1. LCLS Drive Laser Timing Stability Measurements
Department of Energy Review of the Linac Coherent Light Source (LCLS) Project Breakout - SC5 Control Systems August 11, Ron Akre

2. LCLS Machine Stability Tolerance Budget
Lowest Noise Floor Requirement
0.5deg X-Band = 125fS
Structure Fill time = 100nS
Noise floor = 11GHz 5MHz BW
476MHz
X-band X-
RMS tolerance budget for <12% rms peak-current jitter or <0.1% rms final e− energy jitter. All tolerances are rms levels and the voltage and phase tolerances per klystron for L2 and L3 are Nk larger, assuming uncorrelated errors, where Nk is the number of klystrons per linac.
P. Emma

3. LINAC RF and Timing System
LCLS must be compatible with the existing linac operation including PEP timing shifts
Master Oscillator is located 1.3 miles from LCLS Injector
1.3 Miles to LCLS Injector
PEP PHASE SHIFT ON MAIN DRIVE LINE
MDL RF with TIMING Pulse – Sync to DR

4. Linac Phase Reference System
Main Drive Line - 3 1/8 Rigid Coax Anchored to Concrete Floor Every Sector
Phase Reference Line - Each Sector Independent 1/2 “ Heliax
Must not introduce noise over 2 miles

5. Linac Phase Reference System
Phase Reference Line
½ inch Heliax Cable with 1.2 Watts
Phase Reference for 8 PADs (Klystrons) in the sector
Length = 1 Sector, 0.5 furlongs, 332ft, 400kS in ½” Heliax
Temperature Coefficient 4ppm/C
Waveguide Water T = 0.1C rms
85% of the cable is regulated to 0.1C rms
15% may see variations of 2C rms
Average Temperature Variation = 0.4C rms
 = 0.64S rms
Main Drive Line
3 1/8 inch Rigid Coax with 30watts input power 30mW out
Length = 31 Sectors, 15.5 furlongs 2miles, 3km : Velocity = 0.98c
Anchored at each sector next to coupler and expansion joint
Purged with dry nitrogen
Phase Length Range 100S/Year
Phase Length Range 40S/Day
Accuracy Based on SLC Fudge Factor
0.5S/Sector Total Variation
0.2S rms / Sector

6. Phase Noise of SLAC Main Drive Line
Old Oscillator
New Oscillator
Noise Floor -120dBc/38Hz = -136dBc/Hz = 120fS rms Jitter in 5MHz BW
Noise Floor -133dBc/38Hz = -149dBc/Hz < 60fS rms Jitter in 5MHz BW
New Oscillators Have a noise floor of 476MHz
11fS rms Jitter in 5MHz BW or 31fS rms Jitter in 40MHz BW
Above plots give upper limits, much of which could be from measurement system

7. Phase Noise of SLAC Main Drive Line
Old Oscillator
New Oscillator
New Oscillators Have a noise floor of 476MHz
11fS rms Jitter in 5MHz BW or 31fS rms Jitter in 40MHz BW
Above plots give upper limits, much of which could be from measurement system

8. SLAC Linac RF
The PAD measures phase noise between the reference RF and the high power system. The beam sees 3.5uS of RF from SLED cavity which the klystron fills and is then dumped into the accelerator structure.

9. LINAC RF MEETS ALL LCLS SPECIFICATIONS
for 2 Seconds when running well
Amplitude fast time plots show pulse to pulse
variation at 30Hz. Standard deviation in percent
of average amplitude over 2 seconds are
0.026% for 22-6 and 0.036% for 22-7.
Phase fast time plots show pulse to pulse variation
at 30Hz. Standard deviation in degrees of 2856MHz
over 2 seconds for the three stations are
0.037 for 22-6 and 0.057 for 22-7.

10. LINAC RF is Out of LCLS Specs in 1 Minute
Phase
22-6
1.2 Deg pp
Amplitude
22-6
0.20%pp
Amplitude
22-7
0.43%pp
Phase
22-7
1.2 Deg pp
14 minutes data taken using the SCP correlation plot
Note that 22-6 and 22-7 are correlated in phase and amplitude
They also track the temperature of the water system

