AAWSAP DIRD, Inertial Electrostatic Confinement Fusion, March 2010

UNCLASSIFIED//FOR OFFICIAL USE ONLY The basic principle of this detection method, shown in Figure 2.5, is common to most NAA but is now specialized for detecting the basic elements in the land mines. Key design considerations are the source strength required, the neutron energy desired (i.e. D-D vs D-T fusion) and the type and location of neutron and x-ray detectors (from Reference 2.7). UNCLASSIFIED//FOR OFFICIAL USE ONLY How to Detect Landmine Neutron yield of ~10^8 is required neutron source γ-ray detector neutron detector Atomic ratio of TNT explosive H | C | N | O 3 | 7 | 3 | 6 captured γ-ray neutron ray back scattered neutron Atomic ratio of explosives fixed thermal neutron > neutron-captured γ ray (kind of LM) H(n,γ) • • • 2.22 MeV γ ray emission N(n, γ) • • • 10.83 MeV γ ray emission landmine (explosive) > back-scattered neutron (existence of LM) H(n, n') • • • H scatter neutron Inst. of Advanced Energy, Kyoto Univ. Figure 2.5. Scheme for Landmine Detection Using a Hybrid Magnetron Type IEC Neutron Source (From Reference 2.7) The IEC developed for this work used a magnetron ion generation technique to improve the neutron production efficiency (Reference 2.6). A built-in magnetron discharge ion source was installed in the IEC. With the magnetron discharge, ions are produced in the vicinity of the vacuum chamber (anode) at negative electric potential. Therefore, the ions produced are expected to have nearly full energy corresponding to the applied voltage to the IEC cathode but slightly smaller energy than the anode potential. This prevents them from hitting the anode of the opposite side improving both fusion reaction rate and ion recirculation life. (Note that thiis approach is yet another way to address the problem of preventing ions created externally from escaping after entering the potential well. The technique here is to use the internal source to create the ions at a potential level less than the height of the potential! well). In addition to an internal source, the magnetron can produce ample ion current to maintain the discharge under low-pressure conditions. Ions generated in the ion source are attracted by the IEC central cathode because of its high negative electric potential. Therefore, the Kyoto investigators expected that a higher applied voltage would increase the extraction current, giving a higher IEC cathode current. However, it was 18 UNCLASSIFIED//FOR OFFICIAL USE ONLY

UNCLASSIFIED//FOR OFFICIAL USE ONLY found that there is an optimum voltage in terms of a maximum IEC cathode current. Ions supplied by the magnetron ion source are essential to maintain the hybrid (glow and magnetron) discharge under low gas pressure conditions. The reason for this voltage limit is not clear. Unfortunately this effect limits the cathode voltage despite the need for high voltage for neutron production near the peak energy of the fusion cross section. Thus this issue deserves more study to optimize use of a hybrid magnetron source IEC operation. Still the design worked reasonably well for the initial mine detection experiments. Unfortunately, the project was terminated prematurely due to financial constraints, so information on optimization possibility remains incomplete. The design of the ion source also depends on the ion species being injected. Sources described thus far have focused on deuterium or, in some cases on tritium. However, workers at the University of Wisconsin (U. Wisc.) have had a great interest in 3He reactions (both D-3He and 3He-3He), so have developed a gun specialized to 3He ion production (Reference 2.8). To maximize the ion current, a Helicon source was selected since Helicons are well known for production of very high density plasmas from which high ion currents can be extracted. This source is illustrated in Figure 2.6 and discussed in Reference 2.8. They state that this source has produced steady-state ion currents of 10 mA into IEC systems with background gas pressures as low as 200 µtorr. [FIGURE: Figure 2.6. 3He Ion Source for Use in 3He-3He Fusion Rate Studies at the U of Wisconsin] These developments are aimed at observation of the 3He-3He reaction in an IEC device. Scoping calculations of beam-background fusion rates predict that a 3He-3He reaction product spectrum should be distinctly observable in an IEC operating below 200 kV. 19 UNCLASSIFIED//FOR OFFICIAL USE ONLY

