ASTRA Injector Setup 2012

Julian McKenzie17/02/2012

Baseline:Gun voltage 350 kV

Bunch charge 60 pC

Laser spot diameter 4 mm flat-top

Laser pulse length 7 ps Gaussian / 28 ps flat-top ?

Sol 1 peak field 330 G

Sol 2 peak field 187 G

Buncher power 1.6 kW

BC1 gradient 8 MV/m

BC1 phase -20

BC2 gradient 5 MV/m

BC2 phase +30

Post-booster beam energy 6.5 MeV

Simulations using ASTRA (07/04/2008 win32)No intrinsic emittance – could expect up to 1.2 mm mrad from photocathode

7 ps Gaussian vs 28 ps flat-top

Buncher power [W]

Buncher power scans

• Bunch length required at entrance to linac to achieve energy spread for FEL ~7ps

• We still don’t understand booster to linac longitudinal dynamics...

Red = 7 ps GaussianBlue = 28 ps flat-top

Yuri reckons 1.6 mm FWHM

BC1 scans

Red = 1 kW buncher powerGreen = 1.6 kW buncher power

For 7 ps Gaussian laser pulse

• For 1kW buncher power, choose +15 BC1 phase• Set SOL-02 to minimise transverse beam size• Set BC2 phase to minimise chirp (-13)

But phase space isn’t good:

Is RMS bunch length even a good quantity to optimise on?Need to look at phase space plots

Phase space plots (longitudinal)

Red = 7 ps GaussianBlue = 28 ps flat-top

-20/+30 -10/+10(as per original model)

Using “nominal” setup detailed on slide 1

Looks similar to Bruno’s:Lots of charge at the “crossover point”

NB// head to the right.z [m] vs pz (eV/c)

BC1 phase for minimum curvature:BC1 = -6 BC1 = 0

Bunc

her =

1 k

WBu

nche

r = 1

.6 k

WFor 7 ps Gaussian laser pulse

Sol2 scans

Red = 1 kW buncher powerGreen = 1.6 kW buncher power

For 7 ps Gaussian laser pulse

BC2 phase?

BC1 at -6SOL-02 at 220G

Red = 1 kW buncher powerGreen = 1.6 kW buncher power

For 7 ps Gaussian laser pulse

To do list:

• Emittance vs SOL-02 for 7/28ps with identical bunch length from buncher

• At minimum emittance from above, BC2 phase scan to look at minimum energy spread

• Investigate lowering energy gain from BC1

• Anything else?