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Rosat-Green bank sample of intermediate BL Lac objects

Description: The Rosat-GreenBank BLLac sample consists of 119 objects and smoothly bridges the gap between the previously disparate subclasses of radio- and X-ray-selected objects. Further study of this sample should provide useful constraints to the unified scheme and help determine if modifications are necessary.
Date: April 1, 1997
Creator: Laurent-Muchleisen, S.A.; Kollgaurd, R.I. & Feigelson, E.D.
Partner: UNT Libraries Government Documents Department

Ultrashort x-ray backlighters and applications

Description: Previously, using ultrashort laser pulses focused onto solid targets, we have experimentally studied a controllable ultrafast broadband radiation source in the extreme ultraviolet for time-resolved dynamical studies in ultrafast science [J. Workman, A. Maksimchuk, X. Llu, U. Ellenberger, J. S. Coe, C.-Y. Chien, and D. Umstadter, ``Control of Bright Picosecond X-Ray Emission from Intense Sub- Picosecond Laser-Plasma Interactions,`` Phys. Rev. Lett. 75, 2324 (1995)]. Once armed with a bright ultrafast broadband continuum x-ray source and appropriate detectors, we used the source as a backlighter to study a remotely produced plasma. The application of the source to a problem relevant to high-density matter completes the triad: creating and controlling, efficiently detecting, and applying the source. This work represented the first use of an ultrafast laser- produced x-ray source as a time-resolving probe in an application relevant to atomic, plasma and high-energy-density matter physics. Using the x-ray source as a backlighter, we adopted a pump-probe geometry to investigate the dynamic changes in electronic structure of a thin metallic film as it is perturbed by an ultrashort laser pulse. Because the laser deposits its energy in a skin depth of about 100 {Angstrom} before expansion occurs, up to gigabar pressure shock waves lasting picosecond in duration have been predicted to form in these novel plasmas. This raises the possibility of studying high- energy-density matter relevant to inertial confinement fusion (ICF) and astrophysics in small-scale laboratory experiments. In the past, time-resolved measurements of K-edge shifts in plasmas driven by nanosecond pulses have been used to infer conditions in highly compressed materials. In this study, we used 100-fs laser pulses to impulsively drive shocks into a sample (an untamped 1000 {Angstrom} aluminum film on 2000 {Angstrom} of parylene-n), measuring L-edge shifts.
Date: August 1, 1997
Creator: Umstadter, D., University of Michigan
Partner: UNT Libraries Government Documents Department

Faraday cup measurements of the plasma plume produced at an x-ray converter

Description: The next generation of radiographic machines based on induction accelerators is expected to generate multiple, small diameter x-ray spots of high intensity. Experiments to study the interaction of the electron beam with the x-ray converter are being performed at the Lawrence Livermore National Laboratory (LLNL) using the 6-MeV, 2-kA Experimental Test Accelerator (ETA) electron beam. The physics issues of greatest concern can be separated into two categories. The multiple pulse issue involves the interaction of subsequent beam pulses with the expanding plasma plume generated by earlier pulses striking the x-ray converter. The plume expands at several millimeters per microsecond and defines the minimum transverse spacing of the pulses. The single pulse issue is more subtle and involves the extraction of light ions by the head of the beam pulse. These light ions might propagate at velocities of several millimeters per nanosecond through the body of the incoming pulse resulting in a moving focus prior to the converter. In this paper we describe Faraday cup measurements performed to quantify the plasma plume expansion and velocities of light ions.
Date: August 17, 1998
Creator: Garcia, M; Houck, T L & Sampayan, S E
Partner: UNT Libraries Government Documents Department

X-Ray Scattering Applications Using Pulsed X-Ray Sources

Description: Pulsed x-ray sources have been used in transient structural phenomena investigations for over fifty years; however, until the advent of synchrotrons sources and the development of table-top picosecond lasers, general access to ligh temporal resolution x-ray diffraction was relatively limited. Advances in diffraction techniques, sample excitation schemes, and detector systems, in addition to IncEased access to pulsed sources, have ld tO what is now a diverse and growing array of pulsed-source measurement applications. A survey of time-resolved investigations using pulsed x-ray sources is presented and research opportunities using both present and planned pulsed x-ray sources are discussed.
Date: May 23, 1999
Creator: Larson, B.C.
Partner: UNT Libraries Government Documents Department

