Trapping antimatter for space propulsion applications

. zyxwvut zy zyxwv zy AIAA 95-2891 TRAPPING ANTIMATTER FOR SPACE PROPULSION APPLICATIONS M.H. Holzscheiter, R.A. Lewis, J. Rochet and G.A. Smith Laboratoty for Elementary Particle Science Department of Physics Pennsylvania State University University Park, PA 16802 . 31st AIAA/ASMUSAUASEE Joint Propulsion Conference and Exhibit July-I0-12,1995/San Diego, CA zyxwvuts For permisslon to copy or rapubllsh, contact the American lnstltute of Aeronautics and A ~ t r o ~ u t l 370 L'Enfant Promenade, S.W.. Warhlngton, O.C. 20024 zy zyxw AIAA-95-2891 zyxwv zy zyx zyxwv zyxwvutsrqp zyxw TRAPPING ANTIMATTER FOR SPACE PROPULSION APPLICATIONS* M.H. Holzscheiter, R.A. Lewis, J. Rochet and G.A. Smith Laboratory for Elementary Particle Science Department of Physics PENNSYLVANIA STATE UNIVERSITY BBSTRACT increasing the "stacking" rate by a factor of IO, correspondingto a maximum production capacity of 140 ng per year. This would place Fermilab in the IO-1000 ng range specified above. Of c o m e , to proceed the relevant federal funding agencies would have to see fit to produce antiprotons in large numbers for purposes other than high energy physics, i.e. space propulsion. Production and trapping of antiprotons for space propulsion applications are reviewed. Present and foreseeable production rates at Fermilab are discussed, and experiments presently underway on trapping, confimement and transport of large quantities of antiprotons are outlined. P I " In a separate paper presented at this conference, it bas been shown that amounts of antiprotons in the range 101000 nanograms (ng) can enable manned exploration of the planets, using antiproton-catalyzed microfissiodfusion reactions.' The purpose of the present paper is to demonstrate that these amounts of antiprotons can be trapped and transported into space using existing technologies. We review antiproton production methods and yields, and apparatus for trapping, holding and transporting large numbers of antiprotons into space. A program ofresearch and experiments is outlined for the next several years. -.\ Antiproton trapping work is currently being done at the Low Energy Antiproton Ring (LEAR) at CERN. LEAR provides low energy (5 MeV) antiproton beams, presently not available at Fermilab. A schematic layout of the "catcher" trap being utilized by our group is shown in Figure 1 The 5 MeV antiproton beam is degraded in the SF, gas cell and A1 foil down to an energy of 10-30 KeV. In a 250 nanosecond (ns) pulse, the negatively charged antiprotons spiral down the axis of the 6T superconducting "Oxford Magnet," where they are repelled by a 12.5 KeV negative potential at the far end of the "Trap" electrode structure. They reverse direction, and in less than 250 ns a 12.5 KeV negative potential is placed on the upstream end of the "Trap"electrode shucture. The antiprotons are now trapped radially by the magnetic field, and axially by the two confining electrostatic potentials. The harmonic frequencies of these two motions are about 300 and 5 M H z respectively. A third harmonic "magnetron" motion is also present. This precession around the direction of the E x B vector is at a rate of about 80 fib. Antiproton sources exist worldwide at two sources, CERN in Geneva, Switzerland and Fermilab, in Batavia, Illinois. These two laboratories utilize high energy proton synchrotron accelerators, with accumulator storage rings attached to collect antiprotons produced by collisions of protons on targets. Details ofthe operation of these facilities go beyond the scope of this paper. It is important to comment, however, on the current and anticipated levels of production of antiprotons, especially at Fermilab which would be more likely to support a U.S. space program in the future. d After injection, it is important to measure the actual number of antiprotons trapped. This is done by lowering the potential of the far electrode, allowing the antiprotons to spill out of the trap and strike the "MCP," where they annihilate into charged pions. These pions ("Dump I") are then detccted in the "Scintillators". Figure 2 shows the correlationbetween number of scintillator counts in "Dump I", and the numbcr of antiprotons actually injected into the trap. Since the number of antiprotons injected was arbitrary formorc than thc onc hundred shots shown in Fig.2, wc are confident that we can trap 10' antiprotons per injection shot from LEAR at will. Presently, Fermilab "stacks" 6 x IO" antiprotons pcr hour in its Accumulator. This means that in onc ycar of dedicated production, it could produce a maximum of 0.85 ng of antiprotons. A new and funded facility, called the Main Irjcctor, will turn on in 1998, with a maximum annual production capacity of 14 ng. Discussions currently in progress about the development of a ucw Accumulator located inside the Main Injector ring are centcrcd around zyxwvu zyxwvutsr "Copyright 0 1995 by the American Institute of Aeronautics and h<trotronautics,Inc. All rights reserved." I 3 2 zyxwvutsrqpo zyxwvutsrqpo zyxwv zyxwvutsrq zyxwvutsrqp t 1 -150 - -100 Foll Ladder h -50 - 0 L +50 2 1.25kQ +IO0 L Z(cm) n Figure 1 - Schematic of the Antiproton Catcher Trap at CERN. lifetimes of up to several hours, corresponding to vacua of the order of 10" torr. The next step is to electron cool trapped antiprotons. This then permits "stacking" of