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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Electron Bunch Length Monitors using Spatially Encoded Electro-optical Technique

A single-shot, nondestructive, electro-optical, electron bunch length monitor is experimentally verified by encoding the Coulomb field of the bunch profile on the spatial intensity distribution of an unchirped femtosecond laser pulse in an orthogonal geometry (hence, a temporal-to-spatial transformation). This electron bunch measurement scheme can simultaneously measure large timing jitter (?ps) with a wide measurement timespan covering picosecond to subpicosecond ranges.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Sub-nanosecond switching and acceleration to relativistic energies of field emission electron bunches from metallic nano-tips

The authors explore the generation of short electron bunches from a field-emitter array cathode consisting of nanometer-sized metallic tips that is compatible with an acceleration electric field above 10 MV/m. Sub-nanosecond field emission electron bunches were generated by applying fast electrical pulses to an on-chip electron extraction gate electrode of the cathode. The subsequent acceleration of the field emission electron bunches to 5 MeV was demonstrated using the combined diode-RF cavity SwissFEL electron gun test facility.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Effect of nonuniform radial density distribution on the space charge dominated beam bunching

Beam dynamics of a space charge dominated beam during the bunch compression is studied self consistently for the case of fixed shape non-uniform bell shape and hollow shape density distributions in the transverse direction. We have used thick slices at different parts of the beam to account for variation in the beam radius in the study of the transverse dynamics. The longitudinal dynamics has been studied using the disc model. The axial variation of the radius of the slices and emittance growth arising from the phase dependence of the transverse rf forces are also included in the simulation. We have modified the beam envelope equation to take into account the longitudinal space charge effect on the transverse motion which arises due to the finite bunch size. To demonstrate the application of the theoretical formulations developed, we have studied a sinusoidal beam bunching system and presented detailed numerical results.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Energy enhancement of quasi-monoenergetic proton bunches using a slice-cone target

A slice-cone target is proposed for the generation of quasi-monoenergetic proton bunches. In this new target structure, two symmetrical solid slices are adjoined obliquely to the tip of a hollow cone. Two-dimensional particle-in-cell simulations show that a large number of hot electrons are pulled out from the solid slices and accelerated forward by direct laser acceleration. Compared with the hollow cone target, a stronger electrostatic field at the rear surface of the slice-cone tip is set up by the hot electrons from the cone and the slices. As a result, the energy of the quasi-monoenergetic proton bunch produced through the target-normal sheath acceleration mechanism can be improved by 75%. It shows that the proton energy scales proportional to the square root of the laser intensity. For the incident laser with the focused intensity about 5 x 10{sup 20 }W/cm{sup 2}, one can obtain proton bunches with central energy 165 MeV and energy spread 13%.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Note: Absolute calibration of two DRZ phosphor screens using ultrashort electron bunch

This article gives the absolute calibration of two types phosphor screens (DRZ) that were used to detect and characterize electron bunches driven by laser-plasma accelerator. The test was performed with picoseconds electron bunch at a radio frequency linear electron accelerator in Tsinghua University. The photons emitted from DRZ screens showed good linear responses to the charge of incident electron bunch and cosine angular distribution in space. An energy conversional efficiency of effective scintillant matter was also calculated.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Acceleration of laser-driven ion bunch from double-layer thin foils

Generation of monoenergetic ion bunch from a double-layer thin-foil target irradiated by an intense linearly polarized laser pulse is investigated using two-dimensional particle-in-cell simulation. The protons in the front low-density hydrogen target layer accelerated by the space-charge field of the laser-driven hot electrons can penetrate through the high-Z high-mass and high-density ion layer, resulting in an energetic proton bunch. A part of the latter is further accelerated by the space-charge field of the hot electrons in the vacuum behind the high-Z ion layer. With this scheme, quasi-monoenergetic proton bunches can be produced using presently available laser pulses of moderate contrast and duration.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Energy spread inhibition of compact electron bunch driven by circularly polarized laser pulse