UNCLASSIFIED/ /FOR OFFICIAL USE ONLY This capability can provide valuable data regarding 3He fusion cross sections at "low" energies with better counting statistics than accelerator measurements. It appears that good progress has been made in this direction. CLOSING COMMENTS The experiments selected for this section are far from exhaustive. The main concentration here is on ion-injected IECs such as studied at the UIUC, although various electron injected devices such as the "Polywell" are mentioned. The experiments were selected then to explain some issues and status relative to gridded devices for near-term applications such as neutron sources and also to address some issues such as ion injection related to future fusion power units. The latter issues revolve around how to create deep potential wells in the IEC and trap the reacting ions in the well while excluding neutral gas atoms. The use of external ion sources with differential pumping then becomes a key approach for production of ions while keeping ultra low background pressure in the reacting chamber. This is the approach used at the UIUC. However, introduction of the source into the configuration such that the ions are born at potentials below the well depth is another possibility as shown by the hybrid magnetron source work in Japan. Another point noted is the advantage of using pulsed operation to obtain high peak ion currents to take advantage of the ion density squared scaling for beam-beam reactions. REFERENCES 2.1 R. L. Hirsch, "Inertial-Electrostatic Confinement of Ionized Fusion Gases," J. Appl. Physics 38, no.11, (1967) pp. 4522-4534. 2.2 A. L. Gardner, "Studies of Charged-Particle Distributions in an Electrostatic Confinement System, "U. S. Atomic Energy Commission Final Report N. C00-2180-7, Washington, D. C. (1974). 2.3 G. H. Miley, Y. Gu, J. M. DeMorea, R. A. Stubbers, T. A. Hochberg, J. H. Nadler, and R. A. Anderl, "Discharge Characteristics of the Spherical Inertial Electrostatic Confinement (IEC) Device," IEEE Transactions Plasma Science, Vol. 24, No. 4, (1997) pp, 733-739. 2.4 T.J. McGuire and R.J. Sedwick, "Improving IEC Particle Confinement Times Using Multiple Grids" 7th US-Japan IEC Workshop, Los Alamos National Laboratory, NM, March 14-16 (2005). 2.5 R.A. Anderl, J.K. Hartwell, J.H. Nadler, J.M. DeMora, R.A. Stubbers, and G.H. Miley, "Development of an IEC Neutron Source for NDE," 16th Symposium on Fusion Engineering, eds. G.H. Miley and C.M. Elliott, IEEE Conf. Proc. 95CH35852, IEEE, Piscataway, NJ, (1996) pp. 1482-1485. 2.6 Y. Gu, M. Williams, R. Stubbers, and G. Miley, "Pulsed Operation of Spherical Inertial-Electrostatic Confinement Device", Fusion Technology, Vol. 30, no. 3, (1996) pp, 1342-1346. 20 UNCLASSIFIED/ /FOR OFFICIAL USE ONLY

UNCLASSIFIED/FOR OFFICIAL USE ONLY 2.7 T. Takamatsu, T. Kyunai, S. Ogawa, K. Masuda, H. Toku, and K. Yoshikawa, "A Magnetron Discharge Ion Source for an Inertial Electrostatic Confinement Fusion Device" 7th U.S.-Japan IEC Workshop, Los Alamos National Laboratory, NM, March 14-16, (2005). 2.8 G. R. Piefer, J. F. Santarius, R. P. Ashley, G.L. Kulcinski "Progress in the Development of a 3He Ion Source for IEC Fusion", 7th U.S.-Japan IEC Workshop, Los Alamos National Laboratory,, NM, March 14-16, (2005). Section III. Other Geometries A unique feature of the IEC is the ability to vary its geometry to adapt to a number of important near term and future applications. Here we consider cylindrical IEC geometries, the IEC Jet extraction geometry, dipole assisted, and magnetically-coupled IEC unit which add flexibility for use in some power applications. Other important configurations, which are quasi-spherical, include the magnetic assisted HEPS (Polywell) configuration, the Penning trap IEC, and the POPS oscillating IEC. These concepts are discussed briefly elsewhere in this report so will not be included here. CYLINDRICAL IECS The prime alternate geometry studied for IECs is cylindrical. While originally developed at the UIUC, the configuration has spread to other labs including the University of Wisconsin, Kyoto University, and the Tokyo Institute of Technology. The objective is to obtain a dense core region extending along the axis of the cylinder. This is especially important for neutron sources since it offers a very long source that can be used for broad area coverage of large objects such as container boxes. Other conventional sources would require multiple "ganged" sources to do the same. A downside however, is the high power input required for such configurations. Thus the advantage of source length must be weighed against the alternative of moving a smaller point source over the surface of interest. It is not clear that the cylinder is useful for scaling to a power reactor. It can be viewed as a 2-D version of the spherical unit. As such, the beam convergence (compression) is limited to lower values, hence lower core denslties (an important effect for beam-beam fusion desired for power reactors, but less so for beam-background reactions used in most current neutron sources). Two types of cylindrical sources (References 3.1-3.5), shown schematically in Figure 3.1, have been studied - a gridded type which is essentially the spherical unit converted into a cylinder, and a quite different hollow cathode design. The gridded design was a natural variation of the original Farnsworth device and was first studied experimentally in the 1970s by T. Dolan at the UIUC who used laser diagnostics with a noble gas discharge to study density-temperature and species profiles. The hollow cathode design was later proposed by G. Miley as an attempt to retain the long axial reaction region but do away with grids. UNCLASSIFIED/FOR OFFICIAL USE ONLY 21

UNCLASSIFIED/ /FOR OFFl@IAL ~81: 8HLY a) b) ~ I Reflector / Figure 3.1. Two Types of Cylindrical IECs. The hollow cathode on the left (often termed the C-Device) and the 2-D gridded version on the right, often just called "the" cylindrical IEC. The hollow cathode "C-Device" of Figure 3.1 has an insulated vacuum chamber with an alternating series of hollow cylindrical cathodes and anodes spaced along a common longitudinal axis. Biased end plates serve as charged particles "reflectors". The anodes, cathodes and end plates are biased to steady state and/or pulsed voltages, depending on the operational mode. This configuration is used to initiate a plasma discharge, resulting in electrostatic confinement of fusion fuel ions in both the axial and radial directions (Reference 3.4). Present operation produces about 107 n/s (D-D) steady state while for pulsed output 109 n/s (D-D) is obtained. In "the" cylindrical version 2-D IEC (Figure 3.1), a cylindrical cathode grid is placed with its axis concentric with the axis of the surrounding vacuum vessel. This is then, in effect, a 2-D version of the spherical IEC. It operates by convergence of ions created between the grid and wall onto a small volume along the axis, hence has sometimes been called the "Radial Converging IEC (RC-IEC)". As already noted, the basic physics of this version was originally studied in pioneering work by T. Dolan in 1970. However, the concept lay dormant until revised and upgraded several decades later with improved grid designs for neutron production by UIUC workers . ELECTRICALLY- DRIVEN IEC JET THRUSTER The use of an !EC design for space propulsion was originally proposed by R.W. Bussard (Reference 3.6). (His concept was for a high thrust scram jet device. While very attractive, this concept (and Miley et al.'s "Spaceship I & II concepts discussed later) are for far-term use. Here we discuss near-term electronically driven IEC designed for space applications. In this case, electrical power would come from a solar panel. The IEC jet thruster is intended as an ultra-maneuverable space thruster for satellite and small probe thrust operations. The IEC Jet design potential offers a unique capability to cover a wide range of powers (few Watts to Kilowatts) with good efficiency while providing a plasma jet that can start with a large diameter but be narrowed directionally to focus on targets. The IEC thruster uses a spherical configuration, wherein ions are generated and accelerated towards the center of a spherical vacuum chamber. A virtual cathode forms in the high-density central core region, and combined with a locally distorted cathode grid potential field, extracts accelerated ions into an UNCLASSIFIED/ /5i0A OFFIQlal.k W&E or•tY 22 UNCLASSIFIED//FOR OFFICIAL USE ONLY

intense quasi-neutral ion jet. The configuration, low gas leakage, and good heat removal make it possible to scale the design to either low powers or high powers, covering a range of interest for present small satellites on to future medium and large satellites. In addition to maneuverable thrusting, the jet channel extraction technique enables directing and focusing the plasma stream down on an asteroid or other object for interrogation of it. Analysis of the plasma emission spectra would provide an identification of the materials and surface features of the object. With further development the IEC system potentially offers an attractive fusion power source. Another advantage of the IEC jet thruster is that it provides a step towards a future p-11B IEC power source and/or thruster for satellite operations. This possibility is also briefly discussed here. Relation to Other Prior Thrusters NASA and other laboratories have worked toward developing advanced Hall Thrusters