1,257 Matching Results

Search Results

Advanced search parameters have been applied.

Accelerating structure with linear excitation

Description: The switched power linac (SPL) structures require a ring-shaped laser beam pulse of uniform intensity to avoid transverse field components of the accelerating field at the center. In order to also utilize the reflection of the outgoing EM wave, the switching element has to be very close to the outer edge of the structure to ensure nearly synchronous superposition at the beam hole with the original inward going wave. It is sometimes easier to produce linear (flat) laser beams, e.g., from powerful excimer lasers which have beams of rectangular cross section. Such flat beams could be used to excite linear photocathode switches or be used to produce flat electron beam pulses in electron sources. In this paper, an accelerator structure is proposed which may be considered a variant of the SPL disk structure, but could be used with linear beams. The structure utilizes a double parabolic horn. 8 refs., 9 figs.
Date: March 1, 1988
Creator: Fischer, J. & Srinivasan-Rao, T.
Partner: UNT Libraries Government Documents Department

Testing the Nature of Kaluza-Klein Excitations at Future Lepton Colliders

Description: With one extra dimension, current high precision electroweak data constrain the masses of the first Kaluza-Klein excitations of the Standard Model gauge fields to lie above {approx_equal} 4 TeV. States with masses not much larger than this should be observable at the LHC. However, even for first excitation masses close to this lower bound, the second set of excitations will be too heavy to be produced thus eliminating the possibility of realizing the cleanest signature for KK scenarios. Previous studies of heavy $Z'$ and $W'$ production in this mass range at the LHC have demonstrated that very little information can be obtained about their couplings to the conventional fermions given the limited available statistics and imply that the LHC cannot distinguish an ordinary $Z'$ from the degenerate pair of the first KK excitations of the {gamma} and Z. In this paper we discuss the capability of lepton colliders with center of mass energies significantly below the excitation mass to resolve this ambiguity. In addition, we examine how direct measurements obtained on and near the top of the first excitation peak at lepton colliders can confirm these results. For more than one extra dimension we demonstrate that it is likely that the first KK excitation is too massive to be produced at the LHC.
Date: September 3, 1999
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Experiments on the beam--beam effect in e/sup +/e/sup -/ storage rings

Description: The maximum luminosity in a positron electron storage ring is fundamentally limited by the beam--beam effect. This is the perturbing effect of the electromagnetic field of one beam on the trajectory of every single particle of the other beam. The electromagnetic field of a charged particle beam is highly nonlinear. At a large distance from the beam center the field falls off like the inverse of the distance. Right in the center of the beam where we have a more or less uniform density distribution over a limited region the field rises linear with the distance from the center. So the field rises from the center of the beam, saturates at some distance and going further out falls off again as 1/r. The amplitude of the field depends on the charge density as well as the aspect ratio of the beam. If the electromagnetic field of one beam gets too large, particles of the other beam get lost which leads to a reduced beam lifetime. This effect has been observed in all electron--positron or electron--electron storage rings built so far and is considered the fundamental limit of the performance of electron--positron storage rings. Over the years many measurements have been performed at various laboratories to find the maximum permissible perturbation and the parametric dependence of that perturbation. In this paper, new measurements performed at SPEAR are presented and compared with measurements from ACO, ADONE, and VEEP-2M. Results from other storage rings have been ignored because they either show lower permissible perturbations or because of insufficient published data.
Date: May 1, 1979
Creator: Wiedemann, H.
Partner: UNT Libraries Government Documents Department

Vacuum-to-air interface for the advanced test accelerator beam director

Description: A vacuum-to-air transition was created to facilitate the Lawrence Livermore National Laboratory's Advanced Test Accelerator (ATA) electron beam 1-Hz pulse rate. It is necessary that a pulsed particle beam go from a region at 10/sup -6/ torr through a 1-cm-diam maximum aperture into a region at 760 torr. This must be accomplished without the use of windows or solid barriers. Two tests will be conducted on the vacuum-to-air interface. The first determines pressure profiles through 1.0-mm- and 10.0-mm-diam orifices. The second test employs an expendable foil and foil advancement mechanism. In this paper, the experimental results of the orifice test are presented and the analytical results are compared with the empirical results. The foil advancement test will be documented after the test is completed. The mechanism serves both as an orifice and as a fast-acting vacuum valve. In operation, the electron beam penetrates the thin foil, thereby creating an aperture of minimum geometry. During the balance of the pulse cycle, after the beam duration, the foil is advanced to seal the opening and recover the almost negligible loss in vacuum.
Date: January 1, 1986
Creator: Cruz, G.E.; Edwards, W.F.; Kavanagh, D.P.; Addis, R.B.; Weiss, W.C. & Livenspargar, C.M.
Partner: UNT Libraries Government Documents Department

