SLIDE 1
Outline
- MO System Description
- Performance
Phase Jitter – Energy Spread Phase Drift – Beam Energy Amplitude Stability – Beam Energy/ Gradient Calibration
- Monitoring and Maintenance
- Future Plans
Tomasz Plawski Jefferson Lab OPS Stay Retreat, July 15th, 2015 - - PowerPoint PPT Presentation
Tomasz Plawski Jefferson Lab OPS Stay Retreat, July 15th, 2015 - - PowerPoint PPT Presentation
MO/LO Performance Summary and Maintenance Plans Tomasz Plawski Jefferson Lab OPS Stay Retreat, July 15th, 2015 Outline MO System Description Performance Phase Jitter Energy Spread Phase Drift Beam Energy Amplitude Stability
SLIDE 2
SLIDE 3
MO System Description
SLIDE 4
Performance
Why MO performance is important ? Master/Local oscillators used for two purposes:
- down/up-conversions
- clock synthesis for ADC and DAC in digital LLRF systems or
phase reference in analog LLRF ones are the largest contributors of uncorrectable inaccuracies of cavity accelerating field !
SLIDE 5
Performance – Phase Noise
LLRF stability requirements:
Correlated Uncorrelated Amplitude RMS error 2.2 x 10-5 4.5 x 10-4 Phase RMS error 0.25° 0.5°
499 MHz LO / R&S +B22 option 340 fs (shown) will cause 180 mdeg of phase noise on 1427 MHz LO signal Slight Concern: FM modulation used for path control (CEBAF circumference can change significantly) rises phase noise up to 230 mdeg 10/70 MHz MO / Wenzel Associates, Inc. and CDCM7005 based system for DLLRF Slight Concern: PM modulation used for Beam-Based Phase Stabilization, rises phase noise by about 70 mdeg
SLIDE 6
Performance – Phase Drift
Drift Mitigation
- Linac, Injector LO and MO lines temperature stabilization
- Precision Beam-Based RF Phase Stabilization
- Hall D Phase Drift Monitor ( New optical fiber based RF distribution system)
- Service Building Temperature Control
- Careful Selection of RF Cables
Weakness
Phase drift between Injector and NL uncontrolled Phase drift between MCC and W1/W2 uncontrolled
Possible improvements
- Phase feedback between MCC and local MO chassis
- Well-known good solution, Phase Averaging Line, is not practical for CEBAF
SLIDE 7
Performance – Amplitude Stability
The concern is amplitude stability of LO signal used for RF signals heterodyning in LLRF systems
Typically for C100 - DLLRF Systems: 1 % of LO amplitude variation will cause 0.25 % of cavity gradient variation !
18 % of LO level drop level adjustment
May 2015 NL LO events
repair
Problem has been fixed by increasing 499 MHz signal level before frequency trippler rather than adjusting 1427 MHz drive signal level Why it happened ? We have different “flavor” of 1427 MHz synthesizer while drive level was set identically Future mitigation:
- Documentation updates
- Diagnostic/ repair plans
SLIDE 8
Performance – Amplitude Stability
LO Amplifier Specification
LCW temperature LO level [mV]
- Max. cooling water temperature for 500 W Bruker amplifier is 35° C ( 95°F) !
We learned it by experiencing the consequences. Impending plans:
- LCW 19” Rack Mount Water Chiller ( temp. stability ± 0.1 °C) - 4 local MO racks
SLIDE 9
Performance – Amplitude Stability
Amplitude Stability
LCW temperature LO level [mV]
Recent LO level ( LOPW) stability is 0.5% thus gradient measurement may vary by 0.13% Installation of LCW chiller may reduce this number down to 0.01% . At this accuracy contribution of other RF system components will overcome this value. Considered option : LO Amplifier Automatic Gain Control Pros: keep amplitude stable Cons: could and will cause phase shift
SLIDE 10
What else can be done ?
- Increase LO signal level by 1 dB ( from 250 W to 320 W) for better LLRF mixer
“saturation” in order to reduce modulation index ( currently .25) Pros: Reduction of modulation index from .25 down to ~ .15 Cons: All LLRF system will required re-calibration
SLIDE 11
Monitoring and Maintenance
- Every LLRF system contains LO and MO power detector and these signals
are archived
- LO lines temperatures are controlled and monitored
- Since phase measurement is relative we can’t monitor LO/MO phases
unless feedback loop will be added ( Hall D case)
- MO diagnostic chassis + software provide some level of diagnostic for MCC
located MO system
- Most critical spare parts are stored and occasionally tested
SLIDE 12
Future Plans
- LCW 19” Rack Mount Water Chiller ( temp. stability ± 0.1 °C) - 4 local MO
racks
- Remove obsolete EIPCS Screens
SLIDE 13
Thank you for your attention !
Special thank to Larry Farrish and Clyde Mounts for continued support of MO operation.
SLIDE 14
Backup Slides
SLIDE 15
LO Line Coupler
SLIDE 16
Expected Phase drift:
LFC78-50J-TC
RF cable
SLIDE 17