The LCLS Injector
C.Limborg-Deprey
Emittance compensation
linear emittance compensation for ideal laser beams
limits of emittance?
thermal emittance
Nominal and alternate tunings
Beamline layout
1nC,
0.2 nC
last year modifications
laser heater
RF structures
How much can we believe PARMELA
GTF, DUVFEL PARMELA vs experiment
Code comparison
What could we be missing?
Commissioning measurements
Spectrometers
Emittance measurement
6D measurements
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Emittance Compensation
Photocathode RF gun
adequate to generate coldest electron beam
photoemission produces some transverse momentum px
“thermal emittance” ~  x  px
also called “intrinsic emittance” or “minimum” emittance
We want to preserve at best the beam emittance along the transport line
(space charge, wakefield, CSR …)
Space charge very strong at low energy  generates large energy spread
• Appropriate choice and tuning of components
allow to compensate for variation in transverse
dimension (size, divergence) due to chromatic
effects
Gun Solenoid
Linac
= Compensate for the mismatch between slices
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Single Particle Dynamics
Single particle dynamics in gun
Gun
focusing
defocusing
defocusing
focusing
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Single Particle Dynamics
RF effects are non linear
Electric field effects
RF Kicks are time dependent: so vary
along the bunch
Are not be compensated for
Very small contribution to total
~ 0.1 mm.mrad in our S-Band Gun
focusing
defocusing
defocusing
Magnetic field effects
focusing
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Single Particle Dynamics
Gun
Solenoid
Gun Solenoid
Linac
Solenoid focusing
focal length energy dependent
Focusing kick at entrance of Linac
Time dependent
Used in emittance Compensation process
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Simulations
Gun Solenoid
Linac
Diverging: Space charge
RF kick at exit cell
December 3rd 2004
Theory Club: The LCLS Injector
Converging: Solenoid
RF kick at entrance cell
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Emittance Compensation
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Gun S1
S2
Movies 1,2,3 : thermal = 0.72 mm.mrad
Movie 4 : thermal = 0 mm.mrad
Linac
Movie 3
Movie 1
Movie 4
Movie 2
3D Ellipsoid
Space Charge linear
with r ,
 optimal shape for
perfect emittance
compensation
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Movie 1
December 3rd 2004
Theory Club: The LCLS Injector
Movie 2
Movie 3
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Movie 4
Preinjector:
VA
TR
EA
TM
CU
UM
EN
MP
S
HA
MB
ER
PU
T
C
LO
A SS NG
EM B EL
BL LO
Y WS
SP
SE O OL
AL S
SECTOR 20
FR
O
M
VA
H
LV
E
CA
TH
OD
E
UH
G ATV A
E LL
VA ME
LV TA
ES L
PO
RC
OL U
DE PIN
R E
VAULT
SLAC Main Linac Beamline
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Goal parameters
Parameter
Value
Peak Current
100 A
Charge
1 nC
Normalized Transverse
Emittance: Projected/Slice
< 1.2 / 1.0 micron (rms)
Repetition Rate
120 Hz
Energy
135 MeV
Energy Spread@135 MeV:
Projected/Slice
0.1 / 0.01 % (rms)
Gun Laser Stability
0.50 ps (rms)
Booster Mean Phase
Stability
0.1 deg (rms)
Charge Stability
2 % (rms)
Bunch Length Stability
5 % (rms)
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
6 MeV
 = 1.6 m
,un. = 3keV
Gun S1
S2 L0-1
63 MeV
 = 1.08 m
,un. = 3keV
L0-2
135 MeV
 = 1.07 m
,un. = 3keV
‘Laser Heater’
135 MeV
 = 1.07 m
,un. = 40keV
DL1
19.8MV/m 24 MV/m
Spectrometer
‘RF Deflecting
