Laser engineered surface structures for custom design of secondary electron yield

Secondary Electron Yield (SEY) [3, 5] occurs in a system when a primary electron impinges a material's surface and induces the emission of a 1^st and potentially 2^nd generation secondary electrons (see Figure 1, Left). The total number of secondary electrons per primary electron is the SEY. This phenomenon forms a highly challenging problem in many systems, for example in particle accelerators, where significant levels of SEY form as an electron cloud and can perturbate the circulating beams and generate a high level of heat load to be absorbed by cooling and cryogenics. The Large Hadron Collider (LHC) has a 54-km beam pipe [1] in which copper-laminated steel beam-screens are placed in order to shield the beam pipes from heat loads, but inherently result in unwanted SEY. As such, the development of methods which mitigate the SEY are increasingly appealing [2], including surface texturing, shaping the geometry and orientation of patterns etched into the surfaces [3], and carbon-coating of the interior of the beam pipes in the Super Proton Synchrotron (SPS) [4]. Previously we have shown that nanosecond pulsed laser treatment of copper surfaces at 532 nm could significantly increase the optical absorbance of the surface [6], and furthermore reduce the SEY to close to 1 [7]. More recently we demonstrated that surface structures produced by a picosecond pulsed laser at 532nm exhibited SEY values below 1 and were successfully tested in a dipole magnet in the Super Proton Synchrotron (SPS) accelerator at CERN [8].