FPC Chamber's “Hat Trick"

  A New Energy Source

A Practical Approach to Fusion Power

Using a Heavy lon Driver for lnertial Confinement and lgnition

  Introduction

Energy is the lifeblood of the world economy and a key ingredient for the American way of life.  The rapid rise in energy prices in the spring and summer of 2008 brought home the fact that fossil fuel energy resources are limited and thus it is critical that a new large energy source be brought on line.  For more than five decades fusion has held the promise of providing the new energy source for the world’s unmet need for energy.  Despite billions of dollars spent on research, fusion, as an energy source, still is perceived as being many decades away. 

This perception is wrong!

Successful power-producing fusion requires that the technologies used be capable of providing the extreme conditions needed to initiate and maintain the fusion burn.  Two techniques for providing these conditions have been studied for years – magnetic confinement and inertial confinement by use of lasers.  Neither of these methods is held to be capable putting fusion power on the grid in the next few decades.  But there is another inertial confinement technology that can allow fusion to deliver the energy needed in the time scale needed by society.  This technique is Heavy Ion Fusion (HIF).

For a controlled fusion “burn” to take place we must confine and heat fusion fuel materials, such as the two heavy isotopes of hydrogen - deuterium and tritium, to very high temperatures.  We express this in terms of the energy and power required to initiate “propagating burn”.   To ignite ICF before the fuel flies apart, energy in the range of 3 to 20 MJ (the energy released in the explosion of some pounds of TNT) must be deposited in the target in something like 10 nanoseconds (10 billionths of a second).  

Our search for the past 5 decades has been for a way to do this.  It is generally thought that this search has been unsuccessful, yet a means to achieve fusion was discovered more than 3 decades ago: the high-energy heavy ion driver.  The method would have produced the very large amounts of fusion energy we need.  However, HIF was considered to be “too big” and to “cost too much”, so the line of research fell into neglect here at home in favor of research that might be able to make controlled fusion energy available with smaller facilities.  The time has come for a re-examination of this old means of providing civilization with access to this abundant energy source.

The passage of three decades has brought a need for HIF’s large power production and with its major economies of scale, HIF's size is the opposite of a drawback.  Europe and Russia have continued on the original path of HIF development, although hampered lack of funds and by the absence of participation by US scientists.

   Details of the Technology

The technique for harnessing controlled fusion proposed in the 1970's was to use the exceptional properties of accelerators to accelerate heavy element ions to moderate velocity before using the impact of the ions on a D-T target to initiate compression to high density simultaneously with heating the target to temperatures needed for a fusion burn.  The history of high energy particle accelerators, and the physics research for which they were developed and serve, occupies rooms full of documentation filled with designs, construction, and operational experience. The  science they support fills libraries and classrooms, has changed humankind’s understanding of the natural world, and has been awarded untold numbers of the World’s top marks of recognition.  Industrial applications also abound and include medical applications, food service applications, ion implantation for changing the properties of metals, and the polymerization of plastics.

In 1975, one spark of appreciation revealed that this vast, hard-come-by trove of information meant that fusion energy was simply a matter of the dedicated pursuit of an objective with the same zeal and commitment that was applied to the (then) just-completed Apollo project. The key realization was that accelerating ions with high atomic number (Z), such as xenon (Z=54), would allow packing more energy into each particle in a short-pulse (ca. 10 nanoseconds) of ion beam. This meant the canonical parameters needed for fusion could be met.

Heavy ions to drive fusion targets can pack tens of “GeVs” of kinetic energy each, because the strength of the decelerating force increases with Z². Though they pack a lot of energy, the ions stop in the required short distance (a few millimeters) in harmless materials, as needed to result in one or more of:

1.    Ablation (rocket driven fuel compression),

2.    Emission of soft xrays (Ulam-Teller compression),

3.    Thermal Expansion (pusher-driven, tamped compression), and/or

4.    Direct heating of fuel (if fuel is pre-compressed).

The accelerator technology in 1975 was more ready to drive the release of “inertial confinement fusion” (ICF) in power plants than rocketry was for the “moon shot” in 1961.  Moreover, RF systems, vacuum systems, controls systems, and many more technologies that make up a HIF driver system are all mature and are applied regularly in industrial processes.

To this day, high-energy accelerator technology steadily develops increased beam intensity and current, as these translate to signal strength regarding the scientific discoveries being sought throughout the world. HIF accelerator driver constructs could have been immediately applied, even in 1975, to known component technology and known ways to size and configure it, to achieve predicated objectives, in this case, the beam parameters needed to ignite fusion, repetitively, with good driver-efficiency. HIF drivers will be big accelerator systems, but not larger or more complex than some in existence today.

   Meeting lCF lgnition Requirements

A canonical ICF ignition number is a peak power of 1000TW, or 1PW (T for tera, a thousand billion  and P for peta, a million billion, are standard prefixes in metric units).   Keeping a power level like this on for ca. 10 nanoseconds (10 billionths of a second) indicates the total beam energy needed: of order 10MJ - the amount of energy  released by exploding five pounds of TNT.  TNT however explodes much to slowly to be used for this application.

