Nonelectric Applications of Fusion

Executive Summary

This report examines the possibility of non-electric applications of fusion. In particular, FESAC was asked to consider "whether the Fusion Energy Sciences program should broaden its scope and activities to include non-electric applications of intermediate-term fusion devices." During this process, FESAC was asked to consider the following questions:

• What are the most promising opportunities for using intermediate-term fusion devices to contribute to the Department of Energy missions beyond the production of electricity?
• What steps should the program take to incorporate these opportunities into plans for fusion research?
• Are there any possible negative impacts to pursuing these opportunities and are there ways to mitigate these possible impacts?

The panel adopted the following three criteria to evaluate all of the non-electric applications considered:

1. Will the application be viewed as necessary to solve a "national problem" or will the application be viewed as a solution by the funding entity?
2. What are the technical requirements on fusion imposed by this application with respect to the present state of fusion and the technical requirements imposed by electricity production? What R&D is required to meet these requirements and is it "on the path" to electricity production?
3. What is the competition for this application, and what is the likelihood that fusion can beat it?

It is the opinion of this panel that the most promising opportunities for non-electric applications of fusion fall into four categories:

1. Near-Term Applications
2. Transmutation
3. Hydrogen Production
4. Space Propulsion

The order that these are presented in is not meant in any way to imply priority. Based on the information available to the panel, and presented in this report, the panel makes the following recommendations. It is important to note that these opportunities should not be pursued at the expense of existing programs, particularly since the fusion program has seen many significant budget cuts, particularly in the area of technology.

Near-Term Applications

Findings. The use of fusion reactions to provide relatively inexpensive PET isotopes in low population density areas for the diagnosis of cancers and other abnormalities can be a big help in keeping related Medicaid and Medicare health care costs down. Small quantities of PET isotopes have already been produced in low Q fusion devices and future scale up of existing facilities could have impact in a 5-10 year time frame. A modest plasma physics effort will be required to increase the current PET isotope production rate to a commercially competitive level.

The production of neutrons from DD reactions in small portable fusion devices can contribute to the nation's Homeland Security mission. The detection of clandestine materials (explosives, chemical and biological weapons, drugs, etc.) is of vital importance to our national security and is an area where existing low Q fusion devices are already at the proof of principle stage. Scale up and miniaturization could be achieved by modest investments in plasma physics research.

Recommendations. The DOE-OFES should identify a small, but steady, source of funding to specifically look at near-term applications that are not related to electricity production. This should not be done at the expense of existing programs, but rather could be accomplished by an SBIR-like process that includes opportunities for universities, industry, and national laboratories.

Transmutation

Findings. There are a number of important neutron transmutation missions (destruction of long-lived radioisotopes in spent nuclear fuel, 'disposal' of surplus weapons grade plutonium, 'breeding' of fissile nuclear fuel) that perhaps can be best performed in sub-critical nuclear reactors driven by a neutron source. The physics requirements on a fusion neutron source for such transmutation missions are less demanding than for commercial electrical power production. A tokamak fusion neutron source based on the current physics and technology database (ITER design base) would meet most of the needs of the transmutation mission; however, achieving the availability needs would require advances in component reliability and quasi steady-state physics operation.

Recommendations. DOE-NE currently has a program to look at spent fuel recycling, including transmutation with fission reactors. DOE-OFES should establish a 'watching brief' of these fuel cycle activities to guide any future expansion of the existing fusion transmutation of waste program. Such an expansion of the small ongoing systems/conceptual design investigation of the application of fusion to the transmutation mission is a necessary first step for evaluating the possibility of incorporating a transmutation mission into the OFES program. Evaluation of the competitiveness of sub-critical reactors driven by fusion neutron sources for the destruction of long-lived radioisotopes in spent nuclear fuel and identification of the required R&D would be the first objective of these studies. These investigations should initially be based on the most developed tokamak confinement concept (using the ITER physics and technology databases) and on adaptation of the reactor technology being investigated/developed in the nuclear program.

Hydrogen Production

Findings. From the design and evaluation studies done over the past 30 years, fusion could provide a long-term source of hydrogen by low temperature electrolysis, high temperature electrolysis or thermochemical water-splitting. Hydrogen production by low temperature electrolysis would have no impact on the fusion power plant, and in fact, could be done remotely for distributed production of hydrogen where it is needed. The requirements on the fusion power plant are essentially identical with the requirements for commercial electric power production. A decision does not need to be made on which process appears best for fusion until that demonstration has been done. By this time, the development work currently underway on high temperature electrolysis and thermochemical water-splitting under other programs will have provided a firmer basis for comparison and selection.

