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Simulation studies of the LAMPF proton linac

Description: The LAMPF accelerator consists of two 0.75-MeV injectors, one for H{sup +} and the other for H{sup {minus}}, a separate low-energy beam transport (LEBT) line for each beam species, a 0.75 to 100-MeV drift-tube linac (DTL) operating at 201.25-MHz, a 100-MeV transition region (TR), and a 100 to 800-MeV side-coupled linac (SCL) operating at 805-MHz. Each LEBT line consists of a series of quadrupoles to transport and transversely match the beam. The LEBT also contains a prebuncher, a main buncher, and an electrostatic deflector. The deflector is used to limit the fraction of a macropulse which is seen by the beam diagnostics throughout the linac. The DTL consists of four rf tanks and uses singlet FODO transverse focusing. The focusing period is doubled in the last two tanks by placing a quadrupole only in every other drift-tube. Doublet FDO transverse focusing is used in the SCL. The TR consists of separate transport lines for the H{sup +} and H{sup {minus}} beams. The pathlengths for the two beams differ, by introducing bends, so as to delay arrival of one beam relative to the other and thereby produce the desired macropulse time structure. Peak beam currents typically range from 12 to 18-mA for varying macropulse lengths which give an average beam current of 1-mA. The number of particles per bunch is of the order 10{sup 8}. The work presented here is an extension of previous work. The authors have attempted to do a more complete simulation by including modeling of the LEBT. No measurements of the longitudinal structure of the beam, except phase-scans, are performed at LAMPF. The authors show that, based on simulation results, the primary causes of beam spill are inefficient longitudinal capture and the lack of longitudinal matching. Measurements to support these claims are not presently made at LAMPF. ...
Date: May 1, 1995
Creator: Garnett, R.W.; Gray, E.R.; Rybarcyk, L.J. & Wangler, T.P.
Partner: UNT Libraries Government Documents Department

Simulated performance of the superconducting section of the APT linac under various fault and error conditions

Description: The current design for the production of tritium uses both normal-conducting (NC) and superconducting (SC) structures. To evaluate the performance of the superconducting part of the linac which constitutes more than 80% of the accelerator, studies have been made to include the effects of various error and fault conditions. Here, the authors present the simulation results of studies such as effects of rf phase and amplitude errors, cavity/klystron failure, quadrupole misalignment errors, quadrupole gradient error, and beam-input mismatches.
Date: August 1, 1997
Creator: Gray, E.R.; Nath, S. & Wangler, T.P.
Partner: UNT Libraries Government Documents Department

Beam dynamics aspects for the APT integrated linac

Description: The accelerator-based production of tritium calls for a high-power cw proton linac. The current Los Alamos design uses an integrated approach in terms of accelerating structure. The front part of the accelerator uses normal-conducting (NC) structures while most (>80%) of the linac structure is superconducting (SC). Here, the authors report the beam-dynamics rationale used in the integrated design and present particle simulation results.
Date: August 1, 1997
Creator: Nath, S.; Gray, E.R. & Wangler, T.P.
Partner: UNT Libraries Government Documents Department

Overview of the APT high-energy beam transport and beam expanders

Description: The APT high energy beam transport (HEBT) and beam expanders convey the 1700-MeV, 100-mA cw proton beam from the linac to the tritium target/blanket assembly, or a tuning beam stop. The HEBT includes extensive beam diagnostics, collimators, and beam jitter correction, to monitor and control the 170-MW beam prior to expansion. A zero-degree beamline conveys the beam to the beam stop, and an achromatic bend conveys the beam to the tritium production target. Nonlinear beam expanders make use of higher-order multipole magnets and dithering dipoles to expand the beam to a uniform-density, 16-cm wide by 160-cm high rectangular profile on the tritium-production target. The overall optics design will be reviewed, and beam simulations will be presented.
Date: August 1, 1997
Creator: Shafer, R.E.; Blind, B. & Gray, E.R.
Partner: UNT Libraries Government Documents Department

