971 Matching Results

Search Results

Advanced search parameters have been applied.

Analysis of longitudinal bunching in an FEL driven two-beam accelerator

Description: Recent experiments have explored the use of a free-electron laser (FEL) as a buncher for a microwave two-beam accelerator, and the subsequent driving of a standing-wave rf output cavity. Here the authors present a deeper analysis of the longitudinal dynamics of the electron bunches as they are transported from the end of the FEL and through the output cavity. In particular, the authors examine the effect of the transport region and cavity aperture to filter the bunched portion of the beam.
Date: August 1, 2000
Creator: Lidia, S.; Gardelle, J.; Lefevre, T.; Donohue, J.T.; Gouard, P.; Rullier, J.L. et al.
Partner: UNT Libraries Government Documents Department

Compensation of RF-Induced Energy Spread in the CEBAF Injector Chopping System

Description: The CEBAF injector chopping system must generate three interleaved 499 MHz pulse trains of independently variable current from a DC input beam prior to axial compression. The chopper consists of two deflection cavities with an aperture midway between them. Lenses flanking the aperture focus the beam from the first cavity into the center of the second, where the RF deflection from the first cavity is removed. The symmetry of the RF energy spread across any time-slice of the beam is dominantly odd. The inverting optics used to focus the beam into the second cavity causes near cancellation of the energy spread from the two cavities. We present experimental measurements of the energy spread effects from a fundamental frequency (1497 MHz) chopper prototype producing a beam of suitable transverse emittance and energy spread, and discuss the expected performance of the subharmonic chopper system to be used for commissioning starting in January 1994.
Date: May 1, 1993
Creator: Tiefenback, M.G. & Krafft, G.A.
Partner: UNT Libraries Government Documents Department

Group-Velocity-Matched Three Wave Mixing in Birefringent Crystals

Description: We show that the combination of pulse-front slant, k-vector tilt, and crystal birefringence often permits exact matching of both phase and group velocities in three wave mixing in birefringent crystals. This makes possible more efficient mixing of short light pulses, and it permits efficient mixing of chirped or broad bandwidth light. We analyze this process and present examples. Differences in the group velocities of the three interacting waves in a nonlinear crystal often limits the effective interaction length. For example, in mixing very short pulses, temporal walk off can stretch the pulses in time unless the crystal is very short. Efficient mixing with such short crystals requires high irradiances, but the irradiances are limited by higher order nonlinear effects such as intensity-dependent refractive index and two-photon absorption. Improved matching of the group velocities can alleviate this problem, allowing longer crystal and lower irradiances. Similarly, for high energy pulses, practical limits on crystal apertures mandate temporally stretching the pulses to reduce irradiances. For the resulting chirped pulses, temporal walk off restricts the chirp range unless the group velocities are well matched. In addition to perfectly matching the group velocities of all three waves, it is sometimes useful to match two velocities, such as the signal and idler in parametric amplification, permitting broadband parametric amplification, or to arrange the velocities of two inputs to bracket the generated sum frequency pulse, giving pulse compression under suitable circumstances.
Date: December 12, 2000
Creator: SMITH,ARLEE V.
Partner: UNT Libraries Government Documents Department

VARIABLE MOMENTUM COMPACTION LATTICE STUDIES.

Description: The VUV storage ring at the National Synchrotron Light Source was used to study the impact of changes in the momentum compaction factors over a large range from positive to negative values. Changes in bunch length and synchrotron tune were measured versus current and RF parameters for these different lattices. By controlling both the first and second-order momentum compaction factors, a lattice was developed in which a pair of alpha buckets was created within the energy aperture of the vacuum chamber and beam was stored simultaneously in both buckets.
Date: March 29, 1999
Creator: KRAMER,S. & MURPHY,J.B.
Partner: UNT Libraries Government Documents Department

A COST OPTIMIZED SMALL APERTURE 2 IN 1 VLHC.