Recommendations. The immediate need is to include production of hydrogen as a goal of the Fusion Program, and as an element in the fusion research planning. The Fusion Program should immediately become an active participant in the U.S. Interagency Hydrogen Research and Development Task Force. A small task should be established to review hydrogen production techniques and recommend technical areas, such as tritium control, that may need additional study. The progress on development of hydrogen production technologies in other programs should be monitored and the results incorporated into the understanding of and directions for fusion production of hydrogen. As in all aspects of fusion energy, the possibility of new discoveries for fusion production of hydrogen should not be ignored.

Space Propulsion

Findings. Manned interplanetary space travel is one of the great uplifting dreams that enriches the spirit of humanity. It appears, from mass-thrust considerations, that fusion and anti-matter are the only conceivable bases for propulsion systems for heavy payload deep-space or manned missions. Because the fusion confinement concepts that have been approved for advanced space missions are not yet sufficiently developed to allow identification of the detailed technical requirements, the technical challenges of fusion propulsion for space are not known in detail. They may be significantly different such that some technology/physics development areas may be more difficult than those required for terrestrial electrical power production while others may be relaxed.

Recommendations. The OFES program should be responsive to any NASA request for support in evaluating (and subsequently developing) space fusion propulsion systems. As a first step, we recommend that DOE contact NASA about establishing a joint task force (led by NASA) to evaluate at the conceptual level the feasibility of fusion for space propulsion.

I. Introduction and Background

This report examines the possibility of non-electric applications of fusion per the charge to FESAC from James F. Decker, then Acting Director of the Office of Science (see Appendix A). In particular, FESAC was asked to consider "whether the Fusion Energy Sciences program should broaden its scope and activities to include non-electric applications of intermediate-term fusion devices." During this process, FESAC was asked to consider the following questions:

• What are the most promising opportunities for using intermediate-term fusion devices to contribute to the Department of Energy missions beyond the production of electricity?
• What steps should the program take to incorporate these opportunities into plans for fusion research?
• Are there any possible negative impacts to pursuing these opportunities and are there ways to mitigate these possible impacts?

FESAC assembled a panel to carry out this study, the panel membership is listed in Appendix B. While the panel charge focuses on intermediate-term devices, the panel agreed it was important to expand the focus somewhat, and include nearer-term applications, as well as, applications that may not be economical or feasible until fusion electricity can be produced economically.

Historically, the primary focus of the U.S fusion program has been to address the need for electricity, seeking to develop fusion characteristics that might compete in the future electricity market. The May, 2001 report of the President's National Energy policy Group clearly indicated the need for a comprehensive national energy policy that could address a variety of national energy needs including alternative fuels and improved efficiency as well as electricity. For example, the NEPD Group recommended that the President direct the Secretary of Energy to:

• develop next-generation technology—including hydrogen and fusion
• develop an education campaign that communicates the benefits of alternative forms of energy, including hydrogen and fusion.
• focus research and development efforts on integrating current programs regarding hydrogen, fuel cells, and distributed energy.

Fusion might contribute a non-electric product such as hydrogen fuel directly or indirectly by helping fission produce the same product, such as by using fusion to produce fissile fuel, or by transmuting nuclear waste of fission reactors that produce the product. There are non-energy applications of fusion as well as non-electric energy applications that are valuable to US industry or public health, such as production of valuable radioactive isotopes, for example. In some cases the pursuit of non-electric applications may require the same research for fusion configuration optimization and fusion technology as for electricity production, and in some cases not.

The traditional way of looking at what benefits fusion has to offer beyond electricity has been to point to the "spin-off" from plasma research and technology that has resulted from the construction of complex plasma experiments. Several Government summaries, individual reviews, and even a recent conference have addressed the indirect benefits of these spin-offs to society that result from funding the fusion program. These benefits are real and impressive. However, essentially all of these commercial products come from non-fusion plasmas or equipment not specifically designed to handle fusion plasmas. The use of plasmas to provide UV to dry printed material, the use of RF generated plasmas to generate light for home use, and the use of RF generated plasmas for etching are only a few examples of commercial products that do not require an actual fusion event, just energetic ions (usually protons) or electrons. It can be convincingly argued that people are happy to accept the benefits that come from this research, but the fusion program is not funded to generate "spin-off", but rather to produce fusion energy in the long run. Therefore, this report will concentrate on only those products that come from fusing plasmas.

