Transcript Folie 1
Design Considerations of table-top FELs DESY, June 20; recap of FLS 2006, May 15, 2006 LMU: F. Grüner, U. Schramm, S. Becker, R. Sousa, T. Eichner, D. Habs MPQ: S. Karsch, M. Geissler, L. Veisz, J. Meyer-ter-Vehn, F. Krausz UCLA: S. Reiche • laser-plasma accelerators • principal possibility of table-top FELs • possible VUV and X-ray scenarios • new experimental status • critical points review • cooperation with DESY… Laser-Plasma accelerators: “bubble acceleration” TW laser, 5-50 fs electron bunch: e.g. 170 MeV (LOA), 1.2 GeV (Berkeley) M. Geissler PIC code 5fs, a=5 Discharge capillary ~4 cm 300 µm gas-filled capillary electrodes year laser pulse Pulse energy length electron energy energy spread divergence 2004 0.36 J 40 fs 86 MeV 2% 3 mrad 2006* 1.3 J 33 fs 1.2 GeVLeemans < 2% 1.6 mrad laser-plasma* presented at Anomalous Absorpt. Conf., June 6, 2006; submitted to Science acceleration MPQ: since two weeks 0.35 J in 37 fs, soon 1-2 J future (~2009): 5 J, 5 fs (=1 PW), 1 kHz Improvement by capillaries de-phasing • discharge introduces parabolic electron density • laser guiding beyond Rayleigh length → higher energies • de-phasing: reducing energy spread • ion-channel: reducing electron beam diameter and divergence • possible scenario: bubble turns into linear wakefield → GeV- energies with ~0.1% energy spread • started cooperation with Simon Hooker (Oxford) Important feature: ultra-high current typical length scale = plasma wavelength ~ 2 µm only!! ~ nC charge laser pulse ~ 100 kA Principal possibility for table-top FELs simplest estimate: ideal 1d Pierce parameter (no energy spread, emittance, diffraction, time-dependence) current : few 100kA (classical: 5 kA) und. period : few mm (class. few cm) L gain , ideal 1 I u Au 2 I A 2 x beam diameter (optimal!) 2 u 4 3 XieMing L gain ,real L gain , ideal (1 ) L sat 15 L gain 1/ 3 Constraints for table-top FELs saturation length (Xie Ming) for SASE VUV FEL @ ~28nm DESY flash (fs mode): λu= 27 mm (462 MeV) εn = 6 mm·mrad MPQ (GENESIS) ΔE/E = 0.04 % λu= 3 mm (133 MeV) εn = 1 mm·mrad ΔE/E = 0.5 % ~ I Λ (Xie Ming) L gain , real L gain , ideal (1 ) small : keeping ! , u 4 1 / 3 2 • not only table-top size, but 1 4/3 Psat ~ I u sufficient output power: 1 reduction in λu allows a reduction in γ, but needs ultra-high current for keeping ρ and also saturation power large enough ! Start-to-End Simulations electron bunch transport/ focusing/ filter FEL undulator laser own 3d PIC code GPT, Geant CSRTrack, Spur; GENESIS 1.3 A possible first VUV case Parameter DESY (flash, fs-mode) MPQ Current 1.3 kA 160 kA Norm. Emitt. (rms) Energy 6 mm·mrad 1 mm·mrad 461.5 MeV 130 MeV Energy spread 0.04 % 0.5 % Wavelength 30 nm 25 nm Pierce par. 0.0016 0.0117 Sat. Power 0.66 GW 5 GW Sat. Length 19 m 45 cm International competition and a possible first table-top XFEL case Parameter Leemans (FEL2005 conf.) MPQ (TT-XFEL) Current 25 kA 160 kA Norm. Emitt. (rms) 1 mm·mrad 1 mm·mrad Energy 1 GeV 0.9 – 1.2 GeV Energy spread 1% 0.1 % Und. Period 10 mm 1.5 – 3 mm Wavelength 2 nm 0.25 nm Und. length 4.7 m 3m 100 TW, 33 fs 1 PW, 5 fs New Experimental Status few days ago: 40 MeV electrons undulator: 60 periods, 5 mm period, 1.6 mm gap ~1 T field on axis Critical Points Review • space charge influence due to ultra-dense bunches - HOMDYN (L. Serafini): for 1 GeV correlated energy spread 0.5 %, no debunching - GPT/CSRtrack runs (see next talk) - simple analytical estimates in agreement with GPT - linear energy chirp can be compensated with tapering • transverse coherence - 4 valid only for spontaneous source, here: gain guiding - calculate growth rate of next higher mode with GENESIS - transverse coherence important for focusing only? • peak brilliance: 1032 @ 5 keV - comparable with LCLS! (1012 phts/0.1%BW, θ=15µrad, σx=30µm, τ=10fs) Cooperation with you… • verify our GPT results with ASTRA • verify entire feasibility study (publishing a joint paper) • discuss beam features in detail (slice energy spread, etc.) • for experiments: diagnostic methods (FROG) • open questions, such as maximum photon energy • what could you learn from us????