Moir, R W

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Particle Accelerators, 1992, Vols. 37-38, pp. 459-465Reprints available directly from the publisherPhotocopying permitted by license only© 1992 Gordon and Breach Science Publishers, S.A.Printed in the United KingdomHEAVY-ION BEAM AND REACTOR CHAMBERINTERFACE DESIGN*RALPH W. MOIRUniversity of California, Lawrence Livermore National Laboratory,Livermore, California 94550.(Received 20 December 1990)The design of the heavy-ion beam and the HYLIFE-II reactor chamber interface must provide finalfocusing quadruple triplets, neutron shielding, fast shutters, vapor condensation and pumping, thermalinsulation, and blast-resistant structures. The smallest half-angle encompassing all beams striking thetarget might be ± 14° for an array of 4 x 4 beams or ± 9° if the four corner beams are eliminated,given a 12-beam array. The target gain drops considerably from the 0° published values because of thisfinite angle. The assumed one-sided irradiation reduces the number of bending magnets. A 350-MJ yieldmight be achieved with a 5-MJ driver (gain of 58, nominall000-megawatts of electricity (MWe) net power,and a repetition rate of 8 Hz). For either lower repetition rate or lower gain, the yield must be increasedby increasing the driver energy. The beam ports are protected from radiation by an array of vertical andhorizontal, neutronically thick, liquid jets.INTRODUCTIONIn this paper we describe the heavy-ion beam and reactor chamber interface design.The reactor chamber example used is HYLIFE-II, but other designs could equallywell have been used. In two other papers (Refs. 1 and 2) the HYLIFE-II reactor isdescribed.2 BEAM AND CHAMBER INTERFACEThe heavy-ion beams from either a circular or linear accelerator are directed ontothe target in the reactor chamber shown in Figures 1, 2, and 3. A length of about400 m is required for drift compression of the beams. As a base case we considerone-sided illumination of the target so as to minimize bends (which are predicted tocause emittance growth, causing a larger spot size on the target and therefore areduced gain), as shown in Figure 4. We have reduced the distance from the end ofthe last focusing magnet to the target from the 8 m of HYLIFE-I to 5 m forHYLIFE-II to make it easier to put the beams into a spot size of about 2.5 mm radius.We have tried to put a compact array of 12 beams as close together as possibleto reduce the half-angle (±9°) encompassing these beams to as small a value as* This work was performed under the auspices of the u.s. Department of Energy by LawrenceLivermore National Laboratory under Contract W-7405-Eng-48.459~/'260M~AccelJfocu8IIIJ:rt10:a0ER------IfI400Mnottoscal.Driftcomoresslon..etlon140Mdrnto8Cal.Focusingmagets.,J::.0\oFIGURE1Thelast400moftheheavy-ionbeamsystemisusedtoaccomplishdriftcompressionofthebeamsandthelast50misusedforfinalfocusfromonesideontothetargetintheexampleshown.Thedesiredpulseshapecanbeobtainedbycompressing,delaying,andstackingthe12beams.BEAM AND CHAMBER INTERFACE DESIGNHorizontal JetsVertical jetsHYLIFE-ll chamber461.(.JFIGURE 2 Twelve beams are focused onto the target in the HYLIFE-II reaction chamber. The ±9°half-angle encompassing the beams is set by neutron shielding of the magnets.possible. The 4 x 4 array of 16 beams had a half-angle of ±14°. Eliminating thefour corner beams gives an array of 12 beams that fit into ±9°, as shown in Figure2. The approximate effect of the beam array angle on gain is shown in Figure 5.We know the magnets need shielding to reduce the energy deposited in theconductor during a pulse so that the temperature rise stays within the limits requiredto avoid a magnet quench. Steady power removal is probably not a technical limit,TOP VIEWTarget portVIEW A-AO"IOIO~CIII 1m1""1,,,,1FIGURE 3 The walls around the beam ports are protected from neutrons and x rays by neutronicallythick Flibe jets. Counter-rotating shutters protect the beam tube from Flibe splash and vapor.462 R. W. MOIR200 ----.--.....-~------.----------.....-----y =1000 MJ1008060c:·co" 4020\5Driver energy (MJ)10FIGURE 4 Target gain vs driver energy for various beam spot sizes. The gain curves are more fullydiscussed in Ref. 2 and a reference therein. The half angle was zero, the beam ion was 2ooHG: at 10 GeVwith a range of 0.1 g/cm 2.but dose to the conductor and insulator will dictate its lifetime. We have providedover 1 m of line-of-sight shielding against 14-MeV neutrons from the target. In themodel being used for the Monte Carlo neutron shielding calculation shown in Figure6, we have only 30 mm of shielding from multiple-bounce neutrons and their x rays.HIBALL-II 3 used 300 mm shielding. Any increase in shielding from the 30 mm willincrease the outer radius of each of the final focusing magnets and therefore the half403551008060c:7iiC'402000 10 15 20 25 30Half angle of beams, edegFIGURE 5 As the angle encompassing the beams increases, the target gain drops. The driver energywas 5 MJ and the range was 0.1 g/cm 2.BEAM AND CHAMBER INTERFACE DESIGN 463Fe + 10%Borated H202.0 m 3.0 m 0.5 m~FIGURE 6 Model of beam line for shielding analysis. Neutron shielding of final quadrupole focus forsuperconducting magnets sets packing and angle between the 12 beams.angle, thus resulting in reduced gain (Figure 5). Any increase in shielding on theinside of the focusing magnets will move the conductors to a larger