Plasma Traps for Space-Charge Studies : Status and Perspectives Hiromi Okamoto (Hiroshima Univ.)
Acknowlegements Past and Present Contributors to the S-POD Project Hiroshima University Hiroyuki Higaki, Kiyokazu Ito (Students) M. Endo, S. Fujimoto, M. Fujioka, K. Fukata, K. Fukushima, H. Hitomi, K. Homma, M. Kano, Y. Mizuno, K. Moriya, K. Nakayama, S. Ohtsubo, K. Okabe, S. Sakao, H. Sugimoto, H. Takeuchi, K. Tanaka, R. Takai, G. Uchimura, S. Yamaguchi Kyoto University Akihiro Mohri Osaka University Kenji Toyoda LBNL & LLNL Steven M. Lund, Andrew M. Sessler, Peter Seidl, David Grote, Jean-Luc Vay 2
Purpose Systematic experimental studies of various space-charge effects in high-intensity and high-brightness hadron beams Use of non-neutral plasmas physically equivalent to charged-particle beams in periodic AG channels At Hiroshima University, compact non-neutral plasma trap systems have been developed solely for beam physics purposes. The tabletop experimental tool for space-charge studies are called S-POD ( Simulator for Particle Orbit Dynamics ). Three Paul ion traps and a Penning electron trap are now employed to explore the collective behaviors of intense hadron beams systematically. 3
Principle of S-POD Experiments Charged-particle beams in an AG focusing channel Charged-particle Non-neutral plasmas beams in an in AG a trap focusing system channel beam = 1 2 (p 2 x + p 2 y ) + 1 2 K q H Q(x 2 y ) + mγ 3 (βc) plasma = 1 2 (p 2 q x + p 2 y ) + 1 2 K RF (x 2 y 2 ) + q mγ mc φ 3 (βc) φ H = 1 2 plasma 2 (p x 2 H beam = 1 2 (p 2 x + p 2 y ) + 1 2 K Q (x2 y 2 ) + Non-neutral plasmas in a trap system 2 + p 2 y ) + 1 2 K RF (x2 y 2 ) + q mc φ 2 Both interacting many-body systems obey the following equations: Poisson equation Δφ = q ε 0 f (r,p;t)d 3 p Vlasov equation f t + [ f, H ] = 0 Two systems are physically equivalent if governed by similar Hamiltonians. Use this simple fact to study various collective effects in space-charge-dominated beams! 4
Why Traps? Very compact Low cost Table-top size (Our Paul traps are shorter than ~20 cm in axial length.) We have several traps of different designs, each of which costs a few k$. Extremely wide parameter range Easy control of tunes and tune depression (and even lattice structures) High resolution & precision measurements MCPs, Faraday cups, and laser-induced fluorescence (LIF) diagnostics No radio-activation No machine damage from any large particle losses 5
Present Status 6
RF Ion Trap Linear Paul Trap * Operating frequency : 1 MHz * Particle species : Ar +, Ca +, N +, etc. * Plasma lifetime : order of seconds (dependent on plasma conditions) * Tune depression : < 0.8 (without cooling) * Cost : a few thousand USD! Transverse confinement : rf quadrupole Longitudinal confinement : rf or electrostatic potential 7
Magnetic Trap Penning Trap with Multi-Ring Electrodes * Particle species : e - Transverse confinement : axial magnetic field Longitudinal confinement : electrostatic potential (+ magnetic mirror) 8 * Field strength : < 500 G
S-POD S-POD I AC / DC power sources S-POD II MCP or FC RF trap RF trap Paul trap PC control system Doppler laser cooling Coulomb crystals Ultralow emittance beams S-POD III CCD camera Doppler laser cooling Vacuum system e-gun Lattice-dependent effects Collective resonances S-POD IV atomic oven Magnetic trap RF trap Doppler laser cooler Collective resonances Resonance crossing 9 Halo formation Bunch compression S-POD I
Control System Power Supplies All experimental procedures are automated. Lattice input panel Output power PC control panel INPUT PARAMETERS (initial tune, final tune, plasma storage time, number of measurement points, ionization time, end plate voltages, etc.) 10
Ultimate Control of Tune Depression S-POD I S-POD I and End-plate spacing = 6 mm II are equipped with End-plate spacing = 60 mm the Doppler laser cooling system for 40Ca+. Space-charge limit (where tune depression = 0) can be reached experimentally! 7.7ns 397nm laser 13:1 866nm laser 0.7s ＬＩＦ Cooling transition of 40Ca+ 11
Recent S-POD Experiments Collective resonance excitation ( Ar + ) Lattice dependence of stop bands ( Ar + ) Resonance crossing ( Ar + ) Halo formation ( e - ) Ultralow-emittance beam stability ( Ca + ) 12
Stop Bands in Doublets WARP Filling Factor : ξ Collective (l + l )/L Resonance Condition F D Drift Ratio : k ν ζ g /(L g 0 C l l m Δν P ) F D 2m For P = 1, η = 0.9 Linear(m = 2) : ν 0 C 2 Δν 1 4 Third-order (m = 3) : ν 0 C 3 Δν 1 6, 2 6 S-POD n = 1(primary)+ n = 3, 5, 7 n = 1(primary)+ n = 2, 3, 4 13
Stop-Band Splitting : S-POD Experiments When ν 0 x ν 0 y, all stop bands split! Tune Diagram Linear stop band Relative ion number δν ν 0 x ν 0 y 14
Resonance Crossing : S-POD Experiments Crossing Speed u δ / n rf δ : tune-sweep width n rf : rf period for tune sweep 15
Effect of Lattice Superperiodicity S-POD experiments Emittance growth 2D Warp simulations 16
Halo Formation by Sudden External Disturbance e-gun Multi-Ring Electrodes (MREs) Typical e - Plasma Injection & Extraction Scheme FC or MCP with Phosphor screen NO DISTURBANCE DISTURBED V z (maintained V z (40 V at 60V) 50V) 40 V) 17
Summary and Near-Future Plans 18
Present Status What we have now are : Three electric S-PODs based on Paul traps One magnetic S-POD based on a Penning trap 20% space-charge-induced tune shift available without any particular plasma cooling Ar + or Ca + ion plasmas for the Paul traps & pure electron plasmas for the Penning trap What we can do now are : Collective resonance excitation Arbitrary lattice emulation (but mostly the sinusoidal-wave model employed so far) Forward and backward resonance crossing Mismatch-driven halo formation Coulomb crystal generation 19
Possible Near-Future Plans Construction of a new Penning trap Dipole resonance excitation More experiments on longitudinal dynamics Synchrotron resonances Synchro-betatron resonances Longitudinal bunch compression Space-charge effects on bunch aspect ratio and exact lattice structures Detailed study of halo formation Experiment proposals, suggestions, and comments very welcomed! Full-range control of tune depression (from 0 to 1) Plasma stacking scheme RF power generator improvement New cold ion-beam source Fast pulse magnetic-field generator New diagnostic system development Compact emittance monitors Laser-induced fluorescence diagnostics Technical Issues 20