Laser Acceleration Research Articles

Cellular irradiations with laser-driven carbon ions at ultra-high dose rates

Objective. Carbon is an ion species of significant radiobiological interest, particularly in view of its use in cancer radiotherapy, where its large Relative Biological Efficiency is often exploited to overcome radio resistance. A growing interest in highly pulsed carbon delivery has arisen in the context of the development of the FLASH radiotherapy approach, with recent studies carried out at dose rates of 40 Gy s−1. Laser acceleration methods, producing ultrashort ion bursts, can now enable the delivery of Gy-level doses of carbon ions at ultra-high dose rates (UHDRs), exceeding 109 Gy s−1. While studies at such extreme dose rate have been carried out so far using low LET particles such as electrons and protons, the radiobiology of high-LET, UHDR ions has not yet been explored. Here, we report the first application of laser-accelerated carbon ions generated by focussing 1020 W cm−2 intense lasers on 10–25 nm carbon targets, to irradiate radioresistant patient-derived Glioblastoma stem like cells (GSCs). Approach. We exposed GSCs to 1 Gy of 9.5 ± 0.5 MeV/n carbon ions delivered in a single ultra-short (∼400-picosecond) pulse, at a dose rate of 2 × 109 Gy s−1, generated using the ASTRA GEMINI laser of the Central Laser Facility at the Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK. We quantified carbon ion-induced DNA double strand break (DSB) damage using the 53BP1 foci formation assay and used 225 kVp x-rays as a reference radiation. Main Results. Laser-accelerated carbon ions induced complex DNA DSB damage, as seen through persistent 53BP1 foci (11.5 ± 0.4 foci/cell/Gy) at 24 h and significantly larger foci (1.69 ± 0.07 μm2) than x-rays induced ones (0.63 ± 0.02 μm2). The relative foci induction value for laser-driven carbon ions relative to conventional x-rays was 3.2 ± 0.3 at 24 h post-irradiation also confirming the complex nature of the induced damage. Significance. Our study demonstrates the feasibility of radiobiology investigations at unprecedented dose rates using laser-accelerated high-LET carbon ions in clinically relevant models.

Fast neutron radiography by using laser accelerator

Fast neutron radiography by using laser accelerator

Dielectric Laser Accelerators Driven by Ultrashort, Ultraintense Long-Wave Infrared Lasers

Particle acceleration driven by intense lasers has long been a frontier of research in the field of laser engineering physics due to its extremely high acceleration gradient. Recently, dielectric laser accelerators (DLAs) have become a new research hotspot due to their ability to achieve gigavolt-per-meter acceleration gradients on compact chip-level all-optical structures. In comparison to the currently widely used solid-state laser with a 1-μm wavelength, long-wave infrared (LWIR) lasers with a length of about 10 μm offer several unique advantages, including the ability to obtain a large electric charge of particle beams and lower energy divergence. These advantages have been validated in plasma-based laser accelerators as well as DLAs. Although the system is still in its early stages of development, the use of LWIR lasers for driving DLAs has special significance, including but not limited to easier processing of optical chips and larger acceleration channels. This review will provide a detailed introduction to this field from 2 aspects: DLAs and ultrashort and ultraintense LWIR lasers based on CO 2 laser amplifiers.

Introduction to the Special Issue on “Laser Acceleration”

Introduction to the Special Issue on “Laser Acceleration”

Review of the research progress of laser accelerator CLAPA-II

粒子加速器作为核物理科学中的核心仪器设备，是衡量综合国力的一项重要标志。经过多年发展，粒子加速器的相关技术已基本成熟，新加速机制的提出与研究成为了粒子加速器技术的新兴研究方向。由于激光与等离子体作用不存在击穿问题，产生的加速电场梯度远高于常规加速器，具有可以更加经济地实现高能离子加速的潜力，一旦达到工程应用标准，将大幅降低加速器的建造应用门槛。但由于激光加速技术发展时间较短，在实际投入工程应用中仍面临很大挑战。为了实现激光加速技术从实验到实际应用的转化，在国家科技部和北京市的支持下，北京大学在怀柔科学城开展了激光加速器装置CLAPA-II的研发与建造。本文主要介绍了CLAPA-II装置的主要组成，以及关键核心技术相关研究进展。

