Seeded jitter studies

Z. Huang, et al.,

November 7, 2012

Seeding MD (May 15)• 150 pC, SASE vs. Seeded after Kmono• E-beam energy 13.64 GeV, photon energy 8.3 keV• Bragg angle 57.875 deg for 004 seeding (accurate to 0.001 deg)• Kmono bandwidth ~1 eV• Tune on Kmono diode signal not on gas detector BC2 Ipk=2 kA, L1S=-24.5 deg, L1X=-160 deg, U1-2 out

• Gas detector shows 0.5 mJ SASE, and seeded peaks at 1 mJ

average 6.8 (rms intensity jitter 72%)

Seeded jitter sensitivity studies with Kmono

average 11.5 (rms intensity jitter 22%)Filter out energy jitter

Seeded intensity vs. linac energy(rms energy jitter 5e-4)

average 6.8 (rms intensity jitter 72%)

Seeded jitter sensitivity studies with Kmono

average 10.9 (rms intensity jitter 25%)Reduce energy jitter to 1.8e-4

Seeded intensity vs. linac energy(rms energy jitter 5e-4)

1D FEL Simulation

Electron beam at undulator entrance

FEL parameter ρ = 5 x 10 -4

Flat current and electron energy profileRandom electron beam central energy with Gaussian DistributionUncorrelated energy spread with

average = 0.6 ρ rms = 0.1 ρ

Seed LaserFlat seed laser profileIntensity distributed as negative exponential with average 5 MW

central energy

phase

energy

Uncorrelated energy spread

A. Lutman

Electron Beam energy vs Intensity (7 x 10-4 relative energy rms)

2 gl before saturation

2 gl after saturation

4 gl after saturation

2 gl before saturation

2 gl after saturation

4 gl after saturation

Intensity in 1 eV

Total Intensity

Amplification Bandwidth and Fluctuations, comparison with experimental data

Relative energy rms 7.2 x 10-4 Relative energy rms 7 x 10-4

Experimental DataKmono measurement 05/15/2012

Fluctuations 72% Fluctuations (1eV) 70%

Relative amplification bandwidth (fit rms) 3.5 x 10-4

(relative energy)

Simulated Data2 gain lengths after saturation Without taper

Relative amplification bandwidth (fit rms) 3.5 x 10-4 (relative energy)

(111) Seeding at 5.5 keV

Diamond

(004)

(220)

(111)

With input beam perpendicular to theCrystal the photon energy for the (111) is5.21 keV

35.26

2.0

seed beam

J. Hastings

Undulator taper at 5.5 keV

Taper response

Maximum FEL intensity (>400 uJ) responses well to strong undulator taper

40 pC bunch length < 10 fs, maximum peak power > 40 GW

Simulation for energy jitter: blue (on-energy), black (+0.1 %), red ( -0.1 % ), magenta (-0.2 %)

simulation

experiment

Comparison of taper resulton-energy shots

off-energy shots

J. Wu

SummarySeeded FEL power is very sensitive to linac energy jitters.Need to improve energy jitters to < 2e-4 (rms).Seeded FEL responses to energy jitter and undulator taper appear to agree with simulations, but the relevant data set is small.