coil systems which must be meticulously designed and constructed to withstand tremendous forces. Together with the power supplies and control subsystems, the magnet systems required for fusion rival the largest and most sophisticated electrical equipment ever constructed.

To tackle this problem, MFE scientists and engineers have developed innovative approaches to magnet design that include computer-aideddesign and other sophisticated design tools. For example, EFFI is a computerized tool created to design the complicated magnets found in tandem mirrors and other fusion devices. This computer program computes the fields, forces and inductance of magnetic coils of almost any shape. It eliminates the need to experiment or perform calculations based on scale models. It is in use not only on a National scale within the United States but is also used in Germany and Japan.

Fusion scientists have also improved magnet conductors and fabrication methods dramatically. Design tools in hand, they have found ways to use nonmagnetic materials for supporting structures, thereby leading to a major reduction of mechanical stresses within magnetic systems. One such material, Nitronic 33, is a relatively high strength nonmagnetic stainless steel alloy, which is used in the supports and cases of the TFTR's main coils. The forgings used in the TFTR are the largest ever fabricated from this material. Detailed knowledge of the mechanical and thermal environment inside a large magnet also provided the capability to establish the engineering parameters and performance goals for other innovations, such as methods to obtain high strength bonds between conductors and their insulation and new technologies for welding metals particularly adapted to use in the high-field-strength superconducting magnets.

The result of this progress is the capability to design and construct

conventional and superconducting magnets of unprecedented size and power to confine the dense, high temperature plasmas into the shapes needed for fusion reactors. Magnet technology is keeping pace with program needs by building the magnets needed today and the information data base that will make it possible in the future to design, construct, and operate the magnet systems for a fusion reactor.

High Vacuum Technology The development of techniques for large scale titanium getter pumping, the state-of-the-art in high vacuum technology for over 20 years, can be traced directly to the MFE Program.

The plasma fuel of a fusion reaction must be surrounded by a large vacuum chamber to prevent impurities from contaminating the plasma fuel and to aid in the removal of spent fuel and other fusion byproducts which could impede the fusion cycle. A full vacuum-a

Magneform

gaseous density 1/10,000 that of air-must be maintained continuously, despite cyclic releases of spent fuel and fusion byproducts consisting primarily of hydrogen isotopes and helium. When magnetic fusion research began, conventional vacuum technology could not satisfy this requirement. To overcome this limitation, fusion researchers had to push vacuum system technology well beyond the then state-of-the-art. Significant advances were based on the chemical concept of gettering, a mechanism by which gaseous impurities are drawn into a vacuum pump by a special chemical (a “getter”) which attracts specific gaseous molecules to its surface where they are chemically bonded and thus "sucked" out of the vacuum chamber. Chemical "gettering" of gases had long been used in vacuum tubes; and although it presented a conceptual solution to the problem, no one had attempted such a large scale application of

Magneform is a versatile process that allows metals to be welded without heat, riveted without hammering, and shaped without being touched. Hundreds of products are made or assembled using this innovative application of pulsed intense magnetic fields. These vary from metal baseball bats and sanitary caps on bottles of vaccine to automobile fuel pumps and airplane wings. Some, such as disposable cigarette lighters, would not be possible without magneformed parts.

The roots of magneform are in early magnetic fusion devices designed to "pinch" or compress the plasma to fusion conditions. Some of these devices required thin metal liners, and the magnetic fields tended to crush the liners. The fusion experimenters recognized the phenomenon's potential, patented it, and quickly redirected it to performing difficult tasks around the laboratory such as attaching connectors to large electrical conductors. Soon after, the General Atomic Company obtained an exclusive license for use of the Federally owned patent for magneform and developed a small business in magneforming.

Today, high volume assembly lines in the automotive, aerospace, energy, aircraft, electrical, defense, and other major industries throughout the world use the magneform process for fast, simple, high-quality, and economical production. Production cost savings in excess of 60 percent compared with alternative processes are achieved. The manufacture of magneform equipment is a $4 million per year enterprise for Maxwell Laboratories, Inc. The users of magneform realize production cost savings in excess of $8 million annually.

getter films. Building on the getter concept, titanium getter pumps were developed (in the 1960's) to handle hydrogen loads in pulsed and nontritium machines for the next two decades. Titanium getter pumping has since been used in many of the large fusion experiments whenever clean high speed pumping for hydrogen or other chemically active gases is required.