Advanced concepts for acceleration

Description: Selected examples of advanced accelerator concepts are reviewed. Such plasma accelerators as plasma beat wave accelerator, plasma wake field accelerator, and plasma grating accelerator are discussed particularly as examples of concepts for accelerating relativistic electrons or positrons. Also covered are the pulsed electron-beam, pulsed laser accelerator, inverse Cherenkov accelerator, inverse free-electron laser, switched radial-line accelerators, and two-beam accelerator. Advanced concepts for ion acceleration discussed include the electron ring accelerator, excitation of waves on intense electron beams, and two-wave combinations. (LEW)
Date: July 1, 1986
Creator: Keefe, D.
Partner: UNT Libraries Government Documents Department

Recent results from the Los Alamos free-electron laser

Description: In this paper we review the most recent experimental results of the Los Alamos free-electron laser program. Three major effects will be described: lasing at improved efficiency over that previously attained, electron beam improvement, and energy recovery. An extraction efficiency of 2% was achieved with a wiggler having a 12% wavelength taper. The beam has been improved so that limits to its quality are now caused, not by injector performance, but by wake fields related to the high peak currents achieved. Limits to optical power are set by mirror damage. Experiments are described that demonstrate the successful operation of an energy recovery system. 17 refs., 10 figs., 3 tabs.
Date: January 1, 1988
Creator: Feldman, D.W.; Warren, R.W.; Carlsten, B.E.; Stein, W.E.; Watson, J.M.; Brau, C.A. et al.
Partner: UNT Libraries Government Documents Department

Mechanical engineering and design criteria for the Magnetically Insulated Transmission Experiment Accelerator

Description: A single-unit electron beam accelerator was designed, fabricated, and assembled in Sandia's Technical Area V to conduct magnetically insulated transmission experiments. Results of these experiments will be utilized in the future design of larger, more complex accelerators. This design makes optimum use of existing facilities and equipment. When designing new components, possible future applications were considered as well as compatibility with existing facilities and hardware.
Date: February 1, 1978
Creator: Staller, G. E.; Hamilton, I. D.; Aker, M. F. & Fifer, H. G.
Partner: UNT Libraries Government Documents Department

Pulsed power performance of the new RLA (Recirculating Linear Accelerator)

Description: The Recirculating Linear Accelerator (RLA) is returning to operation with a new electron beam injector and a modified accelerating cavity. Upon completion of our experimental program the RLA will capture the injected beam on an IFR guiding plasma channel in either a spiral or a closed racetrack drift tube. The relativistic beam will be efficiently recirculated for up to four passes through two or more accelerating cavities, in phase with the ringing cavity voltage waveforms, and thereby increased in energy to 10 MeV before being extracted. The inductively isolated four-stage injector was designed to produce beam parameters of 4 MeV, 10--20 kA, and 40--55 ns FWHM. The three-line radial cavity is being modified to improve the 1-MV accelerating voltage pulse shape while an advanced cavity design study is in progress. The actual versus predicted pulsed-power performance of the RLA injector and cavity and the associated driving hardware will be discussed in this paper.
Date: January 1, 1991
Creator: Smith, D.L.; Mazarakis, M.G.; Bennett, L.F. & Olson, W.R.
Partner: UNT Libraries Government Documents Department

The design of low emittance electron storage rings

Description: We have considered high tune'' electron storage rings as a possible source of low emittance beams. The parameters of such rings are studied in the limit where the emittance is determined by intrabeam scattering. Rings with either superconducting or conventional magnets are considered. The object is to maximize the ratio of electrons/bunch to invariant emittance while maintaining a certain fixed intensity. We have also calculated the dynamic aperture for one ring of this type.
Date: May 1, 1988
Creator: Hand, L.N. & Lundgren, S.
Partner: UNT Libraries Government Documents Department

Emittance growth from radiation fluctuations

Description: As an electron bunch travels through a transport system, fluctuations in the energy loss of individual electrons cause the size of the bunch to grow. A calculation is given of the quantum-induced growth of the emittance of a beam in one transverse coordinate, making the following approximations: (1) that the transport system is linear; (2) that there is no coupling between the two transverse motions; and (3) that the radiation effects can be described by their values on the central design trajectory. This last assumption means that systems are considered in which the quantum effects from bending magnets are much larger than from the focusing lenses.
Date: December 1, 1985
Creator: Sands, M.
Partner: UNT Libraries Government Documents Department

Pulsed magnetic field for PHERMEX-injected circular accelerator

Description: The PHERMEX accelerator is a standing wave, 50 MHz rf linear accelerator. The rf fields in three cavities are pulsed for a period of 3 ms. The experiments described are directed toward studying injection and trapping of electron rings at modes field strengths (approximately 1 T). A single 200 ns beam macropulse is to be injected transverse to a solenoidal field, which is tilted at a small angle relative to the beam normal so that a beam micropulse does not return and strike the injection point. The pulsed field coils and vacuum chamber are reported under construction, and the capacitor bank being tested. (LEW)
Date: January 1, 1986
Creator: Moir, D.C.; Ruhe, J.R. & Armstrong, W.T.
Partner: UNT Libraries Government Documents Department