Since finite resources for fusion research might result in trade-offs of fusion research between electric and non-electric applications, evaluation of non-electric applications have to include not only feasibility, but also how their pursuit might change the technical direction of the fusion program away from the traditional ones needed for electricity. Such changes to the ongoing fusion program, if required for pursuit of any non-electric applications, would clearly have to be justified in terms of the classical metrics of cost, risk, and benefit. The panel therefore adopted the following three criteria to evaluate all of the non-electric applications considered:

1. Will the application be viewed as necessary to solve a "national problem" or will the application be viewed as a solution by the funding entity?
2. What are the technical requirements on fusion imposed by this application with respect to the present state of fusion and the technical requirements imposed by electricity production? What R&D is required to meet these requirements and is it "on the path" to electricity production? For example, what are the requirements for: Q; power density; pulse length and efficient current drive; availability, reliability and maintainability; tolerable disruption frequency; tritium breeding, handling, and processing; materials; thermal efficiency and high temperature operation; economic operation; schedule to initial commercial operation.
3. What is the competition for this application, and what is the likelihood that fusion can beat it?

The first evaluation criterion is used to judge the magnitude of potential benefit of the fusion application that could justify the cost of its development by the funding agency — in most cases by DOE, but in some cases, by private industry (e.g., for isotope production). The second criterion is used to judge the technical risk of developing the non-electric application relative to that of electric production. The third criterion is used to judge the likelihood that the non-electric fusion product will be competitive with other methods of production.

In the following four sections, four categories of non-electric applications are discussed, including comparison to the evaluation criteria. These categories are:

1. Near-Term Applications
2. Transmutation
3. Hydrogen Production
4. Space Propulsion

The panel recommendations are summarized in Section VI.

(Sections II, III and IV — the detailed chapters on near-term applications, transmutation and hydrogen — are omitted for length; the complete text is at the source. Their findings and recommendations appear in full in the Executive Summary above and in Section VI below.)

V. Space Propulsion

Compared with all other available energy sources, fusion offers a unique potential for advanced space propulsion; that is, to transport large payloads over long distances with acceptable trip times. In particular, many advanced missions involving large robotic platforms and/or human piloted travel to the outer planets of the solar system and beyond are simply impossible for other existing propulsion fuels.

Table 3 compares the specific energy yield and ultimate exhaust velocities from various energy sources. Fusion's unique utility lies in the large fraction of mass converted to energy and the fact that this energy is distributed in a reaction mass available for direct thrust thus attaining very high specific jet power.

(Table 3, Candidate Fuels for Advanced Space Propulsion, is omitted here: the scanned table does not transcribe reliably. It is at the source.)

For propulsion, the objective for the cost of energy is measured in $10's to $100's per kW-hr, rather different from the few cents per kW-hr required for attractive terrestrial electricity generation. Furthermore, by contrast to fission-electric propulsion, it is unnecessary to convert the fusion plasma energy into electricity in that the thermal energy of the fusion plasma can be employed to produce thrust directly. Exhausting of the plasma mass is an integral part of this energy-to-thrust conversion. (For finite-Q, driven fusion systems, it may be required to recirculate a fraction of the fusion power electrically to sustain the fusion reaction; in such cases, there will be a minimum requirement on the plasma-Q. Alternatively, it may be advantageous to provide a separate fission power system for ancillary electric power). Table 4 contrasts the differences in applying fusion to terrestrial electricity production relative to space propulsion.

Table 4. Differences in Applying Fusion to Electric Generation and to Propulsion

| Terrestrial Electric Power | Space Propulsion | | --- | --- | | Fusion energy valued for a few cents per kW-hr | Fusion energy valued for $10's to $100's per kW-hr | | Conversion to electricity mandatory | Conversion to thrust directly | | Cost of electricity is a physics driver | Specific jet power is a physics driver | | Neutrons cherished for their energy, but accentuate reactor material engineering challenge | Neutrons are worse than useless and are vented out freely to space, alleviating the reactor material problems | | Years of low-maintenance operation — inherently favors steady-state fusion approaches | Months of operating duty cycle between major overhauls — open the doors for pulsed fusion approaches | | Terrestrial environment where creating a clean, high vacuum is a non-trivial engineering burden | Space environment where a near perfect clean vacuum is readily available |

