Payton Broaddus, Thilo Egenolf, Dylan S. Black, Melanie Murillo, Clarisse Woodahl, Yu Miao, Uwe Niedermayer, Robert L. Byer, Kenneth J. Leedle, Olav Solgaard
We demonstrate a silicon-based electron accelerator that uses laser optical near fields to both accelerate and confine electrons over extended distances. Two dielectric laser accelerator (DLA) designs were tested, each consisting of two arrays of silicon pillars pumped symmetrically by pulse front tilted laser beams, designed for average acceleration gradients 35 and 50 MeV/m respectively. The DLAs are designed to act as alternating phase focusing (APF) lattices, where electrons, depending on the electron-laser interaction phase, will alternate between opposing longitudinal and transverse focusing and defocusing forces. By incorporating fractional period drift sections that alter the synchronous phase between $\pm 60^\circ$ off crest, electrons captured in the designed acceleration bucket experience half the peak gradient as average gradient while also experiencing strong confinement forces that enable long interaction lengths. We demonstrate APF accelerators with interaction lengths up to 708 $μ$m and energy gains up to 23.7 $\pm$ 1.07 keV FWHM, a 25$\%$ increase from starting energy, demonstrating the ability to achieve substantial energy gains with subrelativistic DLA.
We describe and discuss solutions for an innovating sub-relativistic electron source, based on pulsed DC gun, including linear (1D) Field Emitter Array (FEA) associated immediately with Laser Dielectric Accelerator (DLA) stage. That setup is designed to avoid any standard accelerator component (electrostatic or magnetic macroscopic dipole ...) Parts of the diagnostics, including spectrometer and all diagnostics, are planned to rely on nano-structures. Then the entire setup -pulsed source, laser and measurements ends excepted- should be enclosed inside a decimeter range vacuum chamber. The goal…
Orbital period in a ring accelerator and time of flight in a linear accelerator depend on the amplitude of betatron oscillations. The variation is negligible in ordinary particle accelerators with relatively small beam emittance. In an accelerator for large emittance beams like muons and unstable nuclei, however, this effect cannot be ignored. We measured orbital period in a linear non-scaling fixed field alternating gradient (FFAG) accelerator, which is a candidate for muon acceleration, and compared with the theoretical prediction. The good agreement between them gives important ground for t…
Due to its simplicity the classical cyclotron has been used very early for applications in sciency, medicine and industry. Higher energies and intensities were achieved through the concepts of the sector focused isochronous cyclotron and the synchro-cyclotron. Besides those the fixed field alternating gradient accelerator (FFA) represents the most general concept among these types of fixed field accelerators, and the latter one is actively studied and developed for future applications.
A novel scaling type of Fixed-Field Alternating-Gradient (FFAG) accelerator is proposed that solves the major problems of conventional scaling FFAGs. This scaling FFAG accelerator combines reverse bending magnets of the radial sector type and a spiral edge angle of the spiral sector type to ensure sufficient vertical focusing without relying on extreme values of either parameter. This new concept makes it possible to design a scaling FFAG for high energy (above GeV range) applications such as a proton driver for a spallation neutron source and an accelerator driven subcritical reactor.
In this paper we describe the methods and tools used to characterize a 150 MeV proton scaling Fixed Field Alternating Gradient (FFAG) accelerator at Kyoto University Research Reactor Institute. Many of the techniques used are unique to this class of machine and are thus of relevance to any future FFAG accelerator. For the first time we detail systematic studies undertaken to improve the beam quality of the FFAG. The control of beam quality in this manner is crucial to demonstrating high power operation of FFAG accelerators in future.