NK Muon Beam

Description: The NK Muon Beam will be a modified version of the existing NT beam line. The decision to employ a modified version of the NT beam line was made based on considerations of cost and availability of the beam line. Preliminary studies considered use of other beam lines, e.g., the NW beam line, and even of moving the bubble chamber with its superconducting coils but were rejected for reasons such as cost, personnel limitations, and potential conflicts with other users.
Date: September 28, 1988
Creator: Koizumi, G.
Partner: UNT Libraries Government Documents Department

Muon fluence measurements during the 1987-1988 fixed-target run

Description: Muon fluence and dose equivalent have been observed at the Fermilab site boundary for the MC, MW, and NM beam lines. For MC and MW, the 1987 annual dose equivalents of 2.9 and 1.2 mrem respectively, are less than the 10 mrem site boundary goal. For the new NM beam line, on the other hand, the observed value 13.1 mrem exceeded this operational goal. Indeed, it was this observation that necessitated the additional ''spoilers'' downstream of the E665 experiment. With these magnets in place, however, the 10 mrem goal should not be in jeopardy for future runs.
Date: April 4, 1988
Creator: Elwyn, A. J. & Freeman, W. S.
Partner: UNT Libraries Government Documents Department

Summary of Working Group 7, Part II: Linac protection and collimation of megawatt micron sized 250--500 GeV electron beams

Description: The average beam powers and beam size anticipated for next generation linear colliders make them awesome tools of destruction. Systems for protection will be crucial. A scheme for linac structure protection by sacrificial collimators is presented in Section 3. No matter what precautionary measures are taken, the tails of the beam will be populated by hard coulomb collisions along the linac. To remove these halos before reaching the final focus system optics, where particle showers can blind the detector, it will be necessary to collimate these beams. Section 5 discusses the equations governing the parameters of a conventional collimation system. Wakefields determine gap sizes and lattice functions. Materials properties dictate minimum beam sizes at collimators so they can withstand occasionally mis-steered beams. Spoiler scattering and edge scattering effects mandate that the final doublet phase be collimated twice, and depending on the results of further tracking studies, it may be necessary to collimate each phase two times. Section 6 describes a nonlinear collimation system that can collimate beams to smaller apertures than the conventional system. The tolerances for such systems resemble final focus tolerances. Section T addresses the problem of repopulation of the tails after the collimation system. The main conclusions are that it appears possible to collimate the beams for these machines with conventional passively protected collimation systems. However the length of present designs, which collimate energy and both transverse planes and meet the requirements of complete tail scraping, exceed one kilometer per linac. A collimation system may also be desirable at the low energy end of the linac to minimize collimation of high energy particles.
Date: November 1, 1992
Creator: Irwin, J.
Partner: UNT Libraries Government Documents Department

Emittance measurement in a magnetic field

Description: Emittance can be measured by intercepting an electron beam on a range thick plate and then observing the expansion of beamlets transmitted through small holes. The hole size is selected to minimize space charge effects. In the presence of a magnetic field the beamlets have a spiral trajectory and the usual field free formulation must be modified. To interpret emittance in the presence of a magnetic field an envelope equation is derived in the appropriate rotating frame. 1 ref.
Date: April 15, 1991
Creator: Boyd, J.K.
Partner: UNT Libraries Government Documents Department

Electromagnetic PIC codes on unstructured grids

Description: This report discusses the following topics in relationships to plasma simulation: unstructed grids; particle tracking; and field propagation. (LSP)
Date: October 12, 1990
Creator: Ambrosiano, J.J.; Brandon, S.T. (Lawrence Livermore National Lab., CA (USA)) & Loehner, R. (George Washington Univ., Washington, DC (USA). School of Engineering and Applied Science)
Partner: UNT Libraries Government Documents Department

Electron-beam generation, transport, and transverse oscillation experiments using the REX injector

Description: The REX machine at LANL is being used as a prototype to generate a 4-MV, 4.5-kA, 55-ns flat-top electron beam as a source for injection into a linear induction accelerator of the 16-MeV Dual-Axis Radiographic Hydrotest facility. The pulsed-power sources drives a planar velvet cathode producing a beam that is accelerated through a foilless anode aperture and transported by an air core magnetic lens for injection into the first of 48 linear induction cells. Extensive measurements of the time-resolved (<1-ns) properties of the beam using a streak camera and high-speed electronic diagnostics have been made. These parameters include beam current, voltage, current density, emittance, and transverse beam motion. The effective cathode temperature is 117 eV, corresponding to a Lapostolle emittance of 0.96 mm-rad. Transverse oscillations of the transported beam have been observed via a differenced B-dot technique to be about {plus minus}100 {mu}m at 245 MHz. This beam motion has been correlated via detailed rf measurements of asymmetric transverse cavity modes in the A-K gap. 7 refs., 6 figs.
Date: January 1, 1991
Creator: Carlson, R.L.; Allison, P.W.; Kauppila, T.J.; Moir, D.C. & Ridlon, R.N.
Partner: UNT Libraries Government Documents Department

