Electric fields in plasmas are a unifying theme of many aspects of space plasma physics. This project will focus on two particular questions about space plasma behavior. (1) What are the structure and dynamics of electric fields in return-current auroral regions, and how do they interact with the lower ionosphere? (2) What is the structure of electric fields around charged objects in plasmas such as spacecraft and rocket payloads and their instrumentation, and how do these fields color our interpretation of low energy plasma measurements? The study will involve ground-based observations, the sounding-rocket program at Dartmouth, satellite data analysis and laboratory studies. It will also incorporate extensive student projects, both graduate and undergraduate. The study will weave together the studies of our sounding-rocket Dartmouth College group into a unified scientific effort, providing links and correspondences between the different projects.
The effects of return current auroral regions on magnetosphere/ionosphere coupling are only beginning to be quantitatively explored, and the Dartmouth sounding-rocket group is well placed between the satellite and ground based communities to draw connections between the various data sets. An important part of quantifying the low-altitude, low-energy beginnings of ionospheric coupling is a careful interpretation of spacecraft charging effects on thermal particle measurements; the structure of sheaths around charged instrumentation is a question that interests both space and laboratory plasma physicists. A Dartmouth laboratory facility will be developed to provide a tool for exploring these effects. The student-driven continued development of the laboratory plasma facility at Dartmouth will provide new infrastructure for students in laboratory and space plasmas, and will build connections between the Dartmouth physics program and other space plasma programs.
This CAREER project, directed toward Geospace/ATM interests, studied the structure of electric fields at boundaries,focussing on two specific space plasma questions: (1) What are the structure and dynamics of electric fields in return-current auroral regions, and how do they interact with the lower ionosphere? (2) What is the structure of electric fields around charged objects in plasmas such as spacecraft and rocket payloads and their instrumentation, and how do these fields color our interpretation of low energy plasma measurements? We addressed these questions with two separate inter-related threads of work. The first was the further development and use of our thermal plasma source facility, the ELEPHANT. The second was originally planned as an extension of a FAST spacecraft data study of auroral return current regions, to the Cluster data set. The first goal has been extensively carried out. The second goal evolved as we proceeded and learned, and became a constructive study of auroral thermal plasma using sounding rocket data and our laboratory data. Our ELEPHANT thermal plasma facility has been greatly expanded and made more capable. We have a high-quality and reliable thermal plasma source which has been mapped out and extensively diagnosed. Students have built an additional high-energy beam source which works together with the plasma source to simulate the auroral-ionosphere plasma regime. We have developed extensive diagnostic tools and equipment, including motion tables allowing mapping in a variety of directions. The present graduate student is now adding a computational modelling capability to our lab. Using the ELEPHANT facility, we have been able to develop, calibrate, and model a new low-resource thermal plasma instrument which we have flown on a NASA sounding rocket and propose to fly on other missions. The present graduate student's PhD thesis focusses on the development, modelling, and use of this new instrument. A new student in the lab (not funded under this grant) will continue this work as we move toward our goal of a multipoint observation of the thermal auroral ionosphere, using a localized swarm of CubeSats. Separately, we continue to analyze in situ auroral region data. We studied Cluster data as originally planned in the proposal. These data looked very similar to what was seen on previous work using FAST (surprisingly so, given the high altitude range). However, the bulk of our analysis efforts have moved to more direct studies of the thermal ionospheric response (using sounding rocket data) rather than studies of the auroral return current region drivers (as proposed under the Cluster analysis goal). This has been most constructive and forms the focus of the new direction our lab has taken, enabled by the new capabilities of the expanded ELEPHANT facility. We have completed many additions to the ELEPHANT facility hardware, including probe development; motion table fabrication; a high-energy beam source; mapping and interpretation of the plasma source. We have used the facility to develop a new auroral thermal plasma instrument which forms the core of the new direction for our lab, toward the use of multipoint low-resource ionospheric in situ sensors. This instrument was flown on a recent NASA sounding rocket and we will use it in future missions. Two graduate students have focussed PhD theses on this project, and various undergraduates have completed independent research projects of varying scales. In addition, the facility is used by our other graduate students working on auroral sounding rockets, as we use the facility as a calibration source for the sensors we build. Graduate student Kristen Frederick-Frost defended her PhD thesis based on the first part of the ELEPHANT development. Graduate student Lisa Gayetsky will defend her PhD thesis in Spring of 2014 based on the later developments. Lisa [Gayetsky] Fisher, the present graduate student, is a student participant in the international ISSI working group on spacecraft charging, which has introduced our work to an international audience. Undergraduate Umair Siddiqui (now a graduate student a Wisconsin/Madison in plasma studies) completed his senior honors thesis on the development, calibration and use of the additional beam source. Various undergraduate students have learned experimental techniques under the guidance of the senior and graduate students. We have used the facility for our senior year Introduction to Plasma Physics course. We have invited our colleagues in ionospheric plasma and basic thermal plasma instrumentation to use our facility as a plasma source. The ISSI workshop members have begun to add our facility to their list of thermal plasmas for investigation and modelling. A mentoring project with a nearby local high school was developed and supported by this grant for several years. Overall, we have developed within our group a rigorous understanding of the interaction between ionospheric plasmas and the in situ sensors we use to measure these plasmas. This understanding is critical for our goal of understanding our measurements of the auroral ionospheric plasma response to auroral drivers.
