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Plasma density gradient control of wake phase velocity and trapping threshold in a laser wakefield accelerator produced electron bunches with absolute longitudinal and transverse momentum spreads more than ten times lower than in previous experiments (0.17 and 0.02 MeV/c FWHM, respectively) and with central momenta of 0.76±0.02 MeV/c, stable over a week of operation. Simulations validated against diagnostics show that use of such bunches as a wakefield accelerator injector can produce stable beams with 0.2 MeV/c‐class momentum spread at high energies. Preservation of bunch momentum spread requires high simulation momentum accuracy, and related self‐trapped simulations showed that high order particle weight effectively suppresses simulation momentum errors allowing design of low emittance stages.Plasma density gradient control of wake phase velocity and trapping threshold in a laser wakefield accelerator produced electron bunches with absolute longitudinal and transverse momentum spreads more than ten times lower than in previous experiments (0.17 and 0.02 MeV/c FWHM, respectively) and with central momenta of 0.76±0.02 MeV/c, stable over a week of operation. Simulations validated against diagnostics show that use of such bunches as a wakefield accelerator injector can produce stable beams with 0.2 MeV/c‐class momentum spread at high energies. Preservation of bunch momentum spread requires high simulation momentum accuracy, and related self‐trapped simulations showed that high order particle weight effectively suppresses simulation momentum errors allowing design of low emittance stages.

Ultrashort terahertz pulses with energies in the μJ range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV [1] and energy spreads of a few‐percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because these electron bunches are ultrashort (

A design of a compact free‐electron laser (FEL), generating ultra‐fast, high‐peak flux, XUV pulses is presented. The FEL is driven by a high‐current, 0.5 GeV electron beam from the Lawrence Berkeley National Laboratory (LBNL) laser‐plasma accelerator, whose active acceleration length is only a few centimeters. The proposed ultra‐fast source (∼10 fs) would be intrinsically temporally synchronized to the drive laser pulse, enabling pump‐probe studies in ultra‐fast science. Owing to the high current (≳10 kA) of the laser‐plasma‐accelerated electron beams, saturated output fluxes are potentially greater than 1013 photons/pulse. Devices based both on self‐amplified spontaneous emission and high‐harmonic generated input seeds, to reduce undulator length and fluctuations, are considered.

The LOASIS Laser Wakefield Accelerator (LWFA) has achieved quasi‐mono‐energetic electron beams with energies up to 1 GeV [1]. These beams offer the potential for use with insertion devices such as wigglers and undulators to create tabletop XUV and x‐ray free‐electron laser (FEL) sources. To achieve a high quality light source producing high brightness radiation requires an electron beam with low energy spread and low emittance. Here we discuss the use of an undulator to generate XUV radiation to characterize in a single shot the electron beam energy spread and emittance with high precision.

Laser wakefield acceleration experiments were carried out by using a hydrogen‐filled capillary discharge waveguide. For a 15 mm long, 200 μm diameter capillary, quasi‐monoenergetic e‐beams up to 300 MeV were observed. By de‐tuning discharge delay from optimum guiding performance, self‐trapping was found to be stabilized. For a 33 mm long, 300 μm capillary, a parameter regime with high energy electron beams, up to 1 GeV, was found. In this regime, the electron beam peak energy was correlated with the amount of trapped electrons.

We present observation and characterization of microjoule‐MV/cm‐level THz pulses from a laser wakefield accelerator. THz emitted as coherent transition radiation from the plasma‐vacuum boundary is collected and refocused by off‐axis parabolas to a test stand where a suite of diagnostics is performed, including energy measurement by a Golay cell and electro‐optic sampling of the spatio‐temporal electric field using a probe pulse split from the main laser. Frequency Domain Holography is also implemented for the first time to capture spatio‐temporal field distributions in a single shot. The four techniques strongly corroborate detection of THz pulses of ∼0.4 ps duration, with peak fields of several hundred kV/cm and energies of 5–10 μJ. The advantages and disadvantages of each technique are discussed.