Auxiliary Plasma
Heating Technologies

Progress in plasma heating has resulted both from technological advances and greatly improved understanding of the microscopic processes underlying propagation and deposition of energy in nonuniform plasmas. Until the early 1970's, the primary technologies for heating plasmas to high temperatures were magnetic compression and resistance heating; but new technologies were needed to attain plasma temperatures for energy break-even. With new technologies such as neutral beams and radiofrequency heating developed in the 1970's and improved in the 1980's, the heating of plasmas to break-even temperatures has become reality.

The development of neutral beam particle accelerators, high power radiofrequency systems, and microwave sources at high power and high frequency have enabled researchers to reach plasma temperatures of 200 million degrees-more than three times what had previously been possible without auxiliary heating. Neutral Beam Particle Injectors Neutral beam heating using particle injectors is the method now used to heat plasmas to fusion temperatures. It involves the injection of high energy atoms of deuterium into the confined plasma. Before they are injected, they must be accelerated to very high energy. This is done in the following manner. Positive-charged deuterium ions or nuclei (both are the atoms stripped of its electrons) are first generated and then passed

through a series of electrical grids which focuses the ions into a beam and accelerates the beam. Before the high energy ion beam passes into the fusion chamber and penetrates the confining magnetic field, the positive-charged ions are neutralized by putting a negativecharge, an electron, back on each of them.

The resulting super high energy atoms in the beam then collide with ions (nuclei) and electrons which are already present within the confined plasma. When these collisions occur, the extremely high energy of the atoms from the beam is transferred to the plasma nuclei and electrons; and their temperature rises accordingly. In the heat of the fuel chamber, the injected deuterium atoms themselves ionize into plasma, thus enriching the plasma fuel.

The research on neutral beam technology in the fusion program has precipitated qualitative advances in the understanding and manufacture of neutral beam systems. Beam performance has grown from tens of kilowatts of beam power for 10-20 thousandths of a second to tens of thousands of kilowatts of power for as long as 30 seconds. The development of large area sources of ions, essential to the broad uniform ion beams used by the thin film industry, materials modification industry, and semiconductor industry has been heavily influenced by the "bucket source" which was invented in the fusion program in 1975. Technology for fabricating key components-novel cathodes to cause ionization, multiaperture grids to control and focus beams, and cooling channels-have all matured significantly. Computer programs to describe beam behavior and response to focusing have also been augmented. Diagnostic instruments, such as the pinhole camera developed by the Oak Ridge National Laboratory and infrared grid scanner developed by the Princeton Plasma Physics Laboratory, lead the state-of-the-art.

Radiofrequency Plasma Heating Radiofrequency wave heating uses a steady beam of electromagnetic waves and radar waves, which are directed into the confined plasma with a special antenna. Heat energy is transferred as in a microwave oven; those particles moving at the same frequency as the beam have their temperature increased, and the temperature of the plasma goes up accordingly.

The principal engineering advantage of radiofrequency heating is the ability to locate the bulk of the equipment in an area remote from the reactor core, thus adding to reliability, simplifying maintenance, and reducing the size of the reactor hall. Other advantages include more efficient utilization of power supply, increased component life, and reduced complexity of required support equipment. In addition, radiofrequency heating offers the ability to direct the heat to specific locations in the plasma such as the center or edge, and thereby control the distribution of heat in the plasma.

The MFE Technology Development Program has led in the development of high-power gyrotrons, a class of high power microwave tubes a million times more powerful than previous ones of the same frequency. Similar technological advances have been made in components for carrying the microwave signal to the reactor hall and in high power antenna systems to send the waves into the plasma fuel. To make it possible to direct the waves from an antenna housed outside the vacuum chamber, new ceramic windows have been developed. These windows, installed in the vacuum wall, allow the waves to enter the chamber without disturbing the vacuum inside. Keeping the antenna outside the vacuum simplifies construction and maintenance of a reactor system.

