- Email: [email protected]
The IEC star-mode fusion neutron source for NAA — status and next-step designs
Applied Radiation and Isotopes 53 (2000) 779±783
www.elsevier.com/locate/apradiso
The IEC star-mode fusion neutron source for NAA Ð status and next-step designs George H. Miley a,*, J. Sved b a
Fusion Studies Laboratory, University of Illinois, Urbana-Champaign Campus, 103 S. Goodwin Avenue, Urbana, IL 61801, USA b DaimlerChrysler Aerospace Ð Space Intrastructure, Bremen, Germany
Abstract Based on research at the University of Illinois, a commercial neutron source has been developed by Daimler Chrysler Aerospace using a small grided-type Inertial Electrostatic Con®nement (IEC) plasma device (Miley and Sved, 1997) This device employs a unique ``Star-Mode'' deuterium plasma discharge to create ion-beam driven fusion reactions in a plasma target (Miley et al., 1997a, 1997b, 1997c; Miley, 1999). As such, it represents the ®rst commercial application of a con®ned fusing plasma. The Star-Mode discharge is an essential feature of this device since it minimizes ion-grid collisions and also allows tight beam focussing. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Neutron generator; Plasma target; IEC fusion
1. Introdution As dependable high gain (i.e., high Q-value = fusion energy out/energy in) fusion devices evolve, a wide variety of possible applications should progressively emerge (Abdou et al., 1996). These include neutron sources for fusion materials testing for tritium production (Stacey et al., 1997), and for both nuclear and chemical/biological waste management (Gough and Eastland, 1991). However, acceptance of this new technology in industrial applications has to be achieved ®rst with IEC devices of low-Q as low-level neutron sources for neutron activation analysis (NAA) (Miley et al., 1997a, 1997b; Kulcinski et al., 1997). To be
* Corresponding author. Tel.: +1-217-333-3772; fax: +1217-333-2906. E-mail addresses: [email protected] (G.H. Miley), [email protected] (J. Sved).
competitive with established neutron generators and neutron source radioisotopes, the unique selling features of the IEC devices have to be exploited. Since the IEC device has no solid target, aging eects, such as target sputter erosion and consequent metal ®lm deposition are greatly mitigated. The target is the central zone, where most fusion collisions occur. Fig. 1 shows a video frame picture of the electrode and fusion zone, at the intersection of the ion beams. The target is continuously renewed by the available gas supply. The low parts count and rugged durability of the industrial grade IEC device enable a cost which is competitive, in terms of life cycle cost, which Californium 252 neutron sources.
2. The IEC Ð basic concepts The basic IEC concept traces back to Philo Farns-
0969-8043/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 0 0 ) 0 0 2 1 5 - 3
780
G.H. Miley, J. Sved / Applied Radiation and Isotopes 53 (2000) 779±783
Fig. 1. FusionStar IEC Star Mode ion beams intersect at the centroid of the electrode.
worth, the inventor of electronic television, but the neutron source versions are a modi®cation based on University of Illinois research where ion guns are replaced with a grid-produced plasma discharge, operating in the unique ``Star-Mode'' (Miley et al., 1997a). Both spherical and cylindrical versions have been developed. In the spherical design, illustrated in Fig. 2,
Fig. 2. Cross section of the spherical IEC device.
the transparent grid biased at ÿ60 kV acts as a cathode relative to the grounded vacuum vessel wall. When deuterium is used, ions produced in the discharge are extracted from the plasma by the cathode grid, accelerated, and focused at the center where reactions occur. The grid provides recirculation of the ions, increasing the power eciency. At high currents, a potential structure develops in the non-neutral plasma, creating virtual electrodes that further enhance ion containment and recirculation (Miley et al., 1997a, 1997c) (see Fig. 3). So far steady-state experimental IEC versions produce almost 107 DD n/s, while advanced pulsed versions extend to 1011 n/s (this would be 1013 n/s for DT 14 MeV neutrons). The DaimlerChrysler commercial FusionStar IEC-PS1 has being upgraded, prior to ®rst shipments, to produce almost 1 107 DD n/s with a dramatic reduction of key component temperatures. Further near term enhancements are aimed at 5 107 DD n/s in continuous mode (Please refer to www.fusionstar.com for actual performance speci®cations.) The unique feature of the IEC is that it develops a ``fusion-grade'' plasma in a small volume (few cm3), while avoiding bulky magnets, injectors, etc. In addition, the star mode (Miley et al., 1997a) creates ion beams that reduce grid bombardment, which combined with use of a ``damage free'' plasma target (the dense core of Fig. 3) provides long lifetime units. Thus, the IEC provides a ``®rst step'' in what will hopefully be a progression of uses for fusion-grade plasmas prior to actual fusion power plants. The cylindrical version uses a hollow electrode de-
Fig. 3. Illustration of the spherical potential structure in the dense plasma core of an IEC. The central ``well'' traps ions, providing ecient local recirculation.
