Post on 22-Dec-2015
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20071
RF Gun Commissioning Experience
David H. Dowellfor the LCLS Injector Team
Facility Advisory Committee Meeting April 16, 2007
•Description of Gun Design & Parameters•Results of Gun High-Power Tests in Klystron Lab•Installation at S20 and Pre-Beam Testing•First Photo-Beam!•Results & Observations of Initial Gun Commissioning•Summary
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20072
Z-coupling: reduces pulsed heatingincreases vacuum pumping
Racetrack to minimize quadrupole fieldsDeformation tuning to eliminate field emission from tunersIris reshaped reducing field 10% below cathodeIncrease 0-pi mode separation to 15MHzAll 3D features included in modeling:
laser port and pickup probes 3D fields used in Parmela simulation
3D RF Design of Gun
RF Parameters
f0 (GHz) 2.855987
Q0 13960
β 2.1
Mode Sep. f (MHz) 15
E0:E1 0.999:1
Slide Compliments of Z. Li & L. Xiao
C. Limborg et al., “RF Design of the LCLS Gun”, LCLS-TN-05-3β
r/m
m-0.008
-0.006
-0.004
-0.002
0.000
0.002
0.004
0.006
0.008
-180 -120 -60 0 60 120 180
rf phase
cylindrical cavity
racetrack cavity withd=0.124"racetrack cavity withd=0.14"racetrack cavity withd=0.134"β
r/m
m-0.008
-0.006
-0.004
-0.002
0.000
0.002
0.004
0.006
0.008
-180 -120 -60 0 60 120 180
rf phase
cylindrical cavity
racetrack cavity withd=0.124"racetrack cavity withd=0.14"racetrack cavity withd=0.134"
L. Xiao et al., “Dual feed rf gun design for the LCLS,” Proc. 2005 Particle Acc. Conf.
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20073
Gun-Solenoid AssemblyCut-away view of LCLS Gun
Cathode weld assembly
August 2005 LCLS RF Gun Mechanical Design Review
Compliments E. Jongewaard
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20074
Gun Design and Measured Specifications
RF Parameters Design Measured
f (GHz) 2.855987 2.855999
Q0 13960 13900
β 2.1 2.03
Mode Sep. f (MHz) 15 15.17
Field Balance 1 1Measurements compliments ofJ. Wang and J. Lewandowski
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20075
Conditioning Time to 120 MV/m& Dark Charge per RF Pulse
Conditioning of Gun-1 (Shemp) at 30Hz
40
50
60
70
80
90
100
110
120
130
9:36 12:00 14:24 16:48 19:12
Time on Nov 9, 2006
Ca
tho
de
Fie
ld (
MV
/m)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Da
rk C
ha
rge
(n
C)
Cathode Field
Dark Charge
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
80 90 100 110 120 130
Cathode Field (MV/m)
Dar
k C
har
ge
(nC
)
High-Power Gun1 Test in Klystron Lab
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20076
20
25
30
35
40
45
50
11/9/06 9:36 11/9/06 12:00 11/9/06 14:24 11/9/06 16:48 11/9/06 19:12
Date/Time
Pro
be
Tem
per
atu
re (
deg
rees
C)
Upper Probe, -55.4dB
Inner Probe, -54.7dBLower Probe, -59.5dB
Outer Probe, -60.3dB
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12
Gun FWD Power (MW)
gu
n f
wd
/ u
pp
er
pro
be
0
5
10
15
20
25
30
35
40
45
Pro
be
te
mp
era
ture
(d
eg
C)
gun fwd/upper probe
upper probetemp(degC)
Results of Gun High-Power Tests in Klystron Lab:Only concern is the heating of the RF probes
Probe external temperatures during Nov 9 conditioning to 120MV/m
Upper probe temperature and calibration vs. RF power
Therefore, the gun rate will be limited to 30 Hz during 2007 Commissioning.New probes for Gun 2 will have -75dB coupling and be copper plated.
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20077
Lowering the Gun-Solenoid Assemblyinto the Sector 20 Injector Vault
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20078
Gun-Solenoid Assembly is Home!