for future satellite applications. Such thrusters, however, do not scale well to lower powers for small satellites, nor are exhaust plasma modifications possible to provide fast maneuverability. The IEC-jet thruster appears uniquely able to address both issues. Conventional plasma thrusters such as the Hall thruster have undergone much more experimental study than the IEC-jet thruster. However, the simplicity of the IEC-Jet thruster design and its thermal scalability makes it feasible to quickly develop and test, making the lack of data base less of a liability. In the jet thruster concept the plasma target at the center of the chamber, created by the intersection of the multiple ion beams, serves to deflect ions into the escaping jet plasma. The resulting virtual anode, in combination with curved potential lines created by the cathode grid diverts ions, forming a strong plasma jet. This is channeled out through an enlarged hole and guide structure in the grid (Figure 3.2). This design promises a good efficiency and thrust while providing a low weight, and due to the very open accelerator grid structure, a very long lifetime. Thus it provides a good thruster for basic satellite operations and with the added jet control/focusing also provides maneuverability. In addition the IEC jet offers two added features that increase its potential effectiveness for probing various space objects. The fact that the IEC jet can be controlled to form over multiple areas around the sphere would allow the platform to maneuver itself close to a target and then simply open a second jet offset 180 degrees from the propulsive one. The second jet would serve the integration purpose of the platform without having to expend time or additional resources such as fuel to reorient itself to direct the plume at the target. Other current systems, such as Hall thrusters, would first have to position itself close to the target, and then reorient such that the exhaust plume is properly oriented. Thus, the IEC jet thruster would not be subject to expending the resources of time and fuel that other platforms require. Another option for the IEC jet thruster is to operate as a pulsed device. This becomes especially important when considering how long it may take to disable a defensive target (the platform's impulse time to disable). The use of an intense pulsed jet could disable the target before it has time to maneuver or apply defensive layers. As discussed later, the basic IEC has been operated experimentally in a pulsed mode using a capacitive power unit. However, to date, formation of the jet has only been studied under steady-state operation. UNCLASSIFIED//FOR OFFICIAL USE ONLY 23 UNCLASSIFIED//FOR OFFICIAL USE ONLY

UNCLASSIFIED/ /FOR OFFICIAL USE ONLY An added long-term potential advantage of developing the IEC-jet thruster is that the concept can eventually be extended to an ultra high impulse fusion power/propulsion unit. Indeed, the thruster concept arose from work on a fusion based IEC (Reference 3.5). To move to fusion power, however, would require advances such as discussed for terrestrial IEC power plants as Section VI. JET Extraction From a Spherical IEC A plasma jet can be extracted from the gridded spherical IEC by enlarging a grid opening. This forms the basis for various exciting applications including a jet thruster and various plasma processing uses such as gasification of municipal wastes and future materials recycle. Here, to illustrate this asymmetrical geometry, we briefly consider the IEC jet thruster for use in satellite operations and maneuvering (Reference 3.6). Description of the IEC Jet Thruster For conventional star mode operation, such as discussed earlier, the IEC grid is designed to be highly symmetric so that the microchannel beams are also symmetric, providing good convergence. However, experiments have demonstrated that enlarging one of the grid openings distorts the potential surfaces. This results in the creation of a very intense, tightly coupled space-charge-neutralized ion jet directed outward from the central core plasma region (see Figure 3.2) (Reference 3.7), and it is this mode of operation (star with jet) that would be employed for the proposed thruster. UNCLASSIFIED/ /FOR OFFICIAL USE ONLY (figure labels: Emitters, Xenon, Electron Guide, +100V, -1kV, Insulator, Plasma Jet, Accelerating Grid, Electron Emitters) Figure 3.2. (a) Jet Operational Mode in Experimental IEC Device and (b) Jet Set-up The jet formation has been explained theoretically (Reference 3.5) in terms of the large distortion of the potential surface at the enlarged grid opening. The local gradient initiates electron flow that in turn drags ions out across the surface. The result is the formation of the intense space charge neutralized ion beam (or "plasma jet") at that location. Such operation has been routinely obtained in laboratory IEC devices under steady-state operation, with the plasma jet being maintained for hours. The power carried by the jet has been demonstrated by heating a target plate placed in its path. Over half of the energy imparted to the ions by the accelerating grid is effectively funneled into the jet, and no major losses of ions to the vacuum chamber wall or grid 24 UNCLASSIFIED/ /FOR OFFICIAL USE ONLY