cavity’ TCAV1
3 screen
emittance
measurement
UV Laser 200 J,  = 255 nm, 10ps, r = 1.2 mm
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
 ~19 parameters to optimize
1- Analytic formula  emittance compensation
2- Envelope equation code (Homdyn , Trace3D)
define components
3- Fine tuning + sensitivity studies (multiparticle tracking code: PARMELA, ASTRA …)
Gun
Solenoid
Solenoid 2
Linac0-a
E (MV/m)

Balance
Position
Length
Field
Position
Length
Field
Position
E(MV/m)
Linac0-b
Position
E(MV/m)
Laser Parameters
Longitudinal (length, rise time, flatness)
Transverse(r, uniformity, pointing spot)
Energy  charge
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Nominal tuning
proj = 0.954 , 80 = 0.89 mm.mrad
Rise/fall
0.7 ps
1.0ps
1.5 ps
projected [mm.mrad]
0.954
1.028
1.141
80% [mm.mrad]
0.894
0.935
0.986
<slice >10..90[mm.mrad]
0.849
0.877
0.901
<slice >1..100[mm.mrad]
0.906
0.953
1.004
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Tolerance as a function of single parameter
variation
Solenoid 1 0.3%
Egun 0.5%
gun 2.5 
Balance~ 3% is ok
Solenoid 2 20%
Linac Field 12 %
(EFinal = 150 MeV )
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Stability
Requirements
Stability
requirements
Defined after combining errors
Param.
Nom.
Units
Stability
Requirements
Sol1
2.7235
kG
 0.02 %
Sol2
0.748
kG
1%
Gun
27.25 
 /0-X
 0.1
Gun Field
120
MV/m
 0.5%
Charge
1
nC
 5%
L01Field
18
MV/m
 2.5%
Phase
 Small margin left for laser parameters variation
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Tolerances – Alignment and Laser Uniformity
Param.
Type
Tolerance
Units
Solenoid 1
Transverse Position
500
m
Angular Position
1.5
mrad
Laser
Transverse Position
100
m
Laser Uniformity
Transverse (Slope)
 10 %
NA
Transverse (Cross)
 10 %
NA
Longitudinal
30% ptp
Freq.> 1THz (1ps)
Longitudinal
20% ptp
Freq.< 1THz
Transverse Position
150
m
Angular Position
120
rad
Linac 1
Linac 2
Same as Linac 1
Solenoid 2
Same as Solenoid 1
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Requirements on Laser Pulse - Summary
Transverse
10 % ptp maximum on emission
uniformity
Longitudinal
 =120 m
 =240 m
 =480 m
5% ok for emittance
But too much for LSC
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Alternate tunings for cylindrical bunch
1nC, long pulse
th = 0.6 mm.mrad per mm laser spot size
reduce rlaser to 0.85 mm BUT to keep charge density same order lengthen
bunch
Start with th = 0.51 mm.mrad
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Alternate tunings for improving 
Name
Q
(nC)
Laser
pulse
(ps)
r
(mm)
th
(m.rad)
80
RF
(m.rad) ()

80  5%
Nominal
1
10
1.2
0.72
0.9
32
2.5
1 nC, 17.5 ps
1
17.5
0.85
0.5
0.75
33
1.5
0.2nC,10ps
0.2
10
0.39
0.234
0.38
37
2.5
0.2nC,5ps
0.2
5
0.42
0.25
0.37
32
5
• th = 0.6 mm.mrad per mm laser spot size
• minimum r best , BUT limit on minimum radius = space charge limit
(ignoring Shottky)
Esc = Q / ( r2 o)
example:
for 1nC, r = 1.2mm, Esc = 25 MV/m ( 12)
for 1nC, r = 0.85 mm, Esc = 50 MV/m ( 25)
42)Limborg-Deprey
December 3rd 2004 for 0.2 nC, r = 0.3mm, Esc = 80 MV/m (
Cecile
Theory Club: The LCLS
Injector
limborg@slac.stanford.edu
for 0.2
nC, r = 0.42mm, Esc = 40 MV/m
( 20)
0.2nC
A 5ps laser pulse improves dramatically the peak current
compared to the 10ps laser pulse case
without damaging too much the slice emittance
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Ellipsoid emission bunch
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Ellipsoid emission bunch
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Ellipsoid emission bunch
