Kyoto ICR, Uji, Kyoto
MPI-K, Heidelberg
Kyoto IAE, Kyoto
HU/AdSM, Higashi-Hiroshima
NIRS, Chiba-shi
JINR, Dubna, Moscow Region
Experiments of transverse laser cooling for 24Mg+ beam have been performed at the small ion storage and cooler ring, S-LSR. It is predicted that the longitudinal cooling force is transmitted to the horizontal direction with synchro-betatron coupling at the resonant condition*. The laser system consists of a 532nm pumping laser, a ring dye laser with variable wavelength around 560nm, and a frequency doubler. The horizontal beam size and the longitudinal momentum spread were optically measured by a CCD and a PAT (Post Acceleration Tube) respectively**, ***. The CCD measures the beam size by observing spontaneous emission from the beam and records in sequence of 100ms time windows the development of the beam profile. The time variation of the beam size after beam injection indicates the transverse cooling time. The initial horizontal beam size, which was about 1mm, was decreased by 0.13mm in 1.5s. The longitudinal momentum spread measured by PAT is increased at the resonant condition. This suggests transverse temperature was transferred to longitudinal direction by synchro-betatron coupling. Both measurements denote the horizontal cooling occurred only in the resonant condition ****.
* H. Okamoto, Phys. Rev. {E50}, 4982 (1994)
** M. Tanabe et. al, Appl. Phys. Express 1 (2008) 028001
*** T. Ishikawa Master Thesis, Kyoto Univ.(2008)
**** H. Souda et. al., contribution to IPAC10.
Kyoto ICR, Uji, Kyoto
MPI-K, Heidelberg
Kyoto IAE, Kyoto
HU/AdSM, Higashi-Hiroshima
NIRS, Chiba-shi
JINR, Dubna, Moscow Region
Transverse laser cooling with the use of a synchro-betatron coupling is experimentally demonstrated at the ion storage/cooler ring S-LSR. Bunched 40keV 24Mg+ beams are cooled by a co-propagating laser with a wavelength of 280nm. Synchrotron oscillation and horizontal betatron oscillation are coupled by an RF drifttube at a finite dispersive section (D = 1.1m) in order to transmit longitudinal cooling force to the horizontal degree of freedom*. Time evolution of horizontal beam size during laser cooling was measured by a CCD camera**. Horizontal beam sizes were reduced by 0.13mm within 1.5s after injection when the tune values satisfy a difference resonance condition, νs - νh = integer, at the operating tunes of (νh, νv, νs)=(2.067, 1.104, 0.067) and (2.058, 1.101, 0.058). Without resonance condition, the size reduction was negligibly small. The momentum spread was 1.7x10-4 on the resonance otherwise 1.2x10-4. These results show that the horizontal heats are transferred to the longitudinal direction through the synchro-betatron coupling with the resonance condition and are cooled down by a usual longitudinal bunched beam laser cooling.
* H. Okamoto, Phys. Rev. E 50, 4982 (1994).
** M. Nakao et. al., contribution to this conference.
Hiroshima University, Higashi-Hiroshima
Osaka University, Graduate School of Science, Osaka
HU/AdSM, Higashi-Hiroshima
Space charge effects due to the strong Coulomb interactions expected in high intensity accelerator beams result in undesirable beam degradation and radio-activation of the vacuum tubes through halo formations. Various space charge effects have been studied intensively with particle simulations. This is partly because the analytical formulation of the nonlinear evolution in high intensity beams is not possible in general cases. And the systematic study of space charge effects with the real accelerators is not feasible. Although the development of computation environment is outstanding, some approximations are still necessary so far. Thus, it was proposed to use solenoid traps and linear Paul traps for investigating some properties of space charge dominated beams. The key idea is that the charged particles in these traps are physically equivalent with a beam in a FODO lattice. Some experimental results have been reported with the use of Paul traps. Here, a solenoid trap with a beam imaging system composed of a charge coupled device camera and a phosphor screen was employed to study the mismatch induced oscillations of a space charge dominated beams.
HU/AdSM, Higashi-Hiroshima
Hiroshima University, Higashi-Hiroshima
LLNL, Livermore, California
S-POD (Simulator for Particle Orbit Dynamics) is a tabletop, non-neutral plasma trap system developed at Hiroshima University for fundamental beam physics studies. The main components of S-POD include a compact radio-frequency quadrupole trap, various AC and DC power supplies, a vacuum system, a laser cooler, several diagnostics, and a comprehensive computer control system. A large number of ions, produced through the electron bombardment process, are captured and confined in the RFQ trap to emulate collective phenomena in space-charge-dominated beams traveling in periodic linear focusing lattices. This unique experiment is based on the isomorphism between a one-component plasma in the laboratory frame and a charged-particle beam in the center-of-mass frame. We here employ S-POD to explore the coherent betatron resonance instability which is an important issue in modern high-power accelerators. Ion loss behaviors and transverse plasma profiles are measured under various conditions to identify the parameter-dependence of resonance stopbands. Experimental observations are compared with PIC simulation results obtained with the WARP code.
