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

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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.

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Part 1: Calibration of mixer phase detectors

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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.

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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

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MKS03: Phase in the pulse

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RF phases

New treated:Calibrated: fitted parameter

All three measurements are consistent.

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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

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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!

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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.

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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

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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.

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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.

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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

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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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MKS05: Power jitter

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