Showing papers by "John R. Cary published in 2014"
TL;DR: In this article, the authors present design principles for two-pulse colliding laser pulse injection mechanisms, which can meet the requirements of high charge, low energy spread, and low emittance.
Abstract: Laser plasma based accelerators have the potential to reduce dramatically the size and cost of future particle colliders and light sources. Production of high quality beams along with reproducibility, tunability, and efficiency are required for many applications. We present design principles for two-pulse colliding laser pulse injection mechanisms, which can meet these requirements. Simulations are used to determine the best conditions for the production of high quality beams: high charge, low energy spread, and low emittance. Simulations also allow access to the internal dynamics of the interaction, providing insight regarding further improvement of the beam quality. We find that a 20 pC beam can be accelerated to 300 MeV in 4 mm with only a few percent energy spread and transverse normalized emittance close to 1 mm mrad, using a 10 TW laser. We demonstrate that this design scales according to linear theory. Control of the laser pulse mode content and subsequent evolution in the plasma channel are shown to be critical for achieving the highest beam quality.
6 citations
TL;DR: In this article, a 12 GHz hybrid dielectric PhC accelerating cavity based on a triangular lattice of sapphire rods is simulated and transverse wakefields are observed, on average an order of magnitude higher than those in the 12 GHz waveguide-damped Compact Linear Collider copper cavities.
Abstract: Photonic crystal (PhC) defect cavities that support an accelerating mode tend to trap unwanted higher-order modes (HOMs) corresponding to zero-group-velocity PhC lattice modes at frequencies near the top of bandgaps. The effect is explained quite generally by photonic band and perturbation theoretical arguments. Transverse wakefields resulting from this effect are observed (via simulation) in a 12 GHz hybrid dielectric PhC accelerating cavity based on a triangular lattice of sapphire rods. These wakefields are, on average, an order of magnitude higher than those in the 12 GHz waveguide-damped Compact Linear Collider copper cavities. The avoidance of translational symmetry (and, thus, the bandgap concept) can dramatically improve HOM damping in PhC-based structures.
3 citations
TL;DR: The ability to maintain stability beyond the CFL limit for the Dey-Mittra method without discarding any cells is shown and convergence of the ADI method is considered as compared to the standard explicit method that is limited by the CFL condition.
Abstract: The alternating direction implicit (ADI) method is an attractive option to use in avoiding the Courant- Friedrichs-Lewy (CFL) condition that limits the size of the time step required by explicit finite-difference time-domain (FDTD) methods for stability. Implicit methods like Crank-Nicholson offer the same advantages as ADI methods but they do not rely on simple, one-dimensional, tridiagonal system solves for which there are well-known fast solution methods. To date, the ADI method applied to the FDTD method for curved domains has been used within the context of subgridding (i.e., local refinement) or for stairstepped boundaries that are only first-order accurate. A popular second- order accurate approach to representing smooth domains with the FDTD method is the Dey-Mittra embedded boundary method. However, to be useful in a realistic setting, the cells with only a small fraction of their volume inside the domain need to be discarded from simulations for stability considerations or else the time step size will be prohibitively small. Using the ADI method instead of the explicit method implies that time step can be chosen to depend on accuracy and no cells need discarding. We show in this paper the ability to maintain stability beyond the CFL limit for the Dey-Mittra method without discarding any cells. We also consider convergence of the ADI method as compared to the standard explicit method that is limited by the CFL condition.
2 citations