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LCLS Drive Laser Timing Stability Measurements

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LCLS Drive Laser Timing Stability Measurements

Department of Energy Review of theLinac Coherent Light Source (LCLS) ProjectBreakout - SC5 Control SystemsAugust 11, 2004Ron Akre

X-

X-band

Lowest Noise Floor Requirement

0.5deg X-Band = 125fS

Structure Fill time = 100nS

Noise floor = -108dBc/Hz @ 11GHz 5MHz BW

-134dBc/Hz @ 476MHz

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

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

- 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

- 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, 400kS in ½” Heliax
- Temperature Coefficient 4ppm/C
- Waveguide Water T = 0.1C rms
- 85% of the cable is regulated to 0.1C rms
- 15% may see variations of 2C rms
- Average Temperature Variation = 0.4C rms
- = 0.64S 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 100S/Year
- Phase Length Range 40S/Day
- Accuracy Based on SLC Fudge Factor
- 0.5S/Sector Total Variation
- 0.2S rms / Sector

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 -157dBc/Hz @ 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

Old Oscillator

New Oscillator

New Oscillators Have a noise floor of -157dBc/Hz @ 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

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.

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.

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

Accelerator Water Temperature Effects on SLED Phase[1]

The tuning angle of the SLED cavity goes as:

= tan -1 (2QLT), Where T = L/L = -/

QL= 17000= 10-5 / F Thermal expansion of copper.

=tan -1 (0.34T)Where T is in F.

For small T, (S)= 20T(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:

/ = 0.35just after PSK (S)= 7T(F)

/ = 0.50800nS after PSK (S)= 10T(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:

= fWhere = phase through structure

= Angular frequency

f = Filling time of structure

= f = / x f/ = -L/L = -T = -10-5 T / F for copper

= -10-5 T / F22856MHz0.84S = -0.15 T rad/F = -8.6 T S / F

/ T = -8.6 S / F for Accelerator Structure

Water / Accelerator Temperature Variation is 0.1F rms

through structure is 0.86F rms

[1] Info from D. Farkas

[2] Info from P. Wilson

- Accelerator Water Temperature Effects on the Phase Through the Accelerator-8.6 S / F
- SLAC Linac Accelerator Water TemperaturesT< .08Frms
- 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

RF Stability < 50fS rms : Timing/Trigger Stability 30pS rms

Using LASER as LCLS RF OSCILLATOR is UNDER CONCIDERATION

100ft ½” Heliax = 0.3ºS/ºF

Tunnel Temperature < 0.1deg F rms

R. Akre, A. Cavalieri

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

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 R. Akre, A. Cavalieri

R. Akre, A. Cavalieri

Laser Phase Error – Output Phase to Input Reference - Modulated with 1 Hz Square Wave

0.25pS pk Square Wave

2.0pS pk Square Wave

SLAC Linac

1 GeV

30 GeV

e- Energy (MeV)

BPM

9 GeV

sE/E0 0.06%

Df 21/2< 0.1 deg (100 fs)

P. Emma

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.

- LCLS Laser~200uS Off Scale Below
- LCLS Gun1.1uS
- SLED / Accelerator 3.5uS
- Phase Detector (Existing)30nS
- Distribution System200nS
- 1km @ c-97%c=100nS

- Far Hall Trigger2uS
- 3km @ 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

- 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.

- 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

- 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