The more total energy effectively coupled into the target, the less the fuel must be compressed prior to ignition. Compression to many-times the normal solid density of the fuel (at the cryogenic temperatures of frozen hydrogen) is a key requirement and challenge, and it is made easier by maintaining the temperature as low as thermodynamically possible during compression.[1]  Following such compression, propagating burn is ignited by directly heating a small portion of the fuel to ca. 10keV (100 million ^oC) with a spike on the tail end of the driver pulse. 

Providing more total energy into the target, to accomplish the two processes of compressing the fuel and raising it to ca. 100 million ^oC for ignition, relaxes the requirement for high compression relative to its normal solid (at cryogenic temperatures) density. To assure the needs of ignition are amply serviced, a HIF driver can deliver 100MJ if that were to be needed, but it is safe to say that it will not be needed.  The goal of the National Ignition Facility is ignition with a laser pulse of just under 2 MJ.  The essential point is that a HIF driver can deliver many times the ICF driver beam requirements set forth in the 1960s—which, importantly, did not envision the advantages of the “fast ignition” approach outlined in this paragraph.

Figure 1. Ignition and burn parameter space.

Figure 1 illustrates the dependence of fusion energy output (slanted, dotted lines) on energy input (horizontal axis) and plans to achieve these energies, especially by the USA’s National Ignition

Facility.  The ignition processes have been analyzed in greatest detail for ICF research with lasers, but once the driver energy is deposited, the dynamics of targets rely on the same databases.  The parameter space shown for HIF drivers shows the key strength they bring to the task.

ICF experimentations with large, pulsed laser systems have borne out the accuracy of ICF simulations based on the database of fusion explosions.  The computer “codes” are trusted and accurately predict the conditions needed and the results expected from any given experiment.   The long struggle has been to deliver the quantity (MJ) of beam energy that the simulations have long called for.

As with any approach to generating extremely high peak power, a HIF driver compresses energy in space and time up to the power density needed to drive the dynamics of igniting inertially confined fusion.  Acceleration packs energy into each particle.  The beam power then is the product of particle kinetic energy and particle current: more kinetic energy per particle, less particle current. 

    Power (PW) = Particle Kinetic Energy (GeV) x Particle Current (MA)

To be focused on targets with radial dimensions of a millimeter or less, the ion beams must have high “quality” at the magnetic lenses (bore diameter ca. 30 cm) that focus them on the millimeter fusion target from a distance like ten meters, outside the chamber.  Accelerators had demonstrated the required focusing quality long before 1975. 

To have the required quality at the fusion target requires that the ion beam that leaves the source, at the beginning of the accelerator, be of higher intrinsic “quality”, since beam transport and manipulation tend to degrade the quality in known ways. Understanding the effects of beam handling operations on the beam quality has been a large segment of successfully developing the tools for complex particle accelerators over the past eight decades.

Known ion source technology, coupled with analysis of overall accelerator system constructs, leads to using a source current ca. 0.1A.  Demonstrating 0.1A heavy ion beam with the required source quality was deemed to be the first validating experiment—perhaps the only basic issue facing realization of the HIF driver.  The demonstration was immediately (1977) undertaken at the Argonne National Laboratory, with collaboration by the Hughes Research Laboratories, and the required xenon beam parameters were measured in 1979-80.

The first HIF conceptual system designs amplified the heavy ion current from the source by five techniques:

1.    Funneling synchronized RF beams fed by multiple, independent ion sources.

2.    Multiple-turn injection into a number (10-20) storage rings.

3.    Compressing the beams axially in the storage rings by low frequency RF.

4.    Final axial compression with linear induction cavities.

5.    Hitting the fusion target with multiple, simultaneous beams.

Each of these factors has a range of practicality and known limitations.   The product of these five factors needs to multiply the source current to reach the current needed for ignition, which is the power required for ignition divided by the particle energy.

Current Multiplication Product = Power ÷ (Particle Kinetic Energy x Source Current)

A beam of 20GeV ions, for example, delivering 1PW to the target will have a 50kA current, and the product of the current multiplying factors needs be 500,000.  From 1976 to the present, the ability of HIF driver concepts to deliver the required beams has been analyzed and reconfirmed numerous times. 

In 1996-7, another multiplicative factor was included as a result of the thorough, Germany-based study known as the HIDIF, for Heavy Ion Driven Inertial Fusion.  The latest factor to be included, factor number 6, proposed and studied by author RJB at Argonne in 1978, exploits the freedom to use various types of ions for HIF by using ten different ions in a manner such that they slide into each other, or “telescope”, just before reaching the target.  HIDIF’s end-to-end conceptual design picked three ions to study, and showed that the multiple-ion concept was practical.  Thus the 6^th item is:

6.    Telescoping beams of distinct ionic species having various combinations of the factors b (velocity ÷ speed of light), g (total energy ÷ rest mass energy), A (mass), and q, charge state (+1 is standard for HIF) that give the same value of bgA/q.

