1. LCLS RF Stability Requirements
LCLS Requirements
The SLAC Linac
SLAC Linac Stability Data
SPPS Measurements
LCLS RF System

2. LCLS INJECTOR / LINAC
P. Emma

3. 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

4. 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

5. 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.

6. 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.

7. 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

8. Linac Phase Reference System
Main Drive Line - 3 1/8 Rigid Coax Anchored to Concrete Floor Every Sector
Phase Reference Line - Each Sector Independent ½ inch Heliax
MDL 200fS rms / Sector
PRL 640fS rms

9. 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

10. 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

11. 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

12. 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
LASER to BEAM
Jitter
Adrian Cavalieri et al., U. Mich.

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

14. SPPS Laser Phase Jump Tracking ~ 200uS
Laser Phase Error – Output Phase to Input Reference - Modulated with 1 Hz Square Wave
0.25pS pk Square Wave
2.0pS pk Square Wave

15. 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 10/22/03

16. 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

17. RF Distribution Phase Noise
New Master Oscillator in Linac Front End
Less than 25fS rms jitter in Bandwidth from 38Hz to 5MHz
R. Akre, K. Schaffold

18. RF Distribution Phase Noise
Integrated Noise - Timing Jitter fs rms
Integral end 5MHz 10kHz
Integral start 1M 100k 10k 1k
Master Osc
PEP Phase
Master Amp
MDL
Sector miles
Need to lower phase noise in PEP Phase Shifter and Master Amplifier

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

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

21. 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.

22. LCLS RF System Injector RF – FY06 X-Band RF system – FY06
Upgrade of existing system / Lower Noise Timing requirements
Injector/L1 Phase Reference System
Phase and Amplitude measurement system
Solid State Sub-Boosters
Beam Phase Monitor System
X-Band RF system – FY06
Linac Phase Reference System – FY07
Linac Feedback Control – FY07
Feedback Development – FY07
Far Hall Trigger – FY08

23. Near Term (6 Month) Tasks
Measure Phase Noise of SPPS Laser
Lower phase noise in PEP phase shifter and Master Amplifiers
Determine Type of RF Phase and Amplitude Measurement System

24. FY05/06 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