Design of micrograting structures for laser acceleration of electrons

The next generation of linear colliders for high energy physics research will undoubtedly require accelerating gradients much greater than presently achievable today in order to be cost and size effective. A number of schemes have been proposed in the hopes of reaching accelerating gradients of 1 GeV/m. To put this in perspective, a 20 TeV collider which utilized accelerating cavities with a gradient of 1 GeV/m would have a total length of 40 km, which is about half the circumference of the SSC. The same collider with conventional cavities providing 30 MeV/m gradient would have a length greater than 1,300 km. Experiments at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory will investigate laser accelerating of electrons utilizing a short pulse CO2 laser (λ = 10.5 μm) as the power source and a micrograting structure as the accelerating cavity. The advantage of such a scheme may be the high electric fields (∼ 1 GeV/m) that the laser can provide. These short pulses are not expected to damage the micrograting structure. This system lends itself to synchronization easily since the ATF is equip with a laser driven photocathode gun. Preliminary modeling of micrograting structures indicate that gratings can be designed to support the π-mode for acceleration of β congruent 1 electrons