G.H. Miley, J. Sved / Applied Radiation and Isotopes 53 (2000) 779±783
sign where ions recirculate between two outer anodes producing a ``line-like'' neutron source within the hollow cathode region. Neutron yields from the cylindrical design are comparable with those from the spherical IEC, but the lack of virtual electrode formation limits its ultimate fusion rate. This unit may be most useful for applications requiring broad area extended sources, e.g., luggage inspection, and NAA of materials, such as ores, on a conveyer belt. If the IEC line source can be manufactured at a cost that is less than two or three point sources, this unique type of neutron source may ®nd customers who manufacture on-line NAA systems. 3. Development strategy The present commercial version of the IEC oers a competitive low-level portable neutron source for industrial NAA. However, it appears possible to extend IEC to a variety of added applications (Stacey et al., 1997; Gough and Eastland, 1991). This future development can follow two paths. One path involves the development of higher yield (``intense'') neutron sources for application, such as neutron tomography, medical and industrial isotope production, medical applications, such as boron neutron capture therapy (BNCT), and studies of neutron damage of materials and advanced medical applications. The other path involves development of units for non-neutron applications, such as a variable spectrum soft X-ray source (electron injected spherical device); Fullerene production (species separation in a recombining methanehelium plasma); jet heating for rocket thrust (spherical device jet mode) plasma processing, cutting, and welding surface implantation. To follow one or more of these paths, however, requires additional research and development (R&D) devoted to speci®c issues related to each application. In the following section, we will brie¯y outline some key issues related to such developments. 4. High intensity fusion neutron sources The need for a high-intensity fusion neutron source is widely recognized. The IEC device, if extended to high neutron intensities, might also compete in these areas, but would represent remarkably a dierent type of facility, being considerably smaller. The IEC plasma scales in velocity space rather than in terms of plasma surface to volume ratio. Consequently, the IEC size is principally set by voltage breakdown and heat removal considerations (Chacon and Miley, 1998). Another distinctive advantage of a device like the IEC is that, due to its small size, hence modest unit
781
cost, the required steps for experimental scale-up could be done relatively quickly. The key scale-up issue, however, involves uncertainties in the physics, including the ability to maintain required electrostatic potential structures in the central fusion volume and ®nding ways to control or avoid ion beam instabilities. These issues have received some theoretical study, but benchmark experiments are essential to evaluate how large of a neutron yield can ultimately be obtained. Potential applications would expand at each step as the neutron yield (and Q-value) is increased. In the eort at the University of Illinois, pulsed power techniques are under development in order to take advantage of the favorable scaling with ion current (Miley et al., 1997d). In addition, a technique (RIDO) to create bunching of the ions through re-circulation and acceleration is under development (Jurczyk et al., 1997). As improvements of performance become demonstrated, the FusionStar business unit will implement an engineering project to incorporate this know-how into a reliable and aordable product. Development of an intense IEC source would compliment, not replace, other souces such as the accelerator Ð Li target device. The IEC would lend itself to construction of small neutron units, placed in various laboratories desiring them for specialized research. The volumetric source would provide a large central facility capable of incorporating full-sized components for testing. It would also be a step toward other largescale applications, such as tritium production and waste treatment. The smaller IEC facilities would provide multiple groups with the capability of supporting research on basic aspects of neutron damage in materials. It would accommodate miniature samples and could also lead to other applications, such as neutron tomography, special isotope production, etc. A variant would use energetic protons produced in D±3He fueled IEC reactors for applications, such as in PET scans and proton therapy. Since the D±3He and D±D cross sections are comparable in the current 60± 100 kV operating range, IEC operation with D±3He is a relatively straightforward variant of neutron source devices.