In this paper, we investigate the stability of the particle trajectories in Fixed Field alternating gradient Accelerators (FFA) in the presence of field errors: The emphasis is on the scaling radial sector FFA type: a collaboration work is on-going in view of better understanding the properties of the 150 MeV scaling FFA at KURRI in Japan, and progress towards high intensity operation. Analysis of certain types of field imperfections revealed some interesting features about this machine that explain some of the experimental results and generalize the concept of a scaling FFA to a non-scaling o…
NORMA is a design for a normal-conducting race track fixed-field alternating-gradient accelerator (FFAG) for protons from 50 to 350 MeV. In this article we show the development from an idealised lattice to a design implemented with field maps from rigorous two-dimensional (2D) and three-dimensional (3D) FEM magnet modelling. We show that whilst the fields from a 2D model may reproduce the idealised field to a close approximation, adjustments must be made to the lattice to account for differences brought about by the 3D model and fringe fields and full 3D models. Implementing these lattice corr…
Vertical excursion fixed-field alternating gradient accelerators can be designed with tunes that are invariant with respect to momentum and trajectories that are scaled images of each other displaced only in the vertical direction. This is possible using guiding fields that have a vertical exponential increase, with a skew quadrupole component in the magnet body and a solenoid component at the magnet ends. Because of the coupling this introduces, orbit and optics calculations and optimisation of parameters need to be performed numerically. In this paper, idealised magnetic fields are calculate…
The concept of dielectric-laser acceleration (DLA) provides the highest gradients among breakdown-limited (nonplasma) particle accelerators and thus the potential of miniaturization. The implementation of a fully scalable electron accelerator on a microchip by twodimensional alternating phase focusing (APF), which relies on homogeneous laser fields and external magnetic focusing in the third direction, was recently proposed. In this Letter, we generalize the APF for DLA scheme to 3D, such that stable beam transport and acceleration is attained without any external equipment, while the structur…
The widespread use of high energy particle beams in basic research, medicine and coherent X-ray generation coupled with the large size of modern radio frequency (RF) accelerator devices and facilities has motivated a strong need for alternative accelerators operating in regimes outside of RF. Working at optical frequencies, dielectric laser accelerators (DLAs) - transparent laser-driven nanoscale dielectric structures whose near fields can synchronously accelerate charged particles - have demonstrated high-gradient acceleration with a variety of laser wavelengths, materials, and electron beam …
In this paper, a novel concept combining a fixed field alternating gradient accelerator with time-varying quadrupoles is presented which solves some of the major problems of conventional fixed field accelerators. This concept combines a stable racetrack fixed field configuration with dispersion free straight sections to enable continuous variable energy extraction. In the long straight sections, a time-varying synchrotron-like alternating gradient focusing structure makes it possible for the first time to correct the beam optics of an FFA accelerator in order to heuristically maximize the beam…
Not long after the laser was invented, it has been marked as a candidate source of strong, high-frequency electromagnetic radiation for acceleration of particles. Indeed, while the complex particle accelerator facilities today are an astonishing culmination of decades of work contributed by generations of physicists, engineers, and a host of scientists, new trends and acceleration technologies have been recently proposed and demonstrated. One of these technologies involves the miniaturization of particle accelerators, which is achieved by replacing the radio-frequency electromagnetic fields ac…
This paper reports on the conclusions of a 2013 Joint DOE/NCI Workshop, and translates clinical accelerator facility requirements into accelerator and beam-delivery technical specifications. Available or feasible accelerator technologies are compared, including a new concept for a compact, CW, and variable energy light ion accelerator currently under development. This new light ion accelerator is based on advances in non-scaling Fixed-Field Alternating gradient (FFAG) accelerator design. The new design concepts combine isochronous orbits with long (up to 4m) straight sections in a compact race…
Dielectric laser accelerators (DLAs) use the nearfields created when a laser pulse impinges on a dielectric structure to accelerate charged particles. We provide an overview of the theory of operation of photon driven accelerators, from photons interacting with charged particles in a vacuum, to the advantages gained by introducing dielectric structures, with a discussion of their advantages and limitations. Furthermore we show the state of the art of the current development of dielectric laser accelerators, including acceleration, focusing, deflection, beam position monitoring, and advanced to…
