had our first real success. I created a series of paper dams with increasingly small holes in the bottom, and managed to get a single-file stream of 700-micron granules dropping off of the end of the track. Encouraged by this success, we stuck with the feeder concept, and my role for the rest of the internship was to continuously run granules through the feeder and observe their motions, in order to develop further revisions that would optimize the feeder's performance for three granule sizes: 700, 500, and 300 microns.
At the end of my internship, I prepared a poster to show off my research into the dropper design. Click here to view my poster. The poster includes a number of images, including CAD models and photos. Today, on the last day of my internship, I presented my work to a group of students, teachers, my mentor and colleagues, and anyone else in the DIII-D facility who was interested in seeing my presentation. (My mentor, Alex, has all of his interns present at the ends of their internships, so most of the DIII-D employees were accustomed to the idea, and there was a pretty large turnout.) My presentation slides can be viewed here.
This will be my final blog post. I couldn't have enjoyed internship more. DIII-D was a great working environment, and I'll miss being there.
For my internship project, I worked on the Lithium Granule Injector (LGI), which is exactly what it sounds like. The DIII-D reactor creates fusion inside of a controlled plasma, and the LGI shoots small (300-900 microns) granules of lithium - and potentially other materials - into the plasma. Its purpose is to induce small Edge Localized Modes (ELMs), which are disturbances in the plasma whereby it builds up pressure and ejects some mass from its magnetic confinement. Research is ongoing to learn about the nature of ELMs, but the concept is similar to solar flares. During normal reactor operations, ELMs occur naturally as the magnetic fields generated by the plasma interact with the magnetic confinement fields and produce disturbances. These ELMs are typically explosive and unpredictable, and although they don't damage DIII-D, they will damage ITER, a reactor under construction in France for which DIII-D is conducting experiments. The LGI induces small ELMs at extremely regular intervals with a frequency of around 200 per second in order to prevent larger disturbances from being able to form. The ELMs generated by the LGI will be harmless to ITER.
The entire concept hinges on the lithium granules being injected with extreme regularity, however, which the current design cannot accomplish. In my project, I ran experiments to test concepts and develop new ones, all with the goal of dropping granules into an impeller (which hits the granules into the plasma like a ping-pong paddle) with extreme regularity. All of the concepts I experimented with hinged on the idea of sorting the granules by size and then getting a group of granules of a single size to line up single-file to be dropped into the impeller. (Because lithium is a dangerous material, we used graphite granules for our tests.) The first two concepts involved stacking the granules in a tube and controlling the rate at which they fell. Unfortunately, this concept had too many issues with clogging inside the tube, so we had to change gears. Next, we tried using a linear vibratory feeder to move the granules along a track while employing various methods to narrow the granule flow down into a single stream. This was where, about a week and a half into the internship, we had our first real success. I created a series of paper dams with increasingly small holes in the bottom, and managed to get a single-file stream of 700-micron granules dropping off of the end of the track. Encouraged by this success, we stuck with the feeder concept, and my role for the rest of the internship was to continuously run granules through the feeder and observe their motions, in order to develop further revisions that would optimize the feeder's performance for three granule sizes: 700, 500, and 300 microns.
At the end of my internship, I prepared a poster to show off my research into the dropper design. Click here to view my poster. The poster includes a number of images, including CAD models and photos. Today, on the last day of my internship, I presented my work to a group of students, teachers, my mentor and colleagues, and anyone else in the DIII-D facility who was interested in seeing my presentation. (My mentor, Alex, has all of his interns present at the ends of their internships, so most of the DIII-D employees were accustomed to the idea, and there was a pretty large turnout.) My presentation slides can be viewed here.
This will be my final blog post. I couldn't have enjoyed internship more. DIII-D was a great working environment, and I'll miss being there.