CONTINUING THE DEVELOPMENT OF A 100 FEMTOSECOND X-RAY DETECTOR

Description: The detector is an x-ray streak camera running in accumulation mode for time resolved x-ray studies at the existing third generation synchrotron facilities and will also be used for the development and applications of the fourth generation x-ray sources. We have made significant progress on both the detector development and its applications at Synchrotron facilities.
Date: June 20, 2005
Creator: Chang, Zenghu
Partner: UNT Libraries Government Documents Department

Physical vapor deposited aluminum foils from high energy density physics experiments

Description: Fabrication of cylindrical aluminum load foils and graded thickness aluminum vacuum opening switch foils is described. Load foils are vaporized by joule heating and imploded by J {times} B forces to stagnate on axis and create soft x-rays. Plasma flow switch foils are mounted to shunt the vacuum power flow channel of a coaxial gun and are vaporized by joule heating. The resultant graded density plasma is magnetically driven down the annular power flow channel. Opening switch action occurs when the shunt plasma crosses a load slot in the center conductor. These foil components have been used in both the Pegasus and Procyon experiments.
Date: September 1, 1995
Creator: Barthell, B.L.; Anderson, W.E.; Gomez, V.M.; Henneke, B.F.; Moore, J.E.; Reeves, G.A. et al.
Partner: UNT Libraries Government Documents Department

Transient x-ray diffraction and its application to materials science and x-ray optics

Description: Time resolved x-ray diffraction and scattering have been applied to the measurement of a wide variety of physical phenomena from chemical reactions to shock wave physics. Interest in this method has heightened in recent years with the advent of versatile, high power, pulsed x-ray sources utilizing laser plasmas, electron beams and other methods. In this article, we will describe some of the fundamentals involved in time resolved x-ray diffraction, review some of the history of its development, and describe some recent progress in the field. In this article we will emphasize the use of laser-plasmas as the x-ray source for transient diffraction.
Date: December 1, 1997
Creator: Hauer, A.A.; Kopp, R.; Cobble, J.; Kyrala, G. & Springer, R.
Partner: UNT Libraries Government Documents Department

Cryogenic xenon droplets for advanced lithography

Description: A cryogenic xenon droplet production system for use in anadvanced laser plasma source for x-ray lithography has been designed, fabricated, and tested at ORNL. The droplet generator is based on proven (ink jet printer) drop-on-demand.
Date: April 1, 1996
Creator: Gouge, M.J. & Fisher, P.W.
Partner: UNT Libraries Government Documents Department

Development of a Dynamic Spot Size Diagnostic for Flash Radiographic X-Ray Sources

Description: There has been considerable work in recent years in the development of high-brightness, high-dose flash x-ray radiographic sources. Spot size is one of several parameters that helps characterize source performance and provides a figure of merit to assess the suitability of various sources to specific experimental requirements. Time-integrated spot-size measurements using radiographic film and a high-Z rolled-edge object have been used for several years with great success. The Advanced Radiographic Technologies program thrust to improve diode performance requires extending both modeling and experimental measurements into the transient time domain. A new Time Resolved Spot Detector (TRSD) is under development to provide this information. In this paper we report the initial results of the performance of a 148-element scintillating fiber array that is fiber-optically coupled to a gated streak camera. Spatial and temporal resolution results are discussed and the data obtained from the Sand ia National Laboratories (SNL) RITS-3 (Radiographic Integrated Test Stand) accelerator are presented.
Date: June 1, 2003
Creator: Droemer, D. W.; Lutz, S.; Devore, D.; Rovang, D.; Portillo, S. & Maenchen, J.
Partner: UNT Libraries Government Documents Department