History and Background

A major effort to address the application of fusion in space was undertaken by the former NASA Lewis Research Center (now renamed as the Glen Research Center) between 1958 and 1978. The research, however, was formulated to address the application of fusion to generate electrical power in space, as well as for propulsion. From considerations above, these two applications are somewhat orthogonal, though the underlying plasma and fusion science are similar. The NASA Lewis program was narrowly focused on the simple mirrors and the electric field bumpy torus — both steady-state MFE fusion approaches. The program was cancelled in 1978 for budgetary reasons as NASA was preparing to embark on the shuttle program.

During the same period, several conceptual studies considered the application of ICF to propulsion. Hyde, Wood and Nuckolls at Lawrence Livermore and Bond et al. in the U.K. considered laser-driven ICF, whereas Winterberg considered relativistic electron beams driven ICF. In the 1980's and 1990's, a number of propulsion concepts were studied. A modern version of an ICF driven spacecraft was proposed by Orth in 1987. Borowski considered the application of the spherical torus (ST) and spheromak to propulsion and performed a comparison between fusion and antimatter propulsion. A more elaborate embodiment of the ST concept was later provided by Williams, et al. in 1998. Both Santarius and Carpenter studied the use of the tandem mirror in 1988 and 1993 respectively. Teller, et al. considered the use of the dipole fusion concept in 1992. Nakashima and co-workers considered the use of field reversed configuration in 1994. Kammash in 1995, and later Emrich in 1998, studied the use of the gasdynamic mirrors. Kammash also considered the use of magneto-inertial confinement fusion (MICF) for propulsion. Smith and co-workers studied the use of anti-proton catalyzed fusion and fission-fusion hybrid. Perkins et al. have examined the issues underlying antiproton-driven inertial confinement fusion. Another version of fission-fusion hybrid was considered by Winterberg for propulsion. There were a number of studies made to discuss the engineering issues including the fusion fuels generic to fusion for propulsion and for space power, for example, Hilton, Roth, Wittenberg, and Santarius and co-workers. The reviews by Schulz and by Santarius and Thio updated the arguments on why is it timely for NASA to begin undertaking an aggressive program to develop fusion propulsion.

Most of the above studies involved propulsion units with extremely large powers and with masses typically more than 1000 tonnes. More recently, Thio considered the use of magnetized target fusion driven by plasma jets and a plasma (i.e. non solid) liner. Slough studied the acceleration of FRCs to high velocities; he employed their kinetic energy for self compression through a series of tapering coils and conductors to produce fusion burn and expanded the resultant plasma through a magnetic nozzle. Miley (and earlier, Bussard) assessed the inertial electrostatic confinement fusion approach. These later studies suggested that fusion propulsion units might be achievable with masses below 200 metric tons and with specific jet power exceeding 10 kW/kg. The propulsion systems of Thio and Slough involved pulsed fusion approaches, whereas that of Miley was steady state. The propulsion concept of Thio was later given a more thorough evaluation for a human piloted mission to Callisto, a moon of Jupiter, by NASA in the project HOPE (Human Outer Planet Exploration); this is part of a larger NASA study, RASC (Revolutionary Aerospace System Concepts).

The Rationale for Fusion Propulsion

To send humans and/or heavy robotic equipment (≥20 tonnes) to the outer planets of the solar system and beyond, we will need propulsion technology with much higher performance than can be provided by present-day chemical and nuclear fission propulsion. There are physiological reasons for wanting to limit the length of flight time. Skeletal and muscular atrophy will occur in astronauts after approximately a hundred days in zero gravity. Interactions of cosmic radiation with spacecraft structure result in neutron showers that subject astronauts to high radiation doses. The risk becomes unacceptably high after one year in orbit unless the spacecraft is heavily shielded. Mission cost in general grows with the length of the mission. Ultimately, the length of any mission must be reasonably limited for practical reasons including sustaining public and scientific interest, maintaining social and scientific relevance and, ultimately, obtaining political support. Accordingly, given the enormous distances to the planets, very high cruising speeds are required. Additionally, the ability for an emergency abort to Earth as well as rapid evasive maneuvers to avoid collisions with asteroids or other space objects would be highly desirable.