A nonlinear optical pulse cleaning technique based on cross‐polarized wave (XPW) generation filtering [1] has been implemented to improve laser pulse contrast, and consequently to control pre‐ionization in laser‐plasma accelerator experiments. Three orders of magnitude improvement in pre‐pulse contrast has been achieved, resulting in 4‐fold increase in electron charge and improved stability of both the electron beam energy and THz radiation generated as a secondary process in the gas‐jet‐based LWFA experiments.

Staging laser plasma accelerators is an efficient way of mitigating laser pump depletion in laser driven accelerators and necessary for reaching high energies with compact laser systems. The concept of staging includes coupling of additional laser energy and transporting the electron beam from one accelerating module to another. Due to laser damage threshold constraints, in‐coupling laser energy with conventional optics requires distances between the accelerating modules of the order of 10 m, resulting in decreased average accelerating gradient and complicated e‐beam transport. In this paper we use basic scaling laws to show that the total length of future laser plasma accelerators will be determined by staging technology. We also propose using a liquid jet plasma mirror for in‐coupling the laser beam and show that it has the potential to reduce distance between stages to the cm‐scale.

Design considerations for a next‐generation electron‐positron linear collider based on laser‐plasma‐accelerators are discussed. Several of the advantages and challenges of laser‐plasma‐based accelerator technology are addressed. An example of the parameters for a 1 TeV laser‐plasma‐based collider is presented.

Laser plasma accelerators are able to produce high quality electron beams from 1 MeV to 1 GeV. The next generation of plasma accelerator experiments will likely use a multi‐stage approach where a high quality electron bunch is first produced and then injected into an accelerating structure. In this paper we present scaled particle‐in‐cell simulations of a 10 GeV stage in the quasi‐linear regime. We show that physical parameters can be scaled to be able to perform these simulations at reasonable computational cost. Beam loading properties and electron bunch energy gain are calculated. A range of parameter regimes are studied to optimize the quality of the electron bunch at the output of the stage.

The propagation of a short and intense laser pulse in a plasma channel is investigated through the nonlinear paraxial wave equation. An analytic condition describing quasi-matched laser propagation (i.e., when the second order normalized-intensity-weighted transverse moment of the laser-pulse remain constant) is obtained. For any arbitrary temporal laser pulse profile and any prescribed transverse density profile in the channel, we determine the laser intensity distribution along the pulse, i.e., the slice-dependent laser waist, ensuring quasi-matched propagation. For the case of a Gaussian laser with an initially uniform spot throughout the pulse, we determine the optimal channel depth that minimizes spot size oscillations. The analytical and semi-analytical results obtained for both cases are validated through comparison with numerical simulations.

Transverse stability of the drive beam is critical to plasma wakefield accelerators. A long, relativistic particle beam propagating in an overdense plasma is subject to beam envelope modulation and hosing (centroid displacement) instabilities. Coupled equations for the beam centroid and envelope are derived. The growth rate for beam hosing is examined including return current effects (where the beam radius is of order the plasma skin depth) in the long-beam, strongly-coupled, overdense regime.

Recent progress on a staged laser-plasma accelerator (LPA) experiment is reported. The experiment utilizes a 40 TW class laser which is split into two laser pulses. The first laser drives the first LPA module to produce an electron beam. The second laser drives the second LPA module in a dark-current free regime and accelerates the electron beam from the first LPA. Injection from the first stage, triggering of plasma mirror and reflection of the second laser, and laser guiding in the second stage with the laser pulses reflected off the plasma mirror has been successfully demonstrated. Optical spectral redshift of driving laser is analyzed to estimate the wakefield amplitude and electron energy gain in the second stage.

We demonstrate, for the first time, single-shot, ultrafast computed-tomography reconstructions using a new technique of spectral multiplexing. High-precision, picosecond-resolved, position and morphology measurements of a heterogeneous plasma object are presented.

We present current results on staged electron acceleration in the LOASIS program at the Lawrence Berkeley National Laboratory. The goal is to experimentally demonstrate laser driven electron acceleration in two stages, where each stage is driven by a separate laser pulse. This technology could provide the key to built compact laser driven accelerators which could potentially reach up to TeV in electron energy.

The operational plasma density and laser parameters for future colliders based on laser-plasma accelerators are discussed. Beamstrahlung limits the charge per bunch at low plasma densities. Reduced laser intensity is examined to improve accelerator efficiency in the beamstrahlung-limited regime.

