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Power, J G

Publications and source records attributed to Power, J G.

12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Generation of Picosecond Electron-Bunch Trains with Variable Spacing Using a Multi-Pulse Photocathode Laser

We demonstrate the generation of a train of electron bunches with variable spacing at the Argonne Wakefield Accelerator. The photocathode ultraviolet laser pulse consists of a train of four pulses produced via polarization splitting using two alpha-BBO crystals. The photoemitted electron bunches are then manipulated in a horizontally-bending dogleg with variable longitudinal dispersion. A downstream vertically-deflecting cavity is then used to diagnose the temporal profile of the electron beam. The generation of a train composed of four bunches with tunable spacing is demonstrated. Such a train of bunch could have application to, e.g., the resonant excitation of wakefield in dielectric-lined structures. We have presented preliminary measurements on a simple technique to generate a train of electron bunches with variable separation. In the initial experiment appreciable density modulation down to wavelengths of {approx}1.8 mm (corresponding to a temporal separation of {approx}6 ps) were achieved for a total charge of 0.5 nC. Finding ways to reach smaller separations is being explored with the help of numerical simulations and will be presented elsewhere.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Experimental Demonstration of Wakefield Acceleration in a Tunable Dielectric Loaded Accelerating Structure

We report on a collinear wakefield experiment using the first tunable dielectric loaded accelerating structure. By introducing an extra layer of nonlinear ferroelectric, which has a dielectric constant sensitive to temperature and dc bias, the frequency of a dielectric loaded accelerating structure can be tuned. During the experiment, the energy of a witness bunch at a fixed delay with respect to the drive beam was measured while the temperature of the structure was scanned over a 50 deg. C range. The energy change corresponded to a change of more than half of the nominal structure wavelength.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Emittance-Exchange-Based High Harmonic Generation Scheme for a Short-Wavelength Free Electron Laser

Generation of short-wavelength radiation by a free-electron laser using up-frequency conversion of an electron bunch density modulation is currently an area of active research. We propose a new scheme for producing the longitudinal electron bunch density modulation similar to the recently proposed echo-enabled harmonic generation but based on an emittance exchange beam line and a multislit mask. Beam line analysis and start-to-end simulation are presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Dielectric wakefield accelerator to drive to the future FEL light sourcei.

X-ray free-electron lasers (FELs) are expensive instruments and the accelerator holds the largest portion of the cost of the entire facility. Using a high-energy gain dielectric wake-field accelerator (DWA) instead of the conventional accelerator may facilitate reduction of the facility size and significant cost saving. We show that a collinear dielectric wake-field accelerator can, in principle, accelerate low charge and high peak current electron bunches to a few GeV energy with up to 100 kHz bunch repetition rate. Several such accelerators can share the same tunnel and same CW superconducting linac (operating with a few MHz bunch repetition rate) whose sole purpose is feeding the DWAs with wake producing low energy, high charge electron bunches with a desirable periodicity. Then, ten or more x-ray FELs can operate independently, each using its own linac. In this paper, we present an initial case study of a single stage 850 GHz DWA based on a quartz tube with a {approx}100MV/m loaded gradient sufficient to accelerate a 50 pC main electron beam to 2.4 GeV at a 100 kHz bunch repetition rate in just under 30 meters.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Overview of Photoinjectors

High-brightness electron beam sources play a crucial role in many advanced acceleration schemes as well as linac-based light sources such as Energy Recovery Linac (ERL) based light sources and FELs. Three varieties electron sources (photo, thermionic, and field emission) the photoinjector is especially attractive due to its innate ability to control the time structure of intense electron bunches with low transverse and longitudinal emittance. In all cases, the quality of the bunch begins with the intrinsic emittance and time response of the photocathode, and we discuss the trade-offs involved between the various material choices. A variety of longitudinal laser pulse-shaping techniques are currently being developed to linearize space charge forces or create trains of ultra-short bunches. The emittance compensation technique mitigates the growth of the projected emittance due to the linear space charge force while the bunch is accelerated and compressed in an injector. While the normal conducting rf photoinjector is the workhorse of this field, the dc photoinjector is being pushed to its high-voltage limits, and the year 2010 promises to be a critical year for the superconducting rf photoinjector. Parallel to the development of the hardware, rapid progress has also been made with modeling codes, theory, and bench marking of diagnostics. We attempt to give both a tutorial of photoinjectors and a review of the current state of the art in this rapidly developing field.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Development of X-Band Dielectric-Loaded Accelerating Structures

This paper presents a progress report on the development and testing of X-band dielectric-loaded accelerating structures. Recent tests on several quartz DLA structures with different inner diameters are reported. Designs for gap-free DLA structures are presented. Also, planned new experiments are discussed, including higher gradient traveling-wave and standing-wave structures and special grooved structures for multipactor suppression.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Recent Experiment on Wakefield Transformer Ratio Enhancement at AWA

One technique to enhance the transformer ratio beyond the ordinary limit of 2 in a collinear wakefield acceleration scheme is to use a ramped bunched train (RBT). The first experimental demonstration has been reported in [1]. However, due to the mismatch between the beam bunch length and frequency of the accelerating structure, the observed transformer ratio was only marginally above 2 in the earlier experiment. We recently revisited this experiment with an optimized bunch length using the laser stacking technique at Argonne Wakefield Accelerator (AWA) facility. A transformer ratio of 3.4 has been measured using two drive bunches. Attempting to use four drive bunches met with major challenges. In this article, measurement results and data analysis from these experiments are presented in detail.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Dielectric-Based Wakefield Power Extractor

In the Two Beam Accelerator (TBA), wakefield power extractors which extract high power RF from a high current beam are used to power high gradient accelerating structures. A dielectric-based Wakefield Power Extractor (DWPE) is one option in addition to the metallic structures considered previously, like the CLIC PETS (Power Extraction and Transfer Structure). 7.8 GHz and 26 GHz DWPE prototypes have been successfully built and tested at the Argonne Wakefield Accelerator (AWA) facility. We are currently designing an X-band version for a potential application with the CLIC beam. In this article, we report on test results of the 26 GHz DWPE and the preliminary design of the X-band structure. Future plan and possible difficulties in the development of DWPEs are also discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Design and Analysis of a Single-Shot Longitudinal Phase Space Measurement Diagnostics at the Argonne Wakefield Accelerator

A single-shot longitudinal phase space diagnostics is currently being assembled at the Argonne Wakefield Accelerator (AWA). The diagnostics consists of mapping the longitudinal phase space coordinates to the transverse position space plane using a beamline that incorporates two magnetic dipoles arranged as a dogleg followed by an rf deflecting cavity. The deflecting cavity streaks the beam vertically while the dipole magnets bend horizontally. In this paper, we analyze analytically and via numerical simulations the performances of such diagnostics and their limitations. Simulations done in IMPACT-T shows good reconstruction of the longitudinal phase space.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Using an Emittance Exchange Scheme for High Harmonic Generation by Free-Electron Lasers

We propose combining a transverse-to-longitudinal emittance exchange beam line and a conventional modulator to generate high harmonics with short-wavelength free-electron lasers. The key point of this scheme is the use of a multi-slit mask to create a transverse-shaped beam. In an emittance exchange beam line, the transverse-shaped bunch will produce a longitudinal-shaped one, resulting in separated energy bands. The modulator that follows this step will generate micro-bunches containing high harmonics. A coherent synchrotron radiation effect is also considered in this paper; compared to the two-modulator scheme, the method investigated here is more flexible and can be used to relax the coherent synchrotron radiation effect.

43 PARTICLE ACCELERATORS↗