Consider for example a mission to one of the moons of Jupiter. The orbital separation between Jupiter and the Earth is approximately 650 million kilometers. To complete the outbound trip in 5 months (about 13 million seconds) would require a mean cruising speed of 50 km/s, or a peak velocity increment (Δv) of at least 100 km/s. The round-trip flight time would require approximately ten months. With about two months stay at the destination, the complete mission could be accomplished within a calendar year. Historically this appears to be reasonable for an exploratory expedition to maintain the political attention span.

Exhaust velocities of several hundreds of km/s are required for advanced missions. The propellant exhaust velocity is proportional to the specific impulse of the propellant, defined (in units of seconds) as the thrust imparted to the rocket (in pounds) per mass rate of propellant expended (in pounds/second). Exhaust velocity is a direct measure of the fraction of fuel mass converted to energy. Fusion offers the highest potential in this regard — see Table 1 — other than (very speculative) matter-antimatter annihilation.

Exhaust velocities from chemical propellant are generally limited to less than 5 km/s. Fission heated hydrogen could produce exhaust velocities in the region of about 10 km/s. Advanced gas-core fission reactors could potentially eject gases at a velocity of 20 km/s to 50 km/s. Exhaust velocities from these propulsion devices are far too low to enable efficient human and heavy robotic missions to the outer planets and beyond within reasonable cost and time.

In principle, nuclear fission could be used to generate electricity to accelerate charged particles or plasmas to high exhaust velocities. However, the thermal-to-electric conversion process necessarily produces a large amount of waste heat due to fundamental thermodynamic inefficiencies. Since blackbody radiation (governed by the T4 law) is the only means of getting rid of waste heat in space, the rejection of the attendant large amount of waste heat at relatively low temperature gives rise to a large amount of thermal mass for the propulsion system. Adding to this is the mass of the power equipment (diodes, transformers, switches, etc.) required to condition the electrical power, i.e., to produce the correct voltage-current characteristic to power the electric thruster. The large mass introduced by the thermal radiators and the power conditioning equipment results in low acceleration for the spacecraft.

Given the exhaust velocity of the propellant, the mean acceleration is limited by the mean jet power per unit mass of the spacecraft, that is the mean specific jet power. For the Jupiter example above, if the spacecraft were to accelerate for one-third of the distance up to a velocity of 100 km/s, coast at constant velocity for the second third of the journey, and decelerate for the last third of the course (a nearly optimum trajectory), the required acceleration is about 0.025 m/s2. Assuming a reasonable payload fraction (m/m0) of 0.75 for the outbound trip, the rocket momentum equation dictates a propellant exhaust velocity of 350 km/s. Accordingly, the mean specific jet power of the rocket must exceed 4 kW/kg. Higher values of specific jet power are required for safety, for evasive maneuvers, and for more ambitious mission profile or more distant planets. The specific jet power of nuclear fission powered electric rocket is generally limited to less than 0.1 kW/kg (though claims of higher specific power up to 1 kW/kg have been made occasionally), and is inadequate for meeting the propulsion demands of the high energy space missions considered here.

To attain the very high specific impulses and the very high specific jet power required for advanced missions: (1) nuclear energy is required because of its high specific energy, (2) the nuclear energy should be released in the form of a high-temperature plasma at millions of degrees, and (3) this plasma should be used to generate thrust directly by pushing against a magnetic field, without converting the thermal energy into electricity to power an electric thruster. Thermonuclear fusion is the only near-term physical process that could produce this desirable combination. Only a very small fraction of the fusion energy would be used to generate electricity to provide the auxiliary power required to drive the fusion reactor.

Critical Issues for Fusion Propulsion

There are many scientific, technical and operational issues that must be resolved before fusion propulsion can become a reality. Feasibility is a fundamental issue followed closely by projected costs. However, in fusion's favor is the fact that many advanced missions are simply impossible for other propulsion fuels. Moreover, what is considered too costly in one era might not be so in the next. In the foreseeable future, it is thought by many that $50 B (current worth) is about the maximum that would be tolerated for any human or robotic planetary mission, and that the price tag per mission would need to be considerably lower than this to have any real political support. Budget figures such as $20 B per mission have been suggested as the "threshold of pain" by NASA senior managers. For reference, in the first conceptual study for a human piloted mission to Mars undertaken under former President Bush's Space Exploration Initiative (SEI) based upon mainly chemical propulsion in 1991, a mission cost estimate of more than $400 B was cited by the study group. The high mission cost was a major factor that led to the demise of SEI.