The problem of energy dispersion of a direct laser accelerated electron bunch emerging from a nano-meshed graphene target is investigated. To study the effects of the laser polarization state on the energy spread, numerical calculations and particle-in-cell simulations of evolving one-dimensional confined electron bunch dynamics are performed. It is proved that a circularly polarized laser pulse can inhibit energy dispersion more efficiently than a linearly polarized laser pulse with the same laser and target parameters. That is because the Coulomb expansion of the electron bunch gets more attenuated for a circularly polarized laser pulse compared with a linearly polarized pulse due to the slowly varying temporal laser intensity.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Electron diffraction using ultrafast electron bunches from a laser-wakefield accelerator at kHz repetition rate

We show that electron bunches in the 50-100 keV range can be produced from a laser wakefield accelerator using 10 mJ, 35 fs laser pulses operating at 0.5 kHz. It is shown that using a solenoid magnetic lens, the electron bunch distribution can be shaped. The resulting transverse and longitudinal coherence is suitable for producing diffraction images from a polycrystalline 10 nm aluminum foil. The high repetition rate, the stability of the electron source, and the fact that its uncorrelated bunch duration is below 100 fs make this approach promising for the development of sub-100 fs ultrafast electron diffraction experiments.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

A field programmable gate array-based time-resolved scaler for collinear laser spectroscopy with bunched radioactive potassium beams

A new data acquisition system including a Field Programmable Gate Array (FPGA) based time-resolved scaler was developed for laser-induced fluorescence and beam bunch coincidence measurements. The FPGA scaler was tested in a collinear laser-spectroscopy experiment on radioactive {sup 37}K at the BEam COoler and LAser spectroscopy (BECOLA) facility at the National Superconducting Cyclotron Laboratory at Michigan State University. A 1.29 μs bunch width from the buncher and a bunch repetition rate of 2.5 Hz led to a background suppression factor of 3.1 × 10{sup 5} in resonant photon detection measurements. The hyperfine structure of {sup 37}K and its isotope shift relative to the stable {sup 39}K were determined using 5 × 10{sup 4} s{sup −1} {sup 37}K ions injected into the BECOLA beam line. The obtained hyperfine coupling constants A({sup 2}S{sub 1/2}) = 120.3(1.4) MHz, A({sup 2}P{sub 1/2}) = 15.2(1.1) MHz, and A({sup 2}P{sub 3/2}) = 1.4(8) MHz, and the isotope shift δν{sup 39,} {sup 37} = −264(3) MHz are consistent with the previously determined values, where available.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

High quality electron bunch generation with CO{sub 2}-laser-plasma interaction

CO{sub 2} laser-driven electron acceleration in low-density plasma is demonstrated using particle-in-cell simulation. An intense CO{sub 2} laser pulse of long wavelength excites a wake bubble that has a large elongated volume for accelerating a large number of electrons before reaching the charge saturation limit. A transversely injected laser pulse is used to induce and control the electron injection. It is found that an electron bunch with total charge up to 10 nC and absolute energy spread less than 16 MeV can be obtained. As a result, the charge per energy interval of the bunch reaches up to 0.6 nC/MeV. Intense CO{sub 2}-laser based electron acceleration can provide a new direction for generating highly charged electron bunches with low energy spread, which is of much current interest, especially for table-top X-ray generation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Negative-mass mitigation of Coulomb repulsion for terahertz undulator radiation of electron bunches

It is proposed to utilize the effect of negative mass for stabilization of the effective axial size of very dense and short electron bunches produced by photo-injector guns by using combined undulator and strong uniform magnetic fields. It has been shown that in the “abnormal” regime, an increase in the electron energy leads to a decrease in the axial velocity of the electron; due to the negative-mass effect, the Coulomb repulsion of electrons leads to their attraction and formation of a fairly stable and compact bunch “nucleus.” An undulator with a strong uniform magnetic field providing the negative-mass effect is designed for an experimental source of terahertz radiation. The use of the negative-mass regime in this experiment should result in a long-pulse coherent spontaneous undulator emission from a short dense moderately relativistic (5.5 MeV) photo-injector electron bunch with a high (up to 20%) efficiency and a narrow frequency spectrum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Generation of attosecond electron bunches upon laser pulse propagation through a sharp plasma boundary

