James Billen

POISSON/SUPERFISH on PC compatibles

We have adapted the POISSON/SUPERFISH codes to run on 486 or 386 PCs. The PC version includes features not found in the standard version, including programs for automatically tuning RFQ, DTL, and CCL cavities; a complex version of the RF field solver; memory allocation for temporary data; many line regions for dividing the mesh into fine or coarse sections; full support for multiple-cell DTL cavities; plotting of resonance-search and transit-time data; and on-line documentation. We modified AUTOMESH to generate self-consistent logical and physical coordinates. This new, more robust code greatly reduces the number of crashes in LATTICE caused by ill-formed mesh triangles along boundaries. The codes solve arbitrarily large problems. Each program allows free-format entry of CON array elements, and provides error checking of user entries. Standard release 4 now uses our root finder and convergence criteria.<<ETX>>

The Los Alamos Accelerator Code Group

The Los Alamos Accelerator Code Group (LAACG) is a national resource for members of the accelerator community who use and/or develop software for the design and analysis of particle accelerators, beam transport systems, light sources, storage rings, and components of these systems. Below we describe the LAACGs activities in high performance computing, maintenance and enhancement of POISSON/SUPERFISH and related codes and the dissemination of information on the INTERNET.

Advanced Beam-Dynamics Simulation Tools for RIA

We are developing multi-particle beam-dynamics simulation codes for RIA driver-linac simulations extending from the low-energy beam transport (LEBT) line to the end of the linac. These codes run on the NERSC parallel supercomputing platforms at LBNL, which allow us to run simulations with large numbers of macroparticles. The codes have the physics capabilities needed for RIA, including transport and acceleration of multiple-charge-state beams, beam-line elements such as high-voltage platforms within the linac, interdigital accelerating structures, charge-stripper foils, and capabilities for handling the effects of machine errors and other off-normal conditions. This year will mark the end of our project. In this paper we present the status of the work, describe some recent additions to the codes, and show some preliminary simulation results.

Physics design of APT linac with normal conducting rf cavities

The accelerator based production of tritium calls for a high-power, cw proton linac. Previous designs for such a linac use a radiofrequency quadrupole (RFQ), followed by a drift-tube linac (DTL) to an intermediate energy and a coupled-cavity linc (CCL) to the final energy. The Los Alamos design uses a high-energy (6.7 MeV) RFQ followed by the newly developed coupled-cavity drift-tube linac (CCDTL) and a CCL. This design accommodates external electromagnetic quadrupole lenses which provide a strong uniform focusing lattice from the end of the RFQ to the end of the CCL. The cell lengths in linacs of traditional design are typically graded as a function of particle velocity. By making groups of cells symmetric in both the CCDTL and CCL, the cavity design as well as mechanical design and fabrication is simplified without compromising the performance. At higher energies, there are some advantages of using superconducting rf cavities. Currently, such schemes are under vigorous study. This paper describes the linac design based on normal conducting cavities and presents simulation results.

A versatile, high-power proton linac for accelerator driven transmutation technologies

We are applying the new coupled-cavity drift-tube linac (CCDTL) to a conceptual design of a high-current, CW accelerator for transmutation applications. A 350-MHz RFQ followed by 700-MHz structures accelerates a 100-mA proton beam to 1 GeV. Several advantages stem from four key features: (1) a uniform focusing lattice from the start of the CCDTL at about 7 MeV to the end of the linac, (2) external location and separate mechanical support of the electromagnetic quadrupole magnets, (3) very flexible modular physics design and mechanical implementation, and (4) compact, high-frequency structures. These features help to reduce beam loss and, hence, also reduce potential radioactivation of the structure. They result in easy alignment, fast serviceability, and high beam availability. Beam funneling, if necessary, is possible at any energy after the RFQ.

A compact high-power proton linac for radioisotope production

Conventional designs for proton linacs use a radio-frequency quadrupole (RFQ), followed by a drift-tube linac (DTL). For higher final beam energies, a coupled cavity linac (CCL) follows the DTL. A new structure, the coupled-cavity drift-tube linac (CCDTL) combines features of an Alvarez DTL and the CCL. Operating in a /spl pi//2 structure mode, the CCDTL replaces the DTL and part of the CCL for particle velocities in the range 0.1/spl les//spl beta//spl les/0.5. We present a design concept for a compact linac using only an RFQ and a CCDTL. This machine delivers a few mA of average beam current at a nominal energy of 70 MeV and is well suited for radioisotope production.

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.

Linear accelerator for tritium production

For many years now, Los Alamos National Laboratory has been working to develop a conceptual design of a facility for accelerator production of tritium (APT). The APT accelerator will produce high energy protons which will bombard a heavy metal target, resulting in the production of large numbers of spallation neutrons. These neutrons will be captured by a low‐Z target to produce tritium. This paper describes the latest design of a room‐temperature, 1.0 GeV, 100 mA, cw proton accelerator for tritium production. The potential advantages of using superconducting cavities in the high‐energy section of the linac are also discussed and a comparison is made with the baseline room‐temperature accelerator.

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>>

Tuning and Cold Test of a Four-Vane RFQ with Ramped Inter-Vane Voltage for the Compact Pulsed Hadron Source

A four-vane radio-frequency quadrupole (RFQ) accelerator is under construction for the Compact Pulsed Hadron Source (CPHS) project at Tsinghua University. The 3 m-long RFQ will accelerate a 50keV proton beam from the ECR source to 3MeV, and deliver it to the downstream drift tube linac (DTL) with a peak current of 50mA, pulse length of 0.5 ms and beam duty factor of 2.5%. The inter-vane voltage is designed to increase with the longitudinal position to produce a short RFQ. Coupling plates are therefore not necessary. The cavity cross section and vane-tip geometry are tailored as a function of the longitudinal position, while limiting the peak surface electric field to 1.8 Kilpatrick. The RFQ is designed, manufactured, and installed at Tsinghua University. We also present the tuning and cold test results of the RFQ accelerator. After final tuning, the relative error of the quadrupole field is within 2%, and the admixture of the two dipole modes are less than 2% of the quadrupole mode.