The IEC Fusion-Plasma Torch - A Path For Closing The Materials Cycle
There are two interrelated requirements for achieving a sustainable modern world: 1) the availability of clean energy sources, and 2) the ability to close the materials cycle from use to reuse. Nature has always operated on a closed cycle process powered by solar energy. After the industrial revolution humans increasingly embarked upon an open cycle process extracting resources from the earth, dispersing them, and depositing the wastes into the earth's life support systems of air, water, and soil. Fusion energy has unique capabilities for addressing the root cause of the resulting energy-environment-economy dilemma that our planet now faces. We propose an industrial evolutionary path for solving the dilemma based on the hydrogen-boron (p- 11β) fusion fuel cycle and the application of ultra-high temperature plasmas (fusion plasmas) for materials recycling. This concept is known as the Fusion Torch and would return waste material back to its original 92 elemental states. An Inertial Electrostatic Confinement fusion device is proposed due to its characteristic non-Maxwellian plasma which enables burning p-11β.
To sustain the ecological foundation that Nature has provided us, humanity must alter the technological base that modern society has created. There exist two basic technological requirements for achieving such a sustainable modern world. These interrelated requirements are the availability of clean energy and the ability to close the materials' cycle from use to reuse. We believe that the technological potential to achieve this goal exists today. These technologies when combined and developed into a system will permit all nations to potentially achieve material wealth without destruction of the environment.
Fig.1. Ecology and economy are intimately ties together. Maintenance of the ecology requires a closed materials cycle which is the goal for the fusion torch. [Illustrator: Robert Bourdeaux]
They will also enable a closed cycle economy in which the economy becomes a subsystem of ecology.
One, if not the only, way of achieving a sustainable future involves the concept proposed in 1968 by B. Eastlund and W. C. Gough known as the Fusion Torch. 1,2 The basic idea is that the ultra-high temperatures of fusion plasma that can totally ionize all materials. Thus, the millions of chemical compounds and contaminated materials in modern society can be returned to the basic 92 elements that Nature has provided. There are four interrelated components necessary for achieving this goal: the fusion plasma (ionized gas) generator, the material ionization process, the element separation process, and the energy conversion process. Next we briefly discuss each of these sub-components.
I.A. Fusion Plasma Generator
The unique fusion system we propose here would use inertial electrostatic confinement (IEC) with the hydrogen-boron fusion fuel cycle (p-11β). p-11β is the ideal fuel since neutron activation and tritium contamination of the materials are avoided. The IEC is chosen for this demanding task since its characteristic non-Maxwellian plasma if favorable for burning p-11β and the hot plasma can be conveniently coupled out via a jet-like electrostatic "divertor" into the processing region. The challenge for a fusion system using p-11β is to increase the temperature and density-confinement time parameters by an order of magnitude over target values for future D-T magnetic fusion reactors. Theoretical research now shows that p-11β fusion is possible. 3,4 The required ion temperature conditions for p-11β have already been achieved in IECs at several labs. 5 However, the confinement time for the IEC ion beams must be increased and the stability of its non-Maxwellian plasma must be maintained. The boron fusion fuel supply is abundant and ubiquitous. The United States is a primary producer of boron. Most people are familiar with household use of Borax and boric acid; the biggest industrial use of borates is in the glass industry. Last year's world's output of boron was equivalent to the production of about 84 quad of fusion energy of which over 20 quads is the U.S. share. -- compared to the total U.S. energy consumption of 100 quad. A quad is equal to 10 15 BTUs. For fusion the isotope11β is needed, and fortunately this isotope represents 80% of natural boron. There are now a half dozen small but active p-11β research programs in the United States. In the last five years over 13 patents on boron fusion have been issued. 2
I.B. Material Ionization & Element
The possibility of injecting and ionizing material in fusion plasma has been accomplished and over 300 scientific papers address this technique. The challenge remaining is to do this on a large scale with multiple materials. The plasma process is unique because it provides multiple separation options since elements can be separated by mass, charge, electronic state, or by combinations. At least nine different separation processes have been shown to be useful with the fusion torch after an investment of over $100 million with the issuance of many patents. 2 If the total U.S. waste generation was recycled into basic elements via the Boron Fusion Torch it would require only 0.3 quad compared to the 100 quad total U.S. energy consumption. In addition to separating out toxic elements like mercury and strategic metals like titanium, the process would produce enough hydrogen fuel to power 56 million cars. 2 The challenge is to handle large throughputs of mixed materials.