The presence of low emittance beams in laser-plasma accelerators is indicated by single-shot spectroscopic measurements of betatron X-rays. By matching the X-ray betatron spectra to analytical and numerical models of betatron radiation, the electron bunch radius inside the plasma is estimated to be close to 0.1 micron. Correlations of the bunch radius with electron beam parameters are presented. Photon-counting spectra and statistical fitting are used to establish confidence ranges. Combined with simultaneous electron spectrum and divergence measurements, the normalized transverse emittance is estimated to be as low as 0.1 mm mrad consistent with three-dimensional particle-in-cell simulations.

Controlled injection and staging are critical elements to the improvement of the stability, quality, and tunability of laser plasma accelerators (LPAs) [1, 2]. This paper will discuss techniques such as colliding pulse [3], density tailoring [4, 5], and ionization injection [6, 7, 8], which have recently allowed for the generation of high-energy femtosecond electron beams with percent-level energy spread and stability, and state-of-the-art emittance. Progress on staged acceleration will also be presented, which promises to further increase beam quality, allow for mapping of the wakefield, and overcome the limit of pump depletion [9].

Because of their ultra-high accelerating gradient, laser plasma based accelerators (LPA) are contemplated for the next generation of high-energy colliders and light sources. The upcoming BELLA project will explore acceleration of electron bunches to 10 GeV in a 1 meter long plasma, where a wakefield is driven by a PW-class laser. Particle-in-cell (PIC) simulations are used to design LPA stages relevant to the upcoming experiments. Simulations in a Lorentz boosted frame are used to gain significant speed up and to simulate the 10 GeV stages at full scale parameters, otherwise impractical. As criteria on energy spread and beam emittance become more stringent, PIC simulations become more challenging as high frequency noise artificially increases those quantities. To reduce numerical noise, we consider using a Poisson solve to calculate the beam self-fields. This method allows correct cancelation of the beam transverse self-forces and prevents artificial emittance growth for a matched beam in a linear focusin...

Electro-optic sampling (EOS) is widely used as a technique to measure THz-domain electric field pulses such as the self-fields of femtosecond electron beams. We present an EOS-based approach for single-shot spectral measurement that excels in simplicity (compatible with fiber integration) and bandwidth coverage (overcomes the laser bandwidth limitation), allowing few-fs electron beams or single-cycle THz pulses to be characterized with conventional picosecond probes. Experiments are conducted with a 0.11-THz-bandwidth optical probe and a broadband source (0-8 THz detection bandwidth) rich in spectral features. We observe clear optical sidebands for various electro-optic crystals. Sharp spectral features in the THz source spectrum are resolved. We also provide an outlook towards minimizing the crystal limitations and extending the detection bandwidth to 10's of THz.

Laser plasma accelerators have produced femtosecond electron bunches with a relative energy spread ranging from 100% to a few percent. Simulations indicate that the measured energy spread can be dominated by a correlated spread, with the slice spread significantly lower. Measurements of coherent optical transition radiation are presented for broad-energy-spread beams with laser-induced density and momentum modulations. The long-range (meter-scale) observation of coherent optical transition radiation indicates that the slice energy spread is below the percent level to preserve the modulations.

Recent experiments coupled electron beams from the LOASIS TREX laser plasma accelerator (LPA) [1, 2, 3] to the Tapered Hybrid Undulator (THUNDER). Using the 1.5m, 66 period undulator, followed by an XUV spectrometer, spontaneous radiation was observed at photon energies extending to 100 eV. Previous experiments have reported visible [4] and soft-x-ray [5] radiation. The purpose of our experiments is to do highly precise, single shot diagnostics of the energy spread and emittance for each electron beam. We present recent results including measurements of electron beam transport through the undulator with and without the use of permanent magnetic quadrapoles, and measurements of XUV spectra up to 100 eV from LPA produced e-beams.

Electron injection in a laser plasma wakefield accelerator by transverse colliding pulses is studied using two dimensional Particle-in-Cell simulations. It is demonstrated that beams with extremely small transverse emittance can be obtained, injected by the transverse standing wave created by the colliding pulses. Ionization of neutral gas is used to increase the final injection charge but keep the emittance small.