Miniature light-driven nanophotonic electron acceleration and control

Dielectric laser accelerators (DLAs) are fundamentally based on the interaction of photons with free electrons, where energy and momentum conservation are satisfied by mediation of a nanostructure. In this scheme, the photonic nanostructure induces near-fields which transfer energy from the photon to the electron, similar to the inverse-Smith–Purcell effect described in metallic gratings. This, in turn, may provide ground-breaking applications, as it is a technology promising to miniaturize particle accelerators down to the chip scale. This fundamental interaction can also be used to study and demonstrate quantum photon-electron phenomena. The spontaneous and stimulated Smith–Purcell effect and the photon-induced near-field electron-microscopy (PINEM) effect have evolved to be a fruitful ground for observing quantum effects. In particular, the energy spectrum of the free electron has been shown to have discrete energy peaks, spaced with the interacting photon energy. This energy spectrum is correlated to the photon statistics and number of photon exchanges that took place during the interaction. We give an overview of DLA and PINEM physics with a focus on electron phase-space manipulation.

The Progress and the State-of-Art Processes for Ultra-Intensity Laser-Driven Accelerators

Contemporarily, with rapid development of the laser techniques, it is feasible to accelerate particles based on ultra-intensity laser. Compared to the conventional accelerators, the occupation and costs are much smaller. With this in mind, this article aims to conclude the achievement of laser acceleration in those years. In this paper, the property of the wakefield acceleration, CPA, and optical tweezer are summarized and the achievements of the state-of-art facilities are also demonstrated. However, there are still some influence factors in the acceleration, and the limitations of the laser acceleration are also mentioned. Based on the analysis, the future routine for this scheme will be proposed accordingly. Overall, these results shed light on guiding further exploration for laser-driven accelerators.

Stable and High-Quality Electron Beams from Staged Laser and Plasma Wakefield Accelerators

We present experimental results on a plasma wakefield accelerator (PWFA) driven by high-current electron beams from a laser wakefield accelerator (LWFA). In this staged setup stable and high quality (low divergence and low energy spread) electron beams are generated at an optically-generated hydrodynamic shock in the PWFA. The energy stability of the beams produced by that arrangement in the PWFA stage is comparable to both single-stage laser accelerators and plasma wakefield accelerators driven by conventional accelerators. Simulations support that the intrinsic insensitivity of PWFAs to driver energy fluctuations can be exploited to overcome stability limitations of state-of-the-art laser wakefield accelerators when adding a PWFA stage. Furthermore, we demonstrate the generation of electron bunches with energy spread and divergence superior to single-stage LW-FAs, resulting in bunches with dense phase space and an angular-spectral charge density beyond the initial drive beam parameters. These results unambiguously show that staged LWFA-PWFA can help to tailor the electron-beam quality for certain applications and to reduce the influence of fluctuating laser drivers on the electron-beam stability. This encourages further development of this new class of staged wakefield acceleration as a viable scheme towards compact, high-quality electron beam sources.

Effect of radiation-reaction on charged particle dynamics in a focused electromagnetic wave

The effect of radiation-reaction force on the dynamics of a charged particle in an intense focused light wave is investigated using the physically appealing Hartemann-Luhmann equation of motion. It is found that, irrespective of the choice of initial conditions, radiation reaction force causes the charged particle to cross the focal region, provided the particle is driven into regions where the radiation reaction force dominates over the Lorentz force, thus enhancing the forward energy gained by the particle from the intense light wave. This result is in sharp contrast to the well known result, derived in the absence of radiation reaction forces, where for certain initial conditions the particle reflects from the high intensity region of the focused light wave, thereby losing forward energy. From the perspective of energy gain, our studies clearly show that the parameter space for forward energy gain which is reduced by ponderomotive effects is compensated by radiation reaction effects. These results, which are of relevance to the present day direct laser acceleration schemes of charged particle, also agrees with that obtained using the well known Landau-Lifshitz equation of motion.