II. Near Term Applications
The road to an ecological future can be paved with important near-term applications. A number of arc waste plasma processing plants have already sprung up. However, arc temperatures are relatively low - see Fig.2. An ultra-high temperature plasma using an electrically-driven IEC system would provide improved waste conversion to valuable gases, etc. At the same time this approach would develop a database for going on to the fusion torch and complete recycle to basic elements (vs. gases and sludge as in today's arc processes). One important immediate ecological application would be to combine this unit with current fossil fuel plants. The flue gas from a coal power plant would be directed into the electrically driven IEC plasma to separate the carbon and other elements.
Electricity could be generated by cascading the high electrical conductivity exit gas through a magneto hydrodynamic process (MHD) followed by a steam Rankin cycle. The carbon would have valuable uses such as for electrical conversion via fuel cells. If the energy equivalent of the carbon is added to the MHD electrical production, a net energy output from the overall system appears possible despite the electrical input required to generate the IEC plasma. In the longer run, achievement of a p-11β fusion plasma would add a key positive energy boost to the process, enabling the economic large-scale units needed for complete recycle of materials into elemental products.
The road to an ecological future can be paved with important near-term applications. A number of arc waste plasma processing plants have already sprung up. However, arc temperatures are relatively low - see Fig.2. An ultra-high temperature plasma using an electrically-driven IEC system would provide improved waste conversion to valuable gases, etc. At the same time this approach would develop a database for going on to the fusion torch and complete recycle to basic elements (vs. gases and sludge as in today's arc processes). One important immediate ecological application would be to combine this unit with current fossil fuel plants. The flue gas from a coal power plant would be directed into the electrically driven IEC plasma to separate the carbon and other elements. Electricity could be generated by cascading the high electrical conductivity exit gas through a magneto hydrodynamic process (MHD) followed by a steam Rankin cycle. The carbon would have valuable uses such as for electrical conversion via fuel cells. If the energy equivalent of the carbon is added to the MHD electrical production, a net energy output from the overall system appears possible despite the electrical input required to generate the IEC plasma. In the longer run, achievement of a p-11β fusion plasma would add a key positive energy boost to the process, enabling the economic large-scale units needed for complete recycle of materials into elemental products.
The recycling of wastes has become a growth area for new technology. In 2007 venture capitalists dumped a record $161 million into recycling firms. Municipal solid wastes are already being processed by using plasmas arc technology. Plasma recycling with energy recovery is a worldwide activity involving at least nine companies. To compete with plasma arc systems, we propose a new type of plasma system, the "IEC plasma jet", for onsite waste destruction and waste-to-energy conversion. This unit generates very hot process plasma (~103 times the arc plasma temperature) in an IEC configuration where the plasma flows out through an exit nozzle and interacts with the waste. The ultra-high plasma temperature combined with the large volume of flowing plasma is key to achieving very efficient waste destruction and energy recovery. As an example of an immediate application, the US Army has recognized that field-feeding produces tons of packaging and food waste that must be backhauled to disposal sites at great expense. Solid waste is generated at a rate of 3-4 lbs per person per day for field exercises, short-term deployments, and steady-state base camp operations; thus a typical maneuver battalion or Force Provider complement of 550 soldiers will produce about 2000 lbs of solid waste per day.