The Virtual Detector for Synchrotron Radiation (VDSR) is a parallel C++ code developed to calculate the incoherent radiation from a single charged particle or a beam moving in given external electro-magnetic fields. In this proceedings the code structure and features are introduced. An example of radiation generation from the betatron motion of a beam in the focusing fields of the wake in a laser-plasma accelerator is presented.

Use of counter-propagating pulses to control electron injection in laser-plasma accelerators promises to be an important ingredient in the development of stable devices. We discuss the colliding pulse scheme and associated diagnostics.

The controlled transport and imaging of relativistic electron beams from laser plasma accelerators (LPAs) are critical for their diagnostics and applications. Here we present the design and progress in the implementation of the transport and monitoring system for an undulator based electron beam diagnostic. Miniature permanent-magnet quadrupoles (PMQs) are employed to realize controlled transport of the LPA electron beams, and cavity based electron beam position monitors for non-invasive beam position detection. Also presented is PMQ calibration by using LPA electron beams with broadband energy spectrum. The results show promising performance for both transporting and monitoring. With the proper transport system, XUV-photon spectra from THUNDER will provide the momentum distribution of the electron beam with the resolution above what can be achieved by the magnetic spectrometer currently used in the LOASIS facility.

The controlled imaging and transport of ultra‐relativistic electrons from laser‐plasma accelerators is of crucial importance to further use of these beams, e.g. in high peak‐brightness light sources. We present our plans to realize beam transport with miniature permanent quadrupole magnets from the electron source through our THUNDER undulator. Simulation results demonstrate the importance of beam imaging by investigating the generated XUV‐photon flux. In addition, first experimental findings of utilizing cavity‐based monitors for non‐invasive beam‐position measurements in a noisy electromagnetic laser‐plasma environment are discussed.

Plasma accelerators may be driven by the ponderomotive force of an intense laser or the space‐charge force of a charged particle beam. The implications for accelerator design and the different physical mechanisms of laser‐driven and beam‐driven plasma acceleration are discussed. Driver propagation is examined, as well as the effects of the excited plasma wave phase velocity. The driver coupling to subsequent plasma accelerator stages for high‐energy physics applications is addressed.

The infrastructure of Extreme Light Infrastructure (ELI) provides an unprecedented opportunity for a broad range of frontier science. Its highest ever intensity of lasers, as well as high fluence, high power, and/or ultrafast optical characteristics carve out new territories of discovery, ranging from attosecond science to photonuclear science, laser acceleration and associated beams, and high field science (Four Pillars of ELI). Its applications span from medicine, biology, engineering, energy, chemistry, physics, and fundamental understanding of the Universe. The relativistic optics that intense lasers have begun exploring may be extended into a new regime of ultra‐relativistic regime, where even protons fly relativistically in the optical fields. ELI provides the highest intensity to date such that photon fields begin to feel even the texture of vacuum. This is a singular appeal of ELI with its relatively modest infrastructure (compared to the contemporary largest scientific infrastructures), yet provides an exceptional avenue along which the 21st Century science and society need to answer the toughest questions. The intensity frontier simultaneously brings in the energy horizon (TeV and PeV) as well as temporal frontier (attoseconds and zeptoseconds). It also turns over optics of atoms and molecules into that of nuclei with the ability to produce monoenergetic collimated γ‐ray photons. As such, the ELI concept acutely demands an effort to encompass and integrate its Four Pillars.

The wavefront of a short laser pulse after interaction in a laser‐plasma accelerator (LPA) was measured to diagnose laser‐guiding quality. Experiments were performed on a 100 TW class laser at the LOASIS facility of LBNL using a hydrogen‐filled capillary discharge waveguide. Laser‐guiding with a pre‐formed plasma channel allows the laser pulse to propagate over many Rayleigh lengths at high intensity and is crucial to accelerate electrons to the highest possible energy. Efficient coupling of laser energy into the plasma is realized when the laser and the channel satisfy a matched guiding condition, in which the wavefront remains flat within the channel. Using a wavefront sensor, the laser‐guiding quality was diagnosed based on the wavefront of the laser pulse exiting the plasma channel. This wavefront diagnostic will contribute to achieving controlled, matched guiding in future experiments.