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 20079
y = -19890.437428x + 56842.867661
25
27
29
31
33
35
37
39
2.8559 2.85595 2.856 2.85605 2.8561 2.85615 2.8562 2.85625 2.8563 2.85635
gun frequency (GHz)
Gu
n b
od
y in
sid
e te
mp
(d
egC
)
temp at 2.856GHz = 35.78degC
Measurements: J. VanPelt, A. Vlieks, J. Wang, C. Rivetta
RF windows
Gun
4 gun probeswaveguide
flange
Network analyzer
Erik’s probepanel
Gun temperature
move analyzer cablefrom probe to probe
RF windows
Gun
4 gun probeswaveguide
flange
Network analyzer
Erik’s probepanel
Gun temperature
move analyzer cablefrom probe to probe
Pre-Beam RF Measurements and Water System Test
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200710
Gun Processed at Sector 20 to Nominal RF Power
0
2
4
6
8
10
12
14
16
18
6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5
Time (microseconds)
RF
Po
we
r (M
W)
Gun FWD Power
Gun RFL Power
Gun RF Probe
Thanks to R. Akre, B. Hong
0 2 4 6 8 10 12 14 160
50
100
150
Cathode field (MV/m)Stored energy (0.1J)
Incident power (MW)
Cat
ho
de
E (
MV
/m)
/ S
tore
d e
ner
gy*
10
12010.7
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200711
First Photo-Electrons!!!
It Works!!!
Dark Charge
Images of First Photo-ElectronsApril 5, 2007
Photo-Electrons:After adjusting laser-gun phase
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200712
Early Images of Beam on Yag01 (Gun Exit) and Yag02 (Entrance to L0a)
YAG01 YAG02
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200713
0
2
4
6
8
10
12
14
16
18
6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5
Time (microseconds)
RF
Po
we
r (M
W)
Gun FWD Power
Gun RFL Power
Gun RF Probe
Optimized Macropulse Timing in RF Waveform by Measuring Beam Energy vs. Gun Delay
RF Delay (ns)
Be
am
Mo
me
ntu
m (
Ge
V/c
)
Set Timing Here for Max Energy
•Used measurement to calibrate RF system (Gun RF probes)
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200714
Schottky Scan of Gun Phase Relative to Laser
Zero Crossing of RF Field
Optimum Launch Phase
30deg
Measurement: H. Loos, April 13, LCLS e-log
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200715
0 50 100 150 200 250 300 350 4000
100
200
300
400
500
600
Drive Laser Energy (microJoules)
Gu
n C
har
ge
(pic
oC
ou
lom
bs)
Beam Charge vs. Drive Laser Energy & Launch Phase:Schottky Enhancement of QE
Launch Phase at 30 degrees
Launch Phase at 85 degreesfrom zero crossing
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200716
Regen pockel cell delay = 300.0680 microSecRegen pockel cell delay = 300.0650 microSec
Precise Adjustment of Regenerative Amplifier Pockel Cell Timing is Crucial
measurements: B. White et al., LCLS e-log, April 11, 2007
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200717
YAGG1, Gun Spectrometer
~100keV
YAG01, ~50cm from cathode
YAG02, ~80cm from cathode
Beam Momentum = 4.3 MeV/c
measurements: H. Loos & J. Welch, LCLS e-log, April 13, 2007
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200718
Virtual Cathode Camera YAG01
E-Beam Appears to Preserve the Laser’s Spatial Fluctuations
Laser Image: S. Gilevich et al., LCLS e-log, April 2007
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200719
YAG01 YAG02
Images compliments of P. Emma & R. Iverson, LCLS e-log, April 13, 2007
YAG03
L0a
Gun & Solenoid
Evolution of Beam Along Injector
David H. Dowelldowell@slac.stanford.eduRF Gun Commissioning
LCLS FAC April 16, 200720
SummaryGun is operational at Sector 20:
RF conditioning completeWater temp and LLRF control loops operatingProviding beam for injector commissioningHigh level S/W applications being implemented
Technical Issues:Gun RF probe heating limits gun operation to 115MV/m and 30 Hz. This is fixed on Gun2.Progress hindered by non-functioning, critical diagnostics!!QE is 2 to 4 times lower than expected
Plan for cathode cleaning
Gun-Solenoid assembly appears to be pointing down and to right