are observed. For example, with the device of Figure 3.2b, the input power is about 2 kW with over 1.5 kW being carried out by the jet flow. Consequently, this configuration provides a way to efficiently convert the energy stored by accelerated ions in the symmetric microchannels into a directed beam or jet. Comparison to a Conventional "Plasma" Thruster The IEC thruster can be viewed as transforming a conventional ion thruster into a spherical form. In the IEC thruster of Figure 3.2b, ions are produced in the gas discharge region through the injection and oscillation of electrons about a guide grid that is held to a slightly positive potential. A second grid extracts ions from the discharge region and accelerates them towards the center of the device. This type of ion formation in the IEC has been studied extensively by workers at Nambe Tech, a "spin-off" company by LANL workers (Reference 3.8). In the case of a planar thruster, ions are also formed in a discharge region. However, instead of a guide grid, a magnetic field is used to contain electrons, providing a long path to maximize ionization collisions. The ion source regions are basically the same, then, for both IEC and planar ion thrusters, and the extraction/acceleration provided by the grids and the magnetic fields play equivalent roles in the respective devices. However, the IEC jet thrnster concept must extract a net thrust from the spherical! configuration. That is where the two concepts (planar vs. IEC) diverge, and the star-jet operational mode becomes essential. The micro-channel formation in the STAR mode acts to maintain and store the accelerated ions until they are diverted directionally and escape out through the plasma jet opening. The opening is biased, enabling the control of the potential gradient between the grid and the opening, hence allowing for increased control of the intensity of the plasma jet. The maintenance of STAR mode is then fundamenta I to the success of !EC jet operation. Both experimental data and particle-in-cell (PIC) code simulations show that the energetic ions can be maintained in microchannels for hundreds of passes. The jet opening allows escape into it in less than ten passes. Consequently, a majority of the ions, >95 percent, escape at full energy. Thus, the star-jet provides an amazingly good method to both store and direct the energetic ions. Overall, the IEC configuration offers distinct advantages. First, the grid structures used in the IEC thruster are much more open than those used in the conventional planar thruster designs. When combined with microchannel ion focusing, this prevents ion-grid collisions, greatly reducing grid erosion and significantly increasing the thruster lifetime. Second, transforming the device into a sphere makes the overall unit more compact per unit-ion-source volume, implying a weight reduction advantage. Third, unwanted neutral propellant gas leakage would be reduced, due to the smaller net opening required by the high-density jet, vs. a conventional planar thruster having multiple grid openings. This advantage becomes especially important for thruster applications. Assuming that the IEC thruster efficiency would be comparable to that of the planar Ion thruster design, based on these operational improvements, the !EC thruster then offers significant advantages. [Note that an alternate !EC thruster concept is described later in the section on J. Khachan's work. It too looks very promising.] UNCLASSIFIED/ /[REDACTED] 25 UNCLASSIFIED/ /[REDACTED]