External ion guns are used to form the IEC non-equilibrium plasma in the main fusion chamber. A continuous directed beam-flow of ions and electrons leave the fusion chamber. This IEC plasma jet is an off-shot of a fusion plasma confinement system and provides the large heat capacities needed for the Fusion Torch Process. As such it essentially operates at the Fusion Torch plasma temperature range, around 30 keV as shown in Fig.2. This is 3 orders of magnitude above arc type plasmas which run at a few eV. This enormous temperature advantage translates into the ability to completely vaporize and dissociate waste materials, increasing the production of useful syngas products for electrical energy generation or heating.
III. The Electrically-Driven IEC Plasma Jet Processor
The plasma that is feed into the jet for waste processing is generated in an IEC device. Similar IEC devices have been used for years for research and commercial neutron sources at the University of Illinois and at several other University and National laboratories. 5-10 The neutron source devices operate with deuterium gas to produce DD fusion reactions whereas the jet treatment will employ argon or similar inert gas. However, the physics of operation remains the same. This experience will directly carry over to the jet waste treatment unit. The jet extraction is not used for the neutron generator version, but the coupling occurs quite naturally by opening one of the grids to form an electrostatic-type divertor. The extraction of the plasma jet is discussed in more detail in Ref 6. Experiments using a Faraday cup type calorimeter demonstrated approximately 1kW of energy in the jet ion flow was obtained with two 2-kWe electrical input. This clearly demonstrates the efficient extraction of energy into the flowing jet and provides a basis for scaling up the design for plasma processing. The IEC device is a spherical plasma diode. It uses a ground potential on an outer sphere as the anode and a large negative potential on a transparent inner spherical grid (schematic is shown in Fig. 3, and a photo of the device is shown in Fig. 4. Ions are injected from an external source or in a discharge region between the vacuum chamber wall and the grid. 5,6 Initial experimental studies will use an existing spherical IEC chamber of ~30-cm with a 2-cm diameter ports for beam extraction. In summary, this jet plasma processor offers near term benefits and represent a step towards the ultimate goal of a p-11β fusion torch.
IV. Development of a p-11β Powered Unit
IEC is one of the few approaches to fusion that has the possibility of burning aneutronic fuels such as D- 3 He and p-11β in a reasonable size device. 3,4 If achieved, such a power source would enjoy wide availability of fuels, no greenhouse emissions, minimal radioactivity or radioactive wastes, and direct energy conversion to allow a high efficiency for conversion to electrical power, hence minimizing rejected heat.
Fig. 5. Sketch of proposed 2-kW experimental unit to demonstrate the IEC plasma jet. The jet plasma enters a chamber on the right where a waste sample has been inserted (sample show in withdrawn position in sketch). Off-gases produced exit through tubing at the top of the interaction chamber and enter a gas collection system Sludge is collected on a tray at the bottom of the interaction chamber for removal and analysis. Baffling along the jet guide to helps prevent gas backflow. Nitrogen is used for the plasma discharge.
The non-equilibrium plasma contained by the IEC provides it with an unique ability to effectively burn such fuels, and that in turn leads to charged- particle reaction products which allow use efficient of direct energy conversion technology. 4 Such a power unit has all of the features sought for future power plants needed worldwide to turn the tide of the growing energy crisis. In addition, the light structure system employed in the IEC results in a very high power-to-weight ratio while the charged-particle energy exhaust flow proves a simple means of efficient high-speed propulsion through a magnetic nozzle. Thus the IEC p-11β power plant appears extremely attractive for both terrestrial and space power uses.
Present IEC experiments are designed to burn deuterium fuel to produce neutrons for use in commercial neutron activation analysis applications. Such devices routinely produce about 108 reactions/sec. 11 They use a small spherical vacuum chamber containing an IEC grid held at high voltage (- 80 kV) backfilled with deuterium gas at a few milli-torr pressure. This grid serves to form a plasma discharge and also extracts ions from the plasma formed. These ions are accelerated towards the center of the chamber where they react. For aneutronic fusion, the voltage must be roughly doubled, the ion current increased, the grid removed, and neutral gas eliminated from the vacuum chamber by reducing the background pressure. The fundamental physics involved is to direct incoming ion beams in a way that they form a virtual anode which is surrounded by a virtual cathode formed by electrons. The significance of this "onion skin" type potential structure for fusion was first recognized by Philo Farnsworth (famous inventor of electronic TV in the US). 12, 13 It becomes fundamental to successful operation of the IEC.
