Linac Commissioning

P. Emma LCLS Commissioning Workshop, SLAC

Sep. 22-23, 2004 P. Emma,

SLAC LCLS

LCLS

Commissioning – Sep. 22, 2004

Linac Commissioning Document Available

>23 page DRAFT document describing: initial checkout setup of linac how/where to measure beam what device to scan and by how much expected resolution how/where to correct beam etc…

http://www-ssrl.slac.stanford.edu/lcls/linac/notes/linac_commissioning.ps

(not complete yet, but close) P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

Linac ‘Commissioning’ (Physics)

Initial checkout (tunnel and beam-based) How to setup

I pk

= 3.4 kA, ge  1.2 m m, etc.

What to measure and what to adjust (simulations) Longitudinal phase space Bunch Length Energy Spread (proj. & slice) Transverse phase space Projected Emittance Slice Emittance

LCLS

Commissioning – Sep. 22, 2004 P. Emma,

SLAC

Initial Machine Conditions

Magnets warmed, standardized, and set properly Reasonable quality

e

beam available: Rough beam steering established Rough RF phasing of each klystron (1 or 2 deg) Any beam obstruction and loss issues solved P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

Initial Checkout TUNNEL

Power-on polarity checks of all “new” magnets Validate proper cabling connections (magnets, BPMs, diagnostics…) Rough alignment inspection (tape measure, eye) Verify all insertable devices move in and out, and are finally removed P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

Initial Checkout BEAM-BASED

Take full set of

x

and

y

‘oscillation’ data (checks optics and BPM scaling…) Verify all profile monitor scaling with known centroid shifts (wires, OTR, YAG, screens…) Repeat above at high dispersion points (DL1, BC1, BC2, DL2) using energy changes Calibrate all BPM-charge, and toroid readings based on one well established reference Document all the above for future scrutiny CHECKOUT

MUST BE COMPLETE

BEFORE MEASUREMENTS AND TUNING BEGIN!

P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

Location of Main Linac Diagnostics

5+ energy spread meas. stations (optimized with small 5+ emittance meas. stations designed into optics (

D b

)

y

x

,

y ) BPMs at or near most quadrupoles and in each bend syst.

RF deflectors for slice

e

and

s

E measurements (L0 & L3)

rf gun

T-cav.

ge

x

,

y

ge

x

,

y ...existing linac

s

E



E

 L1 X s

E



E

 L2 ge

x

,

y

T-cav.

s 

E



E

L3 ge

x

,

y

ge s

E



E



x

,

y

P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004 s

E



E



Setup of Linac-0 RF

s

y

= bunch length Establish initial bunch length Phase linac-0

RF-deflector at 1 MV

minimize energy spread with L0 RF phase

RF-deflector

P. Emma,

SLAC

Phasing L0-Linac

LCLS

Commissioning – Sep. 22, 2004

20 m m res. BC1 BPM

Setup of Linac-1 RF

20 m m res. BC1 BPM LX RF phase L1 RF phase

rf gun

Linac-1 RF phase scan (X-band off, BC1 bends at 295 MeV) Linac-X RF phase scan (BC1 bends at 250 MeV)

set phase to

-

25 ˚



0.5

˚ Linac-1

21-1b 21-1d X

set phase to

-

160˚



0.5

˚

Turn on BC1 energy feedback Switch off BC2 chicane Use sec-25 RF-deflector to meas. bunch length ( s

z

1 ) Adjust S-band RF phase (  0.5

˚) to set s

z

1  195  10 m m P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

40 m m res. BC2 BPM

Setup of Linac-2 RF

5 m m res. LTU BPM (NO CSR) L2 RF phase L2 phase L2 Linac-2 RF phase scan (BC2 bends at 5.9 GeV, or…)

set phase to

-

41 ˚



0.5

˚

L3 Scan Linac-2 phase & use LTU BPM to find max. wake-induced energy loss across Linac-3 Turn on BC2 energy feedback Use sec-25 RF-deflector to measure length ( Adjust L2 RF phase (  0.5

