Post on 11-Jan-2016
RF Commissioning
Andy Butterworth BE/RFThanks to: J. Tuckmantel, T. Linnecar, E. Montesinos, J.
Molendijk, O. Brunner, P. Baudrenghien, L. Arnaudon, P. Maesen, F. Dubouchet, D. Valuch, D. Van Winkle, C.
Rivetta and many others
Outline• Introduction• Equipment checkout• Warm commissioning• Cavity conditioning• LLRF commissioning• Data acquisition and diagnostic tools• Controls• Summary
Introduction• Based on experience with LHC and LEP SC RF
commissioning• Assumptions:
– Power plant derived from 800MHz IOT amplifier system currently being specified for the SPS Landau cavities
– Low Level RF similar to the LHC 400MHz system– Controls derived from LHC and SPS RF and integrated into
the LHC control system
Introduction: LHC and SPS systems• LHC acceleration system: 16 SC cavities @ 400MHz
– each driven by 300kW klystron• Power system (slow controls) using PLCs
– high voltage power supplies, klystrons, RF power distribution, cryostats and ancillary equipment
• Low Level system (Cavity servo controller and Beam Control)– digital, FPGA at 80 MS/s, DSP for turn-by-turn (11 kS/s)– in parallel with fast analog for transient beamloading– 2 VME crates per cavity
• SPS Landau cavity system: 2 travelling wave cavities @800 MHz– each driven by 4 x 60kW IOT amplifiers (currently in
procurement)
Commissioning: Equipment check-out• RF and control cables: individual testing
– reflection (short circuit) for cable identification and initial validation
– transmission for phase sensitive signals– reflection tests with termination to assess
damage, faulty connectors etc. – > 100 cables per cavity in LHC...
• Control racks equipped and tested in lab– after installation, signals test up to PLC control
level• Data exchange with vacuum, power
converters, cryogenics• Interlock system: individual test and
validation, access, radioprotection
D. Valuch
Warm commissioning: amplifier• Initial commissioning of power amplifiers done during
reception testsTechnical Specification for
the Power Amplifier for the SPS 801 MHz RF system
12.8 Site acceptance tests•48 hour full power operational test, during which the frequency, phase, linearity, output power, stability and efficiency will be monitored.•Measurement of gain.•Output voltage and current.•Output voltage ripple at specified frequency ranges.•Power factor at full output.•Harmonic injection into the mains supply at selected levels including full output.•Time taken to switch to zero output on receipt of the ‘fast switch-off’ command.•Energy deposited into a short-circuited output.•Effectiveness of internal protection circuits.•Temperature rise during ‘soak’ operation at full power of transformers, inductors and semi-conductors.•Compliance with electromagnetic noise requirements (includes RF, x-rays).•Compliance with acoustic noise requirements.•Purity of IOT RF spectrum.•Thermal run.•Reproducibility check.•Harmonic analysis.•Inrush current measurement.•Power factor correction test.•Mains regulation tests.•Line regulation tests.•High voltage DC test to be carried out at an over-voltage to be agreed.•Power Amplifier RF tests.•etc...
Warm commissioning• ... of complete power system with RF
– waveguides short-circuited to isolate cavities
• HV and RF interlocks: individual tests– water flows, WG arc detectors etc
• Bring amplifier slowly to full RF power– calibration of power measurements (directional couplers)
and attenuators for signal distribution– test and adjust circulator and load
• Long-term power test (100 hours)
If SPS type 800MHz power plant is used, most of the procedures will already be well defined
Low power measurements
• ... on cold cavities• to confirm measurements
from test stand– loaded Q– tuning range
• using resonant frequency and bandwidth measurements with network analyser– drive signal injected via coaxial
transition on waveguide– return signal from cavity field
measurement antenna
We can now remove the short circuit and proceed with high power testing...
