ITHACA, N.Y. -- A new, essentially inexhaustible source of energy for the 21st century may result from experiments under way at Cornell University's Laboratory for Plasma Studies.
Fossil fuels? Forget it. They're a limited resource and pollute when burned. Nuclear fission reactors? Not in my backyard. Too dangerously radioactive. How about creating energy from fusion, the way the sun does?
"The problem of nuclear fusion is very important to society," said Cornell's Ravi Sudan, the IBM Professor of Engineering, professor of electrical engineering and of applied and engineering physics and a principal investigator on both the COBRA and FIREX projects. "We must have alternate energy sources. We must have technical options."
There are two approaches to using controlled nuclear fusion for energy production: magnetic fusion and inertial fusion. In the magnetic approach the hot plasma that generates the fusion reactions is confined by magnetic fields. The mainline approach for achieving magnetic fusion is the Tokamak program. In inertial fusion, tiny fuel capsules or pellets are compressed to 1,000 times liquid deuterium densities and heated to fusion ignition by pulsed, high-powered beams. Because the whole process should take place in only a few nanoseconds, the hot, dense plasma stays together because of its inertia. The mainline approach to inertial fusion uses laser beam drivers.
Cornell's experiments concern alternate approaches to both the mainline magnetic and inertial fusion approaches:
- FIREX, the Field-reversed Ion Ring Experiment, is a Cornell project funded by
the U.S. Department of Energy's Fusion Energy Science Program for $2 million over four
years. The experiment is designed to create an intense ion ring in a single pulse. The
fields of this ring should confine plasma in a new magnetic "bottle."
- COBRA, the Cornell Beam Research Accelerator, is a new 4-megavolt research accelerator, designed and provided to Cornell by DOE's Sandia National Laboratories. The experiments on this accelerator will investigate the advantages of replacing the mainline laser beam drivers in the inertial confinement program with ion beams. Single-pulse, intense ion beams will be focused onto a target to determine if the power density required for pellet ignition can be achieved. This project is funded for $3 million over five years by DOE through Sandia.
Both these projects utilize the technology of intense ion beams generated in diodes that were developed at Cornell. Sudan and Stanley Humphries, former research associate in the Laboratory of Plasma Studies, hold the first patent on this technology.
Bruce R. Kusse, professor of applied and engineering physics and director of the Laboratory of Plasma Studies, said that the general public is not very concerned about finding non-fossil fuel energy sources even though the basic research required to come up with them has to be done well in advance.
"The general public interest has waned because the prices for coal, oil and natural gas are not that bad. But the supplies of these fossil fuels have finite lifetimes," Kusse said. "If we wait until they are exhausted to develop new sources, we will be in trouble."
Early in the next century, scientists anticipate achieving inertial fusion ignition at the National Ignition Facility (NIF). The NIF will focus the energy from an extremely powerful laser to "ignite" small capsules filled with fusion fuel, creating fusion reactions and liberating more energy than was used to start the process. Crandall, NIF project director, described the program at the meeting here. The NIF will cost $1.1 billion dollars and take seven years to build.
The magnetic fusion program, has focused on the Tokamak approach, with the next step a $10 billion international program known as the International Thermonuclear Experimental Reactor (ITER). It is in the design phase and may result in an internationally constructed and operated Tokamak reactor.
The advantages of using fusion energy sources are that the fuel is cheap and plentiful and the reactors will present less of a radiation hazard than the current fission power plants.
"While the fuel for a fusion reactor is cheap, the mainline approaches are leading to large, complicated and, therefore, expensive reactor designs," Kusse said. "This is why it is important to investigate alternative fusion schemes that can result in more compact power plants."
COBRA will be capable of reaching 600 gigawatts of beam power over 20 to 40 nanoseconds. It will investigate the use of ion beams as an alternative to laser beams as a driver for inertial fusion. "Ion production is much more efficient than photon production by lasers. Our experiments are aimed toward the long term, for the next phase after the NIF is finished," Sudan said. Initial experiments on COBRA will look at the transport and focusing of intense ion beams.
"At these high intensities, these currents have never been focused before. We've done a lot of theoretical work on this, to determine what conditions are needed in order to focus such an ion beam," Sudan said, adding that experimental work has been done as well but not at these power levels. Hammer, Kusse and Sudan are principal investigators on this roject. The experimental work is being carried out in collaboration with John Greenly.
FIREX is a 1-megavolt machine that is expected to produce a peak current of 700 kiloamps over 130 nanoseconds. This experiment in magnetic fusion will help determine if the mainline Tokamak scheme, such as the TFTR machine at Princeton University, should be replaced with an alternative.
"We think Tokamaks lead to reactors that are too big and costly," Sudan said. Using resources of the Cornell Theory Center, Yuri Omelchenko, a research associate in the Laboratory of Plasma Studies, has simulated how to form an ion ring using magnets to hannel the ion beam. Based on that, the experiment was designed, and "we expect to produce a field reversed ring within a year," Sudan said. If successful, "then we'll have a long-range program." This work will be carried out as a collaboration among Greenly, Hammer and Sudan.
Currently, the DOE is spending $244 million annually on magnetic fusion (including the U.S. contribution to ITER) and $180 million on inertial confinement fusion (independent of NIF construction). Magnetic fusion funding declined in the last year and, according to the DOE's Davies, has caused the DOE to review its priorities. "While the U.S. participation in ITER will be reduced," Kusse said, "the DOE has indicated an increased interest in the type of alternate fusion schemes that we are pursuing at Cornell."