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Comments on LCLS-IISC Design

Comments on LCLS-IISC Design. G. Penn SLAC 25 September 2013. Next Generation Light Source Soft x-ray FEL facility High repetition rate – 1 MHz CW superconducting Linac to 2.4 GeV Multiple FEL beamlines using identical bunches 3 distinct initial FELs for different science needs

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Comments on LCLS-IISC Design

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  1. Comments on LCLS-IISC Design G. Penn SLAC 25 September 2013

  2. Next Generation Light Source • Soft x-ray FEL facility • High repetition rate – 1 MHz • CW superconducting Linac to 2.4 GeV • Multiple FEL beamlines using identical bunches • 3 distinct initial FELs for different science needs • nominal bunch: 300 pC, 500 A, 0.6 mm emittance, 150 keV energy spread, b = 10 m • use idealized beam, include resistive wake fields

  3. Contours of maximum r3D bandwidth, not gain length! • FEL very delicate for smaller r3D • fix beam but vary energy; ignore undulator constraints 1e-4 2.5e-4 NGLS parameters 5e-4 1e-3 higher K shorter period

  4. 1 kA current and 0.43 mm emittance • LCLS-IISC parameters • better suited to hard x-rays 1e-4 2.5e-4 5e-4 1e-3 2e-3

  5. LCLS-IISC parameters • Planar SCU, Nb3Sn • 7.5 mm magnetic gap 1e-4 2.5e-4 cannot hit resonance 5e-4 1e-3 2e-3

  6. LCLS-IISCparameters main impacts of worse magnet tech: loss of tuning range more undulator length vulnerable to high avg beam power • Planar Hybrid PM undulator • 7.5 mm magnetic gap 1e-4 2.5e-4 cannot hit resonance 5e-4 1e-3 2e-3

  7. Hard X-Ray FEL Requirements • high e-beam brightness and peak current are crucial • any way to push for even smaller emittance? • is main constraint political (not wanting to miss target)? • look at APEX thermal emittance #’s • short bunches are a good choice • higher peak current also helps • slightly less effective than lowering emittance • technical difficulty? • affects linac design • wakes and microbunching get worse • self-seeding fairly robust to energy chirps

  8. Discrete Energy Tuning for LCLS-II • take advantage of continuous tuning of undulator K • only need 2 options for beam energy in South side • resolves most issues with photon energy tuning range and total undulator length • beam at the 2 energies may look slightly different … BC2 L3a L3b 4 GeV beam 2.7 GeV beam South side undulator hall

  9. Discrete Energy Tuning example Example using PM undulator constraints, 7.5 mm gap • fixed 4 GeV • 26 mm pdfor full range • K between 0.6 and 2.7, photon energy > 1.2 keV • need 100 m magnetic length (for SASE) • switch between 4 GeV and 2.7 GeV • 23 mm pd, K between 0.8 and 2.0 • at 4 GeV, covers range 2.2 keV to 5 keV • at 2.7 GeV, covers range 1.0 keV to 2.2 keV • need 70 m magnetic length could go to 2.5 keV

  10. Choice of energy for North side • is 2.7 GeV a better choice than 4 GeV for North side? Example using PM undulator constraints, 7.5 mm gap • fixed 4 GeV requires 40 mm pdfor full range • K>2 always • fixed 2.7 GeV requires 33 mm pd for full range • smallest K ~1.2 • max magnetic length ~ 38 m in both cases • similar tradeoff if consider SCUs (27 mm vs 23 mm pd)

  11. Potential Areas of Collaboration with Partner Labs LCLS-II Overview

  12. Alternate view: NGLS parameters • max r; or max photon energy for beam energy and r 250 eV 500 eV 750 eV 1 keV 2 keV 3 keV 4 keV 5keV 10 keV

  13. Alternate view: LCLS-IISC parameters • max photon energy for a given beam energy and r 500 eV 750 eV 1 keV 250 eV 2 keV 3 keV 4 keV 5keV 10 keV

  14. rho vs photon energyfor different beam energies NGLS parameters

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