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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

Design of an electron beam spectral modification system

Description: We report the design of a spectral modification system (SMS) for use with the proposed NEAL linac-pulse stretcher ring, cw electron beam facility. The SMS allows tailoring of the energy distribution of electrons in beams produced by a pulsed linac operating in the transient beam loading (TBL) regime. Modification of the energy distribution of electrons injected into the pulse strecher ring will increase the duty factor of current extracted from the ring and improve the efficiency of the extraction process. Physically, the SMS consists of an anisochronous, achromatic magnetic lattice followed by a pair of traveling-wave accelerating sections. For beams in the energy range of 500 MeV to 4 GeV, TBL ripple on the energy envelope of microsecond long beam spills is expected to be reduced from 1% peak-peak to less than 0.01% while the desired width of the energy profile due to the phase extent of the microbunches in the beam spill is preserved.
Date: October 1, 1981
Creator: Sheppard, J.C.; York, R.C.; Norum, B.E. & McCarthy, J.S.
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

Interactive data manipulation program. FAWTEK user guide

Description: This report describes the interactive data acquisition and manipulation program FAWTEK.'The program allows users of the electron beam data acquisition facility to control the R7912 digitizers and to perform a variety of mathematical operations on data arrays. Commands are entered in a high level language via a Tektronix 4010 terminal console. Each command directive and associated parameters is described in detail.
Date: February 1, 1980
Creator: Boyer, W. B. & Sauer, S.
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

Report of test beam subgroup

Description: Tasks reported on include: exploration of issues of demand for test beams, and particularly for high energy; fleshing out the possibilities of the High Energy Booster beams; and seeking inexpensive ways of providing high energy facilities. (LEW)
Date: January 1, 1986
Creator: Nodulman, L.; Groom, D.; Harrison, M.; Toohig, T.; Gustafson, R. & Kirk, T.
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

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

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

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

Commissioning and operation of the Nuclear Physics Injector at SLAC

Description: The new Nuclear Physics Injector (NPI) approved for construction in October of 1983 was completed by September of 1984, and delivered short pulse beams for SPEAR ring checkout in mid-October. Long pulse beams of up to 1.6 microsecond length were also demonstrated. The paper describes the startup operation, reviews the performance characteristics, and discusses the beam transport optics used to deliver 1 to 4 GeV beams to nuclear physics experiments in End Station A.
Date: March 1, 1985
Creator: Koontz, R.F.; Miller, R.H.; Leger, G.K. & Iverson, R.
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

Stability requirements of rf linac-driven free-electron lasers

Description: Fluctuations in the output power and wavelength have been observed in two high-power, rf-driven, free-electron lasers (FELs): the 10-/mu/m FEL that has operated at the Los Alamos National Laboratory and the visible FEL at the Boeing Physical Sciences Research Center. The fluctuations have been traced primarily to instabilities in the electron beam. Specifically, these are variations in the electron energy, the charge per micropulse, and the time interval between micropulses. The effects of these instabilities on the performance of one of the FELs is demonstrated. Efforts made to minimize these instabilities are discussed and the subsequent improvements in the operation of each of the FELs are presented. 7 refs., 7 figs.
Date: January 1, 1989
Creator: Stein, W.E.; Johnson, W.J.D.; Power, J.F. & Russel, T.J.
Partner: UNT Libraries Government Documents Department

Minimized emittance growth with elliptical beam pipes in FEL (free-electron-laser)

Description: Wakefield effects can cause emittance growth in free-electron-laser systems and reduce free-electron-laser gain. This paper explains that, by using beam pipes with elliptical cross sections, discontinuities can be allowed along a beam pipe without introducing wakefields. To use a beam pipe with an elliptical cross section, wakefield-less transitions between beam pipes with circular and elliptical cross sections are also needed. A concept to achieve such a transition is discussed. 4 refs., 7 figs.
Date: January 1, 1989
Creator: Chan, K.C.
Partner: UNT Libraries Government Documents Department

