RF measurements in CTF3: Phase Calibration and Jitter Alexey Dubrovskiy inputs from Franck Tecker, Luca Timeo and Stephane Ray CLIC/CTF3 experimental verification meeting 08.07.2014
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RF measurements in CTF3:Phase Calibration and Jitter
Alexey Dubrovskiyinputs from Franck Tecker, Luca Timeo and Stephane
Ray
CLIC/CTF3 experimental verification meeting08.07.2014
2
Motivation• Improve the current measurement of RF
phases;• Assess the capability of RF measurement
systems to detect RF jitter.
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Outline• Part 1: Calibration of mixer phase detectors;• Part 2: Measurement of RF Jitter;• Part 3: Correlation between mixer and diode
signals.
3
Part 1: Calibration of mixer phase detectors
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4
RF measurement layout
Klystron
LO
High-power RF
Directional couplerRF phase
shifter
DiodeMixer
ADC
RF phase shifter
LLRF
High voltage modulator
Passive devices
Controlled devices
Measurement
08.07.2014All RF feed-backs and phase waveform generators were disabled.
5
Algebra of the RF measurement
RF
Diode
ADC
Mixer
ADC
Local oscillator
Phase shift
Power measurement:
Phase measurement:
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MKS03: RF phase calibrationCalibration
Fitted parameters:
Error:
Phase scan with a step of 10 at a given PFN voltage and at a given time within the pulse08.07.2014
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MKS03: calibration at different power levels
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RF phases
8
MKS03: Phase in the pulse
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RF phases
New treated:Calibrated: fitted parameter
All three measurements are consistent.
9
MKS03: Phase at different PFNs
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Difference of RF phases measured at two different PFNs
The current threated signal shows a relatively small phase dependence on the power level
10
Summary of calibration parameters
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Klystron (PKI)
MKS02 162.6 2063.3
MKS03 172.7 2047.6
MKS05 234.5 2110.9
MKS06 211.4 2064.9
MKS07* 269.1 2118.8
RF phase resolution is much smaller for MKS02 and MKS03
(*) Calibration issue on the next slide
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Calibration issue: MKS07
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RF Power should not change at all when the comp. phase changes!
12
Other issues: MKS02 and MKS05
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The current scaling factors of the treaded phase signals PKI02P and PKI05P are off by a factor of about 2 and 4.
13
Part 2: Measurement of RF Jitter
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Algebra of the RF jitter
RF
Diode
ADC
Mixer
ADC
Local oscillator
Phase shift
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Mixer and diode signals jitters
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Similar power jitters were measured using the mixer and diode signals for MKS03 and MKS05
MKS03
16
MKS02: Power jitter
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Measured by diode
Measured by mixer42%
The jitter corresponds to ~0.7 bit std in both cases.=> Both measurements are limited by the ADC sensitivity, but the mixer signal gives a better estimate.
17
MKS06: Power jitter
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Measured by diode
Measured by mixer96%
The mixer jitter corresponds to ~1 bit std and the diode jitter corresponds to ~1.8 bit std .=> The mixer signal gives a better estimate. And there is a strong noise in the diode signal.
Unexplained high jitter level
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Part 3: Correlation between mixer and diode signals
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Correlation between mixer and diode signals
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Case 1: The RF power deviation linearly depends on the phase deviation, for example, like in the case of a pure high voltage jitter:
Then the correlation is given by: Then the correlation is given by:
Case 2: There is only RF power deviations, which induces jitter on both signals:
Case 3: case 1+ case 2
Then the correlation depends on the phase shift and ratio k1 to k2.
Case 4: case 1+ case 2 + measurement noise
Then the correlation depends on the phase shift, k1, k2 and noise levels.
20
Correlation between mixer and diode signals
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Cases 1, 2 and 3 Case 4 with measurement noise
Case 1(k2=0)
Case 2(k1=0)
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MKS05: Correlation between mixer and diode signals
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Model parameters:
Modulator voltage jitter
Power jitter
Diode noise
Mixer noise
=> Measured RF jitter is induced by the klystron modulator
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MKS03: Correlation between mixer and diode signals
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Model parameters:
Modulator voltage jitter
Power jitter
Diode noise
Mixer noise
=> Measured RF jitter is substantially given by the measurement noises
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MKS06: Correlation between mixer and diode signals
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Model parameters:
Modulator voltage jitter
Power jitter
Diode noise
Mixer noise
=> Measured RF jitter is primary given by the diode measurement noise
24
Summary
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• Part 1: Calibration of mixer phase detectors:– New RF phase detection algorithm will provide a slightly better
measurement;– The phase comp. changes the power measurement KPI07A;– PKI02P and PKI05P to be recalibrated.
• Part 2: Measurement of the RF Jitter:– Mixers give significantly better estimates of RF power jitter;– The power jitter measurements are limited by ADC sensitivities.
• Part 3: Correlation between mixer and diode signals:– Measured PKI05 jitter is induced by the klystron voltage jitter;– MKS06 measured RF jitter is primary given by the diode measurement
noise;– MKS02 and MKS03 measured RF jitters are limited by low ADC sensitivity
for diode signals.
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26
MKS05: Power jitter
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