Decoupling injection from acceleration is a key challenge to achieve compact, reliable, tunable laser‐plasma accelerators (LPA) [1, 2]. In colliding pulse injection the beat between multiple laser pulses can be used to control energy, energy spread, and emittance of the electron beam by injecting electrons in momentum and phase into the accelerating phase of the wake trailing the driver laser pulse [3, 4, 5, 6, 7]. At LBNL, using automated control of spatiotemporal overlap of laser pulses, two‐pulse experiments showed stable operation and reproducibility over hours of operation. Arrival time of the colliding beam was scanned, and the measured timing window and density of optimal operation agree with simulations [8]. The accelerator length was mapped by scanning the collision point.

Laser-plasma collider designs point to staging of multiple accelerator stages at the 10 GeV level, which are to be developed on the upcoming BELLA laser, while Thomson Gamma source designs use GeV stages, both requiring efficiency and low emittance. Design and scaling of stages operating in the quasi-linear regime to address these needs are presented using simulations in the VORPAL framework. In addition to allowing symmetric acceleration of electrons and positrons, which is important for colliders, this regime has the property that the plasma wakefield is proportional to the transverse gradient of the laser intensity profile. We demonstrate use of higher order laser modes to tailor the laser pulse and hence the transverse focusing forces in the plasma. In particular, we show that by using higher order laser modes, we can reduce the focusing fields and hence increase the matched electron beam radius, which is important to increased charge and efficiency, while keeping the low bunch emittance required for applications.

We present experimental results on a tape‐drive based plasma mirror which could be used for a compact coupling of a laser beam into a staged laser driven electron accelerator. This novel kind of plasma mirror is suitable for high repetition rates and for high number of laser shots.

Electron injection and trapping in a laser wakefield accelerator by high‐order field ionization is studied theoretically and by particle‐in‐cell simulations. To obtain low energy spread beams we use a short region of gas mixture (H+N) near the start of the stage to trap electrons, while the remainder of the stage uses pure H and is injection‐free. Effects of gas mix parameters, such as concentration and length, on the final electron injection number and beam quality are studied. Laser polarization and shape effects on injection number and final electron emittance are also shown.

Plasma Channel Diagnostic Based on Laser Centroid Oscillations A. J. Gonsalves, K. Nakamura, C. Lin, J. Osterhoff, S. Shiraishi, C. B. Schroeder, C. G. R. Geddes, Cs. Toth, E. Esarey, and W. P. Leemans Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Abstract. A technique has been developed for measuring the properties of discharge-based plasma channels by monitoring the centroid location of a laser beam exiting the channel as a function of input alignment offset between the laser and the channel. The centroid position of low-intensity ( 10 18 Wcm −2 are used for laser plasma acceleration, the intensity was kept low in these experiments so that non-linear effects such as self-focusing [11] could be neglected and the plasma properties measured in a straight- forward way. The technique relies on the fact that a transverse offset of the laser pulse at the entrance of the plasma channel causes the laser beam to undergo transverse oscillations about the channel axis. These oscillations depend on the initial centroid offset and angle with respect to the channel axis, and on the channel properties. As will be shown, measuring the dependence of the exit laser centroid position on the input and on channel formation timing provides direct information on the channel matched spot size and profile. This technique reduces the measurement error compared to interferometry and provides increased precision in channel alignment to minimize pointing errors in LPA applications [12].

The design and current status of experiments to couple the Tapered Hybrid Undulator (THUNDER) to the Lawrence Berkeley National Laboratory (LBNL) laser plasma accelerator (LPA) to measure electron beam energy spread and emittance are presented.

Single‐shot x‐ray spectra from electron bunches produced by a laser‐plasma wakefield accelerator (LPA) [1, 2] were measured using a photon‐counting single‐shot pixelated Silicon‐based detector [3], providing for the first time single‐shot direct spectra without assumptions required by filter based techniques. In addition, the electron bunch source size was measured by imaging a wire target, demonstrating few micron source size and stability. X‐rays are generated when trapped electrons oscillate in the focusing field of the wake trailing the driver laser pulse [4, 5, 6, 7, 8]. In addition to improving understanding of bunch emittance and wake structure, this provides a broadband, synchronized femtosecond source of keV x‐rays. Electron bunch spectra and divergence were measured simultaneously and preliminary analysis shows correlation between x‐ray and electron spectra. Bremsstrahlung background was managed using shielding and magnetic diversion.