Recent developments for high-intensity proton linacs

Description: High-intensity proton linacs are being proposed for new projects around the world, especially for tritium production, and for pulsed spallation neutron sources. Typical requirements for these linacs include peak beam current of about 100 mA, and final energies of 1 GeV and higher, APT, a tritium production linac, requires cw operation to obtain sufficient average tritium production linac, requires cw operation to obtain sufficient average beam power, and H{sup +} ion sources appear capable of providing the required current and emittances. The pulsed spallation neutron source requires a linac as an injector to one or more accumulator rings, and favors the use of an H{sup minus} beam to allow charge-exchange injection into the rings. For both applications high availability is demanded; the fraction of scheduled beam time for actual production must be 75% or more. Such a high availability requires low beam-loss to avoid radioactivation of the accelerator, and to allow hands-on maintenance that will keep the mean repair and maintenance times short. To keep the accelerator activation sufficiently low, the beam loss should not exceed about 0.1 to 1.0 nA/m, except perhaps for a few localized places, where special design adaptations could be made. The requirement of such small beam losses at such a high intensity presents a new beam physics challenge. This challenge will require greater understanding of the beam distribution, including the low- density beam halo, which is believed to be responsible for most of the beam losses. Furthermore, it will be necessary to choose the apertures so the beam losses will be acceptably low, and because large aperture size is generally accompanied by an economic penalty resulting from reduced power efficiency, an optimized choice of the aperture will be desirable.
Date: April 1, 1996
Creator: Wangler, T.P.; Garnett, R.W.; Gray, E.R. & Nath, S.
Partner: UNT Libraries Government Documents Department

Dynamics of beam halo in mismatched beams

Description: High-power proton linacs for nuclear materials transmutation and production, and new accelerator-driven neutron spallation sources must be designed to control beam-halo formation, which leads to beam loss. The study of particle-core models is leading to a better understanding of the causes and characteristics of beam halo produced by space-charge forces in rms mismatched beams. Detailed studies of the models have resulted in predictions of the dependence of the maximum amplitude of halo particles on a mismatch parameter and on the space-charge tune-depression ratio. Scaling formulas have been derived which will provide guidance for choosing the aperture radius to contain the halo without loss.
Date: September 1, 1996
Creator: Wangler, T.P.; Garnett, R.W.; Gray, E.R.; Ryne, R.D. & Wang, T.S.
Partner: UNT Libraries Government Documents Department

New high power linacs and beam physics

Description: New high-power proton linacs must be designed to control beam loss, which can lead to radioactivation of the accelerator. The threat of beam loss is increased significantly by the formation of beam halo. Numerical simulation studies have identified the space-charge interactions, especially those that occur in rms mismatched beams, as a major concern for halo growth. The maximum-amplitude predictions of the simulation codes must be subjected to independent tests to confirm the validity of the results. Consequently, the authors compare predictions from the particle-core halo models with computer simulations to test their understanding of the halo mechanisms that are incorporated in the computer codes. They present and discuss scaling laws that provide guidance for high-power linac design.
Date: August 1, 1997
Creator: Wangler, T.P.; Gray, E.R.; Nath, S.; Crandall, K.R. & Hasegawa, K.
Partner: UNT Libraries Government Documents Department

Development of a commissioning plan for the APT linac

Description: The Accelerator Production of Tritium (APT) facility is based on a linac which incorporates both normal-conducting and superconducting RF technology and accelerates a 100-mA cw proton beam to an energy of 1,030 MeV or higher, depending on the desired production rate. Commissioning plans to achieve full power operation with minimum beam-induced activation of components have been evolving. This paper presents the main issues and the basic approaches that are now being discussed.
Date: December 1998
Creator: Funk, L. W.; Crandall, K. R.; Gilpatrick, J. D.; Gray, E. R.; Regan, A. H.; Rohlev, A. et al.
Partner: UNT Libraries Government Documents Department

Alignment and steering scenarios for the APT linac

Description: The Accelerator for the Production of Tritium (APT) requires a very high proton beam current (100 mA cw). Requirement for hands-on maintenance limits the beam spill to less than 0.2 nA/m along most of the linac. To achieve this, it is important to understand the effects of fabrication, installation and operational errors, establish realistic tolerances, and develop techniques for mitigating their consequences. A new code, PARTREX, statistically evaluates the effects of alignment, quadrupole field, and rf phase and amplitude errors in the linac. This paper reviews the effects of quadrupole misalignments and present two steering algorithms that minimize the potential for particle loss from the beam halo. These algorithms were tested on the 8-to-20 MeV portion of the APT linac.
Date: September 1, 1996
Creator: Stovall, J.E.; Gray, E.R.; Nath, S.; Takeda, H.; Wood, R.L.; Young, L.M. et al.
Partner: UNT Libraries Government Documents Department

Basis for low beam loss in the high-current APT linac

Description: The present evidence that the APT proton linac design will meet its goal of low beam loss operation. The conclusion has three main bases: (1) extrapolation from the understanding of the performance of the 800-MeV LANSCE proton linac at Los Alamos, (2) the theoretical understanding of the dominant halo-forming mechanism in the APT accelerator from physics models and multiparticle simulations, and (3) the conservative approach and key principles underlying the design of the APT linac, which are aimed at minimizing beam halo and providing large apertures to reduce beam loss to a very low value.
Date: December 31, 1998
Creator: Wangler, T.P.; Gray, E.R.; Krawczyk, F.L.; Kurennoy, S.S.; Lawrence, G.P.; Ryne, R.D. et al.
Partner: UNT Libraries Government Documents Department