43302842
Low-energy states of circulating stored ion beams: Crystalline beams.
The low-energy states of a beam of charged particles subject to circumferentially varying guiding and focusing forces is studied by first deriving a Hamiltonian and then using molecular dynamics methods. In an alternating gradient structure, operating below the transition energy (but not in a constant gradient ring), the lowest state is ordered. The nature of the ground state depends upon the beam density and the ring parameters. For very low temperature, the crystal remains intact for a long time, but as the temperature increases it rapidly gains energy from the lattice.
55260265
Intrabeam scattering at low temperature range
During the process of ion beam crystallization, 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. [J. Wei, H. Okamoto, and A. M. Sessler, Phys. Rev. Lett. 80, 2606 (1994)]. This phenomenon has been carefully studied by Y. Yuri, H. Okamoto, and H. Sugimoto [Y. Yuri, H. Okamoto, and H. Sugimoto, J. Phys. Soc. Jpn. 78, 124501 (2009)]. On the other hand, in the traditional IBS theory valid at high temperatures, heating rate is an ever increasing as the temperature becomes lower and lower. [A. Piwinski, Lect. Notes Phys. 296, 297 (1988)]. In this paper we attempt to extend the traditional IBS theory valid at high temperatures to relatively low temperature range, by including some many body effects in the traditional IBS theory. In particular we take into account the static and dynamic effect of the self-electromagnetic field of the beam. We shall show how these effects modify the traditional IBS theory, and present the evaluation of IBS heating rate of an ion beam in the low temperature range.
109312980
Stochastic cooling with a double rf system
Stochastic cooling for a bunched beam of hadrons stored in an accelerator with a double rf system of two different frequencies has been investigated. The double rf system broadens the spread in synchrotron-oscillation frequency of the particles when they mostly oscillate near the center of the rf bucket. Compared with the ease of a single rf system, the reduction rates of the bunch dimensions are significantly increased. When the rf voltage is raised, the reduction rate, instead of decreasing linearly, now is independent of the ratio of the bunch area to the bucket area. On the other hand, the spread in synchrotron-oscillation frequency becomes small with the double rf system, if the longitudinal oscillation amplitudes of the particles are comparable to the dimension of the rf bucket. Consequently, stochastic cooling is less effective when the bunch area is close to the bucket area.
120031547
Longitudinal Dynamics of the Nonadiabatic Regime on Alternating-Gradient Synchrotrons.
55346276
Phonon spectrum and the maintenance condition of crystalline beams
1098-4402= It has been shown that the maintenance condition for a crystalline beam requires that there be no resonance between the crystal’s phonon frequencies, and the frequency associated with a beam moving through a lattice of Nsp periods. This resonance can be avoided provided that the phonon frequencies all are below half the lattice frequency. Here, we study in detail the phonon modes of several crystalline beams. The analytic results obtained in the smooth approximation are compared with numerical evaluations employing Fourier transform of the molecular dynamics (MD) modes. The stability of various crystalline structures is examined through systematic MD simulations based on several different lattice designs. The maintenance condition, when combined with either the simple analytic theory or the numerical evaluation of phonon modes, exhibits excellent agreement with the MD calculations of crystal stability. A confirmed maintenance condition, derived from linear-resonance criteria, is that the lattice frequency must not equal the sum of any two phonon frequencies.
59144790
Design of the CPHS RFQ linac at Tsinghua university
The design progress of the Radio Frequency Quadrupole (RFQ) accelerator for the Compact Pulsed Hadron Source (CPHS) at Tsinghua University is presented in this paper. The RFQ will accelerate protons from 50 keV to 3 MeV, with the RF frequency of 325 MHz. The objective is to obtain the optimum structure of the RFQ accelerator with high transmission rate and tolerable total length. The beam dynamics are studied by the simulation of the proton beam in the RFQ accelerator with the code of PARMTEQM. The output proton beam from the RFQ is well matched into the DTL without Medium-Energy-Beam-Transport (MEBT) between the RFQ and DTL. INTRODUCTION A 325 MHz Radio Frequency Quadrupole (RFQ) accelerator will be built to produce 50mA of proton beam at 3 MeV as an injector of the 13 MeV DTL for the Compact Pulsed Hadron Source (CPHS) project at Tsinghua University. The CPHS project is a universitybased proton accelerator platform (13 MeV, 16 kW, peak current 50 mA, 0.5 ms pulse width at 50 Hz) for multidisciplinary neutron and proton applications [1]. The RFQ system consists of three four-vane resonant cavity sections, one power coupler, 47 slug tuners, 8 dipole-mode stabilizer rods, the RF power supply and its low-level control, vacuum, water cooling, resonance control, beam diagnostics, support and alignment systems. Fig. 1 shows the sketch of the RFQ system and the design parameters are listed in Table 1. Figure 1: Sketch of the 3 MeV RFQ for the CPHS project. To save space and cost, no Medium-Energy-BeamTransport (MEBT) will be placed between the RFQ and DTL. The RFQ is carefully designed to match the beam from the high-energy end of the RFQ to the entrance of the DTL, by reducing the focusing in the exit of the RFQ. The cavity cross section and vane-tip geometry are tailored as a function of longitudinal position. The physics design has been completed. One test section made by aluminium has been machined to verify the capability of the numerically controlled milling machine. The final RFQ cavity is now under construction. This paper summarizes the current physics and mechanical design of the CPHS RFQ and presents the fabrication status of the test section. Table 1: Design Parameters of the CPHS RFQ Parameters Value Unit
30876324
Energy storage in intermediate energy heavy-ion collisions.
A systematic calculation for energy deposition in intermediate energy heavy-ion collisions, concerning the effects of both entrance channel dynamics and intrinsic properties of nuclei, has been carried out by means of the Boltzmann-Uehling-Uhlenbeck (BUU) simulation. The limitation on excitation energy is essentially related to the dynamics of the entrance channel, while the contribution from the mean field may also be quite large and cannot be neglected.