Sandians help shape the future of fusion energy

Several Sandians, including Mike Ulrickson (6428) and Craig Olson (1600), have helped shape the future of fusion energy and extended Sandia’s Z machine into the fusion energy area.

They were among 280 scientists from the United States and the international fusion community who attended the second Snowmass Fusion Summer Study in Snowmass, Colo., this summer (July 8-19, 2002), assessing the major next steps in fusion energy research.

The report resulting from the meeting will be studied by the DOE Fusion Energy Science Advisory Committee (FESAC) to form a strategy to go forward with fusion projects for the US. The report will also be reviewed by a committee of the National Academy of Sciences. A final strategy will be recommended by both entities to the DOE Office of Science early next year — in time to influence the 2004 fiscal year.

“The result might mean a change in direction for our department or a thrust in a different area,” says Mike, Manager of Fusion & Structural Technology Dept. 6428. “The future of fusion hinges on what the DOE Office of Science decides.”

“The clear presence of the z-pinch approach to fusion energy at Snowmass marks the potential start of a significant effort to extend the impressive single-shot results of Z to a repetitive concept for fusion energy,” says Craig, Scientific Advisor for Pulsed Power Sciences Center 1600.

Sandia has been working on fusion since the 1960s. Mike’s department currently has about 10 people devoted to studying plasma-facing components for magnetic confinement fusion research. The Pulsed Power Center, under Jeff Quintenz, Director, and Keith Matzen, Level II Manager of 1670, currently has about 150 people devoted to high-energy density physics and inertial confinement fusion research on Z for the weapons program.

During the Snowmass conference, the two major approaches to fusion energy were discussed. One is magnetic fusion energy in which a large-volume plasma of low density deuterium/tritium fuel is heated to more than 100 million degrees and held in place by powerful magnetic fields. Mike, together with Dennis Youchison (6428), participated in the magnetic fusion discussions.

The other approach is inertial confinement fusion energy, in which small fuel capsules containing a small volume of high-density deuterium/tritium fuel are heated and compressed rapidly by intense energy pulses, and held together briefly by their own inertia. Craig, along with Keith Matzen (1600), Roger Vesey (1674), Steve Slutz (1674), Tom Mehlhorn (1674), Charles Morrow (64150), and Tina Tanaka (6428), participated in the inertial fusion energy discussions.

Magnetic fusion energy

Some 230 people participated in the magnetic fusion discussions, and advocates of three different burning plasma devices presented their cases. A burning plasma is one in which the energetic alpha particles produced in the deuterium/tritium fusion reactions dominate the plasma behavior. The three devices are all tokamaks — the Russian name given to a particular magnetic field configuration shaped like a donut. The three devices are:

• IGNITOR (developed in Italy): The smallest and the one that could achieve burning plasma fastest. It offers the opportunity for the early study of nonstationary burning plasmas aiming at ignition.
• FIRE (developed at Princeton Plasma Physics Laboratory): It has the capability of longer pulses. It would allow the study of burning plasma physics in conventional and advanced tokamak configurations under quasi-stationary conditions and would contribute to plasma technology.
• ITER (developed internationally): The largest device is capable of achieving steady-state conditions and integrates burning plasma physics and technology.

ITER would cost $5 billion or more and would be built outside the US, possibly in France, Japan, or Canada. ITER has been supported by a comprehensive research and development program.

Sandia researchers worked on ITER between 1992 and 1998, and since 1998 have been working on FIRE.

The scientists attending the meeting concluded that the study of burning plasmas is at the frontier of magnetic fusion energy science and that a burning plasma device must be the next step.

Inertial fusion energy

Some 50 people participated in the inertial fusion energy discussions. Inertial fusion energy already has a burning plasma experiment under construction — the National Ignition Facility (NIF) at LLNL. NIF, a multibillion-dollar facility,has been under construction for several years and is scheduled to show ignition and modest energy gain in exploding fusion targets during the next decade. However, NIF uses glass-laser technology that can be used only in single-shot experiments. For fusion energy, the process must occur repetitively, and three major approaches to achieving this repetitive operation were discussed at Snowmass.

Just as in the magnetic fusion sessions, advocates of the three different approaches to inertial fusion energy explained the development paths needed for each approach to achieve fusion energy. Particular emphasis was on the next large step, an Integrated Research Experiment, for each approach. The three approaches are:

• Laser inertial fusion energy: Uses a repetitive, efficient, laser driver that injects laser beams onto a small fusion target at the center of a “dry-wall” chamber. The targets explode, and the energetic neutrons produced deposit their energy in a liquid blanket just outside the first wall of the chamber. This energy would then be used to drive turbines to produce electricity. For this approach, new lasers are being developed, but they are presently at very low energies.
• Heavy-ion fusion: Uses multiple high-energy heavy-ion beams, which are aimed and focused onto a small fusion target at the center of a “thick-liquid wall” chamber. The target explodes, and the energetic neutrons produced deposit their energy in the thick-liquid wall inside the structural chamber wall. For this approach, high-current heavy-ion accelerators are being developed, but they are presently at low energies and low currents.
• Z-pinch inertial fusion energy: Uses a pulsed-power very-high-current pulse to drive a multiwire z-pinch to produce a very intense X-ray source that in turn compresses and heats a small fusion target. A Recyclable Transmission Line (RTL) couples the accelerator to the fusion target, which is at the center of a thick-liquid wall chamber. The RTL is vaporized, and is recycled, so a new one is inserted for each shot. For this approach, fusion targets are already being developed on the Z accelerator at Sandia at very high current levels (20 megaamperes), and it is expected that high yield fusion targets will work with currents of about 60 MA.

“Since z-pinches are the ‘new player’ in fusion energy, it was pleasing to essentially hear universally at this Snowmass conference that ‘lasers, heavy ions, and z-pinches’ are the options for inertial fusion energy,” says Craig.