digital measurement system for the lhc klystron high voltage modulator

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Digital measurement system for the LHC klystron high voltage modulator D. Valuch, A. Mikkelsen, G. Ravida, O. Brunner

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Digital measurement system for the LHC klystron high voltage modulator. D. Valuch, A. Mikkelsen , G. Ravida , O. Brunner. LHC RF power system. Total 16 klystrons Thales TH2167 400.8 MHz, 330 kW, at nominal 58 kV, 9.2 A One klystron per cavity Four klystrons supplied by one HV supply - PowerPoint PPT Presentation

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Page 1: Digital measurement system for the LHC klystron high voltage modulator

Digital measurement system for the LHC klystron high voltage modulator

D. Valuch, A. Mikkelsen, G. Ravida, O. Brunner

Page 2: Digital measurement system for the LHC klystron high voltage modulator

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LHC RF power system• Total 16 klystrons Thales TH2167• 400.8 MHz, 330 kW, at nominal 58 kV, 9.2 A

• One klystron per cavity• Four klystrons supplied by one HV supply• Crowbar to protect klystrons in case of arcing

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

Page 3: Digital measurement system for the LHC klystron high voltage modulator

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LHC RF power system

Crowbar tankSeparator tank

To other modulators and klystrons

+

HV supply0 – 100 kV

40A

Modulator tank

H

H+K

MA

Capacitor tank

Ground level HV bunker UX45 Klystron gallery UX45

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

Page 4: Digital measurement system for the LHC klystron high voltage modulator

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Klystron modulator

• Modulator contains filament transformer and modulation anode control

• Cathode and modulation anode voltage measured using dividers

• Currents measured using external DCCTs

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

Page 5: Digital measurement system for the LHC klystron high voltage modulator

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Present measurement system• Fast interlocks on voltage/currents• Observation/logging

• 1 sample per second during rapid changes• 1 sample per 15 minutes during slow changes

• Post-mortem analysis difficult due to granularity

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

Exa

mpl

e of

a k

lyst

ron

cabl

e fa

ult

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New measurement system in the HV modulator

• Measurement system integrated in the modulator oil tank

• Voltages and currents measured directly at the klystron cathode

• Communication over optical fibre

• VME receiver card for readout, logging and post-mortem analysis

• Currents measured with DCCTs

• Voltages measured with present resistor dividers

Modulation anode control

Filament transformer

Optical fibre

Optical fibre

Cathode + Filament

Filament

MAC10 klystron modulator

Filament power

-HV from separator

Measurement data

Modulation anode

setpoint

10 Ω

Live

Neutral

- HV

Filter + protection

CPLD

Fibre TX

ADC

Measurement card

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

Page 7: Digital measurement system for the LHC klystron high voltage modulator

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Improvements over present system

Channel Range Resolution

Cathode voltage 0 – 100 kV 25 V

Modulation anode voltage

0 – 100 kV 25 V

Cathode current 0 – 15 A 10 mA

Heater voltage ± 50 V 25 mV

Heater voltage RMS

0 – 50 V RMS

25 mV

Heater current ± 50 A 30 mA

Heater current RMS

0 – 50 A RMS

30 mA

• >1 ksps sample rate• 12 bit resolution• Measurements are done at the

source, better accuracy• Over 100 second long post

mortem buffer at full sample rate for all channels

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

Page 8: Digital measurement system for the LHC klystron high voltage modulator

8CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

Digital VME receiver board (for 4 klystrons)Measurement board (floating at -

57 kV, submerged in oil)

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High voltage testing• The recipy:

1) Take some sensitive electronics such as CPLD, ADC, current transducers

2) Put it into a harsh high voltage environment with high fields in a normal operation

3) Or 6000 A, 10 kA/ms, 50 kV/ms in case of faults

What could possibly go wrong…

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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Observed problems• Current transducer develops a large analogue offset after crowbar.

The offset dies-out after several hours

• Complete current transducer failure after tens of crowbars

• ADC upset after every few crowbars

• Crystal oscillator upset after every few tens of crowbars

• But… Not a single problem observed with the CPLD, DC/DCs, optical links!

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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High voltage testing• High voltage compatibility testing

at HV test stand• Decoupling capacitor and solid

state crowbar• Motorized spark gap used to

simulate klystron arcing

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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Test set-up

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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Current transducer protection• Fault currents in case of klystron arc magnetized the current transducers• Different transducers evaluated, all susceptible• Transducer dies completely after multiple faults/crowbars• Protection diodes eliminated problem

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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Induced currents in board traces• Upset of the ADC was observed after spark gap firing• Current transducer power trace found to be sensitive to induced noise

from spark current• Breaking the loop eliminated the problem

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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Crystal oscillator upset• Board outputs serial data at ~20 times normal rate after arc• Noise coupled through DC/DC converter. Grounding of board power input

eliminated problem• Use of a different crystal oscillator model (without PLL, operating at

fundamental frequency)

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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Measurement results with LHC klystron

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

• Plot shows filament voltage and current waveform• Time resolution allows individual 50 Hz mains cycles to be resolved• Buffer length over 100 seconds at 1ms/point resulotion

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Measurement results with LHC klystron• Plot shows filament current waveform after crowbar

Crowbar fires

Cathode current flowing through the filament diminishes

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Test stand power converter ripple• Test stand power converter known to have large amount of ripple• FFT of cathode voltage shows 700 V RMS of 50 Hz ripple• Measurement system gives useful information on power converter condition

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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Project status• Tests with real klystron show very

promising results

• System survived >160 crowbars without any upset or degradation of performance

• System installed in spare LHC modulator for long-term testing in 112 klystron test stand

• System is planned to be installed in one LHC modulator during Long Shutdown 1

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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Summary• A new, state of the art digital measurement system for the klystron

HV modulator was developped

• We have demonstrated that a sophisticated electronics could be successfully integrated into a harsh HV environment

• Increase of measurement precision, time resolution, measurement capabilities

• Early fault diagnostics with observation buffers (tube aging, connectors, HV supply health monitoring)

• Extensive post mortem data buffers for fault diagnostics in the LHC machine

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator

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References

CERN-THESIS-2014-033 https://cds.cern.ch/record/1700591Digital measurement system for the LHC klystron high voltage modulator.Author Mikkelsen, Anders (Department of Electronics Bergen University College)

CWRF2014, Trieste, May 2014

D. Valuch et al.: Digital measurement system for the LHC klystron high voltage modulator