Schlieren observations of density channels in MPPE

Description: Schlieren imaging techniques were used to study the density depressions created by the ATA electron beam 37 cm after the entrance foil. Typical channel depressions were 5--10% of ambient density per pulse. Under IFR guiding channel depths as deep as 30% were seen on single pulse operation. Pulse 5 of the 5 pulse burst has passed through a channel reduced to 30% of ambient density. To lowest order, one would expect channel density depressions to scale as ({Delta}n/n) {proportional to} ({number sign} of pulses * I{sub beam}/channel area). Channel depth observations scaled roughly with beam current, {number sign} of pulses, and inversely with channel area. Pressure scaling was anomalous in that {Delta}n appeared to be less sensitive to pressure than the linear dependence expected. This would require that the energy deposition (stopping power) is independent of pressure and is a surprising result which can only be explained with collective effects. Scaling of channel expansion rates with pressure suggest classical diffusion (D {proportional to} 1/n) for times up to 200 mS. During these early times, the diffusion constant was, however, 3--5 times larger than the classical value. At later times, large scale turbulence was observed and the effective diffusion constant increased by an order of magnitude. This turbulence seemed to develop more quickly for deeper channels.
Date: September 28, 1990
Creator: Guethlein, G. (Lawrence Livermore National Lab., CA (USA)) & Pechacek, B. (Naval Research Lab., Washington, DC (USA))
Partner: UNT Libraries Government Documents Department

Pulse compression system for the ANL 20 MeV linac

Description: This paper describes the pulse compression system being built on the Argonne 20 MeV electron linac. The system is designed to rotate the bunch from the present measured pulse length of 38 psec FWHM, to pulse lengths of 5 to 6 ps with the large instantaneous currents (1 to 4 kA) possible instantaneous current. This system was necessary to extend the study of reactive fragments of molecules to the time scale of a few picoseconds, in particular to examine the chemistry of electrons and ions before and during relaxation of the surrounding media. These experiments are not sensitive to the beam energy spread, High Energy Physics experiments studying wake fields have also been proposed using the short bunches and the facility was designed so that the wake field experiment could share the beam bunching system. The 20 MeV electron linac uses a double gap, 12th subharmonic prebuncher together with a one wavelength 1.3 Ghz prebuncher to produce a single pulse of 38 ps from one occupied rf bucket. Beam emittances of 15.7 mmmr have been measured for 40 nC of accelerated charge and 8 mmmr at 10 nC. The energy spread of dE/E = 1% (FWHM) has been measured at 40 nC. Thus the accelerated beam has excellent time structure, high current, and good emittance.
Date: January 1, 1986
Creator: Mavrogenes, G.; Norem, J. & Simpson, J.
Partner: UNT Libraries Government Documents Department

Design of the magnetic structure of the undulator for the free electron laser experiment

Description: The basic features of the magnetic field in the permanent magnet undulator for the free electron laser at Brookhaven are described. The procedure used to measure the magnetic properties of each magnet block and to arrange them properly in order to minimize the field integrals is also discussed.
Date: January 1, 1982
Creator: Luccio, A. & Yue, L.
Partner: UNT Libraries Government Documents Department

Surface imaging by positron emission

Description: Monoenergetic (/open quote/slow/close quote/) positrons are becoming available in the form of beams having brightness sufficiently high for use in microscope and microprobe applications. When slow positrons are injected into certain solid materials they are re-emitted without need for an externally applied extraction field. This property suggests that a positron emission microscope will have useful capabilities and be less severely impaired by problems that extraction fields impose on electron emission devices. The principles involved in a positron emission microscope are discussed, and an estimate of resolutions that might be achieved in the near future is made. 10 refs., 2 figs
Date: January 1, 1988
Creator: L. D. Hulett, Jr. & Pendyala, S.
Partner: UNT Libraries Government Documents Department

650 mm long liquid hydrogen target for use in a high intensity electron beam

Description: This paper describes a 650 mm long liquid hydrogen target constructed for use in the high intensity electron beam at the Stanford Linear Accelerator Center. The main design problem was to construct a target that would permit the heat deposited by the electron beam to be removed rapidly without boiling the hydrogen so as to maintain constant target density for optimum data taking. Design requirements, construction details and operating experience are discussed.
Date: July 1, 1983
Creator: Mark, J.W.
Partner: UNT Libraries Government Documents Department