Description: Although one must recognize that parametric studies like this are not equivalent to real cost estimates: one can draw some probable conclusions. Clearly, in all cases, there is a cost optimum: at higher fields, magnet costs rise disproportionally; at low fields tunnel and other linear costs are excessive. Fields above 10 T and bellow 3 T appear to be uneconomic. Field in the 4-6 T range seem optimum. Better superconductors raise the optimum field, but by surprisingly small amounts, and offer only small savings. On the other hand, reducing the magnet apertures yield large savings. In particular, we find that a collider with SSC like energy could cost about half that of the SSC if built with 5 T magnets and apertures yielding an impedance equal to that for the proposed transmission line magnet ring. It would also be about half the cost of a ring made with those transmission line magnets.
Date: July 1, 2001
Creator: PALMER,R.B.; PARKER,B. & FOSTER,G.W.
Partner: UNT Libraries Government Documents Department

Large aperture magnets for a future high power proton synchrotron

Description: A high intensity, high power proton synchrotron is currently under consideration at Fermilab. The machine--known as the Proton Driver--would accelerate 3 x 10{sup 13} protons from 400 MeV to 12 GeV (stage I) or 16 GeV (stage II) and ultimately deliver in excess of 1 MW of beam power. To minimize losses and insure beam stability, the space charge-induced tune shift must be kept well below 0.5. This is accomplished by spreading out bunches both longitudinally and transversely. While the former strategy favors high voltage low frequency RF, the latter leads to magnets with unconventionally large apertures. This requirement, combined with a 1.5 T bending field and rapid cycling operation results in a number of serious but not insurmountable challenges. In this paper, they discuss the design of the Proton Driver magnets and the rationale behind it.
Date: August 14, 2001
Creator: Mills, Jean-Francois Ostiguy and Frederick M.
Partner: UNT Libraries Government Documents Department

LABORATORY EXPERIMENTS ON HEAT-DRIVEN TWO-PHASE FLOWS IN NATURAL AND ARTIFICIAL ROCK FRACTURES

Description: Water flow in partially saturated fractures under thermal drive may lead to fast flow along preferential localized pathways and heat pipe conditions. At the potential high-level nuclear waste repository at Yucca Mountain, water flowing in fast pathways may ultimately contact waste packages and transport radionuclides to the accessible environment. Sixteen experiments were conducted to visualize heat-driven liquid flow in fracture models that included (1) assemblies of roughened glass plates, (2) epoxy replicas of rock fractures, and (3) a fractured specimen of Topopah Spring tuff. Continuous rivulet flow was observed for high liquid flow rates, intermittent rivulet flow and drop flow for intermediate flow rates, and film flow for lower flow rates and wide apertures. Heat pipe conditions (vapor-liquid counterflow with phase change) were identified in five of the seven experiments in which spatially resolved thermal monitoring was performed, but not when liquid-vapor counterflow was hindered by very narrow apertures, and when inadequate working fluid volume was used.
Date: May 21, 1998
Creator: PRUESS, TIMOTHY J. KNEAFSEY AND KARSTEN
Partner: UNT Libraries Government Documents Department

The effect of dividing the magnets on the calculation of the recycler dynamic aperture

Description: The modeling of a lattice and the calculation of the dynamic aperture, are exercises fraught with uncertainty and possible error. If we want an accurate value for the dynamic aperture, we must start with an accurate model for the lattice. This model should incorporate the misalignments, including the rolls, of the lattice elements, as well as the error fields in the magnets. These quantities are not always well known. It has been known for sometime that long term tracking must be symplectic. This means that either we utilize a code like MARYLIE which employs a Lie algebraic approach, or a code that employs zero length kicks for the non-linear parts of the magnetic fields. Calculation of the dynamic aperture of the Recycler is particularly difficult because of the large intrinsic sextupole built into gradient magnets. A recent attempt to calculate the dynamic aperture for the Recycler Ring has used MAD. Originally the calculation was done with the magnets treated, as they exist, as single objects. The result was a dynamic aperture of 3:0{sigma}. The calculation was redone with the magnets split into 16 segments and the result was a dynamic aperture of 9:5{sigma}. This report is an attempt to understand the reason for the difference in these two calculations.
Date: May 8, 2001
Creator: Gelfand, Norman
Partner: UNT Libraries Government Documents Department

Design and prototype tests of a large-aperture 37-53 MHz ferrite-tuned booster synchrotron cavity