5. Non-neutron applications The IEC readily lends to non-fusion plasma applications as part of its' ``spin-o'' developments. The variable spectrum X-ray source (Gu and Miley, 1995) and jet operation (Miley et al., 1997d) denoted earlier are two examples. While this seems to deviate from the earlier focus on fusing plasmas, the point is that in both cases later generation units might well use a fusion plasma as the energy supply. For example, the
782
G.H. Miley, J. Sved / Applied Radiation and Isotopes 53 (2000) 779±783
electrically-driven jet mode for welding, etc., may eventually lead to a fusion powered jet rocket. The variable spectrum X-ray source involves modi®cation of the IEC to incorporate electron emitters, auxiliary guide grids, and reverse polarity operation (Gu and Miley, 1995). While operation in such a mode has been demonstrated in preliminary tests, extensive work needs to be done to optimize the design and operation of parameters. Likewise, key features of the jet mode have been tested, but issues related to optimization of eciency and lifetime require further intensive R&D (Miley et al., 1997d). One of the important potential applications for the jet mode of operation would be the ultimate development of a high speci®c impulse fusion propulsion system for advanced space missions (Miley et al., 1998).
6. FusionStar The President of DaimlerChrysler Aerospace Ð Space Infrastructure, requested a trademark name for the business in 1998. The name selection was immediate since the operations of the IEC device can produce a rather beautiful star like plasma. The name also promotes a practical utilization of nuclear fusion and branding of a long-term space utilization scenario (Sved et al., 1995). The development of the products and test facility began in late 1996 at the DASA Center Trauen (Sved, 1997). A former rocket engine test facility was renovated and serves for the extensive development test
program. A life test cell has also been constructed and is shown in the composite view in Fig. 4. The IEC reactor chamber has been developed into a sealed system. The deuterium gas is stored in a getter pump reservoir. The temperature of the getter material is raised to produce the partial pressure required for operation of the device. When the heat-up phase is completed the high voltage is applied and a glow discharge creates the ions. The electrostatic ®eld directs the ions into the start beam trajectories. The characteristics of the chamber and electrode have been developed to a stage where start-up immediately yields a neutron ¯ux that is approximately 70% of the maximum obtainable. This characteristic is important for applications where the neutron ¯ux is required for short periods. The standby mode keeps the gas pressure ready for switch on of the high voltage. Variation of the current gives eective control of the neutron output. The IEC reactor chamber is air cooled. A blower unit forces the air to enter the chamber cowling at the rear. The warmed air exits at the hemispherical front end shown lower left in Fig. 4. The High Voltage (HV) power supply (PS) is an air insulated type. Thus, there are no potentially hazardous coolants or insulation ¯uids in the system. The HV PS was developed for FusionStar by a leading USA manufacturer of very high voltage power supplies. In addition to protection features, the HV PS can be used in most countries without the need for a heavy three-phase transform to provide USA voltage. The ability to tolerate a wide range of input voltage also provides stability in situations where the power
Fig. 4. Views of the FusionStar IEC-PS neutron generator set and life test cell.
G.H. Miley, J. Sved / Applied Radiation and Isotopes 53 (2000) 779±783
supply is somewhat erratic; as seen with diesel generator sets at mines. The automated control is implemented in an industrial computer seen in the inset picture at center right in Fig. 4. The software is being developed to provide user friendly control interface via an operator panel shown in the central inset picture of Fig. 4. Remote interface capability will be provided for integration of the FusionStar neutron generator into NAA systems. The neutron generator set is portable enough to be packed in a large car or small van. In ®xed installations safety regulations mandate appropriate interlocks and security monitoring facilities. These interface facilities are provided. The life test cell has been set up to demonstrate the typical installation solution. The much awaited beginning of a life test run was achieved during February 2000. The hurdles of development of a completely new product have been overcome. The industrial development phase was also a period of new basic research by the University of Illinois, Fusion Studies Laboratory. A recent spurt of new hardware development by FusionStar saw the attainment of both higher neutron output and lower operating temperature of critical components. The repeatability and steady neutron rate have also been demonstrated. These factors enhance the commercial economics of the very new type of neutron generator. 7. Conclusion In view of the long-term nature of fusion power research, the continued spin-o of ``fusion-grade'' technology, such as the IEC neutron generator at each development stage will accelerate development. The development of such technology must rely on identi®cation of both market ``niches'' and use of fusion concepts that can meet the market competition in terms of costs, reliability, and environmental compatibility. The teaming of DaimlerChrysler Aerospace FusionStar with the Univerity of Illinois FusionStudies Laboratory holds the potential for some exciting new industrial radiation products. Acknowledgements Important contributions by the IEC group members Yibin Gu, Robert Stubbers, Brian Jurczyk, John DeMora, Blair Bromley, and Mike Williams at the
783
University of Illinois are gratefully acknowledged. This work was partially supported under contracts with DaimlerChrysler Aerospace.