square
ellipsoid
Exit gun
Exit L01
December 3rd 2004
Theory Club: The LCLS Injector
Longitudinal Phase Space
Ek [MeV] vs T [ps]
Entrance
L01
Exit L02
Cecile Limborg-Deprey
limborg@slac.stanford.edu
6 MeV
 = 1.6 m
,un. = 3keV
Gun S1
S2 L0-1
63 MeV
 = 1.08 m
,un. = 3keV
L0-2
135 MeV
 = 1.07 m
,un. = 3keV
‘Laser Heater’
135 MeV
 = 1.07 m
,un. = 40keV
DL1
19.8MV/m 24 MV/m
Spectrometer
‘RF Deflecting
cavity’ TCAV1
3 screen
emittance
measurement
UV Laser 200 J,  = 255 nm, 10ps, r = 1.2 mm
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Longitudinal Space Charge Instability
LSC observed at the DUVFEL
Courtesy of Timur Shaftan
Also observed at TTF
Simulations and theoretical
studies
Current Density
Energy
Z.Huang et al. PhysRev.
SLAC-PUB-10334
J.Wu et al. LCLS Tech Note ,
SLAC-PUB-10430
G.Geloni. Et al.
DESY 04-112
The self-consistent solution is the space charge oscillation
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
ASTRA/ PARMELA Simulations ,
Amplitude = +/- 5%,  = 100 m
GUN EXIT
6 MeV
ENERGY
CURRENT
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
End L02
135 MeV
ENERGY
CURRENT
Microstructure at the end of the injector
Laser Heater provide enough energy spread (40keV) for “Landau damping” preventing
-further amplification of the microbunching
-December
the increase
an energy spread (as it needs to remain
< the
FEL parameter)
3rd 2004
Cecile
Limborg-Deprey
Theory Club: The LCLS Injector
limborg@slac.stanford.edu
Can we believe PARMELA?
• Sensitivity studies fine since relative evolution
• Meshing : by hand in PARMELA , automated in ASTRA
criteria well understood
• Benchmarks
- w.r.t experiences
Proved importance of data on initial distribution
Fitted the slice parameters such as  , , projected , slice
- w.r.t other codes
Seems that extraction agree with PIC codes (experiment to be revisited for
low accelerating voltage)
Still need to compute fields for lossy copper
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
DUVFEL measurements
200 pC
Good Agreement Slice Emittance and Twiss Parameters for the various
solenoid fields
After including thermal emittance, gun field balance between the two cells,
transverse non-uniformity and longitudinal profile
Solenoid = 98 A
December 3rd 2004
Theory Club: The LCLS Injector
Solenoid = 104 A
Cecile Limborg-Deprey
limborg@slac.stanford.edu
DUVFEL Measurements
Thermal emittance experiment
Confirms the 0.6 mm.mrad
per mm radius of laser spot size
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
R&D Status: GTF Measurements
GTF measurements - 1.5 mm.mrad for 130A
Peak Current (A)
Instantaneous
Peak Current
head
tail
for 130 A
~ close to LCLS
requirements
150
100
50
Similar
measurements at the
DUVFEL facility
Time (ps)
0
n (mm mrad)
-1.5
Slice Emittances
slice = 1.5 mm.mrad
300pC
Spectrometer Image
of Slice Quad Scan Data
Theory Club: The LCLS Injector
-0.5
0
0.5
1
2
1
0
December 3rd 2004
-1
(Spring 2002)
 longitudinal emittance
Slice number
5
10
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Commissioning Diagnostics
1
Uniformity + Thermal emittance
‘Laser Heater’
YAG1 YAG2
2
Gun Spectrometer
December 3rd 2004
Theory Club: The LCLS Injector
‘RF Deflecting
cavity’ TCAV1
Straight Ahead
Spectrometer
3 screen
emittance
measurement
3
4
Cecile Limborg-Deprey
limborg@slac.stanford.edu
1
Emission uniformity
Point-to-point imaging of cathode on YAG1
Laser masking of cathode image at DUVFEL
Above: Laser cathode image of air force
mask in laser room.
