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Insertion Devices - VISA Undulator

  • Demonstrate SASE gain to saturation at 600-800 nm
  • Operate with ATF linac beam (72-85 MeV)
  • Fit in available space in ATF -- 4 m long
  • Must achieve gain length of <0.4 m
  • Must control e-beam walk-off to < 50 mm
  • Need strong focusing
  • Need ultra-precise alignment techniques

VISA Magnetic Structure

Halbach-type Pure-Permanent Magnet Undulator with Distributed Strong Focusing

VISA Undulator Properties

Undulator magnet length [m] 4
Undulator type Planar permanent magnet
Magnet material NdFeB
  40 mm x 10 mm x 4.45 mm
Thickness of magnet block (z) [mm] 4.45 ± 0.05
Length of magnet block (x) [mm] 30 ± 0.1
Height of magnet block (y) [mm] 10 ± 0.1
Separation between magnet blocks [mm] 0.05 ± 0.025
Total Number of magnet blocks 1760
Undulator period lw[mm] 18
Full gap g [mm] 6
Undulator field Bmax [T] 0.75
Undulator parameter K 1.26
aw 0.89
Number of periods per segment 55
Number of segments 4
segment magnet length [m] 0.99
Number of periods Nw 220
Wiggle plane horizontal