References Abdou, M.A., et al., 1996. Results of an international study on a high-volume plasma-based neutron source for fusion blanket development. Fusion Technology 29, 1±57. Chacon, L, Miley, G., 1998. Inertial electrostatic con®nement 3 He breeder for D±3He satellite systems. Fusion Technology 33 (3), 182±209. Gough, W., Eastland, B., 1991. Near term recycling option using fusion grade plasmas, IECNES 91. Trans. of Fusion Technology 20 (Part 2). Gu, Y., Miley, G.H., 1995. Spherical IEC device as a tunable X-ray source. Bulletin APS 11, 185. Jurczyk, B., Gu, Y., Miley, G., 1997. IEC resonant ion driven oscillation (RIDO) concept, poster session. In: Proc. 39th Annual Meeting Division of Plasma Physics, Pittsburgh, PA, 42,10, 1818. Kulcinski, G.L., et al., 1997. Overview of neutron/proton source applications from IEC fusion devices. Trans. of the ANS 77, 507. Miley, G.H., Sved, J., 1997. The IEC: a plasma-target-based neutron source. Applied Radiation and Isotopes 48, 1557± 1561. Miley, G.H., et al., 1997a. Discharge characteristics of the spherical inertial electrostatic con®nement (IEC) device. IEEE Trans. Plasma Science 25 (4), 733±739. Miley, G., et al., 1997b. Research in IEC: a plasma-targetbased neutron source. Trans. of the ANS 77, 505±506. Miley, G.H., Gu, Y., Ohnishi, M., Yamamoto, Y., Hasegawa, M., Yoshikawa, K., 1997c. Potential well structure and scaling studies for the IEC. In: International Sherwood Fusion Theory Conference, Madison, WI, April, 23±26. Miley, G.H, Bromley, B., Jurczyk, B., Gu, Y., 1997d. Progress in IEC research for near-term thrusters and future fusion propulsion. In: NASA JPL Space Propulsion Research Workshop, Pasadena, CA, May, 20±22. Miley, G., et al., 1998. Scaling of the inertial electrostatic con®nement (IEC) for near-term thrusters and future fusion propulsion. In: Proc. 15th Symposium on Space Nuclear Power and Propulsion (STAIF98), January, Part 3, Albuquerque, NM, 1373±1375. Miley, G.H., 1999. Nuclear Instr. and Methods in Physics Research A 422, 16±20. Stacey, W.M., et al., 1997. A tokamak tritium production reactor. Fusion Technology 32, 563±589. Sved, J., Kulcinski, G.L., Miley, G.H., 1995. A commercial Lunar Helium 3 fusion power infrastructure. Journal of the British Interplanetary Society 48, 55±61. Sved, J., 1997. The commercial IEC portable neutron source. Trans. of the ANS 77, 504.