radius and ahigher field at the conductor will be needed for the same focusing strength. This willdrive the cost of the final focusing system up. The shielding calculation and designis an ongoing area of study. If the heating is too much, we will consider normalconducting magnets for the last quadrupole or two in each beam line.Counter-rotating shutters shown in Figure 3 are provided to prevent or discouragefluorine-lithium-beryllium (Flibe) liquid and vapor from entering the beam tubes. Weexpect to operate the beam tube walls for a good distance away from the chamberat a temperature above the melting point of fluorine-lithium-beryllium or "Flibe"(460°C) so that the vapor entering the beam tube will condense on the walls anddrain to a a collection point. The vapor pressure at 475°C is 0.0013 Pa or 1.25 x1011 jcm 3 , as shown in Figure 7. This is well below the vacuum propagation density,where so little beam stripping and Flibe ionization occurs that space charge is notneutralized and focusing would not be effected 5 •A set of nozzles in the chamber provides a continuous spray of droplets of coolFlibe at 600°C. Bai and Schrock4 have shown that the Flibe vapor will condense onthe droplets, bringing the pressure (density) close to the vapor-pressure limit in atime fast enough to permit an 8 Hz repetitive rate. At 1 x 1013 jcm 3 there is predictedto be partial neutralization in the chamber and therefore some defocusing and anincrease in spot size5 . Another analysis6 predicts propagation at a density of 1 x1014jcm 3• In HIBALL-II 3 the required density for propagation was 4 to 8 X1010jcm 3• In HILIFE-II we can have higher density because the distance to the targetis shorter, we allow some partial neutralization defocusing and Flibe has less strippingdue to the lower atomic number. Lower temperature Flibe spray than 600°C nearthe beam path can depress the density if needed. This is an area needing further study.Other jets of Flibe that are neutronically thick (50 em) are directed horizontallyand vertically around the 12 beams and the target injection port (Figure 3), so as toprotect the walls immediately around the ports from neutron and x-ray damage. Theset of jets makes the chamber wall a lifetime component (30 y). The jets also protectnozzles and manifolds that are closer to the neutron source and therefore see a higherflux of neutrons. More design and analysis will be needed to determine the thicknessof the jets that is required to ensure adequate component lifetime.464C")E(,)1012400R. W. MOIR500 600 700 800 900Temperature of Flibe (OC)1000 1100Pinched orchannelpropagation,will pinch form?Ballisticpropagation,filamentation?Stripping andplasma instabilitiesdefocus beamPartialneutralizationsome defocussingof beamVacuumpropagationFIGURE 7 Density of LiF molecules determined by vapor pressure of Flibe (Li2 BeF4)' Condensationof Flibe vapor on Flibe droplets might permit beams to propagate, allowing an 8 Hz repetition rate unlesschemical and kinetic effects are limiting.3 CONCLUSIONSTwelve heavy-ion beams are focused on a target in the HYLIFE-II reactor chamber.Provisions are made to:• shield the final focus magnets (calculations in progress)• provide fast rotating shutters to keep liquid and debris out of the beam tubes• pump Flibe vapor by condensation on cool liquid droplets to permit propagationof the beam at an 8 Hz repetition rate• shield the beam ports and all structures with neutronically thick Flibe jetsThe ± 9-deg half angle between the 12 beams is predicted to degrade the target gainby 160/0. A 3-m difference in path length permits delaying beam arrival times up toBEAM AND CHAMBER INTERFACE DESIGN 46530 ns relative to each other so that the desired pulse shape can be obtained bycompressing, delaying, and stacking the 12 beams.A self-consistent driver/reactor interface design is presented but is not yet completeenough to evaluate feasibility and cost. The shielding design could seriously impactthe cost of electricity from the plant by adding cost for the final focusing system andby increasing the angle of the beams which degrades target performance. We haveshown how the final focusing system affects target design and performance throughthe beam angle effect on target gain. Other effects such as one-sided versus two-sidedillumination have a strong coupling with beam interface design. Clearly much morestudy is needed.ACKNOWLEDGMENTWe thank many people on the ICF program staff at the Lawrence LivermoreNational Laboratory for advice throughout this study and especially Robert Leberfor his mechanical design contributions.REFERENCES1. R. W. Moir, "HYLIFE-II inertial confinement fusion reactor design," Fusion Techno., 19,617 (1991).2. R. W. Moir, "HYLIFE-II inertial confinement fusion power plant design," these Proceedings.3. B. Badger et a!., HIBALL-II-An Improved Conceptual Heavy Ion Beam Driven Fusion Reaction Study,University of Wisconsin report UWFDM-625 (1984), Kfk-3840 and FPA-84-4.4. R. Y. Bai and V. E. Schrock, "An approximate method for analyzing transient condensation on sprayin HYLIFE-II," Fusion Techno!., 19, 732 (1991).5. B. Langdon, "Chamber propagation," these Proceedings.6. Hubbard, R. F., "Target chamber propagation of heavy ion beams in the pressure regime above10- 3 Torr," these Proceedings.

Heavy-ion beam and reactor chamber interface design

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