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Generation of Femtosecond X-Rays by 90 degrees Compton Scattering

Description: We propose Compton scattering of a short pulse visible laser beam by a low energy (but relativistic) electron beam at a right angle for generation of femtosecond x-rays. Simple analysis to determine the qualitative and quantitative characteristics of the x-ray pulse is presented.
Date: December 1, 1992
Creator: Kim, K.-J.; Chattopadhyay, S. & Shank, C.V.
Partner: UNT Libraries Government Documents Department

A method for measuring dark current electron beams in an rf linac

Description: X-ray fluorescence from thin foils inserted into the NPS linac has been used to measure the integrated electron beam intensity when the accelerator is operating with dark current. The measured x-ray flux, the known inner shell ionization cross sections and radiative transition probabilities are used to obtain measurements of dark currents of the order of 10{sup -14} amperes. The same arrangement allows continuous, in-situ energy calibration of our SiLi detector in the electromagnetic noise environment of the linac. This technique was orginally developed to perform absolute production efficiency measurements of parametric x-ray generation in the 5-50 keV range.
Date: December 31, 1993
Creator: Maruyama, X. K.; Fasanello, T.; Rietdyk, H.; Piestrup, M. A.; Rule, D. W. & Fiorito, R. B.
Partner: UNT Libraries Government Documents Department

Improved ETA-II accelerator performance

Description: Improvements have been made in the performance of the ETA-II accelerator that allow a nominal 2 kA, 6 MeV beam to be focused to a spot size less that 1 mm in diameter. The improvements include reducing the energy sweep to less than +/- 0.5 & over 40 ns of the pulse using a real time energy diagnostic and improving the magnetic tune of the accelerator to reduce the emittance to 8 cm-mrad. Finally, an automated tuning system (MAESTRO) was run to minimize the time dependent centroid motion (corkscrew) by adjusting the steering dipoles over the focusing solenoids. The corkscrew motion was reduced to less than +/- 0.5 mm at the output of the accelerator.
Date: March 22, 1999
Creator: Paul, A C; Boyd, J K; Chen, Y J; Clark, J C; Lager, D L & Weir, J T
Partner: UNT Libraries Government Documents Department

Volumetric plasma source development and characterization.

Description: The development of plasma sources with densities and temperatures in the 10{sup 15}-10{sup 17} cm{sup -3} and 1-10eV ranges which are slowly varying over several hundreds of nanoseconds within several cubic centimeter volumes is of interest for applications such as intense electron beam focusing as part of the x-ray radiography program. In particular, theoretical work [1,2] suggests that replacing neutral gas in electron beam focusing cells with highly conductive, pre-ionized plasma increases the time-averaged e-beam intensity on target, resulting in brighter x-ray sources. This LDRD project was an attempt to generate such a plasma source from fine metal wires. A high voltage (20-60kV), high current (12-45kA) capacitive discharge was sent through a 100 {micro}m diameter aluminum wire forming a plasma. The plasma's expansion was measured in time and space using spectroscopic techniques. Lineshapes and intensities from various plasma species were used to determine electron and ion densities and temperatures. Electron densities from the mid-10{sup 15} to mid-10{sup 16} cm{sup -3} were generated with corresponding electron temperatures of between 1 and 10eV. These parameters were measured at distances of up to 1.85 cm from the wire surface at times in excess of 1 {micro}s from the initial wire breakdown event. In addition, a hydrocarbon plasma from surface contaminants on the wire was also measured. Control of these contaminants by judicious choice of wire material, size, and/or surface coating allows for the ability to generate plasmas with similar density and temperature to those given above, but with lower atomic masses.
Date: September 1, 2008
Creator: Crain, Marlon D. (National Security Technologies, LLC, Las Vegas, NV); Maron, Yitzhak (Weizmann Institute of Science, Rehovot, Israel); Oliver, Bryan Velten; Starbird, Robert L. (National Security Technologies, LLC, Las Vegas, NV); Johnston, Mark D.; Hahn, Kelly Denise et al.
Partner: UNT Libraries Government Documents Department

