Hard X-ray S-2-E FEL simulation for LCLS-II CDR

J. WuIn discussion with Y. Ding, P. Emma, Z. Huang,

H.-D. Nuhn 02/01/2011

LCLS-II: Ranges for Individual Bunch Operation

(From H-D Nuhn, 10/13/2010)

Simulation example

Setup

• FEL at 13.5 keV,• Electron Centroid Energy 13.5 GeV; peak

current 3 kA– S2E file down to undulator entrance taken from P.

Emma

• Undulator lw = 3.2 cm; each section is about 4.4 m long with 3.4 m magnetic length; beta-function ~ 20 m

Electron bunch @ undulator entrance

• Current profile (head at right)

Without wakefield

• The S2E input electron distribution function is injected into an ideal undulator without any wakefield effect

FEL power

• Along the undulator: Saturation around 60 m

FEL profile and spectrum

• Along the undulator at 100 m

Energy loss• Along the undulator: entrance (black), 60 m

(red), 120 m (blue), and 150 m (green) – electron bunch head at right

Energy spread• Along the undulator: entrance (black), 60 m

(red), 120 m (blue), and 150 m (green) – electron bunch head at right

Setup

• FEL at 13.5 keV,• Electron Centroid Energy 13.5 GeV; peak

current 3 kA– S2E file down to undulator entrance taken from P.

Emma (No LSC included)

• Undulator lw = 3.2 cm; each section is about 4.4 m long with 3.4 m magnetic length; beta-function ~ 35 m

Electron bunch @ undulator entrance

With resistive-wall wakefield• We assume 5 mm diameter round aluminum

pipe; no surface roughness wake, no geometric wake; head at left

FEL power• Along the undulator: Saturation around 80 m;

with wakefield compensation of 150 keV/m which in reality is a tapering in the undulator

FEL power• Along the undulator: 80 m – electron bunch

head at left

FEL power• Along the undulator: 100 m – electron bunch

head at left

FEL power• Along the undulator: 120 m – electron bunch

head at left

FEL power• Along the undulator: 140 m – electron bunch

head at left

FEL spectrum• At the undulator end: 140 m– electron bunch

head at left

FEL spectrum• The wide spectrum is partially due to the

wakefield induced energy chirp along the electron bunch, head at left