Mission cost can be broken down into the cost of propulsion and the cost to achieve mission objectives. The latter includes the cost of the space vehicle excluding the propulsion unit, and other costs such as that for scientific exploration at the destination. Propulsion cost consists of the cost at the initial orbit in space (IOS) — that is, the launch cost and cost of producing the propulsion unit — plus the in-space cost and the cost at destination. At present the launch cost is about $10K per kg. This might be reduced by an order of magnitude by the 2030's. The projected cost of producing the propulsion unit is much harder to estimate, especially when the technology is not mature. Past experience with the manufacturing of space qualified hardware, however, indicated a range of cost from $20 K to $100 K per kg. Clearly, the cost of manufacturing the propulsion unit would dominate the cost at IOS. If we assume (a) equal distribution of the mission cost between propulsion and the cost to achieve mission objectives, and (b) that the cost of IOS should not exceed half of the budget allocated for propulsion, then the cost at IOS that might be politically sustainable is in the range of $5-10 B. Assuming a mid-range value of $50 K per kg as the rate for manufacturing the propulsion unit, this places a limit of no greater than 500 tons on the propulsion unit. This mass budget would be inclusive of all the auxiliary equipment required by the propulsion unit and the thermal radiators.

Clearly, it will be extremely unlikely that a conventional tokamak or conventional ICF reactor will fit into the above mass envelope. Thus, for practical fusion propulsion, recourse will be necessary to fusion approaches that promise to be more compact and lightweight than the conventional approaches. Such approaches are being investigated in DOE's OFES Innovative Confinement Concepts (ICC) program, and include: the spherical torus, magnetized target fusion, field reversed configurations (FRC), spheromak, levitated dipole, flow stabilized z-pinches, centrifugal confinement, inertial electrostatic confinement, and fast ignition for ICF. Note that some of these approaches have natural divertors. With the exception of the plasma-jet or plasma-liner-driven magnetized target fusion, all these concepts have been formulated for the terrestrial electric program, thus starting with rather different technical objectives and assumptions. So, the fundamental technical issue for future research is to search for and assess confinement concepts that are most appropriate for fusion propulsion.

Because of the severe performance penalty in terms of the thermal management mass, neutrons are in general worse than useless for propulsion unless their kinetic energy can be directly absorbed by the fusing plasma. The latter would have to attain several times solid density; Thio has shown how this might be achieved in some instances. Therefore, fusion schemes and advanced fuels, such as D-He3 that result in reduced neutron production are favored for propulsion application. In addition, would breeding tritium on-board introduce severe mass penalties, or could appropriate physics and technological pathways be found that would make it feasible to breed at least a small quantity of tritium on-board? The answer to this question would determine to what extent tritium could be part of the fusion fuel. Without a feasible approach for regenerating tritium on-board, for practical and safety reasons in the handling and storage of tritium, only a limited quantity could be brought up from Earth to the propulsion vehicle at IOS. This limited quantity, however, might be sufficient for the tritium to be used as a trigger for advanced fuel ICF targets as studied by Perkins and the plasma-liner driven MTF as studied by Thio.

The direct conversion of fusion energy into thrust is a new area of investigation. Though several studies have been made on the subject, relatively very little is known about magnetic nozzles at these power densities, pulsed or steady state. Remote restart capability must be addressed in any propulsion approach; this appears to be a less stringent issue for concepts that use pulsed fusion approaches. Finally, improvements in radiation shielding, nuclear materials and advanced thermal radiators will greatly enhance the performance of the fusion propulsion system.

(We are grateful to Francis Thio for providing the basis for this section)

Response to Evaluation Criteria

1. Will the application be viewed as necessary to solve a "national problem" or will the application be viewed as a solution by the national funding entity?

Fusion propulsion is recognized by NASA as necessary for human exploration of the outer planets and beyond, and for transporting large robotic payloads in a reasonably short trip time. The bigger issue is when NASA will really embark on this type of mission.

2. What are the technical requirements on fusion imposed by this application with respect to the present state of fusion and to the technical requirements imposed by electricity production? What R&D is required to meet these requirements and is it on the path to electricity production?

Although confinement concepts have been proposed for advanced space missions, the detailed technical challenges facing fusion for space propulsion are largely unexplored in a systematic manner. Because of differences in mission they may differ significantly from those for terrestrial fusion applications.

