This award is made in response to a proposal submitted to and reviewed under the NSF/DoE Partnership in Basic Plasma Science and Engineering joint solicitation NSF 08-589. The award provides funds to support travel for a graduate student to scientific conferences and for undergraduate participation in the overall research effort, which is being funded separately by the DoE under contract to UCLA (Science report #09ER55061)
This research will use UCLA's unique LAPD facility and its laser plasma capability to do experiments on the coupling of mass, energy, and momentum from a localized, dense, and rapidly expanding plasmas into a large-scale magnetized background plasma. Using the laser we will generate field-aligned plasma flows that can be varied from supersonic to super Alfvénic. The research program is divided into three main topics: 1) the coupling of plasma jets to compressional Alfvén waves, 2) the creation of wakes and structure with supersonic flows, and 3) the interaction of Alfvén waves with fast-flowing plasmas. The experiments will be complemented by computer simulations using a state-of-the-art PIC code developed at UCLA. The code is capable of resolving skin depth structures as well as tracking Alfvénic phenomena. The nonlinear interaction of Alfvén waves with moving plasmas has been the subject of theoretical studies but has never been probed in laboratory experiments. This study is of relevance to phenomena in the Earth's magnetotail, coronal plume expansion within low beta coronal holes, and could be of relevance to astrophysical jets.
The NSF support of undergraduate participation adds a broader educational impact through the early-year training of students by introducing them to scientific research as a possible career path.
Roughly ninety-nine percent of the visible universe exists in an energetic form of matter called plasma. In this state, electrons and ions are hot enough to separate from each other, and negative and positive charges are allowed to flow. Many plasmas are also permeated with magnetic fields which alter the motions of these charged particles. This is the case for the most familiar example of natural plasma for us: our sun. While usually relatively quiet, the sun sometimes releases enormous amounts of plasma (called coronal mass ejections) that travel through the solar wind and, if we are unlucky enough to be in the way, can interact dramatically with the earth's magnetosphere. In our research, we studied ways in which one energetic plasma flowed along the magnetic field lines of an existing plasma environment. The basic physics governing the expansion was modeled in a laboratory experiment in the Large Plasma Device (LAPD) as part of the Basic Plasma Science Facility (BAPSF) at UCLA. The BAPSF is a national user facility for basic plasma research jointly funded by the National Science Foundation and the U.S. Department of Energy. We built a custom laser periscope to focus a 150MW laser pulse to a solid target embedded in the 20m by 60cm background magnetized LAPD plasma. The laser-produced plasma was carbon while the background plasma was made of argon ions. This difference in atomic species allowed us to use optical techniques to isolate the movement of the ambient plasma caused by the expanding plasma. The key diagnostic is a technique known as laser-induced fluorescence (LIF). This technique uses the Doppler-shifted wavelength of a precise laser frequency to determine the relative number of argon ions as a function of their velocity. Since the LIF laser light is shaped into a thin sheet, two-dimensional images of the expansion process have been acquired using a very fast (10ns) camera. Our measurements have revealed a collisionless transfer of momentum from the expanding, field aligned jet to the ambient plasma. Additionally, in situ probes were used to measure the transfer of energy to the background plasma in the form of a variety of plasma waves which both compressed and sheared the ambient magnetic field. As part of this project, graduate and undergraduate students built or helped to build much of the customized optical systems to deliver and detect the LIF signals, as well as a computer-controlled system to acquire the camera images and mechanically move the laser target. This grant also supported graduate student travel to scientific meetings and to a summer workshop on high-energy density plasma physics.