Description: The Booster synchrotron at Fermilab employs eighteen 37-53 MHz ferrite-tuned double-gap coaxial radiofrequency cavities for acceleration of protons from 400 MeV to 8 GeV. The cavities have an aperture of 2.25 inches and operate at 55 kV per cavity. Future high duty factor operation of the Booster will be problematic due to unavoidable beam loss at the cavities resulting in excessive activation. The power amplifiers, high maintenance items, are mounted directly to the cavities in the tunnel. A proposed replacement for the Booster, the Proton Driver, will utilize the Booster radiofrequency cavities and requires not only a larger aperture, but also higher voltage. A research and development program is underway at Fermilab to modify the Booster cavities to provide a 5-inch aperture and a 20% voltage increase. A prototype has been constructed and high power tests have bee completed. The cavity design and test results is presented.
Date: July 12, 2001
Creator: al., Mark S. Champion et
Partner: UNT Libraries Government Documents Department

Optimizing the Elemental Sensitivity and Focal Spot Size of a Monolithic Polycapillary Optic Using Micro-X-Ray Fluorescence

Description: A commercial micro-X-ray fluorescence (MXRF) instrument with an aperture X-ray guide was used to compare elemental sensitivities and focal spot sizes with those obtained by focusing the source with a monolithic polycapillary optic retrofitted into the system. The capillary provided an intensity gain of 125 at 4 keV vs. using a pinhole beam collimator; however, this gain advantage declined with increasing analyte line energy as a result of the capillary being designed shorter than its optimal length to fit into the commercial instrument. A minimum capillary focal spot FWHM of 36 {micro}m was achieved, whereas the smallest pinhole aperture available of 50 {micro}m in diameter produced a focal spot width of 69 {micro}m FWHM. Hence, better MXRF lateral resolution could be obtained with the capillary with a simultaneous improvement in elemental sensitivity.
Date: October 1, 1998
Creator: Worley, C.; Havrilla, G.; Gao, N. & Xia, Q.-F.
Partner: UNT Libraries Government Documents Department

A fast injection kicker magnet for the Tevatron

Description: A new proton injection kicker system is required for the Tevatron in the Run II era. The new system was designed to supply 1.25 kG-m into a magnetic aperture of 48 mm vertical x 71 mm horizontal x 5 m long with a 396 ns bunch spacing. The system was designed to be upgraded to 132 ns bunch spacing with additional pulse supplies. The design of the magnet incorporated some novel features in order to meet these requirements. These include adjustable bus spacing to set the inductance and balanced positive and negative high voltage buses. This system has been installed in the Tevatron.
Date: July 25, 2001
Creator: Chris C Jensen, Bruce Hanna and Robert Reilly
Partner: UNT Libraries Government Documents Department

Description of Fracture Systems for External Criticality Reports

Description: The purpose of this Analysis/Model Report (AMR) is to describe probabilistically the main features of the geometry of the fracture system in the vicinity of the repository. They will be used to determine the quantity of fissile material that could accumulate in the fractured rock underneath a waste package as it degrades. This AMR is to feed the geochemical calculations for external criticality reports. This AMR is done in accordance with the technical work plan (BSC (Bechtel SAIC Company) 2001 b). The scope of this AMR is restricted to the relevant parameters of the fracture system. The main parameters of interest are fracture aperture and fracture spacing distribution parameters. The relative orientation of the different fracture sets is also important because of its impact on criticality, but they will be set deterministically. The maximum accumulation of material depends primarily on the fracture porosity, combination of the fracture aperture, and fracture intensity. However, the fracture porosity itself is not sufficient to characterize the potential for accumulation of a fracture system. The fracture aperture is also important because it controls both the flow through the fracture and the potential plugging of the system. Other features contributing to the void space such as lithophysae are also investigated. On the other hand, no analysis of the matrix porosity is done. The parameters will be used in sensitivity analyses of geochemical calculations providing actinide accumulations and in the subsequent Monte Carlo criticality analyses.
Date: September 21, 2001
Creator: Nicot, Jean-Philippe
Partner: UNT Libraries Government Documents Department

IMPACT OF MAGNETIC FIELD INTERFERENCE IN THE SNS RING.