Investigations on Absorber Materials at Cryogenic Temperatures

Description: In the framework of the 12 GeV upgrade project for the Continuous Electron Beam Accelerator Facility (CEBAF) improvements are being made to refurbish cryomodules housing Thomas Jefferson National Accelerator Facility┬ĺs (JLab) original 5-cell cavities. Recently we have started to look into a possible simplification of the existing Higher Order Mode (HOM) absorber design combined with the aim to find alternative material candidates. The absorbers are implemented in two HOM-waveguides immersed in the helium bath and operate at 2 K temperature. We have built a cryogenic setup to perform measurements on sample load materials to investigate their lossy characteristics and variations from room temperature down to 2 K. Initial results are presented in this paper.
Date: May 1, 2009
Creator: Frank Marhauser, Thomas Elliott, Robert Rimmer
Partner: UNT Libraries Government Documents Department

Further Analysis of Real Beam Line Optics From A Synthetic Beam

Description: Standard closed-orbit techniques for Twiss parameter measurement are not applicable to the open-ended Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. The evolution of selected sets of real orbits in the accelerator models the behavior of a 'synthetic' beam. This process will be validated against beam profile-based Twiss parameter measurements and should provide the distributed optical information needed to optimize beamline tuning for an open-ended system. This work will discuss the current and future states of this technique, as well as an example of its use in the CEBAF machine.
Date: July 1, 2012
Creator: Ryan Bodenstein, Michael Tiefenback, Yves Roblin
Partner: UNT Libraries Government Documents Department

Part II/Addendum Electron Beam Cooling between EBIS LINAC and Booster; Is Single Pass Cooling Possible?

Description: Due to some miscommunication, incomplete data was erroneously used in examining electron beam cooling for reducing momentum of gold ions exiting the EBIS LINAC before injection into the booster. Corrected calculations still indicate that single pass cooling is, in principle, feasible; momentum spread can be reduced by an order of magnitude in about one meter. Preliminary results suggest that this cooling deserves further consideration.
Date: July 1, 2008
Creator: Hershcovitch,A.
Partner: UNT Libraries Government Documents Department

An Efficient Microwave Power Source: Free-electron Laser Afterburner

Description: A kind of microwave power source, called a free-electron laser afterburner (FEL afterburner) which consists of a free-electron laser buncher and a slow-wave output structure sharing a magnetic wiggler field with the buncher, is proposed. The buncher and the slow-wave structure can operate in either a travelling-wave state or a standing-wave state. In the buncher, the wiggler field together with the radiation field makes an electron beam bunched, and in the slow-wave structure the wiggler field keeps the beam bunched while the bunched beam interacts strongly with the slow-wave structure and so produces rf power. The bunching process comes from the free-electron laser mechanism and the generating process of rf power is in a slow-wave structure. A three-dimensional, time-dependent code is used to simulate a particular standing-wave FEL afterburner and it is shown that rf power of up to 1.57 GW can be obtained, at 17.12 GHz, from a l-kA, 5-MeV electron beam.
Date: March 4, 1993
Creator: Wang, C. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department


Description: The spatial properties of the optical field and hence the performance of a free electron laser depend on the fact that the electron beam, which acts as both an amplifying and a refractive medium, is transversely nonuniform. Under certain circumstances, optical guiding may be realized, where the optical field is stably confined near the electron beam and amplified along the beam over many Rayleigh ranges. We show that the three-dimensional evolution of the optical field through the interaction region can be determined by a guided mode expansion before saturation. Optical guiding occurs when the fundamental growing mode becomes dominant. The guided mode expansion is made possible by implementing the biorthogonality of the eigenmodes of the coupled electron-beam-optical-wave system. The eigenmodes are found to be of vectorial form with three components; one specifies the guided optical mode and the other two describe the density and the energy modulations of the electron beam.
Date: March 1, 1989
Creator: Xie, M.; Deacon, D.A.G. & Madey, J.M.J.
Partner: UNT Libraries Government Documents Department

