W. T. Weng

Accumulator ring design for the NSNS project

The goal of the proposed National Spallation Neutron Source (NSNS) is to provide a short pulse proton beam of about 0.5 /spl mu/s with average beam power of 1 MW. To achieve such purpose, a proton storage ring operated at 60 Hz with 1/spl times/10/sup 14/ protons per pulse at 1 GeV is required. The Accumulator Ring (AR) receives 1 msec long H/sup -/ beam bunches of 28 mA from a 1 GeV linac. Scope and design performance goals of the AR are presented, other possible technological choices and design options considered, but not adopted, are also briefly reviewed.

The NSNS high energy beam transport line

In the National Spallation Neutron Source (NSNS) design, a 180 meter long transport line connects the 1 GeV linac to an accumulator ring. The linac beam has a current of 28 mA, pulse length of 1 ms, and 60 Hz rep rate. The high energy transport line consists of sixteen 60/spl deg/ FODO cells, and accommodates a 90/spl deg/ achromatic bend, an energy compressor, collimators, part of the injection system, and enough diagnostic devices to measure the beam quality before injection. To reduce the uncontrolled beam losses, this line has nine beam halo scrapers and very tight tolerances on both transverse and longitudinal beam dynamics under space charge conditions. The design of this line is presented.

The SNS Ring to Target Beam Transport line

The Ring to Target Beam Transport (RTBT) line connects the Spallation Neutron Source (SNS) accumulator ring to the target, with the required footprint for the accelerator complex. This line also provides four sets of beta collimators to clean any beam halo. This 160 meter long transport line consists of eleven 90 degree FODO cells, beam extraction and a beam spreader system, in addition to a ring extraction dump line.

Ultra-high intensity proton accelerators and their applications

The science and technology of proton accelerators have progressed considerably in the past three decades. Three to four orders of magnitude increase in both peak intensity and average flux have made it possible to construct high intensity proton accelerators for modern applications, such as: spallation neutron sources, kaon factory, accelerator production of tritium, energy amplifier and muon collider drivers. The accelerator design focus switched over from intensity for synchrotrons, to brightness for colliders to halos for spallation sources. An overview of this tremendous progress in both accelerator science and technology is presented, with special emphasis on the new challenges of accelerator physics issues such as: H/sup -/ injection, halo formation and reduction of losses.

AGS upgrade to 1-MW with a superconducting linac injector

It has been proposed to upgrade the Alternating Gradient Synchrotron (AGS) accelerator complex at the Brookhaven National Laboratory (BNL) to provide an average proton beam power of 1 MW at the energy of 28 GeV. The facility is to be primarily used as a proton driver for the production of intense neutrino beams. This paper reports on the feasibility study of a proton superconducting linac (SCL) as a new injector to the AGS. The linac beam energy is 1.2 GeV. The beam intensity is adjusted to provide the required average beam power of 1 MW at 28 GeV. The repetition rate of the SCL-AGS facility is 2.5 beam pulses per second.

Beam Transfer Lines for the Spallation Neutron Source

Beam transfer lines for the Spallation Neutron Source (SNS) are designed to have low beam losses for hand on maintenance while satisfying the facility footprint requirements. There are two main beam transfer lines, High Energy Beam Transport (HEBT) line which connect super conducting linac to the accumulator ring and Ring to Target Beam transport (RTBT) which transfers beam from accumulator ring to the target. HEBT line not only transfer the beam from linac to ring but also prepare beam for ring injection, correct the energy jitter from the linac, provide required energy spread for the ring injection, clean the transverse and longitudinal halo particles from the beam, determine the linac beam quality, and provide the protection to the accumulator ring. RTBT line transport the beam from ring to target while fulfilling the target requirements of beam size, maximum current density, beam moment on the target in case of ring extraction kicker failure. and protect the target from the ring fault conditions.

Achromat with linear space charge for bunched beams

The standard definition for an achromat is a transport line having zero values for the spatial dispersion (R16) and the angular dispersion (R26). For a bunched beam with linear space charge this definition of achromaticity does not hold. The linear space charge in the presence of a bend provides coupling between (a) bunch spatial width and bunch length (R15) and (b) bunch angular spread and bunch length (R25). Therefore, achromaticity should be redefined as a line having zero values of the spatial dispersion (R16), the angular dispersion (R26), and matrix elements R15 and R25. These additional conditions (R15 = R25 = 0) can be achieved, for example, with two small RF cavities at appropriate locations in the achromat, to cancel space charge effects. An example of the application of this technique to the Spallation Neutron Source (SNS) high energy beam transport line will be presented.

Effects of Halo on the AGS Injection from 1.2Gev Linac

BNL is conducting a design study of a 1.0 MW super neutrino beam facility. It requires 230 turns charge exchange injection from a 1.2 GeV superconducting linac with 28 mA current for 0.72 msec. This report studies the impact of halo distribution of the linac beam on the efficiency of injection and the final beam distribution in the AGS as functions of the injection orbit bump and the foil thickness. Another important consideration is the residual radiation generated on the accelerator components near the injection area. If necessary, radiation hardened components and local shielding have to be provided.

Space charge and coherent effects in the NSNS storage ring

The goal of the proposed National Spallation Neutron Source (NSNS) is to provide a short pulse proton beam of about 0.5 {mu}s with average beam power of 1-2 MW. To achieve such a purpose, a proton storage ring operate at 60 Hz with 1-2 x 10 {sup 14} protons per pulse at 1 GeV is required. The proton storage ring is one of the major systems in the design of the NSNS. The function of the storage ring is to take the 1.0 GeV proton beam from the Linac and convert the long Linac beam of about 1 ms into a 0.5 {mu}s beam in about one thousand turns. The final beam has 1 x 10 {sup 14} proton per pulse, resulting in 1 MW average beam power at 60 Hz repetition rate. Provision has been reserved for a future upgrade to 2 MW by doubling the storage beam to 2 x 10{sup 14} proton per pulse. The lattice of the storage ring is a simple FODO lattice with three-fold symmetry and the dispersion function is reduced to zero at straight sections by the missing magnet scheme. The total circumference of the ring is 208.6 m and the transition energy is 3.43, higher than the operating energy of 1 GeV to avoid the difficult instability problem that are expected above transition. Other salient design parameters are shown in Table 1.

Design of the AGS Upgrade for a Broad Band Neutrino Superbeam

BNL plans to create a very long base line super neutrino beam facility by upgrading the AGS from the current 0.14 MW to 1.0 MW and beyond. The proposed facility consists of two major components. First is a 1.5 GeV superconducting linac to replace the booster as injector for the AGS, second is the performance upgrade of the AGS itself for higher intensity and repetition rate. The major contribution for the higher power is from the increase of the repetition rate of the AGS from 0.3 Hz to 2.5 Hz, with moderate increase from the intensity. The accelerator design considerations to achieve high intensity and low losses for the new linac and the AGS will be presented. The design aspect for high power operation and easy maintenance will also be covered.