28 Matching Results

Search Results

Advanced search parameters have been applied.

Measurement of np elastic scattering spin-spin correlation parameters at 484, 634, and 788 MeV

Description: The spin-spin correlation parameters C/sub LL/ and C/sub SL/ were measured for np elastic scattering at the incident neutron kinetic energy of 634 MeV. Good agreement was obtained with previously measured data. Additionally, the first measurement of the correlation parameter C/sub SS/ was made at the three energies, 484, 634, and 788 MeV. It was found that the new values, in general, do not agree well with phase shift predictions. A study was carried out to determine which of the isospin-0 partial waves will be affected by this new data. It was found that the /sup 1/P/sub 1/ partial wave will be affected significantly at all three measurement energies. At 634 and 788 MeV, the /sup 3/S/sub 1/ phase shifts will also change. 29 refs., 21 figs., 16 tabs.
Date: March 1, 1989
Creator: Garnett, R.W.
Partner: UNT Libraries Government Documents Department

The Brown-Servranckx matching transformer for simultaneous RFQ to DTL H{sup +} and H{sup {minus}} matching

Description: The issue involved in simultaneous matching of H{sup +} and H{sup -} beams between an RFQ and DTL lies in the fact that both beams experience the same electric-field forces at a given position in the RFQ. Hence, the two beams are focused to the same correlation. However, matching to a DTL requires correlation of the opposite sign. The Brown-Servranckx quarter-wave ({lambda}/4) matching transformer system, which requires four quadrupoles, provides a method to simultaneously match H{sup +} and H{sup -} beams between an RFQ and a DTL. The method requires the use of a special RFQ section to obtain the Twiss parameter conditions {beta}{sup x}={beta}{sup y} and {alpha}{sub x}={alpha}{sub y}=0 at the exit of the RFQ. This matching between the RFQ and DTL is described.
Date: September 1, 1996
Creator: Wadlinger, E.A. & Garnett, R.W.
Partner: UNT Libraries Government Documents Department

A design approach for superconducting high-current ion linacs

Description: An approach for designing superconducting high-current ion linacs is described. This approach takes advantage of the large velocity acceptance of high-gradient cavities with a small number of cells. It is well known that this feature leads to a linac design with great operational flexibility. Algorithms which have been incorporated into a design code and a beam dynamics code are discussed. Simulation results using these algorithms are also presented.
Date: September 1996
Creator: Garnett, R. W. & Wangler, T. P.
Partner: UNT Libraries Government Documents Department

Space-charge calculation for bunched beams with 3-D ellipsoidal symmetry

Description: A method for calculating 3-D space-charge forces has been developed that is suitable for bunched beams of either ions or relativistic electrons. The method is based on the analytic relations between charge-density and electric fields for a distribution with 3-D ellipsoidal symmetry in real space. At each step we use a Fourier-series representation for the smooth particle-density function obtained from the distribution of the macroparticles being tracked through the elements of the system. The resulting smooth electric fields reduce the problem of noise from artificial collisions, associated with small numbers of interacting macroparticles. Example calculations will be shown for comparison with other methods. 4 refs., 2 figs., 1 tab.
Date: January 1, 1991
Creator: Garnett, R.W. & Wangler, T.P.
Partner: UNT Libraries Government Documents Department

Linear accelerator for tritium production

Description: For many years now, Los Alamos National Laboratory has been working to develop a conceptual design of a facility for accelerator production of tritium (API). 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.
Date: December 31, 1995
Creator: Garnett, R.W.; Billen, J.H. & Chan, K.C.D.
Partner: UNT Libraries Government Documents Department