www.elsevier.com/locate/apradiso
The IEC star-mode fusion neutron source for NAA Ð status and next-step designs George H. Miley a,*, J. Sved b a
Fusion Studies Laboratory, University of Illinois, Urbana-Champaign Campus, 103 S. Goodwin Avenue, Urbana, IL 61801, USA b DaimlerChrysler Aerospace Ð Space Intrastructure, Bremen, Germany
Abstract Based on research at the University of Illinois, a commercial neutron source has been developed by Daimler Chrysler Aerospace using a small grided-type Inertial Electrostatic Con®nement (IEC) plasma device (Miley and Sved, 1997) This device employs a unique ``Star-Mode'' deuterium plasma discharge to create ion-beam driven fusion reactions in a plasma target (Miley et al., 1997a, 1997b, 1997c; Miley, 1999). As such, it represents the ®rst commercial application of a con®ned fusing plasma. The Star-Mode discharge is an essential feature of this device since it minimizes ion-grid collisions and also allows tight beam focussing. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Neutron generator; Plasma target; IEC fusion
1. Introdution As dependable high gain (i.e., high Q-value = fusion energy out/energy in) fusion devices evolve, a wide variety of possible applications should progressively emerge (Abdou et al., 1996). These include neutron sources for fusion materials testing for tritium production (Stacey et al., 1997), and for both nuclear and chemical/biological waste management (Gough and Eastland, 1991). However, acceptance of this new technology in industrial applications has to be achieved ®rst with IEC devices of low-Q as low-level neutron sources for neutron activation analysis (NAA) (Miley et al., 1997a, 1997b; Kulcinski et al., 1997). To be
* Corresponding author. Tel.: +1-217-333-3772; fax: +1217-333-2906. E-mail addresses: [email protected] (G.H. Miley), [email protected] (J. Sved).
competitive with established neutron generators and neutron source radioisotopes, the unique selling features of the IEC devices have to be exploited. Since the IEC device has no solid target, aging eects, such as target sputter erosion and consequent metal ®lm deposition are greatly mitigated. The target is the central zone, where most fusion collisions occur. Fig. 1 shows a video frame picture of the electrode and fusion zone, at the intersection of the ion beams. The target is continuously renewed by the available gas supply. The low parts count and rugged durability of the industrial grade IEC device enable a cost which is competitive, in terms of life cycle cost, which Californium 252 neutron sources.
2. The IEC Ð basic concepts The basic IEC concept traces back to Philo Farns-
0969-8043/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 0 0 ) 0 0 2 1 5 - 3
780
G.H. Miley, J. Sved / Applied Radiation and Isotopes 53 (2000) 779±783
Fig. 1. FusionStar IEC Star Mode ion beams intersect at the centroid of the electrode.
worth, the inventor of electronic television, but the neutron source versions are a modi®cation based on University of Illinois research where ion guns are replaced with a grid-produced plasma discharge, operating in the unique ``Star-Mode'' (Miley et al., 1997a). Both spherical and cylindrical versions have been developed. In the spherical design, illustrated in Fig. 2,
Fig. 2. Cross section of the spherical IEC device.
the transparent grid biased at ÿ60 kV acts as a cathode relative to the grounded vacuum vessel wall. When deuterium is used, ions produced in the discharge are extracted from the plasma by the cathode grid, accelerated, and focused at the center where reactions occur. The grid provides recirculation of the ions, increasing the power eciency. At high currents, a potential structure develops in the non-neutral plasma, creating virtual electrodes that further enhance ion containment and recirculation (Miley et al., 1997a, 1997c) (see Fig. 3). So far steady-state experimental IEC versions produce almost 107 DD n/s, while advanced pulsed versions extend to 1011 n/s (this would be 1013 n/s for DT 14 MeV neutrons). The DaimlerChrysler commercial FusionStar IEC-PS1 has being upgraded, prior to ®rst shipments, to produce almost 1 107 DD n/s with a dramatic reduction of key component temperatures. Further near term enhancements are aimed at 5 107 DD n/s in continuous mode (Please refer to www.fusionstar.com for actual performance speci®cations.) The unique feature of the IEC is that it develops a ``fusion-grade'' plasma in a small volume (few cm3), while avoiding bulky magnets, injectors, etc. In addition, the star mode (Miley et al., 1997a) creates ion beams that reduce grid bombardment, which combined with use of a ``damage free'' plasma target (the dense core of Fig. 3) provides long lifetime units. Thus, the IEC provides a ``®rst step'' in what will hopefully be a progression of uses for fusion-grade plasmas prior to actual fusion power plants. The cylindrical version uses a hollow electrode de-
Fig. 3. Illustration of the spherical potential structure in the dense plasma core of an IEC. The central ``well'' traps ions, providing ecient local recirculation.
