David H. Dowell [email protected] RF Gun Commissioning LCLS FAC April 16, 2007 1 RF Gun...

David H. [email protected] 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



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.



Gun-Solenoid AssemblyCut-away view of LCLS Gun

Cathode weld assembly

August 2005 LCLS RF Gun Mechanical Design Review

Compliments E. Jongewaard



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



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



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.



Lowering the Gun-Solenoid Assemblyinto the Sector 20 Injector Vault



Gun-Solenoid Assembly is Home!



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



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



First Photo-Electrons!!!

It Works!!!

Dark Charge

Images of First Photo-ElectronsApril 5, 2007

Photo-Electrons:After adjusting laser-gun phase



Early Images of Beam on Yag01 (Gun Exit) and Yag02 (Entrance to L0a)

YAG01 YAG02



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)



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



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



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



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



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



YAG01 YAG02

Images compliments of P. Emma & R. Iverson, LCLS e-log, April 13, 2007

YAG03

L0a

Gun & Solenoid

Evolution of Beam Along Injector



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

David H. Dowell [email protected] RF Gun Commissioning LCLS FAC April 16, 2007 1 RF Gun...

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