1 Comparison and discussion of candidate SEE materials Z. Insepov (ANL), V. Ivanov (Muons Inc.) Muons, Inc. 2Outline Motivation Semi-empirical theories Monte Carlo simulations Empirical models Comparison with experiment Summary 3Motivation Gain and TTS can drastically be improved by increasing SEE at first strike Higher QE PC can be obtained by using Al 2 O 3, MgO, and ZnO. Multilayer structures can improve SEE Surface roughness can affect the SEE We need a tool to be able to predict SEE based on materials properties 4 Empirical Models Space charge effect, charging effect of the emitting surface and reflection of incident electrons are not considered. Number of emitted secondary electrons is determined by Poisson distribution having average value from equation below. Secondary electrons have Maxwellian energy distribution and Cosine angular distribution. Guest (1971) adjustable parameter Ito (1984) Yakobson (1966) Agarwal (1958) 5 Comparison SEE models 6 SEE for models vs experiment 7 Comparison between theory and experiment 8 SEE of a rough surface Kawata at al, JNM (1995) The effect of surface roughness on the SEE from Be at E < 1 keV electron bombardment was studied by Monte Carlo simulation. With increasing aspect ratio H/W of the bowl structure, the SEE Yield increases, whereas for large H/W the yield is smaller. Krasnov, Vacuum (2004) 9 Semi-empirical theories Universal law of SE yield Al 2 O 3 - Young (1956) e-e- Joy (1987) primary secondary 10 Low-Energy Monte Carlo codes Algorithm of SEE calculations Screening factor 11 Simulation results: 5 nm Al 2 O 3 Comparison of various models of SEE 12 Simulation results 5 nm Al 2 O 3 SEE vs primary electron angle and energy This parameterized set of SEE yield is used as an input to a macroscopic gain code for MCP simulation 13 Comparison with experiment SE yields of an Al2O3 were measured by a pulsed technique where surface was replenished by electron shower between the two pulses [21]. Materials data used in MC simulations: Z av = 10 A av = 20.4 = 3.9 g/cm 3 = 20 eV, = 60 J = 145 eV None of them are from experiment except for J which is unimportant at low energies 14Summary None of the existing Monte Carlo codes can simulate low- energy SEE from new, engineering materials, and with charge effects. We need to build a MC code that will be able to treat mixtures, rough, multilayer surfaces, low energy, with charge accumulation. Our current approach combines simple MC simulation, empirical models, and comparison to experiment. Al 2 O 3 SE yields were parameterized for two variables: E PE and incident angle and submitted as an input to macroscopic gain code. We obtained a close agreement with experiment for Al 2 O 3. We plan to extend this approach to MgO, ZnO, and Al2O3+ZnO mixtures where experiment is sparse. 15Acknowledgments David C Joy ORNL Pierre Hovington McGill University Raynald Gauvin McGill University