G.H. Miley, J. Sved / Applied Radiation and Isotopes 53 (2000) 779±783
sign where ions recirculate between two outer anodes producing a ``line-like'' neutron source within the hollow cathode region. Neutron yields from the cylindrical design are comparable with those from the spherical IEC, but the lack of virtual electrode formation limits its ultimate fusion rate. This unit may be most useful for applications requiring broad area extended sources, e.g., luggage inspection, and NAA of materials, such as ores, on a conveyer belt. If the IEC line source can be manufactured at a cost that is less than two or three point sources, this unique type of neutron source may ®nd customers who manufacture on-line NAA systems. 3. Development strategy The present commercial version of the IEC oers a competitive low-level portable neutron source for industrial NAA. However, it appears possible to extend IEC to a variety of added applications (Stacey et al., 1997; Gough and Eastland, 1991). This future development can follow two paths. One path involves the development of higher yield (``intense'') neutron sources for application, such as neutron tomography, medical and industrial isotope production, medical applications, such as boron neutron capture therapy (BNCT), and studies of neutron damage of materials and advanced medical applications. The other path involves development of units for non-neutron applications, such as a variable spectrum soft X-ray source (electron injected spherical device); Fullerene production (species separation in a recombining methanehelium plasma); jet heating for rocket thrust (spherical device jet mode) plasma processing, cutting, and welding surface implantation. To follow one or more of these paths, however, requires additional research and development (R&D) devoted to speci®c issues related to each application. In the following section, we will brie¯y outline some key issues related to such developments. 4. High intensity fusion neutron sources The need for a high-intensity fusion neutron source is widely recognized. The IEC device, if extended to high neutron intensities, might also compete in these areas, but would represent remarkably a dierent type of facility, being considerably smaller. The IEC plasma scales in velocity space rather than in terms of plasma surface to volume ratio. Consequently, the IEC size is principally set by voltage breakdown and heat removal considerations (Chacon and Miley, 1998). Another distinctive advantage of a device like the IEC is that, due to its small size, hence modest unit
781
cost, the required steps for experimental scale-up could be done relatively quickly. The key scale-up issue, however, involves uncertainties in the physics, including the ability to maintain required electrostatic potential structures in the central fusion volume and ®nding ways to control or avoid ion beam instabilities. These issues have received some theoretical study, but benchmark experiments are essential to evaluate how large of a neutron yield can ultimately be obtained. Potential applications would expand at each step as the neutron yield (and Q-value) is increased. In the eort at the University of Illinois, pulsed power techniques are under development in order to take advantage of the favorable scaling with ion current (Miley et al., 1997d). In addition, a technique (RIDO) to create bunching of the ions through re-circulation and acceleration is under development (Jurczyk et al., 1997). As improvements of performance become demonstrated, the FusionStar business unit will implement an engineering project to incorporate this know-how into a reliable and aordable product. Development of an intense IEC source would compliment, not replace, other souces such as the accelerator Ð Li target device. The IEC would lend itself to construction of small neutron units, placed in various laboratories desiring them for specialized research. The volumetric source would provide a large central facility capable of incorporating full-sized components for testing. It would also be a step toward other largescale applications, such as tritium production and waste treatment. The smaller IEC facilities would provide multiple groups with the capability of supporting research on basic aspects of neutron damage in materials. It would accommodate miniature samples and could also lead to other applications, such as neutron tomography, special isotope production, etc. A variant would use energetic protons produced in D±3He fueled IEC reactors for applications, such as in PET scans and proton therapy. Since the D±3He and D±D cross sections are comparable in the current 60± 100 kV operating range, IEC operation with D±3He is a relatively straightforward variant of neutron source devices.
5. Non-neutron applications The IEC readily lends to non-fusion plasma applications as part of its' ``spin-o'' developments. The variable spectrum X-ray source (Gu and Miley, 1995) and jet operation (Miley et al., 1997d) denoted earlier are two examples. While this seems to deviate from the earlier focus on fusing plasmas, the point is that in both cases later generation units might well use a fusion plasma as the energy supply. For example, the
782
G.H. Miley, J. Sved / Applied Radiation and Isotopes 53 (2000) 779±783
electrically-driven jet mode for welding, etc., may eventually lead to a fusion powered jet rocket. The variable spectrum X-ray source involves modi®cation of the IEC to incorporate electron emitters, auxiliary guide grids, and reverse polarity operation (Gu and Miley, 1995). While operation in such a mode has been demonstrated in preliminary tests, extensive work needs to be done to optimize the design and operation of parameters. Likewise, key features of the jet mode have been tested, but issues related to optimization of eciency and lifetime require further intensive R&D (Miley et al., 1997d). One of the important potential applications for the jet mode of operation would be the ultimate development of a high speci®c impulse fusion propulsion system for advanced space missions (Miley et al., 1998).
