A5001064460- Particle Accelerators and Free-Electron Lasers
- Particle accelerators and beam dynamics
- Gyrotron and Vacuum Electronics Research
- Advanced X-ray Imaging Techniques
- Laser-Plasma Interactions and Diagnostics
- Magnetic confinement fusion research
- Superconducting Materials and Applications
- Particle Detector Development and Performance
- Ion-surface interactions and analysis
- Photocathodes and Microchannel Plates
- Plasma Diagnostics and Applications
- Advanced Electron Microscopy Techniques and Applications
- Electron and X-Ray Spectroscopy Techniques
- Laser-induced spectroscopy and plasma
- Atomic and Molecular Physics
- Laser-Matter Interactions and Applications
- Muon and positron interactions and applications
- Advancements in Photolithography Techniques
- Distributed and Parallel Computing Systems
- Pulsed Power Technology Applications
- Microwave Engineering and Waveguides
- Integrated Circuits and Semiconductor Failure Analysis
- X-ray Spectroscopy and Fluorescence Analysis
- Diamond and Carbon-based Materials Research
- Terahertz technology and applications
SLAC National Accelerator Laboratory
2006-2018
Menlo School
2002-2014
Stanford Synchrotron Radiation Lightsource
1992-2011
Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati
2010
Istituto Nazionale di Fisica Nucleare
2010
University of Southern California
2010
Stanford University
1992-2009
Argonne National Laboratory
2007
Linac Coherent Light Source
2006-2007
Coherent (United States)
2007
Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible to laboratory investigation. At high densities, the interatomic forces bind solids and determine many their properties substantially altered. Here, we present detailed mapping carrier densityâdependent potential bismuth approaching a solid-solid phase transition. Our experiments combine stroboscopic techniques use high-brightness linear electron acceleratorâbased x-ray source...
The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics liquids and solids. An accelerator-based source femtosecond x-ray pulses allowed us follow directly atomic displacements an optically modified landscape, leading eventually transition from crystalline solid disordered liquid. We show that, first order in time, are inertial, we place constraints shape curvature transition-state surface. Our measurements point toward analogies between this...
Linear-accelerator-based sources will revolutionize ultrafast x-ray science due to their unprecedented brightness and short pulse duration. However, time-resolved studies at the resolution of duration are hampered by inability precisely synchronize an external laser accelerator. At Sub-Picosecond Pulse Source Stanford Linear-Accelerator Center we solved this problem measuring arrival time each high energy electron bunch with electro-optic sampling. This measurement indirectly determined...
A plasma-wakefield accelerator has accelerated particles by over 2.7 GeV in a 10 cm long plasma module. 28.5 electron beam with 1.8 x 10(10) electrons is compressed to 20 microm longitudinally and focused transverse spot size of at the entrance column lithium vapor density 2.8 10(17) atoms/cm3. The bunch fully ionizes create then expels electrons. These return one-half period later driving large amplitude wake that turn accelerates back more than GeV.
The onset of trapping electrons born inside a highly relativistic, 3D beam-driven plasma wake is investigated. Trapping occurs in the transition regions Li confined by He gas. support wake, and higher ionization potential atoms are ionized as beam focused ions can be trapped. As amplitude increased, observed. Some gain up to 7.6 GeV 30.5 cm plasma. experimentally inferred threshold at 36 GV/m, good agreement with an analytical model PIC simulations.
We propose a novel method to characterize the temporal duration and shape of femtosecond x-ray pulses in free-electron laser (FEL) by measuring time-resolved electron-beam energy loss spread induced FEL process, with transverse radio-frequency deflector located after undulator. Its merits are simplicity, high resolution, wide diagnostic range, noninvasive user operation. When system is applied Linac Coherent Light Source, world's most powerful FEL, it can provide single-shot measurements...
Generation of femtosecond to sub-femtosecond pulses is attracting much attention in X-ray free-electron laser user community. One method use a slotted, emittance-spoiling foil which was proposed before (P. Emma et al., Phys. Rev. Lett. 92, 074801 (2004)) and has been widely used at the Linac Coherent Light Source. Direct experimental characterization slotted-foil performance previously unfeasible due lack appropriate diagnostics. With recently installed X-band radio-frequency transverse...
A traveling wave transverse rf deflecting structure is discussed as a toot for bunch length measurement and an aid to detailed phase space diagnostics in future FEL projects. The high frequency time variation of the fields used 'pitch' or 'yaw' electron where resulting beam width measured on simple profile monitor represents reliable, single-shot measure absolute length. small shift, from zero-crossing, adds net centroid kick so that it intercepts off-axis screen. then pulsed at much lower...
Femtosecond time-resolved small and wide angle x-ray diffuse scattering techniques are applied to investigate the ultrafast nucleation processes that occur during ablation process in semiconducting materials. Following intense optical excitation, a transient liquid state of high compressibility characterized by large-amplitude density fluctuations is observed buildup these measured real time. Small-angle measurements reveal snapshots spontaneous nanoscale voids within metastable support...