Status of a new switchyard design for LANSCE

Description: Funding was recently received to study modifications of a section of the LANSCE beam switchyard. At present, the switchyard is used to deliver a proton beam to experimental Area A and an H{sup {minus}}-ion beam down Line D. The total H{sup {minus}} repetition rate is 120 Hz, 100 Hz is transported to the Weapons Neutron Research (WNR) area. The remaining 20 Hz is injected into the Proton Storage Ring (PSR). In order to provide H{sup {minus}} beam to other experimental areas without interfering with the PSR operations, a new design of the switchyard is in progress. The authors are presently investigating a solution that would use pulsed kicker magnets to deflect a fraction of the WNR H{sup {minus}} beam down a separate existing beam-line at the demand of the experimenters.
Date: December 31, 1998
Creator: Garnett, R.W.; Rose, C.; Shelley, F. & Zumbro, J.D.
Partner: UNT Libraries Government Documents Department

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

Commissioning plan for a high-current proton linac

Description: High-power proton linacs (E>500 MeV) are potentially useful for transmutation applications, such as the production of tritium. In production applications, high availability is essential. Achieving high availability requires an accelerator design that simplifies maintenance and accommodates commissioning procedures designed to minimize tune-up time. These are worthwhile goals for any accelerator, but the very high beam powers (170 MW) and heavy beam loading of the Accelerator Production of Tritium (APT) linac introduce significant new challenges. This paper will describe the commissioning plan, as developed to date.
Date: September 1, 1997
Creator: Chan, K.C.D.; Barber, R.L. & Garnett, R.W.
Partner: UNT Libraries Government Documents Department

CONCEPTUAL DESIGN OF A LOW-BETA SC PROTON LINAC

Description: In this paper we discuss the conceptual design of a low-{beta} superconducting proton linac based on multi-gap spoke resonator structures. We have demonstrated the feasibility of using superconducting accelerating structures throughout a proton linac for high-peak current applications. The injection energy for this linac is assumed to be 6.7 MeV, which equals the output energy of the CW RFQ built for the Low-Energy Demonstration Accelerator now operating at Los Alamos. The beam is accelerated to 109 MeV using multi-gap spoke resonators. Both 2-gap and 3-gap cavities are used in three accelerating sections with geometric-{beta} values of 0.175, 0.2, and 0.34. Higher beam energies can be achieved by transitioning to elliptical superconducting cavities to further accelerate the beam. Preliminary beam-dynamics simulation results are shown and discussed.
Date: April 1, 2001
Creator: GARNETT, R. W.; WANGLER, T. P & AL, ET
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

Use of the LEDA Facility as an ADS High-Power Accelerator Test Bed

Description: The Low-Energy Demonstration Accelerator (LEDA) was built to generate high-current proton beams. Its successful full-power operation and testing in 1999-2001 confirmed the feasibility of a high-power linear accelerator (linac) front end, the most technically challenging portion of such a machine. The 6.7-MeV accelerator operates reliably at 95-mA CW beam current with few interruptions orjaults, and qualiJes as one of the most powerful accelerators in the world. LEDA is now available to address the needs of other programs. LEDA can be upgraded in a staged fashion to allow for full-power accelerator demonstrations. The proposed post-h!FQ accelerator structures are 350-MHz superconducting spoke cavities developed for the AAA /APT program. The superconducting portion of the accelerator is designed for a IOO-mA proton beam current. Superconducting cavities were chosen because of the signijkant thermal issues with room-temperature structures, the larger superconducting cavity apertures, and the lower operating costs ('because of improved electrical efficiency) of a superconducting accelerator. Since high reliability is a major issue for an ADS system, the superconducting design architecture alIows operation through faults due to the failure of single magnets or superconducting cavities. The presently installed power capacity of 13 MVA of input ACpower is capable of supporting a 40-MeVproton beam at 100 mA. (The input power is easily expandable to 25 MVA, allowing up to 100-MeV operation). Operation at 40-MeV would provide a complete demonstration of all of the critical accelerator sub-systems ofa full-power ADS system.
Date: January 1, 2003
Creator: Garnett, R. W. (Robert W.) & Sheffield, R. L. (Richard L.)
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

Design of a current-independent matching section for APDF

Description: We describe the design of a current-independent matching section which could be used to match a 100-MeV, CW beam from a 7-MeV, 350-Mhz RFQ into a 350-Mhz DTL for the proposed Accelerator Performance Demonstration Facility (APDF). This facility is being proposed to demonstrate the performance of a high-current, CW front-end (up to 40-MeV and including a funnel) which would be applicable for the accelerator production of tritium, accelerator transmutation of waste, and accelerator-based conversion of defense waste programs. A detailed description of the APDF is given in another paper presented at this conference.
Date: September 1, 1994
Creator: Garnett, R. W. & Smith, P.
Partner: UNT Libraries Government Documents Department

Challenge of benchmarking simulation codes for the LANL beam-halo experiment.