Description: The modest size of the SNS accumulator ring and the use of short, large aperture magnets makes unavoidable the overlapping between the magnetic end fields of the quadrupoles with the adjacent multipole correctors. This interference effect can be quantified through magnetic field simulations and measurements. The impact to the beam dynamics is finally discussed.
Date: June 18, 2001
Creator: PAPAPHILIPPOU,Y.; LEE,Y.Y. & MENG,W.
Partner: UNT Libraries Government Documents Department

Issues in Acceleration of A Muon Beam for a Neutrino Factory

Description: We have developed a concept for acceleration of a large phase-space, pulsed muon beam from 190 MeV to 50 GeV as part of a collaborative study of the feasibility of a neutrino factory based on in-flight decay of muons. The muon beam's initial energy spread was {approximately}20% and each bunch has the physical size of a soccer ball. Production of the muons will be quite expensive, so prevention of loss due to scraping or decay is critical. The former drives the system to large apertures and the latter calls for high real-estate-average gradients. The solution to be presented utilizes a 3 GeV linac to capture the beam, a 4-pass recirculating linac to get the beam to 10 GeV, and then a 5-pass linac to get the beam to 50 GeV. Throughout the system, longitudinal dynamics issues far outweighed transverse dynamics issues. This paper focuses on the issues surrounding the choice of superconducting rf structures over copper structures.
Date: June 1, 2001
Creator: Delayen, J.; Douglas, D.; Harwood, L.; Lebedev, V.; Leemann, C. & Merminga, L.
Partner: UNT Libraries Government Documents Department

Beam loss and collimation in the Fermilab 16 GeV proton driver

Description: A high beam power of 1.15 MW in the proposed 16-GeV Proton Driver [1] implies serious constraints on beam losses in the machine. The main concerns are the hands-on maintenance and ground-water activation. Only with a very efficient beam collimation system can one reduce uncontrolled beam losses to an allowable level. The results on tolerable beam loss and on a proposed beam collimation system are summarized in this paper. A multi-turn particle tracking in the accelerator defined by all lattice components with their realistic strengths and aperture restrictions, and halo interactions with the collimators is done with the STRUCT code [2]. Full-scale Monte Carlo hadronic and electromagnetic shower simulations in the lattice elements, shielding, tunnel and surrounding dirt with realistic geometry, materials and magnetic field are done with the MARS14 code [3]. It is shown that the proposed 3-stage collimation system, allows localization of more than 99% of beamloss in a special straight section. Beam loss in the rest of the accelerator is 0.2 W/m on average.
Date: July 20, 2001
Creator: Alexandr I. Drozhdin, Oleg E. Krivosheev and Nikolai V. Mokhov
Partner: UNT Libraries Government Documents Department

VARIABLE MOMENTUM COMPACTION LATTICE STUDIES.

Description: The VUV storage ring at the National Synchrotron Light Source was used to study the impact of changes in the momentum compaction factors over a large range from positive to negative values. Changes in bunch length and synchrotron tune were measured versus current and RF parameters for these different lattices. By controlling both the first and second-order momentum compaction factors, a lattice was developed in which a pair of alpha buckets was created within the energy aperture of the vacuum chamber and beam was stored simultaneously in both buckets.
Date: March 29, 1999
Creator: KRAMER,S. & MURPHY,J.B.
Partner: UNT Libraries Government Documents Department

Optimization of Orbit Correction Systems Using Generalized Response Matrices and its Application to the LHC Injection Transfer Lines

Description: The LHC injection transfer lines will transport intense high-energy beams over considerable distances. Their relatively tight apertures require precise control of the trajectory. An analytic method has been developed to optimize the performance, reliability and cost of these lines. This method invokes a comprehensive set of performance criteria, makes detailed predictions on orbit correction effectiveness, configuration defects and critical elements, and gives indications for improvement. A path approaching an optimized configuration can thus be established based on well-defined quantitative criteria.
Date: June 1, 2001
Creator: Chao, Yu-Chiu
Partner: UNT Libraries Government Documents Department

Corrector magnets: Combined structural analysis of collier 50 mm aperture ordered wound dipoles interior section

Description: The 50mm aperture prototype collider ordered wound dipole connector magnets have been modeled with finite element techniques considering the individual and combined load cases of the preloading from keys, cooldown to 4 K and the effect of magnetic forces during energizing. Results of the analysis are presented as longitudinal, transverse and shear stresses for the ordered wound coils and as maximum von Mises stress for the carbon steel outer laminations, the stainless steel inner lamination, and the carbon steel keys.
Date: April 1, 1993
Creator: Tran, Vu H.
Partner: UNT Libraries Government Documents Department