Strong-field QED experiments using the BELLA PW laser dual beamlines

The Petawatt (PW) laser facility of the Berkeley Lab Laser Accelerator (BELLA) Center has recently commissioned its second laser pulse transport line. This new beamline can be operated in parallel with the first beamline and enables strong-field quantum electrodynamics (SF-QED) experiments at BELLA. In this paper, we present an overview of the upgraded BELLA PW facility with a SF-QED experimental layout in which intense laser pulses collide with GeV-class laser-wakefield-accelerated electron beams. We present simulation results showing that experiments will allow the study of laser-particle interactions from the classical to the SF-QED regime with a nonlinear quantum parameter of up to $\chi\sim$2. In addition, we show that experiments will enable the study and production of GeV-class, mrad-divergence positron beams via the Breit-Wheeler process.

Underdense relativistically thermal plasma produced by magnetically assisted direct laser acceleration

Successive stages of direct laser acceleration driven by two laser pulses in an applied magnetic field enable volumetric generation of bulk-relativistic, persistently hot plasma at gas-jet-accessible and optically diagnosable density. Theory and kinetic simulations demonstrate robustness to experimentally relevant parameters and indicate that this approach is capable of accessing a relativistically thermal plasma regime of significant interest for basic plasma physics, laser-plasma physics, and laboratory astrophysics.

Calibration and test of CsI scintillator ion detection system for tokamak magnetic field diagnosis based on laser-driven ion-beam trace probe (LITP)

As a new diagnostic method of core electromagnetic field, the laser-driven ion-beam trace probe (LITP), is expected to realize the first application of the advanced laser accelerator in magnetic confinement fusion. The detector of the LITP directly measures the distribution of the dispersed pulsed ions after they have passed through the core plasma (Yang 2014 Rev. Sci. Instrum. 85 11E429). In such an environment of high temperature and radiation, the response and lifetime of the ion detector is very crucial. In this work, we have verified the feasibility of the LITP ion detection through systemic experiments. A CsI(Tl) scintillator coupled with an imaging system composed of optical lens and optical fiber array was calibrated on both the 4.5 MV Electrostatic Accelerator and the Compact LAser Plasma Accelerator (CLAPA) at Peking University. We found that the detectable proton density limit is achievable by using a tens of TW level laser system. The CsI(Tl) scintillator system was also tested on the HL-2A tokamak device to measure the real background noise caused by the hot plasma electrons and radiation. It was not damaged by the harsh environment after being placed in the tokamak for three days, and the background noise was completely suppressed when using an ultrafast camera and microsecond shutter. These calibrations and tests verified the feasibility of the LITP detector.

Design study of a dielectric laser undulator

Dielectric laser acceleration (DLA) achieves remarkable gradients from the optical near fields of a grating structure. Tilting the dielectric grating with respect to the electron beam leads to deflection forces and the DLA structure can be utilized as a microchip undulator. We investigate the beam dynamics in such structures analytically and by numerical simulations. A crucial challenge is to keep the beam focused, especially in direction of the narrow channel. An alternating phase focusing scheme is optimized for this purpose and matched lattice functions are obtained. We distinguish synchronous operation with phase jumps in the grating and asynchronous operation with a strictly periodic grating and well-designed synchronicity mismatch. Especially the asynchronous DLA undulator is a promising approach, since a simple, commercially available grating suffices for the focusing lattice design. We pave the way towards experiments of radiation generation in these structures and provide estimates of the emitted radiation wavelength and power. The analytical models are validated by numerical simulations in the dedicated DLA simulation tool DLAtrack6D and Astra, where the underlying laser fields are computed by CST Studio.

