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
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LCLS Machine Stability Tolerance Budget
Lowest Noise Floor Requirement 0.5deg X-Band
125fS Structure Fill time 100nS Noise floor
-108dBc/Hz _at_ 11GHz 5MHz BW -134dBc/Hz _at_ 476MHz
RMS tolerance budget for lt12 rms peak-current
jitter or lt0.1 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
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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
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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

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Linac Phase Reference System

• 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

• 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

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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 lt 60fS rms
Jitter in 5MHz BW
New Oscillators Have a noise floor of -157dBc/Hz
_at_ 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
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Phase Noise of SLAC Main Drive Line
Old Oscillator
New Oscillator
New Oscillators Have a noise floor of -157dBc/Hz
_at_ 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
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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.

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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.
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LINAC RF is Out of LCLS Specs in 1 Minute
Phase 22-6 1.2 Deg pp
Amplitude 22-6 0.20pp
Amplitude 22-7 0.43pp
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
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Phase as Seen by Electron is Difficult to Measure
Accelerator Water Temperature Effects on SLED
Phase1 The tuning angle of the SLED cavity goes
as ?? tan -1 (2QL??T), Where ??T ?L/L
-??/? QL 17000 ? 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) ?? / ?? 0.50 800nS after PSK ??(?S)
10?T(?F) ?? / ?T 8.5 ?S / ?F for SLED
Cavity Accelerator Water Temperature Effects on
the Accelerator Phase2 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 -10-5 ?T / ?F for
copper ?? -10-5 ?T / ?F?2??2856MHz?0.84?S
-0.15 ?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
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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 ?Tlt
  .08?Frms
• Phase Variations Input to Output of Accelerator gt
  0.5ºS-Band rms
• Single Measurement Cant 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

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LINAC SECTOR 20 LCLS INJECTOR
RF Stability lt 50fS rms Timing/Trigger
Stability 30pS rms Using LASER as LCLS RF
OSCILLATOR is UNDER CONCIDERATION
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LCLS RF System Sector 20 Layout
100ft ½ Heliax 0.3ºS/ºF Tunnel Temperature lt
0.1deg F rms
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SPPS Laser Phase Noise Measurement
R. Akre, A. Cavalieri
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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
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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
R. Akre, A. Cavalieri
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SPPS Laser Phase Jump Tracking
R. Akre, A. Cavalieri
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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
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Linac Phase Stability Estimate Based on Energy
Jitter in the Chicane
BPM
9 GeV
sE/E0 ? 0.06
?Df 2?1/2 lt 0.1 deg (100 fs)
P. Emma
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Electro-Optical Sampling
Timing Jitter (20 Shots)
200 mm thick ZnTe crystal
Single-Shot
e-
lt300 fs
TiSapphire laser
e- temporal information is encoded on transverse
profile of laser beam
170 fs rms
Adrian Cavalieri et al., U. Mich.
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LCLS Phase Noise Associated Time Referenced to
Beam Time

• LCLS Laser 200uS Off Scale Below
• LCLS Gun 1.1uS
• SLED / Accelerator 3.5uS
• Phase Detector (Existing) 30nS
• Distribution System 200nS
• 1km _at_ c-97c100nS
• Far Hall Trigger 2uS
• 3km _at_ c-80c2uS

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
-1.1uS Gun Starts to Fill
-2uS Far Hall Trig RF Starts Trip
Beam Time 0 Reference
TIME
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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.

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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

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FY05 Tasks and ResourcesReady 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