Still under development, radiofrequency heating has already been used in a tokamak to attain plasma temperatures in the 50-60 million degree Celsius range.

The Tokamak Fusion Test Reactor with one neutral beam particle injector installed on the left. piping for the vacuum pumps installed on the

upper right, access ports to the vacuum vessel shown in the center.

Plasma Fueling
Technologies

For a sustained fusion reaction, plasma fuel must be continuously fed into the magnetic confinement chamber to replace the plasma fuel consumed by the fusion reaction. Since the confinement chamber operates within a vacuum, the original approach to plasma fueling consisted of injecting small puffs of fuel gases into the vacuum surrounding the confined plasma and allowing the materials to drift into the reaction zone. But, as the machines were scaled up, larger and denser plasmas turned out to be more difficult to fuel by gas injection from the edge because the gas could not work its way into the center of the plasma. This problem has been solved by development of a new approach based on propelling a frozen pellet of deuterium deep into the plasma. The fuel is propelled with sufficient force to penetrate the hot plasma fuel core and then melt, thereby releasing its positive ions and converting to plasma.

Building on this concept, the “pellet gun" was developed. Firing its pellets of frozen deuterium and tritium deep into the center of reactor grade plasmas, the pellet gun now provides the balanced refueling capability necessary in fusion reactors. It is a simple efficient method that is compatible with all heating methods.

Through use of the pellet gun, plasma fuels of record density have been attained, a key factor in attaining an N-tau of 100 trillion on the Alcator C fusion device. So successful is this method that it is now the principal refueling technique being applied on the TFTR and the Joint European Tokamak.

Materials Technologies

Materials technology requires selecting, testing, and evaluating candidate materials for components of

experimental systems and providing the scientific and engineering data base needed to do the same for commercial reactors. Materials research has led to significant advances in

Technology for National Defense

the identification and development of materials for service in the fusion environment. This has expanded the range of designs possible for a commercial power producing fusion

High technology developed for magnetic fusion energy has become increasingly important for the United States National defense program. This is especially true for the so-called directed energy weapons systems. A vital segment of the technology base supporting development of neutral particle beams, electron beams, microwave beams, and free electron lasers is the product of early magnetic fusion energy research. The technology developed for the neutral beam injectors which heat fusion plasmas to millions of degrees has been transferred to the Strategic Defense Initiative (SDI) Program where it is being modified to meet unique defense applications. The neutral beams used in the MFE program are attractive because of the extremely high beam powers which have been attained.

Both the technology and feasibility of producing powerful sharply focused beams of electrons were first demonstrated in association with an early fusion experiment called the Astron Project. It included a high current electron accelerator termed a linac, capable of injecting a tightly collimated beam of very high energy electrons into a long cylindrical vacuum vessel. The project also developed advanced techniques for manipulating such beams.

In the early 1970's, experiments to study the propagation of these beams through gases were begun with the linac. This use of the Astron accelerator continued after the termination of the Astron experiment in 1973. Over time, the linac evolved into the Advanced Test Accelerator, the major National facility for research in electron beam weapon feasibility. The accelerator is also being used for experiments on high power microwave and laser weapons.

Microwave tubes similar to those used in plasma radiofrequency heating have been developed by the same companies for use in various military applications. Building on developments from the gyrotron program, gyroklystrons and gyro-traveling wave tubes have been produced. These oscillators and amplifiers offer advantages such as higher efficiency, compactness, high power and high frequency. For radar use, the higher frequency gives higher resolution of targets, and the higher power results in increased radar range and resistance to jamming. These characteristics are very attractive for strategic defense systems.

Another new technology is being developed using the induction linear accelerator in the Advanced Test Accelerator. The accelerator produces pulses of electrons which are passed through a magnetic "wiggler structure" to produce a laser with extremely high power levels. This socalled free electron laser is being developed by the SDI Office and is a front runner in the current directed energy weapons research program. The free electron laser is also an important potential new heat source for plasma heating.