Subsequent to HIDIF, author RJB (HIF Project Leader at Argonne from 1976-80.) has found accelerator configuration modifications (patent pending) that “rebalance” the multiplicative factors to decrease risk by providing improved accelerator and target performance.  That such improvements would have been forthcoming a decade or two earlier cannot be doubted, had the full talents of the accelerator technology community been brought to bear—as they should have been—on this problem of unsurpassed importance.  What caused this costly hiatus is outside the scope of this document.

Once previously in humanity’s history with nuclear fusion, means were discovered, designed, and caused to work to burn fusion fuel with a high ratio of “energy returned over energy invested.” But never previously had a technology been judged able to provide all the parameters needed to meet the needs of controlled thermonuclear fusion with substantial margins. This judgment has been delivered repeatedly for the HIF process.  The calculations defining these needs are trusted and anchored in data.  The italicized realization above was as exciting then as now.  Data accumulated by ICF research since 1975 has revalidated and sharpened the predictions that are made regarding the ignition requirements. It is time to progress to the realization of the promise of HIF.

  Cost Considerations

When the HIF driver was brought forward in the late 1970’s, it was criticized because it was perceived to “cost too much”.  In view of our current need for a new energy source, our recent experience with escalating energy costs, and our recognition of the scale of capital investment involved in energy production, the mistakenness of this view is evident.

The large size and cost of a HIF-driver system are practical, but context is critical.  Beheld from middle management in bureaucracy or “settled” industrial communities, such as the electric power industry, a $20 billion facility is seen as large.  But it must be viewed based on investment risk and reward.  Urgency of the need, dire though this urgency is, can contribute only to the urgency with which this “viewing” must be carried out.

HIF’s economy of scale is a huge factor in favor of energy cost to end users, building-out the world-wide fusion energy system at the scale and on the schedule needed, and realizing fusion’s promise of cleanness. Accelerators have a natural rep rate at tens of pulses per second.  One HIF system will drive about ten fusion chambers (Figure 2), to produce about 100GW, the amount of thermal power produced by 30 fission reactors.  30 fission reactors would cost on the order of $200 billion.  Seen in this light, $50 or even $100 billion for a fusion system with high power output seems very reasonable. 

Figure 2. Schematic concept of HIF’s expandable fusion power system.

The inaugural power system requires a robust, Apollo-Project-like effort.  Estimates for such a project, guided by fusion power engineering studies and grounded in the vast database of particle accelerator technology, suggest a cost for the inaugural system of about $50 billion (ca. $30 billion capital investment in the facility itself), with subsequent systems able to be built for something closer to $20 billion each. These costs are for the accelerator driver and reaction chambers – the heat producing system – and do not include the generators and transmission lines or facilities for hydrogen and liquid fuel production. But including these systems (except for the transmission lines) would only add a few hundred million to the overall cost.

The rate of energy production of a fully developed fusion system like this is equivalent to over a million barrels of oil per day, comparable to the production of one of the World’s dozen “super giant” oil fields.  At a minimum the annual energy production of each facility will be worth the $20 billion estimated cost to build systems after the first one.  That revenue (with minimal fuel cost and a rule-of-thumb 10% O&M cost) represents only the electricity generated, which is in series / parallel with production of liquid fuels, via first producing hydrogen.  This proposition clearly does not “cost too much.”  It could be viewed as having the potential to “profit too much”.

   Conclusion

Fusion is a new energy source: the new energy source that the World badly needs.  The characteristics of this newness need to be appreciated and not throttled for spurious reasons.  The claim leveled against HIF in the 1970s was “costs too much”.  Then, as now, this problem regards the purview of the sayer and not energy needs or cost to end users, the environment, etc.  Fusion cannot be “shoe-horned” into preconceived notions to fit past energy practices - whose limitations are graphically evident in today’s massive crises in the economy and the environment due to “the way we’ve been getting the energy our economies need.”[2]

Progress never stops.  A desire for small energy sources is natural, and fusion technology eventually may provide sources that are small as well as provide abundant, safe, clean, and affordable energy.  Just as the large HIF system will propel fusion energy from unremitting research to the regime of ever-improving use of the fusion output, robust fusion development in the future has reasonable prospects of burning fuels that are even safer, particularly fuels whose fusion does not produce neutrons.  The HIF system contains the seeds of such development, and alternative fusion constructs may open new paths.  At this crossroads in the World economy and environment, however, when so many have yet to experience the benefits of the vast developments of the past two centuries, it is crucial to firmly hold in mind that we need fusion energy now.

HIF has been poised for a concerted program to produce copious fusion power for over three decades.   Progress on HIF has been slow, but important, while ICF research with lasers has deepened confidence of success when a power-plant capable driver is provided.  Now is the time to capitalize on the total investments made by the USA and the World in the nuclear energy enterprise.  Shift from the age of oil to the age of fusion.  Solve the problems of energy and the environment.  Make the World’s economic pie larger, the key to eradicating poverty.  And open a promising new path to eliminating nuclear weapons, as observed by David E. Lilienthal many decades ago:  “If a safe new method of producing electricity from the atom were in the offing, a method that would not produce bomb materials as the present method does, that prospect might provide the necessary leverage to bring about atomic weapons control.”[3]