Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Modelling of the ERLP injector system Christopher Gerth ASTeC, Daresbury Laboratory

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 ERLP Layout Main objectives: Operation of SC accelerator modules Demonstration energy recovery Operation of an oscillator FEL Underpinning R&D for 4GLS Expertise in sub-ps synchronisation

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Injector Performance The ERLP will drive an oscillator FEL. The FEL parameter ρ scales with brightness Produce a high-brightness beam and transport it to the FEL High brightness source required! Brightness scaling: Both high peak current (short bunch length) and small transverse emittance are required at the FEL

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Injector layout Cathode Anode Solenoid and H & V corrector Light box H & V corrector Buncher Cavity Solenoid and H & V corrector Booster

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Modelling Beam dynamics are space charge dominated at kinetic energies of 350 keV (β = 0.8). Multi-particle tracking code ASTRA was used to model space charge effects. Goal: Find optimum setup of the injector. Parameter space is too large to vary all parameters independently (approx.15 free parameters). Strategy: Add beamline elements gradually while following basic design rules for the modelling of the injector.

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Modelling Due to space charge effects at low beam energies: High brightness beams cannot be produced directly at the gun Common recipe: Start at the cathode with an electron beam having an aspect ratio σ r / σ s << 1, apply then emittance compensation in the transverse plane and do the longitudinal bunch compression at a later stage (or in steps). Initial spot size and bunch length are mainly defined by the cathode laser system

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Cathode Laser Commercial laser system: HighQ Laser Laser system delivered and set up at CLF

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Cathode Laser Laser pulse length (rms) ps20 Longitudinal profileGaussian Spot size (diameter)mm4.0 Transverse profileuniform Power10 W in Infrared 5 W in Green Repetition Rate81.25 MHz (CW) Jitter< 0.5 ps Pulse length at 530 nm: 6-7 ps Due to intrinsic properties of GaAs: a bunch length of 20ps was assumed Parameters for simulation

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Electron Gun A version of the JLab gun (IR-DEMO) is being built at DL GaAs as cathode material (UHV: mbar) HV power supply (500 keV, 8 mA) has been purchased

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Gun & 1 st Solenoid Bunch charge pC80 Beam energy (max)keV500 Beam energy (nominal)keV350 Solenoid positionm0.236 Gun parameters: Solenoid for focusing and emittance compensation Free parameter: Solenoid magnetic field strength

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Gun & 1 st Solenoid Transverse Plane Longitudinal Plane

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Emittance compensation Upstream solenoid x x’ s Higher charge density in the centre slices Idea: Due to different expansion rates, slices overlap in a drift space behind the solenoid. Reduction of projected emittance x x’ Downstream solenoid x

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Beam Dynamics x x’ Transverse Phase Space avoid crossing of centre axis for converging beam – this can lead to bifurcation laminar flow in the transverse plane E s Longitudinal Phase Space avoid crossover (tail overtakes head) try to preserve linear shape for magnetic compression (sextupoles in the arcs for correction)

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Phase Space Distribution B = 350 G

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Phase Space Distribution B = 350 G

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Phase Space Distribution B = 300 G

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Buncher 3 different designs were looked into Normal-conducting single-cell cavity Frequency: 1.3 GHz (LINAC) Zero-crossing acceleration (velocity bunching) No distinct differences were found in the effect on the beam dynamics EU cavity ELBE cavity Cornell design

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Buncher ELBE design is the easiest to manufacture ELBE cavity has proven successful operation

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 2 nd Solenoid Identical to 1 st solenoid Position at 1.45 m Setup of solenoid: 1) Produce beam waist at the entrance of the booster 2) Beam size depends on gradient given by invariant envelope technique (Rosenzweig & Serafini) σ ~ 2-3 mm However, theory only valid for β = v/c ~ 1! σ = I pk 2 3 I A  ’ ’ 1/2

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Beam Dynamics buncher solenoid booster Conclusion: Locate 2 nd solenoid as close as possible to the booster!

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Booster 750 solenoid Two ELBE type SRF modules have been pruchased (03/04) 4 free parameters: Both gradients and phases Constraints: 1) total energy gain (8 MeV) 2) reasonable Twiss parameters at the exit

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Phase Scan 1 st Cavity Gradient: 4MV/m

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 1 st Cavity At 350keV: β = 0.8 bunch slips back w.r.t. RF phase 1 st cell of booster Decrease of kinetic energy in 1 st cell at optimum RF phase

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 2 nd Cavity 1 st cavity Gradient: 4MV/m RF phase: 15 o 2 nd cavity Gradient: 5MV/m RF phase: -20 o

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 2 nd Cavity 1 st cavity Gradient: 4MV/m RF phase: 15 o 2 nd cavity Gradient: 5MV/m RF phase: -20 o We have used elegant to track this particle distribution through the LINAC and up to the FEL

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Summary Matching into the (not beta matched) booster is the most critical part. Required beam parameters can be achieved with the ELBE module (most practical solution). However, a series of single-cell cavities with independently adjustable phases would give better results (on-going design work for 4GLS). Gun ready for commissioning01/05 Diagnostics beamline completed03/05 Booster installation09/05

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Hydrogen Ions ASTRA can also track positrons, protrons and hydrogen ions Kinetic energy of 350 keV: Electrons: β = 0.8 γ = 1.7 H - : β = 0.03 γ = 1.0

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Hydrogen Ions Transverse Plane Longitudinal Plane

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Parameters Laser pulse length (rms) ps20 (Gaussian) Spot size (diameter)mm4.0 (uniform) Bunch chargepC80 Beam energykeV350 1 st Solenoid positionm st Solenoid fieldG305 Buncher positionm1.1 Buncher RF phasedeg90 2 nd Solenoid positionm nd Solenoid fieldG205 1 st Cavity gradientMV/m4.0 1 st Cavity RF phasedeg+15 2 nd Cavity gradientMV/m5.0 2 nd Cavity RF phasedeg-20

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 ERLP Layout

Christopher Gerth DL/RAL Joint Workshop 28-29/4/04 Injector Layout