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Coordinating Committee on ICRH, 9-10 April 2008. ARC detection development and testing on JET. P. Jacquet 1 , G. Berger-By 2 , T. Blackman 1 , F. Durodi é 3 , M-L. Mayoral 1 , I. Monakhov 1 , M. Nightingale 1 , M. Vrancken 3

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arc detection development and testing on jet

Coordinating Committee on ICRH, 9-10 April 2008

ARC detection development and testing on JET

P. Jacquet1, G. Berger-By2, T. Blackman1, F. Durodié3, M-L. Mayoral1, I. Monakhov1,

M. Nightingale1, M. Vrancken3

1UKAEA/Euratom Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB, United Kingdom.

2Euratom-CEA Association, DSM/DRFC, CEA-Cadarache, 13108 St Paul lez Durance, France.

3ERM-KMS, Association EURATOM-Belgian State, Brussels, Belgium.

overview of the jet icrh system 2008
Overview of the JET ICRH system 2008
  • Four different ARC detection systems will be tested on JET during the next campaign
    • VSWR
    • SMAD
    • SHAD
    • AWACS
  • ITER Like Antenna incorporates VSWR, SMAD, SHAD systems

VSWR arc detection on the ILA

  • Only arc detection system to start commissioning of the ILA
  • Issues
    • Protection level in low ZT conditions ?
    • Not efficient to protect against arcing at certain location of antenna (bridge arcing) ?
    • Protection level in mismatch conditions ?
scattering matrix arc detection smad
Scattering Matrix Arc Detection (SMAD)

From RF model

K1, K2, K3 = function(Capa1, Capa2, freq)

V1meas, V2meas, V-3meas, V+3meas: RF measurements

  • SMAD principle of operation:
    • Error function calculated in real time (2s cycle)
    • Arc if breakage in the linear relation between RF measurements (error function above threshold)
  • SMAD operation depends critically on:
    • Accuracy of RF model
    • Accuracy of RF measurements
smad analysis of data from test bed

* : no arc

* , o : 5 nH arc

* , o : 10 nH arc

* , o : 20 nH arc

* , o : 50 nH arc

SMAD, analysis of data from test bed

Simulations: with 20% scatter from measurement and modelling errors, the system should be capable to detect 20 nH arcs

RDL 78, measurements with VNA. Remaining scatter in Δ2 from non perfect modelling and measurements errors




20% error




Thanks to Mark Vrancken

scattering matrix arc detection smad6
Scattering Matrix Arc Detection (SMAD)
  • SMAD system enables:
    • Storage of RF measurements, capacitor positions, frequency, Arc-detected status etc for pulse post analysis
    • SMAD replay capability (run the algorithm with data stored previously)
        • Tune and Test SMAD coefficients, threshold, etc
        • Test new algorithms
transmission line rf measurements and analysis
Transmission Line RF measurements and analysis

Scope measurements during an arc event

FFT analysis

Thanks to Igor Monakhov

arc detection systems iter like antenna
ARC detection systems Iter-Like Antenna
  • Arc events from all three systems time-stamped.
  • Ability to compare operation of the different arc detection systems on the same antenna.
improved trip management system
Improved trip management system
  • Incorporate existing ELM detection into trip logic to modify trip times.
    • If an ELM and an amplifier trip occur at the same time, system reduces the trip time to 1-2ms and uses the fastest ramp rate to recover.
    • This protects the amplifier from the very large reflections caused by the large ELMs but will reapply very quickly ensuring minimum power is lost.
    • Result should be a significant increase in average power during ELMy periods.
  • Electronics redesign will start in 2008 to enhance the ATM (Trip module), and be able to implement advanced logics.
  • Similar /close systems may be useful for ELM tolerant antennas if it appears that arcs are triggered by ELMs

Thanks to T. Blackman

arc detection on jet expected outcomes from the next campaign
Arc detection on JET, expected outcomes from the next campaign
  • ITER Like Antenna commissioning:
    • It is mandatory to have reliable arc protection suitable for each phase of the operation.
  • Characterisation and Validation of new concepts, inputs to ITER.
    • SMAD: powerful hardware/software tools: assessment of this technique on JET, and tune-up of the algorithm.
    • SHAD: measurement tools in place to characterise the operation, and to measure the RF signal at various locations of the TL during operation, including H-mode operation.
  • Complementary approaches:
    • AWACS testing part of the ECT commissioning.
    • Improved Trip management. New hardware and firmware will be tested in 2008.
complementary slide arc detection on the ect project
Complementary slide, arc detection on the ECT project

AWACS will increase protection in the following operational conditions:

  • appreciable non-zero T-junction reference reactance
  • asymmetric loading of the conjugated straps
  • coupling resistance approaching the T-junction reference resistance
  • mismatch due to TRIMP length offsets from target values
  • occurrence of ELMs (!)
complementary slide trip management
Complementary slide, Trip Management

Preliminary resultsT Blackman 2002

‘Improved Trip Management’ not functioning on A12

‘Improved Trip Management’ functioning on A34

NOTE: Time resolution too course to catch all trip events