[en] 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

[en] This report summarizes the study of various longitudinal problems pertaining to the transition-energy crossing in the proposed Relativistic Heavy Ion Collider. Scaling laws are provided for the effects of chromatic non-linearity, self-field mismatch, and microwave instability. It is indicated that the beam loss and bunch-area growth are mainly caused by the chromatic non-linear effort, which is enhanced by the space-charge force near transition. Computer simulation using the program. TIBETAN shows that a ''γT-jump'' of about 0.8 unit within a time period of 60 ms is adequate to achieve a ''clean'' crossing, provided that the remnant voltage of the 160 MHz rf system is less than 10 kV

[en] Since its invention by Palmer in 1988, crab crossing has been explored by many people for both linear and storage ring collides to allow for an angle crossing without a loss of luminosity. Various crab crossing scenarios have been incorporated in the design of newly proposed linear collides and Β-factory projects. For a hadron collider, this scheme can also be employed to lower Β* at the interaction point for a higher luminosity. In this paper, we first review the principle and operational requirements of various crab crossing schemes for storage ring collides. A Hamiltonian formalism is developed to study the dynamics of crab crossing and the related synchro-betatron coupling. Requirements are obtained for the operational voltage and frequency of the crab cavities, and for the accuracy of voltage matching and phase matching of the cavities. For the recently proposed high-field hadron collider, a deflection crabbing scheme can be used to reduce Β* from 0. 1 m to 0.05 m and below, without a loss of luminosity due to angle crossing. The required voltage of the storage rf system is reduced from 100 MV to below 10 MV. With the same frequency of 379 MHz operating in a transverse mode, the required voltage of the crab cavities is about 3.2∼4.4 MV. The required accuracy of voltage and betatron-phase matching is about 1 %

[en] The scaling laws for bunched-beam stochastic cooling has been derived in terms of the optimum cooling rate and the mixing condition. In the case that particles occupy the entire sinusoidal rf bucket, the optimum cooling rate of the bunched beam is shown to be similar to that predicted from the coasting-beam theory using a beam of the same average density and mixing factor. However, in the case that particles occupy only the center of the bucket, the optimum rate decrease in proportion to the ratio of the bunch area to the bucket area. The cooling efficiency can be significantly improved if the synchrotron side-band spectrum is effectively broadened, e.g. by the transverse tune spread or by using a double rf system

[en] In heavy ion storage rings, intra-beam scattering (IBS) between high charge state ions results in a large beam emittance during storage. The ultimate machine performance depends on achieving the highest possible magnetic field quality and alignment accuracy in the insertion-region (IR) triplet magnets during low-β operation when the beam size is the largest in the triplets. Therefore, effective compensation of magnet construction errors and misalignments is crucial. Heavy-ion beams (Au⁷⁹⁺ will be accelerated and stored for 10 hours in the Relativistic Heavy Ion Collider (RHIC) at the energy of 100 GeV/u in two separated rings consisting of superconducting magnets. Due to strong IBS, the transverse beam emittance grows from 10π mm-mr at injection to more than 40π mm-mr at storage. Dipoles and riplets of quadrupoles of large bore are placed on both sides of the six interaction points (IP). In order to maximize the luminosity at two IPs with proposed experiments, the nearby triplets are designed to enable the collision β-function to be reduced to β = 1 m. Consequently, the rms transverse beam size becomes large at the triplets (β_max = 1400 m), increasing from σ = 2.3 mm to 4.7 mm during the period of storage. At the end of storage, the 5σ beam size becomes about 71% of the coil radius (65 mm). The goal if IR triplet error compensation is to ensure satisfactory magnetic field quality and beam long-term stability up to this 5σ radius

[en] Based on assumptions applicable to many circular accelerators, we simplify into analytical form the growth rates of a hadron beam under Coulomb intrabeam scattering (IBS). Because of the dispersion that correlates the horizontal closed orbit to the momentum, the scaling behavior of the growth rates are drastically different at energies low and high compared with the transition energy. At high energies the rates are approximately independent of the energy. Asymptotically, the horizontal and longitudinal beam amplitudes are linearly related by the average dispersion. At low energies, the beam evolves such that the velocity distribution in the rest frame becomes isotropic in all the directions

[en] The understanding of crystalline beams has advanced to the point where one can now, with reasonable confidence, undertake an analysis of the luminosity of colliding crystalline beams. Such a study is reported here. It is necessary to observe the criteria, previously stated, for the creation and stability of crystalline beams. This requires, firstly, the proper design of a lattice. Secondly, a crystal must be formed, and this can usually be done at various densities. Thirdly, the crystals in a colliding-beam machine are brought into collision. We study all of these processes using the molecular dynamics (MD) method. The work parallels what was done previously, but the new part is to study the crystal-crystal interaction in collision. We initially study the zero-temperature situation. If the beam-beam force (or equivalent tune shift) is too large then over-lapping crystals can not be created (rather two spatially separated crystals are formed). However, if the beam-beam force is less than but comparable to that of the space-charge forces between the particles, we find that overlapping crystals can be formed and the beam-beam tune shift can be of the order of unity. Operating at low but non-zero temperature can increase the luminosity by several orders of magnitude over that of a usual collider. The construction of an appropriate lattice, and the development of adequately strong coding, although theoretically achievable, is a challenge in practice

[en] Expressions for the minimum size and speed of a transition-energy (γ_t-) jump needed to diminish the chromatic non-linear effect, the self-field mismatch, and the microwave instabilities in the Relativistic Heavy Ion Collider (RHIC) are obtained. A γ_t-jump of 0.8 units is needed to be performed within 60 ms in order to achieve a ''clean'' transition crossing

[en] The Relativistic Heavy Ion Collider (RHIC) is currently under commissioning after a seven-year construction cycle. Unlike conventional hadron colliders, this machine accelerates, stores, and collides heavy ion beams of various combinations of species. The dominant intensity dependent effects are intra-beam scattering at both injection and storage, and complications caused by crossing transition at a slow ramp rate. In this paper, we present theoretical formalisms that have been used for our study, and discuss mechanisms, impacts, and compensation methods including beam cooling and transition jump schemes. Effects of space charge, beam-beam, and ring impedances are also summarized

[en] During the past decades, large-scale national neutron sources have been developed in Asia, Europe, and North America. Complementing such efforts, compact hadron beam complexes and neutron sources intended to serve primarily universities and industrial institutes have been proposed, and some have recently been established. Responding to the demand in China for pulsed neutron/proton-beam platforms that are dedicated to fundamental and applied research for users in multiple disciplines from materials characterization to hadron therapy and radiography to accelerator-driven sub-critical reactor systems (ADS) for nuclear waste transmutation, we have initiated the construction of a compact, yet expandable, accelerator complex-the Compact Pulsed Hadron Source (CPHS). It consists of an accelerator front-end (a high-intensity ion source, a 3-MeV radio-frequency quadrupole linac (RFQ), and a 13-MeV drift-tube linac (DTL)), a neutron target station (a beryllium target with solid methane and room-temperature water moderators/reflector), and experimental stations for neutron imaging/radiography, small-angle scattering, and proton irradiation. In the future, the CPHS may also serve as an injector to a ring for proton therapy and radiography or as the front end to an ADS test facility. In this paper, we describe the design of the CPHS technical systems and its intended operation.