11. Phase as Seen by Electron is Difficult to Measure
Accelerator Water Temperature Effects on SLED Phase[1]
The tuning angle of the SLED cavity goes as:
 = tan -1 (2QLT), Where T = L/L = -/
QL= = 10-5 / F Thermal expansion of copper.
=tan -1 (0.34T) Where T is in F.
For small T, (S)= 20T(F)
The relation between the tuning angle  and the measured output phase of the klystron 
varies with the time after PSK with about the following relation:
 /  = 0.35 just after PSK (S)= 7T(F)
 /  = nS after PSK (S)= 10T(F)
 / T~ +8.5 S / F for SLED Cavity
Accelerator Water Temperature Effects on the Accelerator Phase[2]
The phase change of the structure goes as follows:
 =  f Where  = phase through structure
 = Angular frequency
f = Filling time of structure
 =  f = / x f / = -L/L = -T = T / F for copper
 = T / F22856MHz0.84S = T rad/F = -8.6 T S / F
 / T = -8.6 S / F for Accelerator Structure
Water / Accelerator Temperature Variation is 0.1F rms
 through structure is 0.86F rms
[1] Info from D. Farkas
[2] Info from P. Wilson

12. Phase as Seen by Electron is Difficult to Measure
Accelerator Water Temperature Effects on the Phase Through the Accelerator -8.6 S / F
SLAC Linac Accelerator Water Temperatures T< .08Frms
Phase Variations Input to Output of Accelerator > 0.5ºS-Band rms
Single Measurement Can’t Determine the Phase the Beam Sees Passing Through the Structure to LCLS Specifications
Feedback on Input Phase, Output Phase, Temperature, Beam Based Parameters (Energy and Bunch Length) is Required to Meet LCLS Specifications

13. LINAC SECTOR 20 – LCLS INJECTOR
RF Stability < 50fS rms : Timing/Trigger Stability 30pS rms
Using LASER as LCLS RF OSCILLATOR is UNDER CONCIDERATION

14. LCLS RF System – Sector 20 Layout
100ft ½” Heliax = 0.3ºS/ºF
Tunnel Temperature < 0.1deg F rms

15. SPPS Laser Phase Noise Measurement
R. Akre, A. Cavalieri

16. SPPS Laser Phase Noise Measurements
Phase Noise of Output of Oscillator with Respect to Input
Measurement done at 2856MHz with External Diode
Need to verify these results and check calibration
R. Akre, A. Cavalieri

17. SPPS Laser Amplitude of Phase Transfer Function
Phase Modulation placed on RF Reference and measured on Diode at Laser output.
During the Blue part of the curve the modulation amplitude was reduced by 12dB to prevent laser from unlocking. Data taken 10/22/ R. Akre, A. Cavalieri

18. SPPS Laser Phase Jump Tracking
R. Akre, A. Cavalieri

19. SPPS Laser Phase Jump Tracking
Laser Phase Error – Output Phase to Input Reference - Modulated with 1 Hz Square Wave
0.25pS pk Square Wave
2.0pS pk Square Wave

20. Linac Phase Stability Estimate Based on Energy Jitter in the Chicane
BPM
SLAC Linac
1 GeV
30 GeV
9 GeV
e- Energy (MeV)
sE/E0  0.06%
Df 21/2 < 0.1 deg (100 fs)
P. Emma

21. Electro-Optical Sampling
Timing Jitter
(20 Shots)
200 mm thick ZnTe crystal
Single-Shot e-
<300 fs
Ti:Sapphire laser
e- temporal information is encoded on transverse profile of laser beam
170 fs rms
Adrian Cavalieri et al., U. Mich.

22. LCLS Phase Noise Associated Time Referenced to Beam Time
LCLS Laser ~200uS Off Scale Below
LCLS Gun uS
SLED / Accelerator 3.5uS
Phase Detector (Existing) 30nS
Distribution System 200nS
c-97%c=100nS
Far Hall Trigger 2uS
c-80%c=2uS
Except for the LASER common mode noise levels below ~100kHz would not cause instabilities – the entire system would track the deviations
-3.5us SLED Starts to Fill
-2uS Far Hall Trig
RF Starts Trip
-1.1uS Gun Starts to Fill
Beam Time 0
Reference
TIME

23. Beam Trigger for User Facility
Single Pulse with 30fS stability (1Hz to 3GHz BW)
Tightest Noise Tolerance of LCLS
Wide Bandwidth
Low Phase Noise
30fS Stability today
10fS Stability tomorrow
1fS The Day After
Currently users are expected to use local beam timing measurement, EO, to achieve this.

24. FY04 Tasks Complete phase measurement system
Complete measurements in the SLAC front end
Preliminary design for SLAC linac RF upgrade
Complete Design of 1kW Solid State S-Band Amp

25. FY05 Tasks and Resources Ready to Ramp Up
Start on X-Band system
Complete SLAC Linac Front End Upgrades
Complete Design of Phase Reference System
Complete Design of LLRF Control System
Define Beam Phase Cavity Monitor
Further Studies on Linac Stability
SLAC Klystron Department to Support 75% of RF manpower
Manpower available from other SLAC groups (ARDA, ARDB, NLC, and Controls) and LBNL