The melting dynamics of laser excited InSb have been studied with femtosecond x-ray diffraction. These measurements observe the delayed onset diffusive atomic motion, signaling appearance liquidlike dynamics. They also demonstrate that root-mean-squared displacement in [111] direction increases faster than [110] after first 500 fs. This structural anisotropy indicates initially generated fluid differs significantly from equilibrium liquid.
The ultrafast decay of the x-ray diffraction intensity following laser excitation an InSb crystal has been utilized to observe carrier dependent changes in potential energy surface. For first time, abrupt onset for surface softening and appearance accelerated atomic disordering a very high average density have observed. Inertial dynamics dominate early stages wide range densities between disordering.
Performance of the x-ray free electron laser Linac Coherent Light Source (LCLS) and Facility for Advanced Accelerator Experimental Tests (FACET) is determined by properties their extremely short bunches. Multi-GeV bunches in both LCLS FACET are less than 100 fs long. Optimization beam understanding free-electron operation require diagnostics with time resolution about 10 fs. We designed, built commissioned a set high frequency $X$-band deflectors which can measure longitudinal space charge...
Plasma production via field ionization occurs when an incoming particle beam is sufficiently dense that the electric associated with ionizes a neutral vapor or gas. Experiments conducted at Stanford Linear Accelerator Center explore threshold conditions necessary to induce by electron in lithium vapor. By independently varying transverse size, number of electrons per bunch, bunch length, radial component controlled be above below for ionization. Additional experiments ionized xenon and...
Secondary electron cascades were measured in high purity single-crystalline chemical vapor deposition (CVD) diamond, following exposure to ultrashort hard x-ray pulses (140fs full width at half maximum, 8.9keV energy) from the Sub-Picosecond Pulse Source Stanford Linear Accelerator Center. We report measurements of pair creation energy and drift mobility carriers two CVD diamond crystals. This was done for first time using femtosecond excitation. Values average found be 12.17±0.57...
We have successfully designed, fabricated, installed, and tested a super compact $X$-band SLAC Energy Doubler system at SLAC. It is composed of an elegant 3 dB coupler--mode converter--polarizer coupled to single spherical energy storage cavity with high ${Q}_{0}$ 94000 diameter less than 12 cm. The available rf peak power 50 MW can be compressed average more 200 in order double the kick for electron bunches transverse deflector greatly improve measurement resolution both x-ray free-electron...
Positrons in the energy range of 3-30 MeV, produced by x rays emitted betatron motion a plasma wiggler 28.5 GeV electrons from SLAC accelerator, have been measured. The extremely high-strength is an ion column induced electron beam as it propagates through and ionizes dense lithium vapor. X 1-50 MeV forward cone angle 0.1 mrad collide with 1.7 mm thick tungsten target to produce electron-positron pairs. positron spectra are found be strongly influenced density length well bunch length. By...
We present results on the commissioning of two-module RadiaBeam / SLAC dechirper system at LCLS. This is first installation and measurement a corrugated high energy (4.4 - 13.3 GeV), short pulses (< 200 fs) while observing its effect an operational FEL. Both transverse longitudinal wakefields allow more flexible electron beam tailoring. verify that, for single module given gap, strength wake axis dipole near agree well with theoretical values. Using direct phase space mapping X-ray FEL...
An important aspect of plasma wake field accelerators (PWFA) is stable propagation the drive beam. In under dense regime, beam creates an ion channel which acts on as a strong thick focusing lens. The causes to undergo multiple betatron oscillations along length plasma. There are several advantages if size can be matched constant radius. First, simulations have shown that instabilities such hosing reduced when [1]. Second, synchrotron radiation losses minimized matched. Third, initially will...
A new class of ion beam lenses is described. The electrostatic coaxial field between a thin central rod and an outer cylinder used as the focusing element. MeV beams may be focused in 100 mm using kilovolts on lens. Both diverging converging made two combined to reduce aberrations. An analysis particle trajectories through these given results for 400 keV proton presented.
The RadiaBeam/SLAC dechirper, a structure consisting of pairs flat, metallic, corrugated plates, has been installed just upstream the undulators in Linac Coherent Light Source (LCLS). As with beam passing between plates on axis, longitudinal wakefields are induced that can remove unwanted energy chirp beam. However, off strong transverse wakes also induced. This mode operation already used for production intense, multicolor photon beams using fresh-slice technique, and is being to develop...
The SLC damping rings function to provide low emittance, short bunches for injection into the linac. As beam intensity in was raised, as part of luminosity improvement program, we observed a threshold above which jitter would occur Frequent machine trios, caused by loss on some bunches, were associated with jitter. These erratic "flier" pulses traced extraction phase errors from rings. This paper covers diagnosis this condition and observations transient bunch length instability phenomena....