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Single Pass SASE Free Electron Lasers A potential 4th generation light source

Linac 0. Linac 1. Linac 2. Linac 3. RF Gun. Undulator. Bunch Compressor 1. Bunch Compressor 2. To Photon Lines. To Existing Linac. To B Factory. 1 km. Single Pass SASE Free Electron Lasers A potential 4th generation light source. EECS 213 Final Report Kevin Bowers

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Single Pass SASE Free Electron Lasers A potential 4th generation light source

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  1. Linac 0 Linac 1 Linac 2 Linac 3 RF Gun Undulator Bunch Compressor 1 Bunch Compressor 2 To Photon Lines To Existing Linac To B Factory 1 km Single Pass SASEFree Electron LasersA potential 4th generation light source EECS 213 Final Report Kevin Bowers May 18, 1999

  2. What is a Single Pass SASE-FEL? • FEL - Free Electron Laser • Electrons traveling through a undulator radiate coherently if bunched in a length much less than the radiation wavelength • Storage ring technology cannot bunch electrons to get radiation wavelength less than about 50 nm • SASE - Self Amplified Spontaneous Emission • Radiation interacts with beam; modulating electron energy • Energy modulation causes electrons to bunch up • Bunched electrons emit more FEL radation, coherently • Single Pass - No optical cavity • The radiation is generated in one pass of the electron beam • Conventional lasers use multiple passes of the radiation through a gain medium; requires optical cavity • Present FELs (IR to UV) also typically use optical cavities

  3. For an electron in an undulator: x z Erad y Beam Bund But, the radiation field changes g: Fields and Electron Trajectory in a typical undulator (Espace chage, Bbeam current and Brad omitted) Erad ne(z,downstream) z z Velocity modulation causes bunching on axis downstream. Bunching enhances Erad which further enhances bunching vx Conditions for SASE z Initial radiation field and z-vx phase space dg/dt z dvz/dt z Bunching occurs here in beam frame The SASE Collective Instability • Beam and Radiation Satisfy a Resonance Condition • Monochromatic Beam • Gain Length shorter than Rayleigh Range • Slippage less than initial bunch length

  4. To Existing Linac RF Gun Linac 0 Linac 1 Bunch Compressor 1 1 km Linac 2 Bunch Compressor 2 Linac 3 • Brightness greatly exceeds 3rd generation Undulator To B Factory To Photon Lines The SLAC LCLS Stanford Linear Accelerator Linac Coherent Light Source • A proposed Single Pass SASE-FEL • Design overview • A RF laser photoinjector shoots a 3 ps (rms) electron pulse into the last km of the linac (120 Hz rep rate). • Electrons are accelerated to 14.3 GeV and compressed up to a peak current of 3,400 A and 67 fs (rms) pulse • The electrons are passed into a 99.8 m undulator (n = 3328, K = 3.7, B = 1.32 T). Some R&D issues here. • SASE FEL interaction produces 820 eV to 8200 eV tunable coherent radiation (1st harmonic). The instability saturates at 90m through the undulator. • Planned construction 2002-2005 ($100M)

  5. Conclusions • FELs are a Promising Technology for 4th Generation Light Sources • Peak brightness about ten orders of magnitude over current 3rd generation facilities • Similar advance from 1st generation X-ray tubes to 2nd and 3rd generation synchrontron sources • Many possible applications • SASE FEL technology not ready for commercial applications though • LCLS $100M on top of an already existing facility • LCLS 1 km linear beam line, 100 m undulator

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