The concept of Dielectric Laser Acceleration (DLA) provides highest gradients among non-plasma particle accelerators. However, stable beam transport and staging have not been shown experimentally yet. We present a scheme that confines the beam longitudinally and in one transverse direction. Confinement in the other direction is obtained by a single conventional quadrupole magnet. Within the small aperture of 420 nm we find the matched distributions, which allow an optimized injection into pure transport, bunching, and accelerating structures. The combination of these resembles the photonics an…
We reconstruct spectra of secondary x-rays generated from a 500 MeV - 2 GeV laser plasma electron accelerator. A compact (7.5 $\times$ 7.5 $\times$ 15 cm), modular x-ray calorimeter made of alternating layers of absorbing materials and imaging plates records the single-shot x-ray depth-energy distribution. X-rays range from few-MeV inverse Compton scattered x-rays to $\sim$100 MeV average bremsstrahlung energies and are characterized individually by the same calorimeter detector. Geant4 simulations of energy deposition from mono-energetic x-rays in the stack generate an energy-vs-depth respons…
The measurement of electron cloud densities in particle accelerators using microwaves has proven to be an effective, non-invasive and inexpensive method. So far the experimental schemes have used continuous waves. This has either been in the form of travelling waves that are propagated, or standing waves that are trapped, in both cases within a segment of the accelerator chamber. The variation in the wave dispersion relation caused by the periodic creation and decay of the electron cloud leads to a phase modulation in the former case, and a frequency modulation in the latter. In general, these…
基于超冷原子的电子源最近已被提出作为在现代粒子加速器中广泛使用的常规光注入器或电子枪的替代物。基于超冷原子的电子源的优点在于从等离子体（由超冷原子的近阈值光电离产生）提取的电子具有非常低的温度，即低至几十开尔文。这些电子的提取具有产生非常低的发射率电子聚束的潜力。这些特性对于下一代粒子加速器至关重要，包括自由电子激光、等离子体加速器和未来的直线对撞机。该源也有许多潜在的直接应用，包括超快电子衍射（UED）和电子显微镜，由于其固有的高相干性。本文讨论了超冷电子束产生的基本机理，介绍了我们研制的超冷低发射度电子源。该源是基于一种新的交流磁光阱（AC-MOT）。对所提出的提取系统的详细模拟表明，对于1 pC的聚束电荷，可获得0.35 mm mrad的束流发射度，其中聚束长度为3 mm，能量扩展为1%。
In the development of high efficiency and high gradient RF-accelerators, RF waveguides and cavities have been designed with Photonic Band Gap (PBG) and fishnet- metamaterial structures. The designed structures are comprised of a periodically corrugated channel sandwiched between two photonic crystal slabs with alternating high to low dielectric constants and a multi-cell cavity-resonator designed with fishnet-metamaterial apertures. The structural designs of our interest are intended to only allow an operating-mode or -band within a narrow frequency range to propagate. The simulation analysis …
Plasma-based accelerators offer the possibility to drive future compact light sources and high-energy physics applications. Achieving good beam quality, especially a small beam energy spread, is still one of the major challenges. For stable transport, the beam is located in the focusing region of the wakefield which covers only the slope of the accelerating field. This, however, imprints a longitudinal energy correlation (chirp) along the bunch. Here, we propose an alternating focusing scheme in the plasma to mitigate the development of this chirp and thus maintain a small energy spread.
Design of a Storage Ring based on a Fixed Field Alternating Gradient Configuration with an Internal Target for Heavy-Ion Beams with Stochastic Charge State Conversions
Institute for Integrated Radiation and Nuclear Science, Kyoto University（京都大学辐射核科学综合研究所）；Advanced Science Research Center, Japan Atomic Energy Agency（日本原子能研究机构先进科学研究中心）
Particle accelerators are essential tools in science, hospitals and industry. Yet, their costs and large footprint, ranging in length from meters to several kilometres, limit their use. The recently demonstrated nanophotonics-based acceleration of charged particles can reduce the cost and size of these accelerators by orders of magnitude. In this approach, a carefully designed nano-structure transfers energy from laser light to the particles in a phase-synchronous manner, thereby accelerating them. However, so far, confinement of the particle beam in the structure over extended distance has be…
We demonstrate a compact technique to compress electron pulses to attosecond length, while keeping the energy spread reasonably small. The technique is based on Dielectric Laser Acceleration (DLA) in nanophotonic silicon structures. Unlike previous ballistic optical microbunching demonstrations, we use a modulator-demodulator scheme to compress phase space in the time and energy coordinates. With a second stage, we show that these pulses can be coherently accelerated, producing a net energy gain of $1.5\pm0.1$ keV, which is significantly larger than the remaining energy spread of $0.88 \,_{-0.…