The electron energy dependence of a scintillating screen (Lanex Fast) was studied with sub‐nanosecond electron beams ranging from 106 MeV to 1522 MeV at the Lawrence Berkeley National Laboratory Advanced Light Source (ALS) synchrotron booster accelerator. The sensitivity of the Lanex Fast decreased by 1% per 100 MeV increase of the energy. The linear response of the screen against the charge was verified with charge density and intensity up to 160 pC/mm2 and 0.4 pC/ps/mm2, respectively. For electron beams from the laser plasma accelerator, a comprehensive study of charge diagnostics has been performed using a Lanex screen, an integrating current transformer, and an activation based measurement. The charge measured by each diagnostic was found to be within ±10%.

We present an overview of diagnostic techniques for measuring key parameters of electron bunches from Laser Plasma Accelerators (LPAs). The diagnostics presented here were chosen because they highlight the unique advantages (e.g. diverse forms of electromagnetic emission) and difficulties (e.g. shot‐to‐shot variability) associated with LPAs. Non destructiveness and high resolution (in space and time and energy) are key attributes that enable the formation of a comprehensive suite of simultaneous diagnostics which are necessary for the full characterization of the ultrashort, but highly‐variable electron bunches from LPAs.

Electro‐optic sampling (EOS) is widely used as a technique to measure THz‐domain electric field pulses such as the self‐fields of femtosecond electron beams. We present an EOS‐based approach for single‐shot spectral measurement that excels in simplicity (compatible with fiber integration) and bandwidth coverage (overcomes the laser bandwidth limitation), allowing few‐fs electron beams or single‐cycle THz pulses to be characterized with conventional picosecond probes. It is shown that the EOS‐induced optical sidebands on the narrow‐bandwidth optical probe are spectrally‐shifted replicas of the THz pulse. An experimental demonstration on a 0–3 THz source is presented.

An overview is presented of the design of a 10 GeV laser plasma accelerator (LPA) that will be driven by a PW‐class laser system and of the BELLA Project, which has as its primary goal to build and install the required Ti:sapphire laser system for the acceleration experiments. The basic design of the 10 GeV stage aims at operation in the quasi‐linear regime, where the laser excited wakes are largely sinusoidal and offer the possibility of accelerating both electrons and positrons. Simulations show that a 10 GeV electron beam can be generated in a meter scale plasma channel guided LPA operating at a density of about 1017 cm−3 and powered by laser pulses containing 30–40 J of energy in a 50–200 fs duration pulse, focused to a spotsize of 50–100 micron. The lay‐out of the facility and laser system will be presented as well as the progress on building the facility.

The numerical modeling code INF&RNO (INtegrated Fluid & paRticle simulatioN cOde, pronounced “inferno”) is presented. INF&RNO is an efficient 2D cylindrical code to model the interaction of a short laser pulse with an underdense plasma. The code is based on an envelope model for the laser while either a PIC or a fluid description can be used for the plasma. The effect of the laser pulse on the plasma is modeled with the time‐averaged poderomotive force. These and other features allow for a speedup of 2–4 orders of magnitude compared to standard full PIC simulations while still retaining physical fidelity. The code has been benchmarked against analytical solutions and 3D PIC simulations and here a set of validation tests together with a discussion of the performances are presented.

In recent experiments plasma electrons became trapped in a plasma wakefield accelerator (PWFA). The transverse size of these trapped electrons on a downstream diagnostic yields an upper limit measurement of transverse normalized emittance divided by peak current, eN,x/I. The lowest upper limit for eN,x/I measured in the experiment is 1.3⋅10−10 m/A.

