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Comment regarding"On the Crooks fluctuation theorem and the Jarzynski equality" [J. Chem. Phys. 129, 091101 (2008)]and"Nonequilibrium fluctuation-dissipation theorem of Brownian dynamics" [J. Chem. Phys. 129, 144113 (2008)] (open access)

Comment regarding"On the Crooks fluctuation theorem and the Jarzynski equality" [J. Chem. Phys. 129, 091101 (2008)]and"Nonequilibrium fluctuation-dissipation theorem of Brownian dynamics" [J. Chem. Phys. 129, 144113 (2008)]

The incongruous"unexpected inapplicability of the [Crook's fluctuation theorem]" is due to an inexplicable, inappropriate use of inconsistent expressions. The girding is secure.
Date: March 4, 2009
Creator: Crooks, Gavin E
System: The UNT Digital Library
Generating Intense Attosecond X-Ray Pulses Using Ultraviolet-Laser-Induced Microbunching in Electron Beams (open access)

Generating Intense Attosecond X-Ray Pulses Using Ultraviolet-Laser-Induced Microbunching in Electron Beams

We propose a scheme that combines the echo-enabled harmonic generation technique with the bunch compression and allows to generate harmonic numbers of a few hundred in a microbunched beam through up-conversion of the frequency of an ultraviolet seed laser. Sending this beam through a short undulator results in an isolated sub-100 attoseconds pulse of x-ray radiation. Using a representative realistic set of parameters, we show that 1 nm x-ray pulse with peak power exceeding 100 MW and duration as short as 34 attoseconds (FWHM) can be generated from a 200 nm ultraviolet seed laser.
Date: March 4, 2009
Creator: Xiang, D.; Huang, Z. & Stupakov, G.
System: The UNT Digital Library
Generation of attosecond x-ray pulses with a multi-cycle two-color ESASE scheme (open access)

Generation of attosecond x-ray pulses with a multi-cycle two-color ESASE scheme

Generation of attosecond x-ray pulses is attracting much attention within the x-ray free-electron laser (FEL) user community. Several schemes using extremely short laser pulses to manipulate the electron bunches have been proposed. In this paper, we extend the attosecond two-color ESASE scheme proposed by Zholents et al. to the long optical cycle regime using a second detuned laser and a tapered undulator. Both lasers can be about ten-optical-cycles long, with the second laser frequency detuned from the first to optimize the contrast between the central and side current spikes. A tapered undulator mitigates the degradation effect of the longitudinal space charge (LSC) force in the undulator and suppresses the FEL gain of all side current peaks. Simulations using the LCLS parameters show a single attosecond x-ray spike of {approx} 110 attoseconds can be produced. The second laser can also be detuned to coherently control the number of the side x-ray spikes and the length of the radiation pulse.
Date: March 4, 2009
Creator: Ding, Y.; Huang, Z.; Ratner, D.; Bucksbaum, P. & Merdji, H.
System: The UNT Digital Library
High sensitivity resonance frequency measurements of individualmicro-cantilevers using fiber optical interferometry (open access)

High sensitivity resonance frequency measurements of individualmicro-cantilevers using fiber optical interferometry

We describe a setup for the resonance frequency measurement of individual microcantilevers. The setup displays both high spatial selectivity and sensitivity to specimen vibrations by utilizing a tapered uncoated fiber tip. The high sensitivity to specimen vibrations is achieved by the combination of optical Fabry-Perot interferometry and narrow band RF detection. Wave fronts reflected on the specimen and on the fiber tip end face interfere, thus no reference plane on the specimen is needed, as demonstrated with the example of freestanding silicon nitride micro-cantilevers. The resulting system is integrated in a DB-235 dual beam FIB system, thereby allowing the measurement of micro-cantilever responses during observation in SEM mode. The FIB was used to modify the optical fiber tip. At this point of our RF system development, the microcantilevers used to characterize the detector were not modified in situ.
Date: March 4, 2009
Creator: Duden, Thomas & Radmilovic, Velimir
System: The UNT Digital Library
ILC Marx Modulator Development Program Status (open access)

