1 F. Dahlgren, 1 T. Kozub, 1 T. Dodson, 1 C. Priniski, 1 C. Gentile, 2 J. Sethian,

1. Magnetic Intervention 1F. Dahlgren,1T. Kozub, 1T. Dodson, 1C. Priniski, 1C. Gentile, 2J. Sethian, 1G. Gettelfinger, 2A. E. Robson, 3A. R. Raffray, 4M. Sawan 1Princeton Plasma Physics Laboratory, 2Naval Research Laboratory, 3University of California-San Diego, 4University of Wisconsin HAPL 16, Princeton Plasma Physics Laboratory, December 12th-13th 2006, Princeton, NJ Abstract Solid Wall Magnetic Deflection 3D Pro-E Modeling of Target Chamber Concept A conceptual design of a magnet system to mitigate the effects of ion erosion on first wall components of a High Average Power Laser (HAPL) driven fusion reactor is presented. A cusp field geometry is used to deflect the ions away from the wall and dissipate their energy via induced currents in the blanket-wall. This effectively deposits the majority of the energy carried by the ions in the volume of the blanket rather than the surface. • Cusp magnetic field stops the radially expanding ion shell • Ion flux to wall is minimized • Field is resistively dissipated in blanket/wall  • Ions, at reduced energy and power, are directed through cusp poles and into mid-plane toroidal dumps  Discussion Baseline Design of Cusp Coils In Direct Drive (IFE) implosions, approximately 28% of energy released is carried by charged particles. The ion species include the usual DT and DD fusion reactions and these charged particles represent the biggest “threat” to the survival of the first wall. To ease this threat, the concept of “Magnetic Intervention” has been proposed using a cusp shaped magnetic field to deflect the ions away from the first wall. In a cusp geometry the field is zero at the target origin and presents a positive (convex) curvature to the expanding ion flux during the pulse. The interaction of the radially directed ions and electrons with this field will result in an induced rotational current in the expanding plasma. This induced current would be opposite that in the coils (clockwise in the upper hemisphere of the plasma, counterclockwise in the lower half) and thus would exclude the magnetic field from the interior of the expanding plasma. Because flux is excluded, the magnetic field is pushed outward and is compressed since it cannot move past the external cusp coils. The expansion will continue until the increased magnetic pressure is balanced by the expanding plasma pressure, i.e. the system produces a beta of ~1.0. If the chamber wall is made of a resistive material, such as SiC, the energy of expanding magnetic field can be dissipated in the wall material as heat, thus effectively converting into a volumetric deposition of that heat. A cusp geometry has an open toroidal belt at the mid-plane and openings at the poles. The ions, with reduced energy eventually leak out these openings. Additional energy would be dissipated via Bremstralung and other photon radiation. The current baseline design of the cusp coils uses a Cable in Conduit Conductor (CICC) comprised of Nb-Ti superconductor with a forced flow super-critical LHe coolant. Two typical cross-sections of the coil are presented in the figures below. A high current density option is considered if AC fields are not present in the coil windings and a much lower current density configuration if a 5 Hz AC field is present (currently under investigation). The coil and case will be force-cooled with 4.5-5 K LHe. An additional LN2 shroud will be positioned around the coil structure and support columns to be a thermal shield. Radiation and neutronics studies* suggest that a minimum 50 cm thick water/316L-SS shield will be required between the SiC blanket and coil. Other coil conductor options, including the use of Rutherford cable and HTS YBCO are also under consideration. *per M. Sawan, U.W., HAPL Meeting, GA, August 8-9, 2006 High Current Density Option General Conceptual Arrangement for a Magnetic Intervention Chamber Low Current Density Option All models are currently under development. Cusp Field Coil Analysis COIL     A       Z       NI           FZ           FR/L         FZ/L         S-HOOP   COMBINED            M       M       AT N             N/M          N/M         N/M SQ    STRESS           IN      IN       AT            LB           LB/IN        LB/IN        PSI          PSI   DFL-R  1   3.400   5.000    4.000E+06   -8.105E+06    2.660E+06   -3.794E+05    1.159E+07       133.858 196.850    4.000E+06   -1.823E+06    1.520E+04   -2.168E+03    1.682E+03  1.912E+03  1.407E-02   2   3.400  -5.000   -4.000E+06    8.106E+06    2.660E+06    3.794E+05    1.159E+07       133.858 -196.850   -4.000E+06    1.823E+06    1.520E+04    2.168E+03    1.682E+03  1.912E+03  1.407E-02  3   6.100   2.250    4.800E+06    4.511E+07    9.559E+05    1.177E+06    7.472E+06       240.157  88.583    4.800E+06    1.015E+07    5.461E+03    6.723E+03    1.084E+03  3.537E+03  1.627E-02  4   6.100  -2.250   -4.800E+06   -4.511E+07    9.559E+05   -1.177E+06    7.472E+06       240.157 -88.583   -4.800E+06   -1.015E+07    5.461E+03   -6.723E+03    1.084E+03  3.537E+03  1.627E-02 Conclusions and Path Forward A conceptual design of a magnet system is being investigated which will produce a sufficient cusp shaped field for the deflection of the charged products from a direct drive inertial fusion target. Further refinements of the design will address the radiation/lifetime, structural supports, busing/joint configuration, fault and quench protection, cryogen requirements, and investigate the feasibility and economies of alternative conductor options.