Tarlochan Bhatia

A High-Performance D-Lithium Neutron Source for Fusion Technology Testing: Accelerator Driver Design

Recent advances in high-current linear accelerator technology have considerably increased the attractiveness of a deuterium-lithium high-energy neutron source for fusion materials and technology testing. This paper describes a new Los Alamos conceptual design for a deuteron accelerator aimed at meeting near-term flux requirements of an International Fusion Materials Irradiation Facility. The new neutron-source driver concept is based on the idea of multiple accelerator modules, with each module consisting of two 125-mA, 175-MHz radio-frequency quadrupoles funneling 3-MeV cw deuteron beams into a 35-MeV, 250-mA, 350-MHz drift-tube linac.

Linac RF structures for the Spallation Neutron Source

The Spallation Neutron Source (SNS) project is a collaboration among Argonne, Brookhaven, Lawrence Berkeley, Los Alamos, and Oak Ridge National Laboratories. Los Alamos is responsible for the linac that accelerates the H/sup -/ beam from 2.5 MeV to 1 GeV. For the baseline design, scheduled for completion in 2005, the linac will deliver to the accumulator ring a beam of 1.1-MW average power. In the SNS linac, a conventional 402.5-MHz drift-tube linac (DTL) accelerates the beam from 2.5 to 20 MeV, at which point 805-MHz structures take over. The 805-MHz linac consists of a coupled-cavity drift-tube linac (CCDTL), followed by a coupled-cavity linac (CCL). The DTL uses permanent magnet quadrupoles inside the drift tubes arranged in FOFODODO lattice; the focusing period is 4/spl beta//spl lambda/ long at 402.5 MHz. The CCDTL and CCL use electromagnetic quadrupole magnets external to the rf structure; the FODO lattice period is 12 ph long at 805 MHz. The cavity field profile maintains smooth longitudinal focusing strength per unit length. High cavity stored energy reduces the effect of beam chopping on the cavity fields. The bore radius is 1.25 cm in the DTL, and increases in the CCDTL and CCL in several steps consistent with adequate shunt impedance, to a final value of 2.0 cm. The rf structures are compatible with a future upgrade to a beam power of 4.4 MW.

Beam dynamics design of an RFQ for the SSC laboratory

The design of the radio frequency quadrupole accelerator for the Superconducting Super Collider (SSC) is presented. The RFQ, which accepts the beam from the ion source through the low energy beam transport line, is designed to accelerate an H/sup -/ beam from 35 keV to 2.5 MeV. Key design considerations and the final design parameters for the RFQ are presented. Results of simulation studies with and without misaligned input beam are also discussed.<<ETX>>

A high-flux accelerator-based neutron source for fusion technology and materials testing

Advances in high-current linear-accelerator technology since the design of the Fusion Materials Irradiation Test (FMIT) Facility have increased the attractiveness of a deuteriumlithium neutron source for fusion materials and technology testing. This paper discusses the conceptual design of such a source that is aimed at meeting the near-term requirements of a high-flux high-energy International Fusion Materials Irradiation Facility (IFMIF). The concept employs multiple accelerator modules providing deuteron beams to two liquid-lithium jet targets oriented at right angles. This beam/target geometry provides much larger test volumes than can be attained with a single beam and target and produces significant regions of low neutron-flux gradient. A preliminary beam-dynamics design has been obtained for a 250-mA reference accelerator module. Neutron-flux levels and irradiation volumes were calculated for a neutron source incorporating two such modules, and interaction of the beam with the lithium jet was studied using a thermal-hydraulic computer simulation. Approximate cost estimates are provided for a range of beam currents and a possible facility staging sequence is suggested.

High-resolution parallel particle-in-cell simulations of beam dynamics in the spallation neutron source linac

Abstract In this paper, we present results of using high-performance parallel computers to simulate beam dynamics in an early design of the Spallation Neutron Source (SNS) linac. These are among the most detailed linac simulations ever performed. The simulations have been performed using up to 500 million macroparticles, which is close to the number of particles in the physical system. The simulations are fully three-dimensional, and utilize RF cavity field data from modeling over 400 RF cavities. Furthermore, they use an improved model of the beam dynamics within the cavities. Traditionally, small-scale two-dimensional simulations have been performed on PCs or workstations. While such simulations are sufficient for rapid design and for predicting root mean square properties of the beam, large-scale simulations are essential for modeling the tails of the beam. The large-scale parallel simulation results presented here represent a three order of magnitude improvement in simulation capability, in terms of problem size and speed of execution, compared with typical two-dimensional serial simulations. In this paper we will show how large-scale simulations can be used to predict the extent of the beam halo and facilitate design decisions related to the choice of beam pipe aperture.

High-performance deuterium-lithium neutron source for fusion materials and technology testing

A new approach to a deuterium-lithium neutron source aimed at meeting the near-term requirements of a high-flux high-energy International Fusion Materials Irradiation Facility (IFMIF) is discussed. The concept employs multiple accelerator modules providing deuteron beams to two liquid-lithium jet targets oriented at right angles. This beam-target geometry provides much larger test volumes than can be attained with a single beam and target and produces significant regions of low neutron-flux gradient. A preliminary beam-dynamics design has been obtained for a 250-mA reference accelerator module. Neutron-flux levels and irradiation volumes were calculated for a neutron source incorporating two such modules, and interaction of the beam with the lithium jet was studied using a thermal-hydraulic computer simulation. Cost estimates are provided for a range of beam currents, and a possible facility staging sequence is suggested.<<ETX>>

Accelerator for the production of tritium (APT)

A collaborative study by Los Alamos and Brookhaven National Laboratories investigating a facility to produce tritium for the USAs defense needs indicates that a 1.6-GeV, 250-mA proton accelerator is required. A reference design of this accelerator starts with two parallel 125-keV injectors feeding the 350-MHz radio-frequency quadrupoles that funnel at 2.5-MeV into a 700-MHz drift-tube linac. This then injects at 100 MeV into a 1400-MHz side-coupled linac. The accelerator will cost about

Longitudinal emittance in high-current linear ion accelerators

1.2B and require 746 MW of electricity. The accelerator components, the control and diagnostics, and the accelerator facility are discussed, and design considerations are presented.<<ETX>>

A High Intensity Linac for the National Spallation Neutron Source

Results of numerical beam-dynamics studies for both the radiofrequency quadrupole (RFQ) and the drift-tube linac (DTL) are presented. The scaling of longitudinal emittance produced during the adiabatic bunching in an RFQ is discussed. The benefits of using ramped DTL accelerating field designs to maintain high longitudinal focusing strength with increasing particle energy are shown. For the RFQ bunching, it is found that: (1) nonlinear RF and space-charge fields are both important, (2) xi /sub 1/ (longitudinal emittance) scales as the product of zero-current separatrix area times a current-dependent factor that decreases with increasing current, and (3) the decrease of xi /sub 1/ with current is correlated with transverse emittance growth. For the DTL, both rapid and slow charge-redistribution emittance growth mechanisms are observed. The rapid growth is consistent with the charge redistribution mechanism studied previously. The slow growth is caused by a gradual weakening of the longitudinal focusing force with increasing beam velocity and can be controlled if the accelerating field can be ramped to compensate.<<ETX>>