Electron storage ring beam lifetime dependence on pressure and pumping speed

Description: The beam loss in electron storage rings depends to a large extent on the interaction of the beam with heavier residual gas molecules such as CO, CO/sub 2/ and A due to Bremsstrahlung and Coulomb scattering. The gas density inside the vacuum chamber is determined by the surface condition of the vacuum chamber which is bombarded by photons (synchrotron radiation) generated by circulating electron beams and by the installed pumping. During the spring shutdown the x-ray ring vacuum system was updated and baked out. Residual gas spectra obtained were typical of a well baked out system, i.e., hydrogen constituted approx. 95% of the gas and the average pressure was in the 10/sup -10/ Torr range. During initial operation the composition of desorbed gases was 43% H/sub 2/, 25% CO and 16% CO/sub 2/ and CH/sub 4/. After 3 months of beam conditioning desorption dropped by a factor of 5 and the CO, CO/sub 2/ and CH/sub 4/ peaks represented smaller percentage of total desorbed gas. Beam lifetime did not, however, show a corresponding increase. The pumping speed of distributed pumps dropped to zero at 1 x 10/sup -9/ Torr pressure but increased rapidly from approx. 20l/s in low 10/sup -9/ as the pressure increased.
Date: January 1, 1984
Creator: Halama, H.J.
Partner: UNT Libraries Government Documents Department

The Brookhaven accelerator test facility injection system

Description: The Brookhaven Accelerator Test Facility (ATF) consists of a 50-MeV/c electron linac and a high-brightness RF-gun both operating at 2856 MHz. An extremely short (a few picoseconds) electron pulse with low transverse emittance is generated by the RF-gun. In order to preserve both longitudinal and transverse emittances, great care must be taken in transporting the electron beam from the RF-gun to the linac. We describe the injection line, present first- and second-order lattice studies of the injection line, and study nonlinear effects on the emittance. 11 refs., 4 figs., 4 tabs.
Date: January 1, 1989
Creator: Wang, X.J.; Kirk, H.G.; Pellegrini, C.; McDonald, K.T. & Russell, D.P.
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

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

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

Practical applications of coherent transition radiation

Description: The predictable nature of transition radiation (TR) emissions has been demonstrated under a wide variety of experimental conditions. The reliable character of TR allows the design of specific practical applications that use emissions from the optical to the x-ray spectral regions. Applications often can be enhanced by the spatial coherence of TR, and some have become highly developed. New applications may be developed through the use of other related radiation mechanisms. 20 refs., 3 figs.
Date: October 2, 1987
Creator: Moran, M.J.
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

Electron-beam induced absorption and hardening in fiber-optic waveguides to 1060 nm laser pulses

Description: For Corning Glass Work (CGW) and Valtec Corporation (VC) fiber-optic waveguides (FOWs), we have determined the coupling efficiencies (output/input energy) before (R/sub 1/) and after (R/sub 2/) electron-beam irradiation, the output energy density, the induced attenuation or loss (L/sub I/) and its decrease as a function of time, and hardening as a function of number of Febetron shots (N/sub T/). The FOWs were electron-beam irradiated with 8.3 to 12.3 J/cm/sup 2/ for a 2.36 to 2.84 x 10/sup 6/ R (/sup 60/Co equivalent) dose. The output laser energy density varied from 0.19 to 2.12 kJ/cm/sup 2/ which was about 50% of the input surface threshold damage level previously measured in similar FOWs. The values of R/sub 1/, 40.1 to 67.0%, were less than those previously measured. The induced attenuation (L/sub I/) as a function of recovery time (after electron-beam irradiation) was linear on log-log plot for a short time (< 2.2 x 10/sup -4/ s), changing from 1.8 to 0.2 dB/cm in slightly larger than a one order of magnitude change in time. The rate of recovery decreased with increasing time so that the total change in L/sub I/ was about 3 orders of magnitude in 6 orders of magnitude change in time. A slight hardening (decrease in R/sub 1//R/sub 2/ occurred in CGW fibers with an increasing number of Febetron electron pulses.
Date: January 1, 1980
Creator: Landry, M.J. & Davis, H.P.
Partner: UNT Libraries Government Documents Department

Induction linacs

Description: The principle of linear induction acceleration is described, and examples are given of practical configurations for induction linacs. These examples include the Advanced Technology Accelerator, Long Pulse Induction Linac, Radial Line Accelerator (RADLAC), and Magnetically-Insulated Electron-Focussed Ion Linac. A related concept, the auto accelerator, is described in which the high-current electron-beam technology in the sub-10 MeV region is exploited to produce electron beams at energies perhaps as high as the 100 to 1000 MeV range. Induction linacs for ions are also discussed. The efficiency of induction linear acceleration is analyzed. (LEW)
Date: July 1, 1986
Creator: Keefe, D.
Partner: UNT Libraries Government Documents Department