High power tests: cavity conditioning• Run cavity up to full power and voltage while observing
vacuum and cavity field emission• Vacuum
– in practice, we are looking at the vacuum in the main input coupler
– difficult to see outgassing in cavity (pumped by the cold surfaces)
• Field emission in the cavity– shows as He pressure excursions RF trips– in LEP, feedback on X-ray emission was possible (total
cryomodule voltage of 40MV)– radiation not detectable in LHC (single cavity, 2MV)
• The input couplers are equipped with a DC bias voltage to suppress multipacting during normal operation: this is switched OFF during conditioning
Cavity conditioning method• Pulsed FM modulated RF power is applied to the cavity in a
controlled way with vacuum feedback• Two loops
– Fast vacuum feedback– Slow computer controlled loop to generate AM envelope and increase
field and power as conditioning progresses (pulse to pulse at 50Hz)
rate of rise rate of fall
flat-top
Total Envelope <= 90sRep-rate 20ms pulse width: 10,20,50us thru 1,2,5,10ms,CW
RF Power0 thru 300kW
Programmable Conditioning Envelope (Not to scale)
J. Molendijk
Cavity conditioning method
Increase Power using a fixed pulsewidth until Pmax is reached.
Increase Pulse width and proceed with the Power as above.
Finish with CW and proceed with the Power as above.
A
B
C
J. Molendijk
Conditioning: Implementation• Conditioning system is fully integrated in LHC Low Level RF
Cavity Controller
Tuner Loop
Switch & Limit
Conditioning DDS
VME CPU
J. MolendijkCavity Controller Tuner/Klystron crate
J.C. Molendijk - CWRF2008 142008-03-27
The Conditioning DDS Module
500MHz Synthesizer
(DDS clock)
4 Channel DDSRF Summing & Gain Control
RF Generator 1
RF Generator 2
Vacuum Loop CPLD
J.C. Molendijk - CWRF2008 15 2008-03-27
Conditioning DDS – I/Q plot of Dual FM sweepsIcFwd
-2500
-2000
-1500
-1000
-500
0
500
1000
1500
-3500 -3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500 3000 3500
I
Q
Actual Data Obtained from Forward Current, I/Q memory in the Tuner loop module
LHC SC RF Conditioning GUI
Envelope & Power
Vacuum Loop
Dual FM Generator & Status
Pulse
Global
Cavity V gapCavity P Fwd
Cont
rols
J. Molendijk/F. Dubouchet
Conditioning: Summary• Typical conditioning time to full power and voltage
for an LHC cavity was a few days to 1 week• Highly automated, but still requires regular human
supervision to adjust parameters• Integrated conditioning system in LLRF hardware has
proved very efficient, and allows conditioning of multiple cavities in parallel
• Main power coupler DC bias switched on only after conditioning
Cavity Servo Controller. Simplified Block Diagram
Technology: DSP
CPLD or FPGA (40 or 80 MHz) Analog RF
Signals: Digital:
Analog:
Digital I/Q pair:
Analog I/Q pair:
X
Digital IQ
Demod
SUM
Tuner Processor
X
Digital IQ
Demod
Dir. Coupler
Single-Cell Superconducting
Cavity
Fwd
Rev
X
Digital IQ
Demod
DAC
Digital RF feedback (FPGA)
1 kHz
60 dB
From long. Damper
Voltage function
I0
Q0
dpdV
Set Point Generation
DA
C
Phase Equalizer
ADCDAC
SUM
Vcav
SUM
SUM
Analog RF feedback
1 kHz
20 dB40 dB
1-Turn FeedforwardWideband
PUDAC ADC
An
alog IQ
Dem
odulator
Ic fwd
X
Digital IQ
Demod
Ic rev
TUNER LOOP
SET POINT
RF FEEDBACK
RF MODULATOR300 kW Klystron
Circ
Ig fwd
Analog IQ
D
emodulator
QI
ANALOG DEMOD
Klystron Polar Loop (1 kHz BW)
AD
C
Gain CntrlSUM
Baseband Network Analyzer
DA
C
noise
X
Digital IQ
Demod
X
Digital IQ
Demod
1-Turn Feedback
Tuner Control
Ic fwd
CONDITIONING DDS SWITCH/PROTECTION
SWITCH
Master F RF
Analog IQ
M
odulator
RF Phase Shifter
Phase Shift
Var G
ain RF
A
mpifier
-
LHC cavity Low Level
Low Level RF commissioning• Tuner loop
– tuner phase adjustment to set the cavity on tune when the loop is closed
• RF feedback– phase alignment of digital and analog feedback branches– adjustment of feedback gain and phase before closing loop– measure closed loop response: important for
• beam loading response• cavity impedance seen by beam• bandwidth of cavity voltage control
– measure phase noise
• Amplifier phase/amplitude loop– adjust gain and phase setpoints– adjust dynamic loop responses
Lots of work with a network analyser, but new tools are at hand...
