The US Heavy-Ion Fusion Program

The Heavy-Ion Fusion (HIF) program has the long-range goal of developing fusion energy as an affordable and environmentally attractive source of electric power. 

What is fusion?
Fusion is the process that powers the sun and other stars. It is the reaction in which two light atoms, such as atoms of  hydrogen, combine or fuse to form a heavier atom, such as an atom of helium.  In the process, some of the mass of the hydrogen is converted into energy.  Hydrogen atoms repel each other due to the electrical charge of their core or nucleus.  For fusion to occur, the atoms of hydrogen must be heated to extremely high temperatures (millions of degrees C) so they have enough thermal energy to overcome this repulsion, and then they must be held together or confined long enough for fusion to occur. The sun and stars are held together by gravity, but this method only works when the amount of fuel is much larger than the earth.  Two alternative methods are being studied to produce controlled fusion on earth. With magnetic confinement fusion, strong magnetic fields hold the electrically charged or ionized atoms together as they are heated.  With inertial confinement fusion (ICF), the method discussed here, a tiny pellet of frozen hydrogen is compressed and heated so quickly that fusion occurs before the atoms can fly apart, so the reaction is confined, in effect, by the inertiaof the fuel. 

Why is fusion power attractive?
Controlled fusion has the potential of becoming an important energy source because the fuel is widely available and because the reaction is relatively clean.

The easiest fusion reaction to produce is combining two forms or isotopes of hydrogen, deuterium (also called heavy hydrogen) and a heavier isotope tritium, to make helium and a neutron. Deuterium is found abundantly in ordinary water, and tritium can be produced by combining the fusion neutron with the light metal lithium.  There is enough deuterium in the oceans to provide an effectively unlimited supply of energy.

Compared with the main sources of electrical energy used now, fusion is a clean source of energy.  Unlike the burning of fossil fuels, like coal and petroleum, fusion  produces no "greenhouse" gases and therefore not contribute to global warming.  Also, even though fusion is a nuclear process, it produces no long-lived radioactive waste.  A properly designed fusion power plant would therefore be safe, and design studies indicate that electricity from such a plant would cost about the same as today.

How do you produce electricity from inertial fusion?
In ICF, energetic laser or charged-particle beams are used to heat a small (~1 cm) inertial fusion target for about 10 nanoseconds (10-8 sec).  The fusion target consists of a metal shell or Hohlraum containing a spherical shell of frozen thermonuclear fuel.  The heated Hohlraum emits intense X-rays that compress the fuel capsule to thousands of times its initial density and heat it, near the center, to thermonuclear temperatures.  The resulting fusion reaction should produce about 100 times more energy than was supplied by the beams. In an operating ICF power plant, typically five to ten fusion targets would be detonated per second.  Energy from these fusion explosions would continuously heat the working fluid of an otherwise conventional electrical power plant.
Sketch of a HIF power plant

Why use heavy ions for inertial fusion?
The key requirements for the beams used to heat an inertial-fusion target are the power density and the repetition rate.
During the brief time the target is being heated, energy must be deposited at a rate of about 4 x 1014 Watts, about forty times the average world-wide electric power consumption.  Both lasers and beams of charged particles or ions are able in principle to meet this requirement, but the accelerators needed to produce the ion beams are far more efficient than laser.  The highest efficiencies achieved by lasers are around 10%, while an induction accelerators can achieve an efficiency above 30%.    Also, the only type of high-power laser able to operate at the needed repetition rate is a diode-pumped solid-state laser (DPSSL), and the present high cost of these devices would make a laser-based power plant impractical.  For these reasons, committees chartered by the US Department of Energy and by Congress have identified heavy-ion accelerators as the most promising drivers for IFE power. 

These topics are discussed at greater length in the HIF tutorial.