Technological Challenges to X-Ray FELs

Description: There is strong interest in the development of x-ray free electron lasers (x-ray FELs). The interest is driven by the scientific opportunities provided by intense, coherent x-rays. An x-ray FEL has all the characteristics of a fourth-generation source: brightness several orders of magnitude greater than presently achieved in third-generation sources, full transverse coherence, and sub-picosecond long pulses. The SLAC and DESY laboratories have presented detailed design studies for X-Ray FEL user facilities around the 0.1 nm wavelength-regime (LCLS at SLAC, TESLA X-Ray FEL at DESY). Both laboratories are engaged in proof-of-principle experiments are longer wavelengths (TTF FEL Phase I at 71 nm, VISA at 600-800 nm) with results expected in 1999. The technologies needed to achieve the proposed performances are those of bright electron sources, of acceleration systems capable of preserving the brightness of the source, and of undulators capable of meeting the magnetic and mechanical tolerances that are required for operation in the SASE mode. This paper discusses the technological challenges presented by the X-Ray FEL projects.
Date: September 16, 1999
Creator: Nuhn, Heinz-Dieter
Partner: UNT Libraries Government Documents Department

Compton scattering in the ALS booster

Description: Femtosecond x-ray pulses may be generated by 90{degrees} Compton side scattering of a short visible laser beam by a well-focused relativistic electron beam. A proof-of-principle experiment is underway using the ALS linac. From this experiment an x-ray pulse of 10{sup 5} photons with a duration of 230 fs in a bandwidth of 10% at 10 Hz is expected. In this paper we explore using the ALS booster instead to increase the average x-ray flux. To generate the small beam size we plan to radiation damp electrons by accelerating them to 600 MeV and decelerate quickly to 50 MeV before intra-beam scattering can increase the beam size. We can achieve a vertical emittance of <5 {times} 10{sup {minus}9} m-rad. With a small modification of the booster lattice it is possible to focus the beam to a vertical beta function of {Beta}{sub y}* = 10 cm. By reflecting the incident laser pulse many times we expect to be able to obtain an increase of the average x-ray flux.
Date: April 1, 1995
Creator: Robin, D.; Kim, C. & Sessler, A.
Partner: UNT Libraries Government Documents Department

Initial lattice studies for the Berkeley Femtosecond X-ray Light Source

Description: We present lattice studies for a proposed femtosecond synchrotron radiation X-ray source based on a recirculating accelerator. After a general description, we cover specific aspects of the lattice that are relevant to this type of machine and show preliminary results of particle tracking and briefly describe a new code developed for a comprehensive particle tracking in recirculating accelerators.
Date: May 30, 2002
Creator: Zholents, A.; Reichel, I.; Robin, D.; Tanabe, J.; Wan, W.; Forest, E. et al.
Partner: UNT Libraries Government Documents Department

A Report on the Workshop on the Uses and Generation ofFemtosecond Radiation

Description: We describe the proceedings of the Workshop on the Uses and Generation of Femtosecond Radiation, held at the E.O. Lawrence Berkeley National Laboratory (LBNL), in February 1998, and some of the ideas that were generated subsequent to the workshop. The motivation for this workshop was to bring together accelerator physicists interested in the generation of ultra-short (< 200 fs) pulses of XUV and x-ray radiation, and scientists interested in using them. The primary purpose of the workshop was to educate the accelerator physicists about the source characteristics necessary to carry out specific experiments, and to inform the user community of ideas currently being explored by the accelerator community. A second objective was to develop a set of parameters and requirements that could form the basis for a broad-based femtoscience user facility. In this paper we describe some of the ideas and techniques that accelerator physicists are pursuing to iilfill the diverse requirements of this expanding community.
Date: July 1, 1998
Creator: Jackson, A.
Partner: UNT Libraries Government Documents Department