ILC Marx Modulator Development Program Status

Development of a first generation prototype (P1) Marx-topology klystron modulator for the International Linear Collider is nearing completion at the Stanford Linear Accelerator Center. It is envisioned as a smaller, lower cost, and higher reliability alternative to the present, bouncer-topology, 'Baseline Conceptual Design'. The Marx presents several advantages over conventional klystron modulator designs. It is physically smaller; there is no pulse transformer (quite massive at ILC parameters) and the energy storage capacitor bank is quite small, owing to the active droop compensation. It is oil-free; voltage hold-off is achieved using air insulation. It is air cooled; the secondary air-water heat exchanger is physically isolated from the electronic components. The P1-Marx employs all solid state elements; IGBTs and diodes, to control the charge, discharge and isolation of the cells. A general overview of the modulator design and the program status are presented.
Date: March 4, 2009
Creator: Burkhart, C.; Beukers, T.; Larsen, R.; Macken, K.; Nguyen, M.; Olsen, J. et al.
System: The UNT Digital Library
Improving the performance of the actinic inspection tool with an optimized alignment procedure (open access)

Improving the performance of the actinic inspection tool with an optimized alignment procedure

Extreme ultraviolet (EUV) microscopy is an important tool for the investigation of the performance of EUV masks, for detecting the presence and the characteristics of defects, and for evaluating the effectiveness of defect repair techniques. Aerial image measurement bypasses the difficulties inherent to photoresist imaging and enables high data collection speed and flexibility. It provides reliable and quick feedback for the development of masks and lithography system modeling methods. We operate the SEMATECH Berkeley Actinic Inspection Tool (AIT), a EUV microscope installed at the Advanced Light Source at Lawrence Berkeley National Laboratory. The AIT is equipped with several high-magnification Fresnel zoneplate lenses, with various numerical aperture values, that enable it image the reflective mask surface with various resolution and magnification settings. Although the AIT has undergone significant recent improvements in terms of imaging resolution and illumination uniformity, there is still room for improvement. In the AIT, an off-axis zoneplate lens collects the light coming from the sample and an image of the sample is projected onto an EUV-sensitive CCD camera. The simplicity of the optical system is particularly helpful considering that the AIT alignment has to be performed every time that a sample or a zoneplate is replaced. The alignment …
Date: March 4, 2009
Creator: Mochi, I.; Goldberg, K.A.; Naulleau, P. & Huh, Sungmin
System: The UNT Digital Library
International X-Band Linear Collider Accelerator Structure R&D (open access)

International X-Band Linear Collider Accelerator Structure R&D

For more than fifteen years before the International Technology Recommendation Panel (ITRP) decision in August, 2004, there were intensive R&D activities and broad international collaboration among the groups at SLAC, KEK, FNAL, LLNL and other labs for the room temperature X-Band accelerator structures. The goal was to provide an optimized design of the main linac structure for the NLC (Next Linear Collider) or GLC (Global Linear Collider). There have been two major challenges in developing X-band accelerator structures for the linear colliders. The first is to demonstrate stable, long-term operation at the high gradient (65 MV/m) that is required to optimize the machine cost. The second is to strongly suppress the beam induced long-range wakefields, which is required to achieve high luminosity. More than thirty X-band accelerator structures with various RF parameters, cavity shapes and coupler types have been fabricated and tested since 1989. A summary of the main achievements and experiences are presented in this talk including the structure design, manufacturing techniques, high power performance, and other structure related issues. Also, the new progress in collaborating with the CLIC, high gradient structures and X-Band structure applications for RF deflectors and others are briefly introduced.
Date: March 4, 2009
Creator: Wang, J. W.
System: The UNT Digital Library
The Quantum Efficiency and Thermal Emittance of Metal Photocathodes (open access)

The Quantum Efficiency and Thermal Emittance of Metal Photocathodes

Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths, with the principle improvements occurring since the invention of the photocathode gun. The state-of-the-art normalized emittance electron beams are now becoming limited by the thermal emittance of the cathode. In both DC and RF photocathode guns, details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance of metal cathodes using the Fermi-Dirac model for the electron distribution. We derive the thermal emittance and its relationship to the quantum efficiency, and compare our results to those of others.
Date: March 4, 2009
Creator: Dowell, David H. & Schmerge, John F.
System: The UNT Digital Library