Description: We compare macroparticle simulations with beam-profile measurements from a proton beam-halo experiment in a study of beam-halo formation in mismatched beams in a 52-quadrupole periodic-focusing channel. The lack of detailed measurement of the initial distribution is an important issue for being able to make reliable predictions of the halo. We have found earlier that different initial distributions with the same Courant-Snyder parameters and emittances produce similar matched-beam profiles, but different mismatched-beam profiles in the transport system. Also, input distributions with greater population in the tails produce larger rates of emittance growth. We have concluded that using only the known Courant-Snyder parameters and emittances as input parameters is insufficient information for reliable simulations of beam halo formed in mismatched beams. The question is how to obtain the best estimate of the input beam distribution needed for more accurate simulations. In this paper, we investigate a new least squares fitting procedure, which is applied to the simulations used to determine the injected beam distribution, in an attempt to obtain a more accurate description of halo formation than fiom simulation alone.
Date: January 1, 2003
Creator: Wangler, Thomas P.,; Lysenko, W. P. (Walter P.); Qiang, J. (Ji) & Garnett, R. W. (Robert W.)
Partner: UNT Libraries Government Documents Department

Availability results for the LANSCE accelerator complex

Description: The results of an analysis of operations data from the 1996 run-cycle of the LANSCE accelerator complex will be presented. Frequency and history of operational events including system and component failures which affect beam availability have been tracked. Some of the significant downtime incidents will be described and analyzed in detail. These results will be used to improve future operations and beam availability.
Date: September 1, 1997
Creator: Callaway, N.T.; Garnett, R.W.; Jones, K.W.; Oothoudt, M.A. & Ray, B.D.
Partner: UNT Libraries Government Documents Department

Nonlinear beam expander for ESNIT

Description: We describe the design of a beam-redistribution and expansion system for the Japanese Atomic Energy Research Institute (JAERI) Energy Selective Neutron Irradiation Test Facility (ESNIT). The system tailors the beam exiting a deuteron accelerator at energies from 20 to 35 MeV for deposition on a lithium neutron-production target. A uniform beam-intensity distribution in a well-defined irradiation area is inquired at the target and is achieved by the use of nonlinear elements. The design of the high-energy beam transport (HEBT) for ESNIT includes a 90{degree} achromatic bend, a matching section with an energy-compacting cavity, a nonlinear beam expander, a target imager, a shielding dipole, and an rf-cavity system to add energy spread to the beam before it impinges on the target. The system meets performance requirements at multiple energies and currents, and for different spot sizes on target.
Date: September 1, 1994
Creator: Rusthoi, D. P.; Blind, B.; Garnett, R. W.; Hanna, D. S.; Jason, A. J.; Kraus, R. H. Jr. et al.
Partner: UNT Libraries Government Documents Department

Error and tolerance estimates for the SSC CCL

Description: A new code, CCLTRACE, has been used to estimate error and tolerance limits for two possible examples of a 1284-MHz, 70--600 MeV CCL for the SSC Linac. By calculating the dynamics of the beam center as well as the beam ellipsoid, CCLTRACE can efficiently perform error studies using Monte Carlo techniques.
Date: January 1, 1990
Creator: Bhatia, T.S.; Garnett, R.W.; Neuschaefer, G.H. (Lawrence Berkeley Lab., CA (USA)) & Crandall, K.R. (AccSys Technology, Inc., Pleasanton, CA (USA))
Partner: UNT Libraries Government Documents Department