successive shots from LEAR, i.e. "stacking" 10 successive shots would yield IO' antiprotonsin the trap. Electron cooling is done by injecting For space propulsion applications, 140 ng of antiprotons corresponds to about 10" antiprotons. One possible scenario therefore would be to transport 1O3traps into space, each holding IO'' antiprotons. It is likely that these IO3 traps would be integrated into a common cryogenic system. Scale-up from traps holding IO' antiprotons io 10" antiprotons will not be trivial. However, traps presently in use have a Brillouin limit of about IO" zyxwv zyxwvutsr electrons (typically 10' or so) into the trap, where by collisions they absorb energy from the antiprotons. This energy is released by the electrons as they spin around the magnetic field in the form of synchrotron radiation. The results of electron cooling 14 shots from LEAR are shown in Figure 3. The characteristic I/e cooling time is 175 seconds, with a 70% efficiency. The data demonstrate AY'' L. 0 0 i a n z r m 3 c L n r W a s r m e m m n ~ COUNS Dump 1 Figure 2 - Total number of antiprotons captured in the trap versus number of annihilations detected in the scintillators. 2 b . . a 0 im zyx zyxwvu zyxw 1J zyxwvut zyxwvutsrqp zyxwvu Cooling T i e R (secadsl Figure 3 -Fraction of antiprotons accumulated and cooled in the central well of the trap versus cooling time. antiproWcc. Therefore, a trap with a volume of 1 liter can hold the reguirednumber of antiprotons. This means that no new technology is required, just scale-up of present systems. This would require building and testing a 1 liter volume trap in the near future. energy density exceeds the magnetic energy density, and there are practical limits to magnetic fields that can be suppolted, accumulations of large numbers of antiprotons must be in the form of electrically neutral atom, i.e. atomic antihydrogen. Portable Penning Trap We are pnsently building a portable antiproton trap.z.' It is designed to carry up to lo9 antiprotons for 10 days. A schematic drawing of the trap is shown in Figure 4. It is a prototype for a trap, not necessarily any larger, capable of carrying 10" antiprotons for up to 120 days (duration of a round trip mission to Mars). Since earlier experiments at LEAR have demonstrated antiproton iietimes up to two months, we are wdident we can achieve this goal. [Scale 1:51 The portable trap is one meter tall, 30 cm across, and weighs 55 kg. It operates at 4K temperature, supported by cryogenic nitrogen and helium reservoirs, and has a unique feature that the wniining magnet is made of permanently magnetic SmCo materials. which should prove to be robust. This fxap will be Wed this summer, then sent to CERN for a filland demonstration journey across Europe. We plan to return a filled trap to the US.in 1996 for experiments planned under USAF sponsorship. zyxwvut zyxwvut AND C 0 " G ANTI" Eleftrid Feed Because Penning traps operate under the Brillouin limit, i.e. instabilities set in when the charged Coulomb Figure 4 - Portable Antiproton Trap. 3 zyxwv zyxwvut zyxwvutsrq [7] M.M. Michaelis and R. Bingham, Laser and Particle Beams6 (1988) 83. Withinthenexttwoyeawe willattempt to synthesize these atoms at CERN, by injecting positronium atoms, i.e. bound electron-positron pairs, into our trap filled with antiprotons. Initially we hope to form and confine thousands of antihydrogen atoms in a trap consisting of a vacuum cylinder within a quadrupole magnet, augmented with confining pinch coils at each end. This technology is currently available from laboratories studying atomic hydrogen," where densities of >IO" atomskc have been achieved.6 u [8] B.R.F. Kendall et al., J. Vac. Sci. Technol. A 5 (1987) 2458. Although these densities are much higher than allowed by Penning traps, instabilities exit which would prohibit their use for long term accumulation. The next step involves forming condensates of atomic antihydrogen, i.e. solid antihydrogen, which would provide densities approaching lO*'atomdcc, i.e. 140 ng of antihydrogen would constitute a spherical volume of about 60 micrometers radius. Confinement ofsolid antimatter has been the subject of extensive studies.' Since solid antihydrogen is diamagnetic, levitation within a confining vessel could be provided by a magnet of modest size.' Serious technical issues include annihilation of surface atoms with residual gas in the confling vessel, and sublimation of surface antihydrogen atoms with resultant annihilation on the walls of the confining vessel. In the latter case, the annihilation could eject matter from the walls, which in turn annihilates with the antihydrogen, starting a chain reaction. We find that for vacua of < 10.'' torr and antihydrogen samples of up to I microgram, these are not serious issues. * Work supported in part by the Air Force Office of Sponsored Research and the Jet Propulsion Laboratory (NASA). zyxwvut zyxwvuts zyxwvutsr zyxwvuts [I] S. Chakrabarti, B. Chwieroth, R.A. Lewis, J. Dailey, G.A. Smith, W.L. Werthman, and B. Watson, "AntiprotonCatalyzed Microfissioflusion Space Propulsion", AIAA 95-2900. [Z] D. Graham, Technology Review, 14 July (1994) 14 [3] J. Warner, New Scientist, 17 September (1994) 20. [4] T.W. Haensch and C. Zimmerman, IIypcrfine Interactions 76 (1 993) 47. [5] J.M. Doyle et al., J. Opt. SOC.A m B, 6 (1989) 2244. [6]R.vanRoijenetal.,Phys.Rev.Lett.61 (1988)931 4