Reconstruct the FEL x-ray profile with X-TCAV after undulator

Y. Ding, C. Behrens3/18/2011

Thanks Zhirong and Paul for helpful discussions.

YAGS2YAGS2

Laser OFF Laser: 40 µJσE/E 45 keVσE/E < 12 keV

RF deflector ON

timeenergy

Laser Heater Measurements

Interaction between laser and electrons in wiggler leads to the increase of energy spread;

Use TCAV and dispersion to measure the longitudinal phase space, and know the heating effects.

FEL process leads to e-beam energy loss and energy spread increase

Total_E_loss = E_loss_FEL + E_loss_sr+E_loss_wake+… = E_loss_FEL + E_loss_FELoff

Total_EnergySpread = sqrt(ES_FEL^2 + ES_sr^2+ES_wake^2+…) = sqrt(ES_FEL^2+ES_FELoff^2)

If we use TCAV to measure the time-resolved e-beam energy loss or energy spread with FEL on and off, then we have the FEL radiation intensity profile.Of course, we also have e-beam distribution profile.

We already have the E-loss scan GUI developed by P. Emma to measure the FEL radiation energy from electron beam energy loss.

We show a few examples:

Hard x-ray ideal Gaussian beam rms = 7 um; Hard x-ray ideal Gaussian beam rms = 1um; Hard X-ray S2E real LCLS beam 3 kA case.

Hard x-ray, Gaussian 7um rms, @ 70mFEL OFF

Und. exit Und. exit

OTRDMPOTRDMP

head

head

FEL ON

Hard x-ray, Gaussian 7um rms, @ 70mReconstruct the x-ray profile with the time-resolved E-loss.

Reconstruct the x-ray profile with the time-resolved energy spread (after arbitrary scaling).

Hard x-ray, Gaussian 7um rms, @ 110m

Und. exit Und. exit

OTRDMPOTRDMP

FEL OFF FEL ON

head

head

Hard x-ray, Gaussian 7um rms, @ 110m

Reconstruct the x-ray profile with the time-resolved E-loss.

Reconstruct the x-ray profile with the time-resolved energy spread (after arbitrary scaling).

Hard x-ray, Gaussian 1um rms, @ 70m

Und. exit Und. exit

OTRDMPOTRDMP

FEL OFF FEL ON

head

head

Hard x-ray, Gaussian 1um rms, @ 70m

Reconstruct the x-ray profile with the time-resolved E-loss.

Reconstruct the x-ray profile with the time-resolved energy spread (after arbitrary scaling).

Hard x-ray, 250pC S2E LCLS beamUndulator entrance

FEL power profile @ undu. exit

Hard x-ray, 250pC S2E LCLS beamFEL OFF FEL ON

head

head

Und. exit Und. exit

OTRDMPOTRDMP

Hard x-ray, 250pC S2E LCLS beam

Reconstruct the x-ray profile with the time-resolved E-loss.

Reconstruct the x-ray profile with the time-resolved energy spread (after arbitrary scaling).

Discussions• A resolution of 1.5 fs to 3 fs may be achieved for e-

beam measurements with X-TCAV;• At the same time, we can have the FEL x-ray profile.

Applicable for all radiation wavelength; Wide diagnostic range, few fs to few hundred fs; Profile, single shot; No interruption with LCLS operation; Both e-beam and x-ray.

Not cheap… Slippage at soft x-ray…