Slide 1

Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Dark Current Transport at FLASH Start-to-end tracking simulation analysis of beam and dark current transport full 3D aperture model Dark current losses identification of hot spots cleaning efficiency of gun and BC2 collimators influence of new gun layout Slide 2 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Simulation Steps Astra simulation of FLASH linac (gundump) space charge up to BC2 entrance no apertures 2500 phase space dumps (one each 10 cm, ~30 GB) runtime: ~2 h (44 processors, 400 000 particles) Aperture check with ApertureLib toolkit full 3D model of the accelerator aperture in cartesian coordinates outputs: phase space at any position, discarded particles, Twiss parameters,... runtime: ~14 min Slide 3 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY 1: Machine Model Slide 4 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Design Optics Slide 5 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Dispersion Slide 6 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Aperture Model (1) AutoCAD DXF file included pre-built aperture elements Astra aperture file Slide 7 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Aperture Model (1) AutoCAD DXF file included pre-built aperture elements Astra aperture file Slide 8 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Aperture Model (2) Slide 9 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Aperture Model (3) Slide 10 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY 2: Dark Current Slide 11 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Dark Current Simulation Dark current emission: Simple field emission model Current: Gaussian around RF gun phase 0 with =16 Homogeneous emission from cathode surface ( 5 mm) Current exiting the gun 200300 A no simulation of collective effects (space charge, CSR,... negligible) Slide 12 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Dark Current Losses (1) ACC1 exit BC2 entrance BC3 entrance BC3 exit transverse collimators energy collimators Slide 13 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Dark Current Losses (1) ACC1 exit BC2 entrance BC3 entrance BC3 exit transverse collimators energy collimators Slide 14 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Dark Current Losses (2) Slide 15 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Darkcurrent Losses (3) Slide 16 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Longitudinal Profile (GUN) Slide 17 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Longitudinal Profile (ACC1) Slide 18 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Transverse Beam Size Slide 19 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY 3: Counter Measures Slide 20 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY BC2+Gun Collimators BC2 collimator Gun collimator Slide 21 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Horizontal Profiles (in front of undulator entrance) Slide 22 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Vertical Profiles (in front of undulator entrance) Slide 23 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Longitudinal Phase Space (in front of undulator entrance) Slide 24 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Dark Current Transmission Relative dc amount 100% 30% 22% 6% 100% 18% 78% 15% Slide 25 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Beam Losses at 8DBC2 darkcurrent dumped on valve 100% 65% 64% 44% Simulation 100% 30% 22% 6% Measurement 100% 65% 64% 44% Slide 26 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY New Gun Layout ? Slide 27 Beam dynamics meeting, 2007/05/14Lars Frhlich, MPY Conclusion More work needed on simulation (finer step size -> include ApertureLib into Astra?) Measurements needed A usable gun collimator will reduce the activation of BC2 components considerably