In vacuum undulator task force report

Description: Historically the NSLS has been active in R&D for state-of-the-art electron beams, photon beams and x-ray optics. One of the available straight sections has therefore been dedicated to insertion device R&D. Over the past five to seven years a program aimed at exploiting the very small vertical {beta} function in the straight sections has yielded first a prototype small gap undulator (PSGU) and then an in-vacuum undulator (IVUN). The IVUN sources attain a brightness similar to the existing hybrid wigglers in X21 and X25. They radiate significantly lower total power than the wigglers but produce higher power densities. They provide undulator rather than wiggler spectra. Because of the small gaps and small periods there is not much tunability in these devices and they will have to be purpose-built for a specific scientific program. The original IVUN parameters were chosen for in-elastic x-ray scattering, similar to the scientific program on X21. This put the fundamental at 4.6 keV and the third harmonic at 13.8 keV. The question that this new possible insertion device poses is what science programs can best take advantage of this new insertion device source? To answer this, a task force was formed by M. Hart, NSLS Department Chair and charged with identifying viable scientific programs that could seek outside funding to construct IVUN beamlines. The task force concentrated on experimental programs that are presently being pursued on new insertion devices worldwide. For example, x-ray photon correlation spectroscopy, which takes advantage of the large coherent flux from undulator sources, was considered. However, this program was not considered as the highest priority. The general area of protein crystallography, however, is ideal for the IVUN source. The unique electron beam optics that makes the IVUN possible in the first place also makes the IVUN ideal as a source for microdiffraction.
Date: June 1, 1998
Creator: Hastings, J.B.; Kao, C.C. & Stefan, P.
Partner: UNT Libraries Government Documents Department

Decoding sequential vs non-sequential two-photon double ionizationof helium using nuclear recoil

Description: Above 54.4 eV, two-photon double ionization of helium isdominated by a sequential absorption process, producing characteristicbehavior in the single and triple differential cross sections. We showthat the signature of this process is visible in the nuclear recoil crosssection, integrated over all energy sharings of the ejected electrons,even below the threshold for the sequential process. Since nuclear recoilmomentum imaging does not require coincident photoelectron measurement,the predicted images present a viable target for future experiments withnew short-pulse VUV and soft X-ray sources.
Date: January 7, 2008
Creator: Horner, Daniel A.; Rescigno, Thomas N. & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

DARHT2 X-ray converter target system comparison

Description: Four short current pulses with various pulse widths and spacing will be delivered to the x-ray converter target on the second-axis of the Dual-Axis Radiographic Hydrodynamic Test (DARHT-II) facility. To ensure that the DARHT-II multi-pulse target will provide enough target material for x-ray production for all four pulses, the target needs either to survive the strike of four electron pulses or to accommodate target replenishment. A distributed target may survive hitting of four electron pulses. For target replenishment, two types of target configurations are being considered: stationary target systems with beam repositioning and dynamic moving target systems. They compare these three target systems and their radiographic performance.
Date: March 24, 1999
Creator: Bergstrom, P. M.; Caporaso, G. J.; Chen, Y. J.; Ho, D. D.; McCarrick, J. F.; Pincosy, P. A. et al.
Partner: UNT Libraries Government Documents Department

Controlling backstreaming ions from X-ray converter targets with time varying final focusing solenoidal lens and beam energy variation

Description: Backstreaming ions emitted from an x-ray converter hit by a tightly focused intense electron beam can form an ion focusing channel and over-focus the electron beam. As the ions move upstream in time, the net focusing strength increases. The final beam spot size on the target would then change in time and typically be larger than intended. We have developed a model to estimate the backstreaming ions´┐Ż neutralization factor in a potential sheath near the target surface and away from the sheath. Performance of high resolution x-ray radiography facilities requires high current electron beams to be focused to a millimeter spot size on an x-ray converter through out the entire current pulse. We have studied the possibility of maintaining a constant final spot size for the entire pulse by using either a time varying final focusing solenoid field or beam energy variation to compensate the time varying ion focusing effects
Date: August 20, 1998
Creator: Caporaso, G J; Chen, Yu-Jiuan & Paul, A
Partner: UNT Libraries Government Documents Department