LCLS undulator diagnostics and commissioning workshopLCLS undulator diagnostics and commissioning workshopJanuary 19-20, 2004 (UCLA)January 19-20, 2004 (UCLA)

Zhirong Huang, SLACZhirong Huang, SLAC1zrh@slac.stanford.eduzrh@slac.stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

Measuring the FEL gain with trajectory distortion

Z. Huang, SLACJanuary 20, 2004

Measuring the FEL gain with trajectory distortion

Z. Huang, SLACJanuary 20, 2004

LCLS undulator diagnostics and commissioning workshopLCLS undulator diagnostics and commissioning workshopJanuary 19-20, 2004 (UCLA)January 19-20, 2004 (UCLA)

Zhirong Huang, SLACZhirong Huang, SLAC2zrh@slac.stanford.eduzrh@slac.stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

IntroductionIntroduction

Stop the FEL amplification in the undulator and measure the radiation properties at the end (TTF results, PRL, 2001)

LCLS undulator diagnostics and commissioning workshopLCLS undulator diagnostics and commissioning workshopJanuary 19-20, 2004 (UCLA)January 19-20, 2004 (UCLA)

Zhirong Huang, SLACZhirong Huang, SLAC3zrh@slac.stanford.eduzrh@slac.stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

Single Kick Error (SKE)Single Kick Error (SKE)

Two effects of SKE (Tanaka et al., FEL2003): reduction in coupling smearing of microbunching

Critical angle to destroy FEL interaction

rad 64105.1 10

gc L

LCLS undulator diagnostics and commissioning workshopLCLS undulator diagnostics and commissioning workshopJanuary 19-20, 2004 (UCLA)January 19-20, 2004 (UCLA)

Zhirong Huang, SLACZhirong Huang, SLAC4zrh@slac.stanford.eduzrh@slac.stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

Trajectory distortion in LCLSTrajectory distortion in LCLS

Offset the quad by Qx amount. If the focal length of the quad is F, then the kick angle is Q = -Qx/F

Set Q = c, since F ≈10m, Qx ≈ 60m, so that the maximum betatron amplitude xQ ≈ 2Qx

LCLS undulator diagnostics and commissioning workshopLCLS undulator diagnostics and commissioning workshopJanuary 19-20, 2004 (UCLA)January 19-20, 2004 (UCLA)

Zhirong Huang, SLACZhirong Huang, SLAC5zrh@slac.stanford.eduzrh@slac.stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

GENESIS simulation resultsGENESIS simulation results

Total power still grows due to interaction with higher-order modes & spontaneous radiation (div. angle up to 100 rad) On-axis power is dominated by the FEL fundamental mode only (~1 rad) and stops growing when Qx~60 m.

LCLS undulator diagnostics and commissioning workshopLCLS undulator diagnostics and commissioning workshopJanuary 19-20, 2004 (UCLA)January 19-20, 2004 (UCLA)

Zhirong Huang, SLACZhirong Huang, SLAC6zrh@slac.stanford.eduzrh@slac.stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

Z-dependenceZ-dependence

Initial stage: no microbunching to destroy, still some weak interaction + a lot of spontaneous

Exponential growth region, works reasonably well

Qx = 60 m Vary Qx

LCLS undulator diagnostics and commissioning workshopLCLS undulator diagnostics and commissioning workshopJanuary 19-20, 2004 (UCLA)January 19-20, 2004 (UCLA)

Zhirong Huang, SLACZhirong Huang, SLAC7zrh@slac.stanford.eduzrh@slac.stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

SummarySummary

It worked (as in TTF,…)

Trajectory distortion can stop further growth of FEL fundamental mode, but other higher-order modes (including spontaneous) increase the background

Collimation helps to pick up on-axis signal, or can we find the hot spot by data analysis?

Measurement results should be cross-checked with other methods, if possible

LCLS undulator diagnostics and commissioning workshopLCLS undulator diagnostics and commissioning workshopJanuary 19-20, 2004 (UCLA)January 19-20, 2004 (UCLA)

Zhirong Huang, SLACZhirong Huang, SLAC8zrh@slac.stanford.eduzrh@slac.stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

Spontaneous fundamental radiation within 3% bandwidth reaches 60 MW, FEL signal can dominate after 40m

Spontaneous v.s. FEL gainSpontaneous v.s. FEL gain

Spontaneous fundamental in 3% BW

(Z. Huang, K.-J. KimFEL2002)