3. What is the competition for this application, and what is the likelihood that fusion can beat it?

Compared with all other available energy sources, fusion offers a unique potential for advanced space propulsion.

Summary and Recommendations

Fusion propulsion will almost certainly be necessary for human exploration of the outer planets and beyond, or for large robotic payloads to be sent with reasonable trip times. Such advanced missions are simply impossible for other existing propulsion fuels. Fusion propulsion appears to be relieved of some of the most challenging constraints burdening the terrestrial fusion electric program; this is because: (a) the allowable cost target are much higher, i.e., about $10's to $100's per kW-hr, (b) the required operating lifetime is months rather than years, and (c) that fusion has no practical technological competitors for advanced missions. In addition, pulsed fusion approaches may be more readily applicable for propulsion than for terrestrial electric power generation.

However, it is important to note that although confinement concepts have been proposed for advanced space missions, the detailed technical challenges facing fusion for space propulsion are largely unexplored. Because of differences in mission they may differ significantly from those for terrestrial fusion applications. An examination of the subject in a coherent fashion taking advantage of the progress made in the fusion energy program is warranted.

Because the technical priorities are sufficiently different, an independent program directed at researching fusion propulsion separately funded from the terrestrial fusion electric program would be needed to pursue space propulsion. The two programs, however, would have many overlaps in underlying physics and engineering, and would likely involve the same community of researchers. The DOE fusion program should be responsive to any NASA request for support on evaluating (and subsequently developing) space fusion propulsion systems. DOE could provide the management and technical expertise in fusion and plasma sciences, especially in the early phases of the program. As a first step, we recommend that a joint NASA-DOE (with NASA in the lead, and providing funding for anything more than "consultation" type of work) program be undertaken to perform conceptual studies of the potential and the feasibility of fusion for propulsion at the systems level, and to develop a long-range R&D plan for its development. The pursuit of the two synergistic but independent applications will stimulate researchers and management to think "out of the box", with the potential for new discoveries for both approaches. In particular, we suggest that the intellectual challenge of deep space exploration will inspire young scientists to enter fusion and plasma science, thus enriching the future work force for both applications.

Recommendations. The OFES program should be responsive to any NASA request for support in evaluating (and subsequently developing) space fusion propulsion systems. As a first step, we recommend that DOE contact NASA about establishing a joint task force (led by NASA) to evaluate at the conceptual level the feasibility of fusion for space propulsion.

Possible Negative Impacts. If somehow the most promising mission for fusion were to be viewed as space propulsion, then the urgency of fusion research could be decreased even further than it is currently.

VI. Findings and Recommendations

It is the opinion of this panel that the most promising opportunities for non-electric applications of fusion fall into four categories:

1. Near-Term Applications
2. Transmutation
3. Hydrogen Production
4. Space Propulsion

The order that these are presented in is not meant in any way to imply priority. Based on the information available to the panel, and presented in this report, the panel makes the following recommendations. It is important to note that these opportunities should not be pursued at the expense of existing programs, in light of the many significant budget cuts the fusion program has seen lately, particularly in the area of technology.

Near-Term Applications

Findings. The use of fusion reactions to provide relatively inexpensive PET isotopes in low population density areas for the diagnosis of cancers and other abnormalities can be a big help in keeping related Medicaid and Medicare health care costs down. Small quantities of PET isotopes have already been produced in low Q fusion devices and future scale up of existing facilities could have impact in a 5-10 year time frame. A modest plasma physics effort will be required to increase the current PET isotope production rate to a commercially competitive level.

The production of neutrons from DD reactions in small portable fusion devices can contribute to the nation's Homeland Security mission. The detection of clandestine materials (explosives, chemical and biological weapons, drugs, etc.) is of vital importance to our national security and is an area where existing low Q fusion devices are already at the proof of principle stage. Scale up and miniaturization could be achieved by modest investments in plasma physics research.

Recommendations. The DOE-OFES should identify a small, but steady, source of funding to specifically look at near-term applications that are not related to electricity production. This should not be done at the expense of existing programs, but rather could be accomplished by an SBIR-like process that includes opportunities for universities, industry, and national laboratories.