The formation of an electron bunch produced due to electron self-injection into a wake wave that is generated by a relativistic-intensity laser pulse propagating through a sharp boundary of semi-bounded plasma is studied in one-dimensional geometry. Analytical expressions are obtained for estimating the bunch length and the energy spread of electrons in the bunch. Numerical simulation is performed which confirms the results of analytical consideration. (paper)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Acceleration of electron bunches injected into a wake wave

The process of trapping and acceleration of nonmonoenergetic electron bunches by a wake wave excited by a laser pulse in a plasma channel is investigated. The electrons are injected into the vicinity of the maximum of the wakefield potential with a velocity lower than the wave phase velocity. The study is aimed at utilizing specific features of a wakefield with substantially overlapped focusing and accelerating phases for achieving monoenergetic electron acceleration. Conditions are found under which electrons in a finite-length nonmonoenergetic bunch are accelerated to high energies, while the energy spread between them is minimal. The effect of energy grouping of electrons makes it possible to obtain compact high-energy electron bunches with a small energy spread during laser plasma acceleration.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Formation of space-charge bunches in a multivelocity-electron-beam-based microwave oscillator with a cathode unshielded from the magnetic field

The influence of the magnitude and configuration of the magnetic field on the parameters of electron bunches formed in a multivelocity electron beam is analyzed. It is shown that the use of a cathode unshielded from the magnetic field and a nonuniform magnetic field increasing along the drift space enables the formation of compact electron bunches. The ratio between the current density in such bunches and the beam current density at the entrance to the drift space reaches 10{sup 6}, which results in a substantial broadening of the output microwave spectrum due to an increase in the amplitudes of the higher harmonics of the fundamental frequency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Bunch Length and Impedance Measurements at SPEAR3

Streak camera measurements were made at SPEAR3 to characterize longitudinal coupling impedance. For the nominal optics, data was taken at three rf voltages and a single-bunch current range of 0-20mA. Both bunchcentroid phase shift and bunch lengthening were recorded to extract values for resistive and reactive impedance. An (R+L) and a Q=1 model were then back-substituted into the Haissinski equation and compared with raw profile data. In the short bunch (low-{alpha}) mode, distribution 'bursting' was observed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Single-shot measurement of the spectral envelope of broad-bandwidth terahertz pulses from femtosecond electron bunches

We present a new approach (demonstrated experimentally and through modeling) to characterize the spectral envelope of a terahertz (THz) pulse in a single shot. The coherent THz pulse is produced by a femtosecond electron bunch and contains information on the bunch duration. The technique, involving a single low-power laser probe pulse, is an extension of the conventional spectral encoding method (limited in time resolution to hundreds of femtoseconds) into a regime only limited in resolution by the laser pulse length (tens of femtoseconds). While only the bunch duration is retrieved (and not the exact charge profile), such a measurement provides a useful and critical parameter for optimization of the electron accelerator.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Electron Bunch Profile Diagnostics in the Few FS Regime Using Coherent Smith-Purcell Radiation

The rapid developments in the field of laser-driven particle acceleration hold the prospect of intense, highly relativistic electron bunches that are only a few fs long. The determination of the temporal profile of such bunches presents new challenges. The use of a radiative process such as Smith-Purcell radiation (SPR), is particularly promising in this respect. In this technique the beam is made to radiate a small amount of e/m radiation and the temporal profile is reconstructed from the measured spectral distribution of the radiation. We summarise the advantages of SPR and present the design parameters and preliminary results of the experiments at the FACET facility at SLAC. We also discuss a new approach to the problem of the recovery of the 'missing phase', which is essential for the accurate reconstruction of the temporal bunch profile.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Experiment and simulations of sub-ps electron bunch train generation at Fermilab photoinjectors

Recently the generation of electron bunch trains with sub-picosecond time structure has been experimentally demonstrated at the A0 photoinjector of Fermilab using a transverse-longitudinal phase-space exchange beamline. The temporal profile of the bunch train can be easily tuned to meet the requirements of the applications of modern accelerator beams. In this paper we report the A0 bunch-train experiment and explore numerically the possible extension of this technique to shorter time scales at the Fermilab SRF Accelerator Test Facility, a superconducting linear electron accelerator currently under construction in the NML building.

43 PARTICLE ACCELERATORS↗