TUB, Beijing
Tsinghua University, Beijing
HU/AdSM, Higashi-Hiroshima
LBNL, Berkeley, California
JAEA/TARRI, Gunma-ken
During the beam crystallization process, the main heating source is Intra-beam scattering (IBS), in which the Coulomb collisions among particles lead to a growth in the 6D phase space volume of the beam. The results of molecular dynamics (MD) simulation have shown an increase of heating rate as the temperature is increased from absolute zero, but then a peak in the heating rate, and subsequent decrease with ever increasing temperature*. This phenomenon has been carefully studied by Y. Yuri, H. Okamoto, and H. Sugimoto**. On the other hand, in the traditional IBS theory valid at high temperatures, heating rate is monotonically increasing as the temperature becomes lower***. In this paper we attempt to understand the "matching" at low temperatures between the MD results and traditional IBS theory, by including many body effects in the traditional IBS theory. In particular the Debye shielding is included. We shall present how the traditional theory is modified by shielding, and show how this effect improves the "matching" with the results from MD.
* J. Wei, H. Okamoto, and A. Sessler, Phys. Rev. Lett. 80, 2606
** Y.Yuri, H. Okamoto, and H. Sugimoto, J. Phys. Soc. Jpn. 78, 124501
***A. Piwinski, Lect. Notes Phys. 296, 297 (1988)
HU/AdSM, Higashi-Hiroshima
The University of Tokyo, Institute of Physics, Tokyo
MPQ, Garching, Munich
RIKEN, Wako, Saitama
Hiroshima University, Graduate School of Advanced Sciences of Matter, Higashi-Hiroshima
Tokyo University of Science, Tokyo
In Antiproton Decelerator (AD) at CERN, unique low energy antiproton beams of 5.6 MeV have been delivered for physics experiments. Furthermore, the RFQ decelerator (RFQD) dedicated for Atomic Spectroscopy And Collisions Using Slow Antiprotons (ASACUSA) collaboration enables the use of 100 keV pulsed antiproton beams for experiments. What is more, Mono-energetic Ultra Slow Antiproton Source for High-precision Investigations (MUSASHI) in ASACUSA can produce antiproton beams with the energy of 100 ~ 1000 eV. Since the successful extraction of 250 eV antiproton beams reported in 2005, continuous improvements on beam quality and equipments have been conducted. Here, the basic properties of a tank circuit attached to MUSASHI trap are reported. Signals from a tank circuit provide information on the trapped antiprotons, as Shottky signals do for high energy beams in accelerators. In fact, it is known that this kind of trap-based beams are physically equivalent with those in a FODO lattice. Monitoring the tank circuit signals will be useful for on-line handling of the low energy antiproton beams from MUSASHI.
HU/AdSM, Higashi-Hiroshima
Hiroshima University, Faculty of Science, Higashi-Hirosima
An ion plasma confined in a compact trap system is Coulomb crystallized near the absolute zero temperature. The emittance of the crystallized ion plasma is close to the ultimate limit, far below those of any regular ion beams. This implies that, if we can somehow accelerate a crystal without serious heating, an ion beam of extremely low emittance becomes available*. Such ultra-low emittance beams, even if the current is low, can be used for diverse purposes including precise single ion implantation to various materials and for systematic studies of radiation damage effects on semiconductors and bio-molecules. We performed proof-of-principle experiments on the extraction of Coulomb crystals from a linear Paul trap system developed at Hiroshima University. A string crystal of 40Ca+ ions is produced with the Doppler laser cooling technique and then extracted by switching DC potentials on the trap electrodes. We demonstrate that it is possible to transport the ultra-low temperature ion chain keeping its ordered configuration.
* M. Kano et al., J. Phys. Soc. Jpn. 73, No.3, 760 (2004).
HU/AdSM, Higashi-Hiroshima
LLNL, Livermore, California
Resonant instabilities of ion plasmas confined in a linear Paul trap are studied using the particle-in-cell code WARP. Transverse two-dimensional model is employed to save computing time and perform systematic investigations. Both applied and self-field forces are calculated with a boundary condition assuming a quadrupole electrode structure. A large number of simulations were carried out with rms matched plasmas to clarify characteristics of the instability caused by linear and nonlinear coherent resonances. Stop band distributions produced by the simulation runs are consistent with theoretical prediction. These results are also compared to experimental results obtained from Hiroshima University Paul trap that is developed to study beam dynamics. It is shown that the stop band distributions of both numerical and experimental results are good agreement each other. We confirmed from these results that coherent resonances are excited when one of the coherent tunes is close to a half integer.