Single-electron nano-chip free-electron laser

A conventional free-electron laser is useful but large, driven by a beam with many relativistic electrons. Although, recently, keV electron beams have been used to excite broadband radiation from material chips, there remains a quest for a chip-size free-electron laser capable of emitting coherent radiation. Unfortunately, those keV emitters from electron microscopes or dielectric laser accelerators usually deliver a small current with discrete moving electrons separated by a distance of a few or tens of microns. To envisage a chip-size free-electron laser as a powerful research tool, we study in this paper achievable laser radiation from a single electron and an array of single electrons atop a nano-grating dielectric waveguide. In our study, thanks to the strong coupling between the electron and the guided wave in a structure with distributed feedback, a single 50-keV electron generates 1.5-µm laser-like radiation at the Bragg resonance of a 31-µm long silicon grating with a 400-nm thickness and 310-nm period. When driven by a train of single electrons repeating at 0.1 PHz, the nano-grating waveguide emits strong laser radiation at the second harmonic of the excitation frequency. A discrete spectrum of Smith–Purcell radiation mediated by the waveguide modes is also predicted in theory and observed from simulation in the vacuum space above the grating waveguide. This study opens up the opportunity for applications requiring combined advantages from compact high-brightness electron and photon sources.

Hydrogen targetry in laser-plasma physics

The development of various types of cryogenic target systems opens new opportunities for laser-matter interaction experiments. Existing systems of solid hydrogen targets, which are used with high-power laser systems for various experiments, including laser acceleration of protons, are considered. The details of target formation techniques are discussed. We also discussed some most challenging issues in target fabrication at low temperature and laser operation high repetition rate.

On the influence of the Gouy phase on the process of direct-field electron acceleration

Direct-field laser acceleration of electrons by radially polarized laser pulses with a tunable total Gouy phase variation (TGPV) is investigated. It is shown, using test-particle simulations, that the Gouy phase plays a fundamental role in the synchronization process between the laser pulse and electrons. Simulations reveal that a smaller TGPV is advantageous and can lead to up to 25% increase in the theoretical energy limit, as well as up to 50% more energy yield, within the limits of the parameter space explored in the present work, as compared to the results predicted for a standard T M 01 pulse. We also examine the possibility of using direct-field laser acceleration in a cascade configuration using pulses with a TGPV smaller than 2 π , pointing out the fundamental limitations of that approach.

Beam distribution homogenization design for laser-driven proton therapy accelerator

CLAPA-II, formerly known as CLAPA-T, is being built by Peking University with the support of China’s Ministry of Science and Technology. The main purpose of this device is to explore and verify the application performance of a laser-driven particle acceleration beam. For proton therapy, it is desirable to have a highly uniform beam distribution during irradiation. Furthermore, according to experimental results and design experience, low particle current will be one of the main challenges in the application of laser beam acceleration. It is important to improve the efficiency of particle transport to increase the particle current available for applications. In order to improve dose uniformity and maximize transport efficiency, we have made an upgrade to our existing beam dynamics design. The modified design keeps the original characteristics of local achromatic transport, but adds a new section for beam homogenization using octupole fields. This beamline can provide continuously-adjustable beam spots at the target point with diameters from 5 mm to 80 mm and energy dispersion of less than 5%. The set of octupoles enables the beam transport system to provide two selectable distributions, which are similar to a Gaussian distribution and a nearly uniform distribution. The beam parameters required by irradiation are taken as the standard, and the results obtained by beam stacking after homogenization have clear advantages. These advantages can improve both the dose uniformity and the beam utilization rate, thereby mitigating the low average particle current from the laser accelerator.

Pulse chirp enhances the laser acceleration of neutral particles.

Accelerating neutral atoms is challenging because such particles are not directly manipulated by electric and magnetic fields as charged particles. In our acceleration scheme, the excited atom requires a sufficiently high gradient acceleration force. The key challenge in laser acceleration experiments is that not only must the photon energy excite atoms to the Rydberg state, but also atoms must not be ionized in an intense laser field. In this Letter, we propose using a chirped laser pulse to achieve the objectives above. The enhancement effect of the pulse chirp on the laser acceleration of neutral particles is investigated via numerical simulation and analytical analysis.