The key to developing a power producing version of this device is to use external ion guns to form and inject ions into the spherical IEC chamber. This eliminates the need for a grid and allows differential pumping between the guns and the main chamber so that the high vacuum needed in the chamber itself can be achieved. The authors have been studying such a system, both theoretically and experimentally. Theoretical studies confirm that, if correctly designed, such IEC plasma can exist stably and has sufficient confinement time for aneutronic fusion. This assumes, however, very precise control is maintained over the energy and angular momentum of injected ions and a balanced supply of electrons is provided. A RF ion injector capable of such operation and has also developed corresponding electron feed techniques. A graded index field is used to increase the ionization efficiency. A key component is the magnetic focusing lens at the extraction port. This allows very efficient differential pumping between the high pressure in chamber and the low pressure IEC chamber.
The RF ion injector is shown attached to an IEC chamber in Fig. 6, These studies did not yet include differential pumping so that number of recirculating passes by an ion was low, roughly 2. The injected ion current, I, was about 50 mA. Still, based on measurements of neutrons using deuterium fuel, the Q (fusion energy gain/energy in) was respectable for such a small device, order of 10-6 . Based on these encouraging results, we now plan to build a new device that will employ six high current injection guns.
The Q scaling for such a device goes as Œ�I/a 2 where a is the radius of the dense core, I is the ion current and Œ� is the number of ion recirculations. This scaling law comes from simulation results described in Ref. 14, but has been found to agree reasonably well to date with bench scale experiments. With the 6 gun design planned, we expect to increase Œ� to ~200, I to 600mA, and reduce a by 10 compared to existing unit of Fig 6. This predicts an increase in Q (compared to prior gun experiment) of ~105 , giving approximately Q = 0.1 (Q=1 is "breakeven"). Such an experiment would provide a proof-of principle for this ion injected IEC concept and provide the physics basis for use of it for p-11β fusion. Note that core density and electron temperatures are the main issues for the IEC since, unlike the typical magnetic confinement device like ITER, the IEC ion energy (effective temperature) is set by the operating voltage. Thus applying ~150 kV is desirable for burning p-11β. This temperature has already been achieved in several IEC experiments as pointed out earlier. This ability to run IECs at such high ion energies is key for making p-11β accessible. If Q = 0.1 is obtained in the six gun experiment as anticipated, this small device would already be at the same levels as recent large Tokomaks such as JET in the UK. Thus, this proof-of-principle experiment would unequivocally establish the physics of the injected p-11β IEC concept. The next step demonstration power unit would include more injection guns to obtain Q >1 with p-11β.
The challenge that lies ahead is to solve the technological issues and integrate the components. The hope is that fusion power will be seen as a unique primary energy source with many technological options. It took the railroads years to recognize that they were in the transportation business and not just the railroad business. Our society should recognize the full potential of fusion power, and the fusion community ought to better appreciate that fusion power does not just represent an electrical source, but has great potential for addressing the ecological issues now facing the world. The p-11β Fusion Torch concept, with its near term applications, can morph over time into an integrated fusion power economy. This process could provide an opportunity to build a significant corporation that initially generates income from CO2 and municipal waste recycling; and evolves into a producer of electricity and transportation fuel, while closing the materials' cycle. The need now is to focus a large number of creative minds on the technological potentials of the p-11β Fusion Torch and to evaluate the possibilities and the most appropriate R&D directions to pursue. As discussed here, the combination of non- Maxwellian IEC fusion to achieve p-11β fusion plus the pathway through near-term electrically driven waste processors provides a road map for development.
Portions of this paper are from a draft by William C. Gough and Bernard (Ben) J. Eastlund, September 25, 2007. Ben, a leading proponent of the fusion torch since he shared in its conception in 1968, is now deceased. This paper is dedicated to him.
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