UNCLASSIFIED//FOR OFFICIAL USE ONLY Jet Extraction To obtain thrust from an IEC device, a valley or trough must be created in the electrostatic potential, and a hole must be physically cut into the ground sphere. This allows high-speed ions to escape in the form of a plasma jet as described in the preceding section. Ions are generated near the ground potential with the aid of electron emitters and additional grids. A central spherical electrical grid accelerates ions to the core region. A cylindrical "channel" grid with the same electrostatic potential as the central spherical grid creates a passage through which ions can escape to the outside. Thus this trough in the electrostatic potential profile across the centerline (thrust axis) of the IEC thruster is a unique feature compared to the linear profile for a planar device. The ion beams finally exit through an opening in the ground sphere of the IEC device. The channel grid must be well insulated from the ground potential to prevent short-circuiting or arc-over; thus a separate insulated feed-through cable maintains the negative potential on the inner spherical and channel grids. Makeup propellant gas is fed into the ionization region through needle-valve-controlled tubing located around the chamber wall. Ionization of the propellant uses the electron emitter-guide grid design described earlier. The inner grid serves to both extract and accelerate ions, forming the microchannels. To control neutralization of the plasma jet, additional electron emitters are attached close to the jet discharge hole. A combination of electron emission rates and jet grid bias can be used to control the beam space charge, hence the growth of focusing of the beam during propagation. In present experiments, however, the electron rate is fixed at a suitable value while the jet grid bias is varied. Control of the jet diameter and focus is obtained in two ways: first, the channel grid will be separately hinged with a small servo motor such that its axis can be moved over a volume defined by a 10 percent cone angle; second, the grid bias can be varied over a range up to the chamber potential to provide focus control over the jet flow. A large negative grid bias will cause a narrow focus while small potential values will allow the plasma to expand giving a broad cross section beam. Experimental Jet Design and Performance Figure 3.3 shows the thruster experiment components. It is also of interest to consider the typical dimensions involved to illustrate the compactness of the unit. The experimental studies use an existing spherical IEC chamber of ~30-cm with a 1-cm diameter port on one side of it for beam extraction. (This is somewhat larger than envisioned for application to micro-satellites). An 8-cm diameter spherical electrical tungsten or tantalum wire grid, having a geometric transparency of ~90 percent, will mount inside the chamber. A ~1-cm diameter hole will be cut into the side of the wire grid, and this hole will be aligned with the hole in the chamber wall and connected to it by a 2-cm diameter cylindrical guide grid. The insulator covering the grounded wall must be of sufficient size to prevent arc-over from the ground to the cylindrical grid. The inner electrical grids are connected to a 500-kV dc power supply through the insulated feed-through cable. A positively-charged outer grid with a variable voltage of ~10-100 V is mounted on a swivel connector at the outside of the beam extraction port of the chamber, in combination with four electron emitters, generates ions. The choice for the voltages on the outer grids is flexible, so long as a sufficient ion 26 UNCLASSIFIED//FOR OFFICIAL USE ONLY

generation rate is achieved. The net accelerating voltage must be kept within the order of 1 kV to ensure that the resultant exhaust velocity is in the range of 30,000 m/s (Isp < 3000 seconds). The mission for a communications satellite is optimized with a specific impulse in this range. A higher specific impulse would reduce propellant requirements, but the power requirements and the mass associated with power source components would increase correspondingly. Xenon is bled into the chamber through holes at appropriate locations around the wall of the vessel. Figure 3.3. Illustration of the IEC Jet Thruster Experiment Showing Central Grid and Two Jet Grids, Opposite to Each Other With On-Off Action Table 3.1 lists the estimated performance parameters for an IEC electrostatic ion thruster based on experimental data available to date plus extrapolation of other ion thruster data. The IEC device will have higher densities and temperatures in the central core plasma than a conventional thruster, but the increased losses due to Bremsstrahlung radiation are still negligible when compared to the other power losses. Thermal radiation losses should be comparable to that in conventional thrusters. The energy expenditure per ion for conventional ion thrusters and is ~300 eV per ion. The energy expenditure per ion for the IEC device has not been established experimentally, but was estimated in Table 3.1 from simulation studies.