A fast injection kicker system for the Tevatron

Description: A new proton injection kicker system is required for the Tevatron in the Run II era. The new system was designed to supply 1.25 kG-m into a magnetic aperture of 48 mm vertical x 71 mm horizontal x 5 m long with a 396 ns bunch spacing. The system was designed to be upgraded to 132 ns bunch spacing with additional pulse supplies. The system design tradeoffs needed to meet these goals is discussed. These include the system topology, the system impedance and the number of magnets. This system has been installed in the Tevatron.
Date: July 25, 2001
Creator: Chris C. Jensen, Robert E. Reilly and Bruce M. Hanna
Partner: UNT Libraries Government Documents Department

Very Large Aperture Diffractive Space Telescope

Description: A very large (10's of meters) aperture space telescope including two separate spacecraft--an optical primary functioning as a magnifying glass and an optical secondary functioning as an eyepiece. The spacecraft are spaced up to several kilometers apart with the eyepiece directly behind the magnifying glass ''aiming'' at an intended target with their relative orientation determining the optical axis of the telescope and hence the targets being observed. The magnifying glass includes a very large-aperture, very-thin-membrane, diffractive lens, e.g., a Fresnel lens, which intercepts incoming light over its full aperture and focuses it towards the eyepiece. The eyepiece has a much smaller, meter-scale aperture and is designed to move along the focal surface of the magnifying glass, gathering up the incoming light and converting it to high quality images. The positions of the two space craft are controlled both to maintain a good optical focus and to point at desired targets.
Date: April 20, 1998
Creator: Hyde, Roderick Allen
Partner: UNT Libraries Government Documents Department

Improved Spatial Filter for high power Lasers

Description: A new pinhole architecture incorporates features intended to reduce the rate of plasma generation in a spatial filter for high-energy laser pulse beams. An elongated pinhole aperture is provided in an apertured body for rejecting off-axis rays of the laser pulse beam. The internal surface of the elongated aperture has a diameter which progressively tapers from a larger entrance cross-sectional area at an inlet to a smaller output cross-sectional area at an outlet. The tapered internal surface causes off-axis rays to be refracted in a low density plasma layer that forms on the internal surface or specularly reflected at grazing incidence from the internal surface. Off-axis rays of the high-energy pulse beam are rejected by this design. The external surface of the apertured body adjacent to the larger entrance cross-sectional area at the inlet to the elongated aperture is angled obliquely with respect to the to direction of the path of the high-energy laser pulse beam to backscatter off-axis rays away from the high-energy pulse beam. The aperture is formed as a truncated cone or alternatively with a tapered square cross-section. The internal surface of the aperture is coated with an ablative material, preferably high-density material which can be deposited with an exploding wire.
Date: June 1, 1998
Creator: Estabrook, Kent G.; Celliers, Peter M.; Murray, James E.; DaSilva, Luiz; MacGowan, Brian J.; Rubenchik, Alexander M. et al.
Partner: UNT Libraries Government Documents Department

Synchrotron radiation issues in future hadron colliders

Description: Hadron machines mostly use high field superconducting magnets operating at low temperatures. Therefore the issue of extracting a SR power heat load becomes more critical and costly. Conceptual solutions to the problem exist in the form of beam screens and photon stops. Cooled beam screens are more expensive in production and operation than photon stops, but they are, unlike photon stops, routinely used in existing machines. Photon stops are the most economical solution because the heat load is extracted at room temperature. They presently consider it most prudent to work with a combined beam screen and photon stop approach, in which the photon stop absorbs most of the SR power, and the beam screen serves only the vacuum purpose. Provided that the recently launched photon stop R and D [10] supports it, we would like to explore solutions with photon stops only. This would allow to reduce the magnet apertures to a certain extent with respect to those required to accommodate high SR power compliant beam screens and reduce cost. The possibility of magnet designs, which have larger vertical apertures where large cooling capillaries can be housed at no additional cost, would allow to soften this statement somewhat and should therefore be pursued as well.
Date: November 21, 2002
Creator: Bauer, P.; Darve, C. & Terechkine, I.
Partner: UNT Libraries Government Documents Department