A unique device for laboratory studies of natural plasmas
The upgraded LAPD, a unique device for research on fundamental properties of naturally occurring plasmas will become operational in the year 2000 at UCLA. When completed, this machine will be the premier instrument in the world for the detailed study ,under controlled conditions, of fundamental plasma processes that play a major role in the behavior of naturally occurring plasmas as are encountered in the neighborhood of the earth, the interplanetary medium, the sun and in astrophysical environments. The device will be instrumented with computerized data acquisition probes and advanced visualization computers that will permit the study of the temporal evolution of complicated three dimensional processes that presently constitute the frontier of space plasma research. This large research device will be extremely flexible in its operation, able to accommodate several simultaneous experiments (through 434 access ports), and generate research-grade plasmas at a one Hertz repetition rate around the clock. These properties make the upgraded LAPD ideally suited for broadly-based collaborative experiments on a scale never before attempted by the worldwide basic plasma science and space communities. If properly supported this device has the potential to move the understanding of the behavior of naturally occurring plasmas to a very high level limited only by the imagination of its users.
The upgraded LAPD is a significant upgrade of the existing Large Plasma Device (LAPD) at UCLA made possible by a Major Research Instrument (MRI) award given by the NSF to the principal investigators, Drs. Walter Gekelman, James Maggs and George Morales. The UCLA administration, under the leadership of Dean Roberto Peccei, has made extraordinary financial contributions toward the success of this effort. An entire floor in the new Science and Technology Research Building (completed in May of 1998), a modern research facility with high electrical power handling capabilities (30 MW) has been allocated to this new machine. The visionary and steady support provided by Office of Naval Research over a decade has permitted the development of the LAPD program to a level of prominence that makes the step to the upgraded machine possible. Present, ongoing research activities in LAPD are sponsored by ONR, DOE and NSF. Support by these agencies has allowed the acquisition of two independent laser systems that will be used in the new device for diagnosing plasma properties and for creating controlled perturbations.
The upgraded LAPD will be 18 meters long with a 75 centimeter diameter plasma column and will be capable of operating with a confining magnetic field up to 4 kiloGauss (steady-state). The plasmas will be generated by two independent cathodes that will permit the creation of controlled plasma flows, a common feature encountered in near-earth plasmas and which plays a key role in space weather. The new machine is designed so that the length of the plasma column(s) can be 6, 12, or 18 meters and the radial density profiles can be tailored to study various physical processes that depend on transverse or axial gradients in density and temperature, as pertains to the generation of ionospheric irregularities. The confining magnetic field can also be controlled and varied to generate various mirror and cusp configurations. Fully ionized plasmas will be routinely available with density in excess of 5x1012 cm-3 and electron temperatures in the 20 eV range. The ion temperature will be varied through the application of 100kW of ICRF power to study phenomena triggered by the presence of energetic ions, a situation frequently observed in space plasmas. Since the device is housed in a radiation -shielded room, it would be possible to implement high -power ECRH to generate relativistic electron populations if the scientific need arises.
In terms of universal scaled parameters that allow the extrapolation of specific laboratory experiments to various situations encountered in naturally occurring plasmas, this new device will span the following range:
e number of particles in a Debye sphere nl D3 (variable from 102 to106)
e magnetization parameter w pe/W e (variable from 3x10-2 to 5x104)
e ratio of plasma kinetic energy density to magnetic energy density b (variable from 10-7 to larger than 2)
e ratio of Alfvén speed to electron thermal velocity vA/ve (variable from .1 to 10)
e number of axial Alfvén wavelengths (.5 to 10).
Naturally occurring plasmas vary widely in their scales parameters. For instance, the value of nl D3 ranges from 4x104 in the F-region of the Earths ionosphere to a value of 4x108 in the hot corona of the sun, while vA/ve in the auroral ionosphere ranges from .5 to 10. The values of plasma b also vary widely in the various natural plasmas. In terms of axial extent the upgraded LAPD is capable of studying lengths that correspond to 5x103 km in the auroral ionosphere and in terms of Debye lengths it samples an equivalent of 103 km of the solar corona.
The wide range in plasma parameters available to experimentalists together with the extraordinary ease of access and relatively short time required to set up experiments will permit the study of a broad range of frontier areas in plasma science related to naturally occurring plasmas as well as fusion plasmas. Noteworthy among these are:
1. Formation and dynamics of density structures (vortices, plasma bubbles, filaments)
2. Kinetic effects associated with flows and shock formation
3. Alfvénic turbulence and electron acceleration
4. Field-line resonances
5. Modeling of auroral current systems
6. Velocity shear -driven instabilities
7. Transformation of electromagnetic waves at density gradients (solar radio noise, scintillations)
8. Simulation of ionospheric heating experiments (HAARP, Arecibo)
9. Lower-hybrid interactions
10. Magnetic reconnection
11. Study of heat and particle transport under a wide variety of heating conditions;
12. Exploration of electrostatic and electromagnetic turbulence;
13. Behavior of edge plasmas;
14. Effect of biasing and rotation on turbulent structures;
15. Development and testing of advanced high-frequency diagnostics;
16. Wave-particle interactions with Alfvén waves;
17. Interactions of current channels;
18. 3-D reconnection processes;
19. Spontaneous generation of fast ions;
20. Formation and development of filamentary structures;
21. Development of microscopic probes and sensors.
It is to be recognized that the experiments in this device will have a major impact on the development of plasma theory, simulation and modeling (including atomic physics codes) because they will generate unambiguous quantitative measurements of phenomena that thus far have not been tested. In essence this device has the potential to solidify the foundations of plasma theory ( by weeding out failing ideas) while simultaneously stimulating its development in different directions with the discovery of new phenomena.
Another important consequence of the activities in the upgraded LAPD will be the establishment of a close link between the community of researchers that make observations on board of rockets and spacecraft and laboratory scientists. It is envisioned that thorugh collaborative experiments in the upgraded LAPD a new generation of space researchers will be trained who will acquire a solid background in plasma physics and space phenomenology.
Wide and enthusiastic interest has been expressed by laboratory and space plasma scientists at the national and international level to develop close collaborations on various experimental efforts in the upgraded LAPD. Some groups expressing interest to the principal investigators include members of the following institutions: MIT( Chang, Bers), Princeton (Yamada), Berkeley (Carlson, Ergun, Mozer), Cornell (Kintner, Seyler), U. of Colorado (Stern, Goldman), U. of Iowa (Batacharjee, Kleitzing, Skiff), NRL (Ossakow, Ganguli, Amatucci, Walker), Los Alamos Laboratory (Abdallah), National Institute for Fusion Science of Japan (T. Sato), Tohoku University (Inutake), University of Sao Paulo, Brazil (Opher), INPE, Brazil (Alves), Australian National University (Boswell), University of Sydney (Melrose), Swedish Institute of Space Physics (Thide, Stasiewicz), National University of Mexico (Valdes), Polytechnic University of Madrid (Alcaide), Bochum University, Germany (Shukla).
The upgraded LAPD program will also involve educational outreach efforts based on the existing Los Angeles-based alliance of high school teachers (LAPTAG) developed by Dr. Gekelman. It is hoped that a support base can be found that will permit the operation of a small laboratory in which high school students and teachers can be exposed to the excitement and challenges of space plasmas in an environment in which they can view firsthand how the frontier of the subject is attacked by working scientists. The laboratory will also be in a strong position to participate in APS scince teachers days and host events to educate the Los Angeles community about plasma science and space physics
Clearly, the upgraded LAPD holds great promise for the advancement of plasma-related disciplines, and, perhaps more importantly, for the training of the next generation of space plasma scientists.