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Electron Beam Control and Alignment LCLS FEL Undulator Commissioning Workshop UCLA Jan. 19-20, 2004 P. Emma, SLAC. Undulator collimation and protection Verification of the convergence of BBA Beam abort and tune-up dumps 15- Å startup for nearly guaranteed FEL gain.

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slide1

Electron Beam Control and Alignment

LCLS FEL Undulator

Commissioning Workshop

UCLA

Jan. 19-20, 2004

P. Emma, SLAC

  • Undulator collimation and protection
  • Verification of the convergence of BBA
  • Beam abort and tune-up dumps
  • 15-Å startup for nearly guaranteed FEL gain
slide2

Two-Phase, Two-Plane Collimation, 1½ Times

p/2

~p/2

3 mm

2.5 mm

edge scattering

2 mm

halo

e- beam

undulator beam pipe

x1

x2

x3

phase-1 again

phase-2

phase-1

(also collimation in y and energy – see next slides)

slide3

LCLS Collimation Proposal (2 energy, 3 x, and 3 y adjustable collimators)

y1

y2

y3

x3 & y3 optional?

muon shielding

E1

E2

x1

x2

x3

undulator

slide4

2-phase, 2-plane, and energy collimation in 2nd-order

2nd-order tracking with all collimators closed and big halo

2.5 mm

well shadowed in x, y, and E

gex,y = 4000 mm,

sE/E = 10% (uniform)

slide5

+ Quadrupole

positions

e trajectory

o BPM readback

Trajectory After BBA Convergence

  • 2-mm BPM resolution
  • 50-mm initial BPM & quad offsets
  • 1-mm mover backlash
  • 14-7-4.5 GeV
  • Dj204°

Trajectory through undulator at 14 GeV after 3 passes of BBA procedure.

slide6

Verify BBA Convergence by noting orbit change from 14 to 4.5 GeV

Before BBA procedure

14.1 GeV

drop energy, reset launch, note change

4.5 GeV

500 mm

BPM read-backs through undulator at 14 GeV (top) and 4.5 GeV (bottom) after rough steering, but before the BBA procedure. The energy is changed and the launch is re-established. Trajectory changes are expected at the 500-mm level.

slide7

Verifying BBA Convergence

After BBA procedure

14.1 GeV

drop energy, reset launch, note change

4.5 GeV

20 mm

BPM read-backs through undulator (note scale change) at 14 GeV (top) and 4.5 GeV (bottom) after three rounds of the BBA procedure, where trajectory changes with energy are expected at the 20-mm level.

slide8

Tune-up Dumps in LTU

120 Hz

abort kicker dump

1 Hz

10 Hz

stopper-2

stopper-1

276 m

undulator

e-measurement

energy and

energy-spread measurement

30-m undulator extension

Abort 2nd bad pulse and tune-up at 120 Hz, 10 Hz, or even 1 Hz, with each rate-limit step allowing closer undulator approach.

slide9

Track 100 times with:

  • DL2 BPM rms res. = 10 mm
  • DL2 BPM rms misa. = 200 mm
  • DL2 Quad rms misa. = 200 mm
  • Undulator Quad rms misa. = 100 mm
  • Correct und-launch, then open stopper-2 for one beam shot…
  • Just 11 of 100 trajectories exceed 2.5 mm within undulator
  • None exceed 3.5 mm

G = 110 T/m

First beam shot through undulator?

slide10

LTU Charge Reducer

(spoil beam and collimate hard)

1 nC

4 collimators (CX1,CY1,CX2,CY2) set tight at 0.5 mm

20 pC

1-mm aluminum screen

DL2 BPM rms misa. = 200 mm,

DL2 Quad rms misa. = 200 mm

Collimators rms misa. = 200 mm

Undulator aligned

slide11

Startup at 15 Å with highly degraded e- beam quality

FEL gain highly likely in initial commissioning stages – can check out undulator, characterize e- beam, and boot-strap up to shorter wavelengths.

slide14

0.1-Gauss Earth’s field in x-direction – standard errors, after BBA

no Earth’s field – standard errors, after BBA