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 6 0.15 GV/m with an extremely small emittance growth, 3.6%, can be expected

Energy efficiency studies for dual-grating dielectric laser-driven accelerators

Dielectric laser-driven accelerators (DLAs) can provide high accelerating gradients in the GV/m range due to their having higher breakdown thresholds than metals, which opens the way for the miniaturization of the next generation of particle accelerator facilities. Two kinds of scheme, the addition of a Bragg reflector and the use of pulse-front-tilted (PFT) laser illumination, have been studied separately to improve the energy efficiency for dual-grating DLAs. The Bragg reflector enhances the accelerating gradient of the structure, while the PFT increases the effective interaction length. In this paper, we investigate numerically the advantages of using the two schemes in conjunction. Our calculations show that, for a 100-period structure with a period of 2 micrometer, such a design effectively increases the energy gain by more than 100 % when compared to employing the Bragg reflector with a normal laser, and by about 50 % when using standard structures with a PFT laser. A total energy gain of as much as 2.6 MeV can be obtained for a PFT laser beam when illuminating a 2000-period dual-grating structure with a Bragg reflector.Comment: 7 pages, 4 Figures, Proceedings of EAAC2017 Conferenc

Measurements of Collimator Wakefields at End Station A

The angular deflection of a 28.5 GeV electron beam passing off-axis between the jaws of a collimator, generating a transverse wakefield, were measured in End Station A (ESA) at SLAC. In total, fifteen different configurations of collimator geometry and material were tested: some were chosen for compatibility with previous measurements while others served to study the effect of geometry and taper angles (geometrical contribution to the wakefield) and the effect of the material resistivity (resistive contribution) to the imparted kick. This paper summarises the last update of preliminary experimental results before they are finalised. The reconstructed kick factor is compared to analytical calculations and simulations

Investigations into dual-grating THz-driven accelerators

Advanced acceleration technologies are receiving considerable interest in order to miniaturize future particle accelerators. One such technology is the dual-grating dielectric structures, which can support accelerating fields one to two orders of magnitude higher than the metal RF cavities in conventional accelerators. This opens up the possibility of enabling high accelerating gradients of up to several GV/m. This paper investigates numerically a quartz dual-grating structure which is driven by THz pulses to accelerate electrons. Geometry optimizations are carried out to achieve the trade-offs between accelerating gradient and vacuum channel gap. A realistic electron bunch available from the future Compact Linear Accelerator for Research and Applications (CLARA) is loaded into an optimized 100-period dual-grating structure for a detailed wakefield study. A THz pulse is then employed to interact with this CLARA bunch in the optimized structure. The computed beam quality is analyzed in terms of emittance, energy spread and loaded accelerating gradient. The simulations show that an accelerating gradient of 348 12 MV/m with an emittance growth of 3.0% can be obtained

How policy interventions influence burning to meet cultural and small-scale livelihood objectives

Fire has cultural and economic significance for Indigenous and rural peoples worldwide, being used to manage landscapes for activities such as hunting, gathering, cropping, and forestry, and for ceremonial and spiritual purposes. Policy interventions by state and non-state organizations, such as regulations, economic incentives, and communication campaigns, can target fire use directly, or affect it indirectly, for example, by restricting land access. Yet evidence of such impacts has not been synthesized at the global scale. We analyzed 512 examples in 68 countries to describe the range of policy interventions by state and non-state organizations that target and/or affect fire use, categorizing interventions based on the broad actor types involved, their mode of operation (e.g., regulation) and their intentionality and/or possible effects vis-a-vis fire use. Of these interventions, 74% involved only state agencies in policy design and implementations, 4% involved only non-state organizations, and 18% involved collaboration between state and/or non-state organizations and/or communities. Three hundred and nine interventions directly targeted fire use, of which 87% aimed to eliminate or constrain fire use. Two hundred and three affected fire use indirectly, of which 88% led to reductions in or constraints upon fire use. Though there is some recognition in the 21st century of a need, in certain contexts, to support local fire use, for reasons related to environmental justice, ecology, wildfire risk and climate change, the literature we reviewed points to several challenges for contemporary efforts toward this end. These include contradictions between policy interventions, mistrust between actors following histories of fire suppression, greater fuel loads increasing the risk of burning where fire has been suppressed, and the need to consider the indirect effects of other types of policy, such as those related to land tenure