US Research on Heavy-Ion Fusion Energy

Considerable development is needed before HIF can be a practical source of power.  Since 1999, the US program on HIF drivers has been co-ordinated through a Virtual National Laboratory for Heavy-Ion Fusion (VNL), sponsored by the Office of Fusion Energy at the US Department of Energy.  The VNL is a collaboration between HIF research groups at Lawrence Berkeley National Laboratory (LBNL),  Lawrence Livermore National Laboratory (LLNL),  and Princeton Plasma Physics Laboratory (PPPL).  The VNL has three primary missions: carrying out small experiments testing all components of a HIF driver, doing source-to-target numerical simulations of drivers, and designing a new accelerator facility, the Integrated Research Experiment (IRE).  The IRE is an essential intermediate step between the present series of small-scale experiments testing accelerator sub-sections and a full-scale HIF driver prototype.  The national IFE experimental program calls for initial construction of the IRE by 2005, and together with target-physics data from the laser-driven National Ignition Facility, it will provide the physics understanding and technology needed to design an Engineering Test Facility (ETF) by 2012.  Smaller programs at the  University of Maryland and the  Naval Research Laboratory (NRL) are carrying out important theoretical and experimental work on ion-beam transport, and  studies of the IFE reactor physics and engineering have begun at the  University of California BerkeleySandia National Laboratory has done extensive work on the use of light ions to drive fusion targets and recently has been exploring z-pinch technology to generate intense X-ray bursts that could be used to compress inertial-fusion targets. There are also IFE system studies in progress at the University of California at Los Angeles and the University of Wisconsin.  Further information about the US research on HIF drivers is found in a brief introduction by the US Program Head, Roger Bangerter.

US work on target physics are underway at several US laboratories.  Since efficiency and repetition rate are not important considerations for target physics, ICF target experiments are presently being done using high-power lasers.  Much early work on ICF target compression was done on the Nova laser at LLNL, and more recently studies on direct-drive targets and on hydrodynamic instabilities during compression have been carried out at the Omega Upgrade laser the University of Rochester and the Nike facility at NRL.   Since 1998 construction has been underway on the National Ignition Facility (NIF) a collaboration of several laboratories led by LLNL.   This facility is expected to achieve the first ignition of an ICF target around 2005 using 192 high-power glass lasers, and it will be used both to carry out detailed studies of target physics and to calibrate target-design codes developed by X-Division at LLNL and elsewhere.   Successful ignition at NIF is crucial to the HIF program because it would validate the concept of inertial-fusion energy.  Furthermore, due the similarity of targets for laser and heavy-ion drivers, HIF target designs could be tested and refined before designing the ETF. 

In Europe, HIF research is distributed among many laboratories and universities.   In contrast to the US laboratories, which favor induction accelerators, European work uses radio-frequency accelerators, which are typically shorter but have much lower current.  To produce the high current needed to ignite a fusion target, European researchers plan to stack beams in a series of storage rings before the final-focus section. Information about these programs can be obtained from the link to the Heavy Ion Driven Ignition Facility (HIDIF) study that is currently underway in Europe.  There is also a French project to build a laser ignition facility similar to NIF, with completion expected in 2006.

Several major areas of HIF research under the VNL are described in the pages below:

VNL Heavy-Ion Fusion Research
A summary of the research objectives, including the Integrated Research Experiment and the High-Current Experiment.
Current LBNL Research Activities
Brief descriptions of some of current research projects, including the Scaled Final-Focus Experiment, the Beam-Combining Experiment, Ion-Source Development, and Plasma-Lens Experiments
Current LLNL Research Activities
Brief descriptions of some of current research projects, including the Small Recirculator and numerical-simulation results
Past HIF Accomplishments
A brief synopsis of significant research progress and conclusions based on past experimental research and development
Recent Reports and Papers (under development)
Recent papers by VNL staff members, as well as titles of unpublished internal  notes and memos.

Follow this link to the HIF 2000 International Symposium

The US Heavy-Ion Fusion Home Page is intended to be a national Web site for all US research on HIF drivers. For comments or questions regarding this site, contact the HIF webmaster