The development of new laser systems based on OPCPA will push Laser Wakefield Accelerators (LWFA) to a qualitatively new energy range. As in the past, numerical simulations will play a critical role in testing, probing and optimizing the physical parameters and setup of these upscale experiments. Based on the prospective design parameters for the future Vulcan 10 PW OPCPA laser system, we have determined the optimal parameters for a single LWFA stage from theoretical scalings for such system, which predict accelerations to the energy frontier, with self-injected electrons in excess of 10 GeV for a self-guided configuration, and above 50 GeV bunches with externally-injected electrons in a laser-guided configuration. These parameters were then used as a baseline for 3D full scale simulations with OSIRIS and QuickPIC. A 12 GeV self-injected beam was obtained with both codes, in agreement with theoretical predictions for the maximum energy gain and the injected charge. Preliminary results on the laser-guided configuration already confirm the accelerating gradients and the stability of the laser guided propagation for long distances required to reach the higher energies predicted by the theoretical scalings for this scenario. © 2009 American Institute of Physics.

Laser wakefield acceleration (LWFA) in a supersonic gas‐jet using a self‐guided laser pulse was studied by changing the laser power and electron density. The recently upgraded HERCULES laser facility equipped with wavefront correction enables a peak intensity of 8×1019 W/cm2 at laser power of 100 TW to be delivered to the gas‐jet using f/10 focusing optics. We found that electron beam charge was increased significantly with an increase of the laser power from 30 TW to 80 TW and showed density threshold behavior at a fixed laser power. Betatron motion of electrons was also observed depending on laser power and electron density.

A CLIC designed 18 cells, low group velocity (2.4% to 1.0% c), X‐band (11.4 GHz) accelerator structure (denoted T18) was designed at CERN, its cells were built at KEK, and it was assembled and tested at SLAC. An interesting feature of this structure is that the gradient in the last cell is about 50% higher than that in the first cell. This structure has been RF conditioned at SLAC NLCTA for about 1400 hours where it incurred about 2200 breakdowns. This paper presents the characteristics of these breakdowns, including 1) the breakdown rate dependence on gradient, pulse width and conditioning time, 2) the breakdown distribution along the structure, 3) relation between breakdown and pulsed heating dependence study and 4) electric field decay time for breakdown changing over the whole conditioning time. Overall, this structure performed very well, having a final breakdown rate of less than 1e‐6/pulse/m at 106 MV/m with 230 ns pulse width.

User experiments aimed toward discovering pathways towards development of high gradient accelerator structures have begun in the Ka‐Band Test Facility at Yale University. This facility is based on use of the Yale/Omega‐P 34.3 GHz magnicon. The first two experiments, a quasi‐optical active pulse compressor and an RF breakdown cavity test cell, have been installed and are undergoing initial testing. The status of these experiments and others awaiting installation will be reviewed.

In the context of the CLIC (Compact Linear Collider) project investigations of DC breakdown in ultra high vacuum are carried out in parallel with high power RF tests. From the point of view of saturation breakdown field the best material tested so far is stainless steel, followed by titanium. Copper shows a four times weaker breakdown field than stainless steel. The results indicate clearly that the breakdown events are initiated by field emission current and that the breakdown field is limited by the cathode. In analogy to RF, the breakdown probability has been measured in DC and the data show similar behaviour as a function of electric field.

We report the generation of radiation in the terahertz (THz) spectral region from an electrostatic field converted by a laser‐produced relativistic ionization front. The THz radiation is generated through spatiotemporal change in electron density induced by a relativistic ionization front propagating in a ZnSe crystal enclosed in a capacitor array. The measured central radiation frequency is 1.2 THz with a bandwidth of 0.7 THz (FWHM), which is attributed to production of an electron density of the order of 1015 cm−3. The amplitude of the linearly polarized THz radiation increased linearly with the voltage applied to the capacitors.

I-TW, 6-ps, circularly polarized CO(2) laser pulses focused onto thin Al foils are used to drive ion acceleration. The spectra of ions and protons generated in the direction normal to the rear surface, detected with a compact magnet spectrometer with CR39, reveals a broad proton high-energy peak at similar to 1 MeV. This observation conforms to the theoretical predictions that circularly polarized laser pulses are less efficient than linearly polarized pulses in driving ion acceleration via the Target Normal Sheath Acceleration (TNSA) mechanism. Instead, there is evidence that the circularly polarized laser may provide direct ponderomotive acceleration of ions and protons. We report also the first application of the BNL proton source in nano-science. Irradiation of graphite and graphene films produced local defects and membranes for variety of applications.