Linear accelerator for production of tritium: Physics design challenges

Description: In the summer of 1989, a collaboration between Los Alamos National Laboratory and Brookhaven National Laboratory conducted a study to establish a reference design of a facility for accelerator production of tritium (APT). The APT concept is that of a neutron-spallation source, which is based on the use of high-energy protons to bombard lead nuclei, resulting in the production of large quantities of neutrons. Neutrons from the lead are captured by lithium to produce tritium. This paper describes the design of a 1.6-GeV, 250-mA proton cw linear accelerator for APT.
Date: January 1, 1990
Creator: Wangler, T.P.; Lawrence, G.P.; Bhatia, T.S.; Billen, J.H.; Chan, K.C.D.; Garnett, R.W. et al.
Partner: UNT Libraries Government Documents Department

Miniature accelerator-driven gamma source concept.

Description: Recent developments in W-band (-100 GHz) traveling wave tube technology at Los Alarnos may lead to a compact high-power W-band RE source. A conceptual design of a compact 8-MeV electron linac that codd be powered by this source is presented, including electromagnetic structure calculations, proposed rnicrojbbrication and manufacturing methods, supporting calculations to estimate accelerator performance, and gumma production rates based on preliminary target geometries and expected output beam current.
Date: January 1, 2003
Creator: Garnett, R. W. (Robert W.); Chan, K. D. (Kwok-Chi D.); Wangler, Thomas P.,; L.), Wood R. L. (Richard; Carlsten, B. E. (Bruce E.) & Kirbie, H. C. (Hugh C.)
Partner: UNT Libraries Government Documents Department

Beam halo in mismatched proton beams.

Description: Progress was made during the past decade towards a better understanding of halo formation caused by beam mismatch in high-intensity beams. To test these ideas an experiment was carried out at Los Alamos with proton beams in a 52-quadrupole focusing channel. Rms emittances and beam widths were obtained from measured beam profiles for comparison with the maximum emittance growth predictions of a free-energy model and the maximum haloamplitude predictions of a particle-core model. The experimental results are also compared with multiparticle simulations. In this paper we will present the experimental results and discuss the implications with respect to the validity of both the models and the simulations. Keywords: beam halo, emittance growth, beam profiles, simulations, space charge, mismatch
Date: January 1, 2002
Creator: Wangler, Thomas P.,; Allen, C. K. (Christopher K.); Chan, D. (Dominic); Colestock, P. L. (Patrick L.),; Crandall, K. R. (Kenneth R.); Qiang, J. (Ji) et al.
Partner: UNT Libraries Government Documents Department

ADPF spoke cavity cryomodule concept

Description: The Accelerator Driven Test Facility (ADTF) is being developed as a reactor concepts test bed for transmutation of nuclear waste. A 13.3 mA continuous-wave (CW) proton beam will be accelerated to 600 MeV and impinged on a spallation target. The subsequent neutron shower is used to create a nuclear reaction within a subcritical assembly of waste material that reduces the waste half-life from the order of 10{sup 5} years to 10{sup 2} years. Additionally, significant energy is produced that can be used to generate electrical power. The ADTF proton accelerator consists of room-temperature (RT) structures that accelerate the beam to 6.7-MeV and superconducting (SC) elements that boost the beam's energy to 600-MeV. Traditional SC elliptical cavities experience structural difficulties at low energies due to their geometry. Therefore, stiff-structured SC spoke cavities have been adopted for the energy range between 6.7 and 109 MeV. Elliptical cavities are used at the higher energies. This paper describes a multi-spoke-cavity cryomodule concept for ADTF.
Date: January 1, 2001
Creator: Kelley, J. P. (John Patrick); Roybal, P. L. (Phillip L.); La Fave, R. P. (Richard P.); Waynert, J. A. (Joseph A.); Schrage, D. L. (Dale L.); Schmierer, E. N. (Eric N.) et al.
Partner: UNT Libraries Government Documents Department