Transmutation

Findings. There are a number of important neutron transmutation missions (destruction of long-lived radioisotopes in spent nuclear fuel, 'disposal' of surplus weapons grade plutonium, 'breeding' of fissile nuclear fuel) that perhaps can be best performed in sub-critical nuclear reactors driven by a neutron source. The physics requirements on a fusion neutron source for such transmutation missions are less demanding than for commercial electrical power production. A tokamak fusion neutron source based on the current physics and technology database (ITER design base) would meet most of the needs of the transmutation mission; however, achieving the availability needs would require advances in component reliability and quasi steady-state physics operation.

Recommendations. DOE-NE currently has a program to look at spent fuel recycling, including transmutation with fission reactors. DOE-OFES should establish a 'watching brief' of these fuel cycle activities to guide any future expansion of the existing fusion transmutation of waste program. Such an expansion of the small ongoing systems/conceptual design investigation of the application of fusion to the transmutation mission is a necessary first step for evaluating the possibility of incorporating a transmutation mission into the OFES program. Evaluation of the competitiveness of sub-critical reactors driven by fusion neutron sources for the destruction of long-lived radioisotopes in spent nuclear fuel and identification of the required R&D would be the first objective of these studies. These investigations should initially be based on the most developed tokamak confinement concept (using the ITER physics and technology databases) and on adaptation of the reactor technology being investigated/developed in the nuclear program.

Hydrogen Production

Findings. From the design and evaluation studies done over the past 30 years, fusion could provide a long-term source of hydrogen by low temperature electrolysis, high temperature electrolysis or thermochemical water-splitting. Hydrogen production by low temperature electrolysis would have no impact on the fusion power plant, and in fact, could be done remotely for distributed production of hydrogen where it is needed. The requirements on the fusion power plant are essentially identical with the requirements for commercial electric power production. A decision on which hydrogen process is best for fusion does not need to be made until that demonstration has been done. By that time, the development work currently underway on high temperature electrolysis and thermochemical water-splitting funded under other programs will have provided a firmer basis for comparison and selection.

Recommendations. The immediate need is to include production of hydrogen as a goal of the Fusion Program, and as an element in the fusion research planning. The Fusion Program should immediately become an active participant in the U.S. Interagency Hydrogen Research and Development Task Force. A small task should be established to review hydrogen production techniques and recommend technical areas, such as tritium control, that may need additional study. The progress on development of hydrogen production technologies in other programs should be monitored and the results incorporated into the understanding of and directions for fusion production of hydrogen. As in all aspects of fusion energy, the possibility of new discoveries for production of hydrogen with fusion should not be ignored.

Space Propulsion

Findings. Manned interplanetary space travel is one of the great uplifting dreams that enriches the spirit of humanity. It appears, from mass-thrust considerations, that fusion and anti-matter are the only conceivable bases for propulsion systems for heavy payload or manned deep-space missions. Because no confinement concept has yet been identified that could conceivably satisfy the requirements of such deep-space missions, the technical requirements are unknown, but they may be significantly different such that some technology/physics development areas may be more difficult than the required for terrestrial electrical power production while others may be relaxed.

Recommendations. The OFES program should be responsive to any NASA request for support in evaluating (and subsequently developing) space fusion propulsion systems. As a first step, we recommend that DOE contact NASA about establishing a joint task force (led by NASA) to evaluate at the conceptual level the feasibility of fusion for space propulsion.

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Kathryn McCarthy (chair), Charles Baker, Edward Cheng, Gerald Kulcinski, Grant Logan, George Miley, John Perkins, Dave Petti, John Sheffield, Don Steiner, Weston Stacey and Lester Waganer, Nonelectric Applications of Fusion, Journal of Fusion Energy 21, issue 3-4, pages 121 to 153 (2002); issued as Non-Electric Applications of Fusion, Final Report to FESAC, 31 July 2003, by the United States Department of Energy Office of Science.

(On this site, the plasma-liner driven magnetized target fusion concept this report singles out for propulsion is at /library/stm-2410928ec7, the inertial electrostatic devices behind the near-term neutron and isotope applications are at /library/stm-cac9786426 and /library/stm-27b0684846, the design case for fusion power plants is at /library/stm-4fed2cae63, the role of fusion energy in a sustainable global energy strategy is at /library/stm-28aae71dd4, the twelve axioms of fusion energy research and development are at /library/stm-ec19ca9fbf, and the Defense Intelligence Reference Document on advanced nuclear propulsion for manned deep space missions is at /library/stm-c75846c5a6.)