Proton acceleration in vacuum using frequency-chirped laser pulses

Recent investigations demonstrate the achievement of protons with energies of several hundred MeV via vacuum laser acceleration mechanisms. However, the symmetric electric field from an unchirped laser pulse is not efficient in generating a high energy proton beam. It is known that a proton can gain energy from a chirped laser pulse through the optimal phase synchronization between the proton and the laser field. In this study, we investigate the proton acceleration by different frequency-chirped laser pulses in vacuum both analytically and numerically. We consider four different situations constituting the unchirped, linear, quadratic, and sinusoidal chirped laser pulses. For the unchirped laser case, the pulse symmetry results in no net energy gain for the proton from the laser field. Conversely, using frequency-chirped laser pulses renders high energy to the proton compared with the unchirped laser pulse. We compared three different chirped cases, and found that a sinusoidal chirped laser pulse renders maximum acceleration to the protons compared to the linear and quadratic chirped situations. There exists an optimal chirp parameter for each type of chirped laser pulse.

Transmission and homogenization of laser-driven proton beams with broadband spectra

<p indent="0mm">Over the past few decades, laser accelerators made continuous progress. Thanks to the ultra-high electric field gradient (100 GV/m) generated by the interaction of laser and plasma, protons can be accelerated to MeV energy at a micron scale, being expected to be a new generation of widely used compact accelerators. The laser-driven proton beam has the characteristics of μm-level size (point source), ampere-level peak current, broadband energy spectrum, and large divergence angle. Irradiation applications need a uniform dose distribution, requiring the transformation from a point source to a large area of uniformly distributed particles. Increase of utilization efficiency requires that beams with energy spread as large as possible can be transmitted, while the chromatic aberrations pose a challenge to the homogenization of the beams, including the homogenization of the beams with the same energy and different initial divergence angles, and the homogenization of the beams with different energies. The weak focusing of the constant gradient magnetic field can focus in the horizontal and vertical directions at the same time, and analyze the energy in the horizontal direction. The integration of focusing and energy analysis can achieve achromatic transmission, or significantly reduce the influence of chromatic aberrations. This paper studies the transmission characteristics of proton beams in weak-focusing magnetic fields. The homogenized transformation for protons with the same energy in the horizontal direction from a point to a large area by point-to-parallel imaging is demonstrated. Point-to-parallel imaging is not a necessary condition for homogenization; transformation without point-to-parallel imaging in the vertical direction also obtains good homogeneity. The conditions for positional achromaticity in the horizontal direction are explored, and the transmission and homogenization of proton beams with 20% energy spread can be achieved with appropriate design. In positional achromatic transmission, the chromatic aberrations still have influence, causing the proton beam with large energy spread to deviate from the center of the beamline in the horizontal direction. In order to reduce the influence of chromatic aberrations, a special steering magnet is designed after the weak-focusing magnet to correct the divergence angle in the horizontal direction. The relationship between the correction amount of divergence angle and the position in the horizontal direction is obtained through parameter scanning, which can be well fitted by a 4 order polynomial. After correcting the divergence angle, the proton beam with large energy spread returns to the center of the beamline at the beamline exit. With a slit and energy spectrum shaping, proton beams with 80% energy spread can be obtained for irradiation with better uniformity. When the deflection radius is designed to be <sc>0.65 m,</sc> the weak-focusing beamline can transmit proton beams with <sc>1–20 MeV</sc> energy, 80% energy spread, and an initial divergence angle of ±50 mrad. After changing the magnetic field direction, electron beams with <sc>1–200 MeV</sc> energy, 40% energy spread can be transmitted. The transmission and homogenization of the proton beam with 80% energy spread greatly improves the utilization efficiency. Higher energy particle beams can be delivered using superconducting or pulsed magnet technology. The study found that the influence of chromatic aberrations is much larger in the beam transmission with a quadrupole triplet lens (strong focusing), and as energy cannot be accurately analyzed, it is difficult to improve. In comparison, the weak-focusing magnetic fields have significant advantages for beam homogenization.