˚) to set Linac-3 phasing is trivial (  5˚) s

z

2  20  s

z

2 ) 2 m m P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

Emittance Meas. Simulation in LCLS

Multiple OTR screens Multiple wire-scanners Quad-scans on single OTR Quad-scans on OTR with RF-deflector OTR1,2,3

BC1

WS11,12,13 P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

135-MeV OTR

x

-profiles from tracking

s

x

 118 m m s

x

 49 m m P. Emma,

SLAC

s

x

 120 m m non-Gaussian ge

x

= 0.75 ± 0.04 m m

LCLS

Commissioning – Sep. 22, 2004

x

-Slice-Emittance Measurement

s

y

RF-deflector at 1 MV



bunch length

slice OTR 10 times P. Emma,

SLAC

“QE03” quad scanned

LCLS

Commissioning – Sep. 22, 2004

x

-Slice-Emittance Measurement Simulation

“QE03” scanned  20% (centered on 106% of its nominal gradient)

Injector at 135 MeV with S-band RF-deflector at 1 MV

(same SLAC slice e code used at BNL/SDL) = meas. sim.

= calc.

=

y

distribution = actual DL1 slice-emit on WS02 P. Emma,

SLAC

slice-5

LCLS

Commissioning – Sep. 22, 2004

y

-slice-Emittance Measurement in BC1

“Q21201” scanned ±20% P. Emma,

SLAC

3.9 mm

LCLS

Commissioning – Sep. 22, 2004

y

-slice-Emittance Measurement Simulation

“Q21201” scanned  20% (centered on 92% of its nominal gradient)

slice-

y

emittance in BC1 using

x

-chirp

= meas. sim.

= calc.

=

y

distribution = actual P. Emma,

SLAC

slice-5

LCLS

Commissioning – Sep. 22, 2004

Empirical BC1/BC2 Dispersion Correction

actual data from SPPS chicane D y

x

  /2

Residual

x

-dispersion (and its angle) is precision minimized using ‘tweaker’ quads in the chicane Correct

h

and (

ah + bh 

), orthogonally with 2 quads

P. Emma,

SLAC

SPPS chicane with quads

LCLS

Commissioning – Sep. 22, 2004

Transverse Wakefield Compensation

All quadrupoles, RF structures, and BPMs misaligned by 300 m m rms Small ‘bumps’ added to correct emittance trajectory after steering steering coils P. Emma,

SLAC

ge

x

ge

y

  2.1 m m 5.2 m m

LCLS

Commissioning – Sep. 22, 2004 ge

x

ge

y

  1.0 m m 1.1 m m

Repeat for 100 Different Seeds

M. Borland D e / e  20% (projected) P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

Energy Jitter Measurement (Feedback)

Two 5 m m BPMs:

x

1

x

2 relative energy centroid resolution: ~0.003% undulator… ( h

x

 125 mm) Difference of BPM

x

-readings is proportional to energy change, and insensitive to incoming trajectory jitter.

P. Emma,

SLAC

LCLS

Commissioning – Sep. 22, 2004

Slice-Emittance Configuration for LTU

nominal optics (proj. emit.) WS31-34 undulator… P. Emma,

SLAC

slice-emit.

meas. optics OTR33 stopper inserted

LCLS

Commissioning – Sep. 22, 2004

Slice-Emittance Measurements in LTU

“QEM3” (or tweaker) scanned  3% (centered on its nominal gradient)

LTU at 14 GeV with S-band RF-deflector at 24 MV

z

P. Emma,

SLAC

y

= meas. sim.

= calc.

=

y

distribution = actual

LCLS

Commissioning – Sep. 22, 2004

Slice Energy Spread Measurements in LTU

s

E

/

E

 10 4

LTU at 14 GeV with S-band RF-deflector at 24 MV

s

x



12

m

m

P. Emma,

SLAC

FEL goal

LCLS

Commissioning – Sep. 22, 2004

Summary

Most diagnostics incorporated into design and simulated (1 st pass) Two RF-deflectors allow time resolved measurements at low and high energy Tune-up algorithms considered, but more refinement needed Feedback systems must maintain setup while tuning progresses (bunch length monitors?)

LCLS

Commissioning – Sep. 22, 2004 P. Emma,

SLAC