Limits to Electron Beam Emittance from Stochastic Coulomb Interactions

Description: Dense electron beams can now be generated on an ultrafast timescale using laser driven photo-cathodes and these are used for a range of applications from ultrafast electron defraction to free electron lasers. Here we determine a lower bound to the emittance of an electron beam limited by fundamental stochastic Coulomb interactions.
Date: August 22, 2008
Creator: Coleman-Smith, Christopher; Padmore, Howard A. & Wan, Weishi
Partner: UNT Libraries Government Documents Department


Description: The 1.6 cell S-band photoinjector cavity has been in operation at the DUVFEL at BNL for the past year. Initial beam measurements indicated a higher than expected emittance and beam divergence at the exit of the gun. field imbalance in the two cells was suspected, but lack of field probes in the cavity prohibited direct confirmation. A detailed SUPERFISH model was constructed of the cavity assembly. Field balance as a function of cathode plate and tuner position was determined using the model. A series of calibrated measurements of both the cavity RF properties and the delivered RF power was undertaken. Electron beam properties were also measured as function of cavity tune. Significant improvements in beam quality were achieved. The simulations and measurements are presented.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Role of Ionizztion in Radiatin Annealing

Description: The role of ionization in the phenomenon of" radiation annealing" of graphite has been studied by using a I-MeV electron beam. Changes in the C-axis of a sample with a Hanford irradiation of 460 Mwd/ct were studied. Two thermal anneals of 4 hours each at 350{degree}C proved sufficient to complete the thermal annealing at this temperature. The samples were then irradiated for 7 {1I2} hrs at a temperature of 340 {degree}c. The samples received an irradiation of 47 microampere-hours, equivalent in ´╗┐ionization to an exposure of 200 Mwd/ct in a Hanford reactor. No changes were noted as a result of the electron bombardment. It is concluded that the ionization is not of major importance in radiation annealing.
Date: October 1, 1954
Creator: McClelland, J.D.; Smith, A.W. & Senkovits, E.J.
Partner: UNT Libraries Government Documents Department

Low-Intensity Nonlinear Spectral Effects in Compton Scattering

Description: Nonlinear effects are known to occur in Compton scattering light sources, when the laser normalized 4-potential, A = e{radical}-A{sub {mu}}A{sup {mu}}/m{sub 0}c approaches unity. In this letter, it is shown that nonlinear spectral features can appear at arbitrarily low values of A, if the fractional bandwidth of the laser pulse, {Delta}{phi}{sup -1}, is sufficiently small to satisfy A{sup 2} {Delta}{phi} {approx_equal} 1. A three dimensional analysis, based on a local plane-wave, slow-varying envelope approximation, enables the study of these effects for realistic interactions between an electron beam and a laser pulse, and their influence on high-precision Compton scattering light sources.
Date: February 23, 2010
Creator: Hartemann, F V; Albert, F; Siders, C W & Barty, C P
Partner: UNT Libraries Government Documents Department

Lifetime of the 1s2s 3S1 metastable level in He-like S14+ measured with an electron beam ion trap

Description: A precision measurement of the lifetime of the lowest exited level of the He-like S{sup 14+} ion carried out at the Livermore EBIT-II electron beam ion trap yielded a value of (703 {+-} 4) ns. Our method extends the range of lifetime measurements accessible with electron beam ion traps into the nanosecond region and improves the accuracy of currently available data for this level by an order of magnitude.
Date: March 16, 2006
Creator: L?pez-Urrutia, J C; Beiersdorfer, P & Widmann, K
Partner: UNT Libraries Government Documents Department

Testing high-Z QED with SuperEBIT: An estimate of the U91+ 1s two-loop Lamb shift based on a measurement of the 2s1/2 - 2p1/2 transition in U89+

Description: Starting from the results of a recent measurement of the 2s{sub 1/2}-2p{sub 1/2} transition in U{sup 89+} has been made on the SuperEBIT electron beam ion trap, which provided a determination of the 2s two-loop QED contribution, we estimate 1.27 {+-} 0.45 eV for the two-loop contribution to the 1s level in U{sup 91+}. This estimate could be improved by a factor of two or more, if the uncertainties associated with the three-photon exchange in the theoretical calculations were eliminated in the future.
Date: July 15, 2005
Creator: Beiersdorfer, P
Partner: UNT Libraries Government Documents Department