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

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  m emittance, 150 keV energy spread,  10 m  use idealized beam, include resistive wake fields

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

1 kA current and 0.43  m emittance  LCLS-IISC parameters  better suited to hard x-rays 1e-3 5e-4 2.5e-41e-4 2e-3

LCLS-IISC parameters  Planar SCU, Nb 3 Sn  7.5 mm magnetic gap 1e-3 5e-4 2.5e-41e-4 2e-3 cannot hit resonance

LCLS-IISC parameters  Planar Hybrid PM undulator  7.5 mm magnetic gap main impacts of worse magnet tech: loss of tuning range more undulator length vulnerable to high avg beam power 1e-3 5e-4 2.5e-41e-4 2e-3 cannot hit resonance

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

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 … BC2L3aL3b 4 GeV beam 2.7 GeV beam South side undulator hall

Discrete Energy Tuning example Example using PM undulator constraints, 7.5 mm gap  fixed 4 GeV  26 mm pd for 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

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 pd for 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)

24 Potential Areas of Collaboration with Partner Labs SLACLBNLFNALJLABANLCornell Wisconsin InjectorXXX UndulatorXX SC linac prototypeXXX SC LinacXX SC cryo lineXX Cryo plantXX LLRFXXXX RF systemsX Beam PhysicsXX Instruments/ Detectors XX PM/IntegrationX InstallationXXX CommissioningX LCLS-II Overview

Alternate view: NGLS parameters  max  ; or max photon energy for beam energy and  250 eV500 eV 750 eV 1 keV 3 keV 2 keV 4 keV 10 keV 5 keV

Alternate view: LCLS-IISC parameters  max photon energy for a given beam energy and  250 eV 500 eV750 eV1 keV 3 keV 2 keV 4 keV 10 keV 5 keV

rho vs photon energy for different beam energies NGLS parameters