Implementation of the asynchronous landing scheme in KSTAR plasma - - PowerPoint PPT Presentation

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Implementation of the asynchronous landing scheme in KSTAR plasma - - PowerPoint PPT Presentation

Dec 12, 2023 357 likes •491 views

Implementation of the asynchronous landing scheme in KSTAR plasma control system MinHo Woo 1) , H.Han 1) , S.H. Hahn 1) , J.Kim 1) , Y. S. Bae 1) , J. G. Bak 1) , M. L. Walker 2) , R. D. Johnson 2) , N. W. Eidietis 2) 1) National Fusion Research

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Implementation of the asynchronous landing scheme in KSTAR plasma control system

MinHo Woo1), H.Han1), S.H. Hahn1), J.Kim1), Y. S. Bae1), J. G. Bak1),

  • M. L. Walker2), R. D. Johnson2), N. W. Eidietis2)

1)National Fusion Research Institute, Daejeon 305-333, Korea 2)General Atomics, San Diego CA, U.S.A

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Outline

  • Motivation
  • Conceptual design
  • Algorithm development
  • Model validation
  • Experiment
  • Conclusion and Future works

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SLIDE 3

Motivation

2013 KSTAR conference, Lotte Buyeo Resort, February 26-27, 2013 3

Consequences of the disruption

  • Sudden thermal load to the first wall
  • Electro-magnetic load on conducting wall
  • Direct collision of run-away electrons to the wall

Cause of the disruption

  • MHD stability limit in high beta plasma
  • Hardware failure
  • Lose of the plasma control

Mitigation and avoidance of the disruption

  • Massive Gas Injection (MGI)
  • ECCD injection to suppress MHD mode
  • Asynchronous (soft) landing
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SLIDE 4

Asynchronous landing

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What is asynchronous landing ? Advantages of the Asynchronous landing How asynchronous landing works ?

  • Switching the poloidal field coil control scheme into the pre-designed

ramp down scenario at any time at any plasma current

  • Catch up disruption precursor or hardware fault
  • Change target plasma current with specified ramp down rate
  • Feed currents to each PF coil with given ramp rate
  • Move the plasma inward with fixed plasma shape
  • Reduce the plasma current before hitting the first wall
  • Reduce the stored energy and eventually wall damage
  • Same damage pattern for different shots
  • Enable the tokamak to operate in more dangerous parameter

regime without concerning wall damage

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SLIDE 5

Conceptual Design

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  • Severe fault

 Immediate termination  Ip min fault  Total MVA fault  PS fault

  • Median fault

 Asynchronous landing  PFC fault  rtEFIT fault  External fault …

  • Intended landing

 Locked mode coil  IVC coil  Zp estimator

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SLIDE 6

Algorithm Development

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  • Flow of the sequence

 Different sequence has different phase for different category  When asynchronous landing triggered sequence changes and so is phase

  • Different types of asynchronous landing
  • 1. Intended landing

 Monitor precursor signal of the MHD  IVC or Zp to determine if plasma has lost control

  • 2. By hardware faults

 External faults by ECH, NBI etc…  PFC armor fault  Ip control error faults

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SLIDE 7

Algorithm Development

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  • Block Diagram for Asynchronous landing
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SLIDE 8

Model Validation

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Red line- before landing Black line – after landing Landing started at 5s  Plasma shape Upper single null to circular  Plasma current Ramp down from actual Ip  Plasma position Move inward about 10cm

  • Plasma control simulator - simserver

Closed loop simulator with plasma current and shape control with model based on real experiments

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SLIDE 9

Experiment

2013 KSTAR conference, Lotte Buyeo Resort, February 26-27, 2013 9

shot 8771

Asynchronous landing at 21.375s due to the NBI-1 failure at 21.125s

 Change of target Ip and actual Ip  Change of the feed forward current  Drop of the electron temperature  Sudden increase in loop voltage  Elongation recovers to 1.85

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SLIDE 10

Experiment

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Landing by IVC

  • Robustness of the asynchronous landing
  • Strong IVC oscillation

before landing

  • Strong IVC at 5s
  • PF5 feed forward

change from 5s

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SLIDE 11

Experiment

2013 KSTAR conference, Lotte Buyeo Resort, February 26-27, 2013 11

Landing by PFC fault  High temperature of the Plasma facing component due to the previous experiment  Fault received from external fault monitoring system  Similar behavior to the IVC fault case

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SLIDE 12

Conclusion and Future Works

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  • Asynchronous landing scheme is developed
  • The model is validated using plasma control simulator
  • It is applied real experiment in 2013 KSTAR campaign
  • Asynchronous landing works well in various situations

Conclusion

Limitations and Future works

  • Changing feed forward PF current technique is very limited
  • Problematic when one of the PF coils are saturated
  • Sudden change in PF request needs to be improved
  • On-line feed forward scheme is under development
  • Extend its applicability to more general dangerous situations in KSTAR