Below: Resulting electron beam at pop 2.
December 3rd 2004
Theory Club: The LCLS Injector
Above: Laser cathode image with mask
removed showing smooth profile.
Below: Resulting electron beam showing hot
spot of emission.
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Courtesy
W.Graves
1
Thermal Emittance
Infinite-to-point imaging
what type of momentum
distribution?
Very good
resolution of
divergence
YAG2
==
Image of
Assumes th = 0.6 mm.mrad
December 3rd 2004
Theory Club: The LCLS Injector
divergence
of source
Cecile Limborg-Deprey
limborg@slac.stanford.edu
2
Gun Spectrometer
YAG01
Spectrometer
Energy
Quadrupoles
Absolute energy
Alignment using laser
Spectrometer field calibration
YAGG1
YAGG2
Correlated Energy Spread for all
charges
Uncorrelated energy spread for
low charges
Introducing a time-energy
correlation (varying injection
phase)
Slice thermal emittance
Relay imaging system from YAG1
to spectrometer screens
Point-to-point imaging in both
planes
Uniformity of line density
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
High Charge Operation : 1nC Nominal tuning – no quadrupole on –
Very good linearity
Longitudinal
at YAG1
YAGG1
December 3rd 2004
Theory Club: The LCLS Injector
YAGG1
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Resolves line density uniformity at high charge
+/- 8% modulation on laser beam
YAG1
RF + 25 / nominal
Quadrupoles on for
manageable image size
Resolves modulation
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
135MeV Diagnostics
6D beam measurements
Horizontal slice emittance
Laser Heater
Vertical deflecting cavity +
3screen
Transverse RF Cavity
OTR Emittance Screens
DL1 Bend
Vertical slice emittance
Quad scan + spectrometer
Quad Scan + Dogleg bend
 Verification of thermal emittance
Longitudinal Phase space
Straight Ahead Spectrometer
Point-to-point imaging of the 75 m waist (OTR5)
December 3rd 2004
Theory Club: The LCLS Injector
Vertical deflecting cavity +
spectrometer
Efficiency of laser heater
(spectrometer has 10 keV
resolution)
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Spectrometer + Vertical deflecting cavity
 Direct longitudinal Phase Space representation
Longitudinal Phase
Space at waist
• Transverse deflecting cavity
 y / time correlation
(1mrad over 10ps )
• Spectrometer
 x / energy correlation
rms
fwhm
From PARMELA simulations (assuming 1m emittance), resolution of less than 10 keV
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
RF Gun – Racetrack in full cell
2d-: no port = benchmark omega3p/sf
3d-cylin: with coupling ports- cell cylindrical x = 0.96 y =1.01
d
b
x = y =0.88
3d-rtrack: with coupling ports- cell racetrack x = y = 0.90
b
Full : with laser ports + racetrack
x = 0.97 , y = 0.99
Full retuned: with laser ports + racetrack+
retuned
x = 0.91, y = 0.915
Quadrupole  r (1/m)
cylindrical cavity (lc=2.475cm)
8
6
4
2
0
-2
-4
-6
-8
-180 -130
racetrack cavity (lc=2.413cm)
with d=0.315cm
racetrack cavity (lc=2.413cm)
with d=0.356cm
-80
-30
20
70
120
170
rf phase (degree)
From L.Xiao, ACD/SLAC
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
RF Studies- L01 coupler
Dipole moment
From Z.Li, L.Xiao,
ACD/SLAC
for 10 ps
Dual
feed
Single feed
Quadrupole moment
December
3rd 2004
Dual feed
Dual feed
Theory
