Kieran Hanahoe

Beam quality study for a grating-based dielectric laser-driven accelerator

Dielectric laser-driven accelerators (DLAs) based on grating structures are considered to be one of the most promising technologies to reduce the size and cost of future particle accelerators. They offer high accelerating gradients of up to several GV/m in combination with mature lithographic techniques for structure fabrication. This paper numerically investigates the beam quality for acceleration of electrons in a realistic dual-grating DLA. In our simulations, we use beam parameters of the future Compact Linear Accelerator for Research and Applications facility to load an electron bunch into an optimized 100-period dual-grating structure where it interacts with a realistic laser pulse. The emittance, energy spread, and loaded accelerating gradient for modulated electrons are then analyzed in detail. Results from simulations show that an accelerating gradient of up to 1.13 ± 0.15 GV/m with an extremely small emittance growth, 3.6%, can be expected.

High quality electron beam generation in a proton-driven hollow plasma wakefield accelerator

Simulations of proton-driven plasma wakefield accelerators have demonstrated substantially higher accelerating gradients compared to conventional accelerators and the viability of accelerating electrons to the energy frontier in a single plasma stage. However, due to the strong intrinsic transverse fields varying both radially and in time, the beam quality is still far from suitable for practical application in future colliders. Here we propose an efficient proton-driven accelerating regime in a hollow channel. In this regime, the electron witness bunch is positioned in the region with a strong accelerating field, free from plasma electrons and ions. We show that the witness electron beam carrying the charge of about 10% of 1 TeV proton driver charge can be accelerated to 0.6 TeV with preserved normalized emittance in a single channel of 700 m. This high quality and high charge beam may pave the way for the development of future plasma-based energy frontier colliders.

GEANT4 simulations for beam emittance in a linear collider based on plasma wakefield acceleration

Alternative acceleration technologies are currently under development for cost-effective, robust, compact, and efficient solutions. One such technology is plasma wakefield acceleration, driven by either a charged particle or laser beam. However, the potential issues must be studied in detail. In this paper, the emittance evolution of a witness beam through elastic scattering from gaseous media and under transverse focusing wakefields is studied.

Multi-proton bunch driven hollow plasma wakefield acceleration in the nonlinear regime

Proton-driven plasma wakefield acceleration has been demonstrated in simulations to be capable of accelerating particles to the energy frontier in a single stage, but its potential is hindered by the fact that currently available proton bunches are orders of magnitude longer than the plasma wavelength. Fortunately, proton micro-bunching allows driving plasma waves resonantly. In this paper, we propose using a hollow plasma channel for multiple proton bunch driven plasma wakefield acceleration and demonstrate that it enables the operation in the nonlinear regime and resonant excitation of strong plasma waves. This new regime also involves beneficial features of hollow channels for the accelerated beam (such as emittance preservation and uniform accelerating field) and long buckets of stable deceleration for the drive beam. The regime is attained at a proper ratio among plasma skin depth, driver radius, hollow channel radius, and micro-bunch period.

Simulation studies of plasma lens experiments at Daresbury laboratory

Experiments are planned to study plasma lensing using the VELA and CLARA Front End accelerators at Daresbury Laboratory. This paper presents results of 2-dimensional particle-in-cell simulations of the proposed experiments. The variation in focusing strength and emittance growth with beam and plasma parameters are studied in the overdense (plasma density much greater than bunch density) regime for the VELA beam. The effect of spherical and longitudinal aberrations on the beam emittance was estimated through numerical and theoretical studies. Simulation results show that a focusing strength equivalent to a magnetic field gradient of 10 T m−1 can be achieved using VELA, and a gradient of 247 T m−1 can be achieved using CLARA Front End.

Design studies and commissioning plans for plasma acceleration research station experimental program

Plasma acceleration research station is an electron beam driven plasma wakefield acceleration test stand proposed for CLARA facility in Daresbury Laboratory. In this paper, the interaction between the electron beam and the plasma is numerically characterised via 2D numerical studies by using VSIM code. The wakefields induced by a single bunch travelling through the plasma were found to vary from 200 MV/m to 3 GV/m for a range of bunch length, bunch radius, and plasma densities. Energy gain for the particles populating the bunch tail through the wakefields driven by the head of the bunch was demonstrated. After determining the achievable field for various beams and plasma configurations, a reference setting was determined for further studies. Considering this reference setting, the beam quality studies were performed for a two-bunch acceleration case. The maximum energy gain as well as the energy spread mitigation by benefiting from the beam loading was investigated by positioning the witness and driver bunches with respect to each other. Emittance growth mechanisms were studied considering the beam-plasma and beam-wakefield interactions. Eventually, regarding the findings, the initial commissioning plans and the aims for the later stages were summarised.

Simulation study of a passive plasma beam dump using varying plasma density

A plasma beam dump uses the collective oscillations of plasma electrons to absorb the kinetic energy of a particle beam. In this paper, a modified passive plasma beam dump scheme is proposed using either a gradient or stepped plasma profile to maintain a higher decelerating gradient compared with a uniform plasma. The improvement is a result of the plasma wavelength change preventing the re-acceleration of low energy particles. Particle-in-cell simulation results show that both stepped and gradient plasma profiles can achieve improved energy loss compared with a uniform plasma for an electron bunch of parameters routinely achieved in laser wakefield acceleration.

A Gas-filled Capillary Based Plasma Source for Wakefield Experiments

A plasma medium can be formed when a gas is discharged via an applied high voltage within a capillary tube. A high voltage discharge based plasma source for plasma wakefield acceleration experiment is being developed. Design considered a glass capillary tube with various inner radii. Glass was preferred to sapphire or quartz options to ease the machining. Electrodes will be attached to the tube using a sealant resistant to high vacuum conditions and baking at high temperatures. Each electrode will be isolated from the neighbouring one using nuts or washers from a thermoplastic polymer insulator material to prevent unwanted sparking outside of the tube. In this paper, general design considerations and possible working points of this plasma source are presented for a range of plasma densities from 1×1020 to 1×1022 m−3. Consideration was also given to plasma density diagnostic techniques due to critical dependence of accelerating gradient on plasma density.

EMITTANCE GROWTH DUE TO MULTIPLE COULOMB SCATTERING IN A LINEAR COLLIDER BASED ON PLASMA WAKEFIELD ACCELERATION

Alternative acceleration technologies are currently under development for cost-effective, robust, compact and efficient solutions. One such technology is plasma wakefield acceleration, driven by either a charged particle or laser beam. However, the potential issues must be studied in detail. In this paper, the emittance growth of the witness beam through elastic scattering from gaseous media is derived. The model is compared with the numerical studies.