6. FusionStar The President of DaimlerChrysler Aerospace Ð Space Infrastructure, requested a trademark name for the business in 1998. The name selection was immediate since the operations of the IEC device can produce a rather beautiful star like plasma. The name also promotes a practical utilization of nuclear fusion and branding of a long-term space utilization scenario (Sved et al., 1995). The development of the products and test facility began in late 1996 at the DASA Center Trauen (Sved, 1997). A former rocket engine test facility was renovated and serves for the extensive development test
program. A life test cell has also been constructed and is shown in the composite view in Fig. 4. The IEC reactor chamber has been developed into a sealed system. The deuterium gas is stored in a getter pump reservoir. The temperature of the getter material is raised to produce the partial pressure required for operation of the device. When the heat-up phase is completed the high voltage is applied and a glow discharge creates the ions. The electrostatic ®eld directs the ions into the start beam trajectories. The characteristics of the chamber and electrode have been developed to a stage where start-up immediately yields a neutron ¯ux that is approximately 70% of the maximum obtainable. This characteristic is important for applications where the neutron ¯ux is required for short periods. The standby mode keeps the gas pressure ready for switch on of the high voltage. Variation of the current gives eective control of the neutron output. The IEC reactor chamber is air cooled. A blower unit forces the air to enter the chamber cowling at the rear. The warmed air exits at the hemispherical front end shown lower left in Fig. 4. The High Voltage (HV) power supply (PS) is an air insulated type. Thus, there are no potentially hazardous coolants or insulation ¯uids in the system. The HV PS was developed for FusionStar by a leading USA manufacturer of very high voltage power supplies. In addition to protection features, the HV PS can be used in most countries without the need for a heavy three-phase transform to provide USA voltage. The ability to tolerate a wide range of input voltage also provides stability in situations where the power
Fig. 4. Views of the FusionStar IEC-PS neutron generator set and life test cell.
G.H. Miley, J. Sved / Applied Radiation and Isotopes 53 (2000) 779±783
supply is somewhat erratic; as seen with diesel generator sets at mines. The automated control is implemented in an industrial computer seen in the inset picture at center right in Fig. 4. The software is being developed to provide user friendly control interface via an operator panel shown in the central inset picture of Fig. 4. Remote interface capability will be provided for integration of the FusionStar neutron generator into NAA systems. The neutron generator set is portable enough to be packed in a large car or small van. In ®xed installations safety regulations mandate appropriate interlocks and security monitoring facilities. These interface facilities are provided. The life test cell has been set up to demonstrate the typical installation solution. The much awaited beginning of a life test run was achieved during February 2000. The hurdles of development of a completely new product have been overcome. The industrial development phase was also a period of new basic research by the University of Illinois, Fusion Studies Laboratory. A recent spurt of new hardware development by FusionStar saw the attainment of both higher neutron output and lower operating temperature of critical components. The repeatability and steady neutron rate have also been demonstrated. These factors enhance the commercial economics of the very new type of neutron generator. 7. Conclusion In view of the long-term nature of fusion power research, the continued spin-o of ``fusion-grade'' technology, such as the IEC neutron generator at each development stage will accelerate development. The development of such technology must rely on identi®cation of both market ``niches'' and use of fusion concepts that can meet the market competition in terms of costs, reliability, and environmental compatibility. The teaming of DaimlerChrysler Aerospace FusionStar with the Univerity of Illinois FusionStudies Laboratory holds the potential for some exciting new industrial radiation products. Acknowledgements Important contributions by the IEC group members Yibin Gu, Robert Stubbers, Brian Jurczyk, John DeMora, Blair Bromley, and Mike Williams at the
783
University of Illinois are gratefully acknowledged. This work was partially supported under contracts with DaimlerChrysler Aerospace.
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