Club: The LCLS Injector
+rtrack
()/m
Head-tail angle
 (rad/m)
SLAC Single feed
0.78
0.078
Symmetric dual
0.63
0.063
Race-track dual
0.04
0.004
Cross Dual
Cecile Limborg-Deprey
0.20
limborg@slac.stanford.edu
0.020
Injector Schedule
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Conclusion
Gained confidence in PARMELA/ASTRA
vs experiment
vs other codes
Injector computations based on large thermal
emittance (Twice the theoretical one for copper)
Discrepancy remains to be understood
Mitigation : running at 0.2 nC
Laser Pulse shaping and uniformity is critical to
reach parameter goals
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Acknowledgements
Many thanks to
S.Gierman, J.Schmerge, J.Lewellen, D.Dowell, W.Graves, T.Shaftan, Z.Huang,
J.Wu, P.Emma, S.Lydia, J.Qi, M.Ferrarrio, K.Floetmann, L.Serafini, P.Bolton,
M.Cornacchia, J.Galayda
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
4
Slice-Emittance Measurement Simulation
RF-deflector at 1 MV
y  bunch length
slice OTR 10 times
quad scanned
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Slice-Emittance Measurement Simulation
(slice-y-emittance also simulated in BC1-center)
Injector at 135 MeV with
S-band RF-deflector at 1 MV
(same SLAC slice- code used at BNL/SDL)
= meas. sim.
= calc.
= y distribution
= actual
slice-5
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
RF Gun – Mode 0 studies
120MV/m
Non-negligeable effect
Study suggested
by T.Smith
dF
3.4 MHz
8 MHz
3s, Vcath. in 0 mode
11.77 MV/m
4.96 MV/m
0.82s, Vcath. in 0mode
10 MV/m
5.7 MV/m
3.4MHz mode separation
December 3rd 2004
Solution : Klystron Pulse shaping
Theory Club: The LCLS
Injector
Study
of
From Z.Li, ACD/SLAC
8MHz mode separation
Cecile Limborg-Deprey
limborg@slac.stanford.edu
12 MHz mode separation
GTF 1.6 cell S-band gun
Laser Port
Photocathode
Currently using
a single crystal
(100) Cu cathode
“Half”
Cell
Electron
Beam
Exit
Full
Cell
0
1"
2"
3"
Scale
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
GTF 1.6 cell S-band RF gun
Waveguide Feed
LCLS Modifications:
Dual rf feed
Cathode plate with
brazed cathode plug
Load lock
120 Hz cooling
Full and ½ cell
power monitors
and remote tuners
Full Cell
Power Monitor
December 3rd 2004
Theory Club: The LCLS Injector
0
1"
2"
Scale
Cecile Limborg-Deprey
limborg@slac.stanford.edu
3"
Single Particle Dynamics
Gun
Solenoid
focusing
defocusing
defocusing
Solenoid focusing
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Search for better tuning for the 2.8 FHWM case
With 1ps rise/fall time, assuming r = 0.42 mm & Retuning
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Tolerance and stability as a function of single parameter variation
Egun 0.5%
gun 2.5 
Egun 0.5%
Solenoid 1 0.3%
Gun S1
S2 L0-1
L0-2
…
19.8MV/m 24 MV/m
December 3rd 2004
Theory Club: The LCLS Injector
Cecile Limborg-Deprey
limborg@slac.stanford.edu
Data
Slice emittance vs solenoid
strength. Charge = 200 pC.
Solenoid = 98 A
Parmela
Projected Values
(parmela in parentheses)
Solenoid
98 A
104 A
108 A
Eyn
3.7 um (3.2)
2.1 um (2.8)
2.7 um (2.7)
Alpha
0.4
Beta
1.3 m (1.3)
(1.0)
-6.9
(-3.6) -9.0
9.8 m (6.8)
45 m
(-9.6)
(36)
Solenoid = 104 A
December 3rd 2004
Theory Club: The LCLS Injector
Solenoid = 108 A
Cecile Limborg-Deprey
limborg@slac.stanford.edu