UNCLASSIFIED/ /FOR OFFICIAL USE ONLY Table 3.1. Estimated Performance Parameters or the IEC Ion Thruster Parameter | IEC Ion Thruster Propellant | Xenon Molecular Weight ( amu) | 131.3 Specific Impulse (s ) | 3000 Thrust (mN) | 34 Jet Power (W) | 500 Net accelerating Potential (V) | 600 Beam Current (mA) | 832 Power Loss to Grid (W) | ≤50 Power Loss to Bresstrahlung Radiation (W) | < 1 Power loss to Ionization of Propellant (W) | 200-250 Input Power (W) | 750-800 Thruster Efficiency (%) | 62-68 In summary, the power efficiency of the IEC thruster appears to be competitive to existing ion thrusters. What are the advantages then? These were outlined earlier and include a more compact design, large heat rejection area, an exhaust jet closer to quasi-neutrality, reduced neutral propellant leakage, and reduced grid erosion. Thus, the mass of the IEC jet thruster system can potentially be reduced compared to a high-power Hall-type thruster and also its lifetime can be increased significantly. In this overall context, then, the IEC thruster potentially offers an important improvement in performance for high power thruster applications. Scale-up to p-11B IEC Space Power Unit/Thruster The electrically driven IEC jet thruster provides an important data base for a next step p-11B IEC jet thruster. Jumping to p-11B for this application may appear overly ambitious. However, neutronless fusion seems essential in a small space thruster to avoid excessive weight from shielding of electronics. Considerable experience with fusing plasmas in IECs has been gained through development of IEC DD neutron sources. These devices operate with ~80-keV D-ion beams using the non-Maxwellian character of the IEC. This important characteristic makes use of p-11B a realistic goal. In fact, operation with circulating ion energies at the desired 150 keV energy for p-11B has already been achieved at the UIUC and several other laboratories working on IECs. The issue then is how to achieve adequate confinement times. The approach being pursued at UIUC is the formation of deep potential wells with angular ion injection using a differentially-pumped RF ion gun, as discussed in later sections. A proposed experiment to demonstrate p-11B physics is discussed in Section VI. In summary, the extraction of a jet plasma from a gridded IEC opens the way to a number of added plasma applications for the IEC. This present discussion is intended to identify an orderly progress of IEC applications in commercial space power, starting with an electrically driven IEC thruster to a self-powered IEC p-11B unit. The attractive characteristics of the electrically driven device, namely light weight, low maintenance, UNCLASSIFIED/ /FOR OFFICIAL USE ONLY 28

low fuel leakage and extreme maneuverability make it a near-term competitor with other devices such as Hall thrusters for future commercial thruster applications in the multi-kW range. The extension to a p-11B self-powered unit would resolve many problems anticipated as larger power requirements develop. It would be extendable to large power units needed for eventual fast deep space propulsion. Much more research and development is required to ensure that step in a timely fashion, however. The Dipole Assisted IEC (DaIEC) The dipole assisted IEC DaIEC is similar to the IEC concept discussed above except a dipole magnet is located in the center of two hemispherical grids (Reference 3. 9). The DaIEC was first proposed by G. Miley at the UIUC and has been under investigation there. This concept is closely related to the levitated dipole reactor (Reference 3.10) but is much simpler, being smaller and not requiring levitation. It also differs considerably in the physics of the associate plasma confinement. Two ion sources inject 40-keV deuterium and helium-3 ion beams toward the center of the dipole magnet. The magnetic field will compress the ion beams by trapping ions along the magnetic field lines; therefore, they fuse within the dipole magnet. The products of the D- 3He fusion reaction are 14. 7-MeV protons and 4-MeV alpha particles. These can be used for direct charged particle propulsion or direct conversion to electricity (or both- propulsion and station keeping). A schematic of the setup is shown in Figure 3.4. [Figure 3.4 diagram] Stabilizing coil Figure 3.4. Dipole Reactor Propulsion Scheme Those ions that exit toward the right in Figure 3.4 are trapped by the magnetic field produced by the stabilizing coil and are exhausted to produce thrust. Since the magnetic field does not close at the nozzle but is open, protons and particles are not required to be neutralized. This configuration of the magnetic field in the DaIEC system reduces the mechanical components. A neutralizer (electron injection into the exhaust) will be required in this system so as to avoid possible charging up at nozzle. 29 UNCLASSIFIED//FOR OFFICIAL USE ONLY