LLRF embedded data acquisition • All LHC LLRF boards have on-
board signal recording memory
• 2 parallel sets of buffers:– Post-Mortem capture– User “Observation”
• 64 turns @ 40Ms/s 128kB/signal
• Revolution frequency tagging
RF feedback board
“Baseband network analyzer” (BBNWA)
• Loops excited with noise• Output signals recorded
digitally• Transfer function
estimate program calculates frequency domain transfer function
• “Fit” an idealized linear model to the measured data and calculate recommended adjustments
0 500 1000 1500 2000 2500 3000 3500 4000 4500-2000
0
2000
Sample #
Cou
nts
White Noise Kernel
0 0.5 1 1.5 2 2.5 3
x 105
-1
0
1
I-O
utpu
t (N
orm
.)
I-Output Signal
0 0.5 1 1.5 2 2.5 3
x 105
-1
0
1
Sample #
Q-O
utpu
t (N
orm
.)
Q-Output Signal
• LLRF boards also have embedded memory buffers for “excitation data”: can inject signals into the loops
D. Van Winkle
MATLAB tools for remote setting-up of LLRF developed with US-LARP collaborators (D. Van Winkle, C. Rivetta et al.)
RF feedback alignment in the comfort of your home
Page 22
Open Loop Alignment
-60 -40 -20 0 20 40 60-80
-70
-60
-50
Frequency (kHz)
Gai
n (d
B)
Measured Magnitude and Phase with Fit of Open Loop
Fit
Data
-60 -40 -20 0 20 40 60-400
-200
0
200
Frequency (kHz)
Pha
se (
degr
ees)
0.0005
0.001
0.0015
0.002
30
210
60
240
90
270
120
300
150
330
180 0
Polar Plot of measurement and Fit of Open Loop
-60 -40 -20 0 20 40 60-80
-70
-60
-50
Frequency (kHz)
Gai
n (d
B)
Measured Magnitude and Phase with Fit of Open Loop
Fit
Data
-60 -40 -20 0 20 40 60-400
-200
0
200
400
Frequency (kHz)
Pha
se (
degr
ees)
0.0005
0.001
0.0015
0.002
30
210
60
240
90
270
120
300
150
330
180 0
Polar Plot of measurement and Fit of Open Loop
Un-Aligned Open Loop Response and Model Fit (SM18)
D. Van Winkle
BBNWA contd.• Comparison of closed loop response measured with
instrument vs. embedded BBNWA measurements
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-20
-15
-10
-5
0
5
10
Frequency (MHz)
Gai
n (d
B)
Closed Loop measure in SM18 (BBNA)
Network analyzer (Agilent) BBNWA
D. Van Winkle
Frequency (MHz)
Automated tuner setup• MATLAB script for Automatic setup of tuner loop
Tuner sweep to find resonance
Sweep across resonance with different phase shifter values
Converge to optimum phase
LLRF: Summary• It took almost 1 month to set up the Low-Level RF of
the first cavity • Once the procedures were well defined, the last few
cavities took about 1 day each
• New automated tools using MATLAB and the BBNWA feature of the LLRF hardware will save a lot of time
Many thanks to our US-LARP colleagues from SLAC
Controls and software• PLCs and Low-Level crates
interfaced via FESA (Front End Software Architecture)– a “FESA class” software module
is written for each type of equipment
– communication via the CERN Controls Middleware
• Application software:– LabView expert synoptic panels– Matlab scripts for more
sophisticated specialist applications
– LSA (standard machine operations software) manages settings and sequencing
– Logging and Post Mortem– Alarms (LASER)– ...
Summary• Power system commissioning procedures will be well
known if using existing power source (SPS type 800MHz)
• Controls and application software should be based on standard CERN controls infrastructure
• LHC low-level electronics has built-in conditioning and diagnostics facilities, and is already well integrated into the control system
• Powerful tools are being developed for LLRF setting-up which could equally be applied to the crab cavity system