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Overview of NCSX Magnetics Diagnostics

Peer Review for NCSX External Saddle Loops and Rogowski Coils B. Stratton, T. Brown, M. Cole, D. Johnson, and G. Labik 4-13-05. Overview of NCSX Magnetics Diagnostics. External saddle loops (this review) Co-wound loops on MC, TF, PF, and trim coils B-dot probes (in VV)

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Overview of NCSX Magnetics Diagnostics

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  1. Peer Review for NCSX External Saddle Loops and Rogowski CoilsB. Stratton, T. Brown, M. Cole,D. Johnson, and G. Labik4-13-05

  2. Overview of NCSX Magnetics Diagnostics • External saddle loops (this review) • Co-wound loops on MC, TF, PF, and trim coils • B-dot probes (in VV) • Rogowski coils (this review) • Diamagnetic loops (in VV) • MC shell saddle loops (on external surface) • External saddle loops and Rogowski coils must be installed during machine assembly because they are trapped in the space between the vacuum vessel and the MC shell

  3. Scope of this review • VV saddle loops: • Choice of cable for saddle loops • Strategy for locating loops on the VV • Strategy for clamping loops to the VV • Strategy for routing leads on the VV • Termination strategy • Installation plan • Plans for documenting loop locations • Rowgowski coils • Routing path for Rowgowski coils • Strategy for holding coil in place • Termination strategy

  4. Requirements for External Saddle Loops • Loops mount on exterior surface of VV within 1/8” clearance provided under heating tubes • Approximately 200 total loops distributed identically between 3 VV periods • Corresponding loops to have reproducible areas (<1%) on all 3 periods • Within a VV period, half the loops are deployed on one half-period and the other half are deployed on the other half-period. If an area is occupied by a loop on one half period, it is empty on the other half period. Nearly complete coverage within a VV period. • Final locations of loops TBD from physics study (Lazarus and Pomphrey) • Positional requirements TBD. • Loop area 50 square inches or greater • Loops electrostatically shielded • Leads twisted to minimize spurious B-field pickup • Leads exit the cryostat region near the vertical ports • Paths of as-built loops accurately measured

  5. Requirements for Rogowski Coils • Rogowski coils to be installed in space between VV and MC shell • Coils must survive during MC shell assembly • Two coils for redundancy, located in same positions on two different VV periods • Coils must completely enclose plasma in poloidal direction

  6. Rogowski Coils

  7. Rogowski Coil Options • Two possible configurations were laid out by T. Brown: • Flat ribbon type as used on NSTX (3/32” X 1-3/16”) • Round cross-section type as purchased for CDX-U (0.4” dia.) • If the round coil fits during MC shell assembly it has several advantages: • Inexpensive commercial product • Available in materials suitable for cryogenic temperatures? • Very flexible for routing around ports and other obstacles • Area near large vertical ports looks best: • Near where MC shell flanges come together during assembly • MC do not pass over this region during MC shell assembly • Leads can be brought out along large vertical ports and share cryostat feedthroughs with external saddle loops • Leads must be high-temperature compatible • Present concept is to mount coils by lacing them to VV insulation

  8. 3/32” x 1-3/16” ribbon option 0.4” Dia cable option

  9. FRONT VIEW

  10. BACK VIEW

  11. The Rogowski coil loop (0.4” dia) is located on top of the VV insulation. • Round cross-section coil clears • MC shell during assembly Some re-routing needed to clear VV boss

  12. Observations • Both coil types can be placed in the in the area near the large vertical ports • Given the contour of the VV, the 0.4” diameter coil would be easier to place and install compared to the wider ribbon. • MC assembly clearances OK for 0.4” diameter coil mounted on VV insulation • Need to investigate whether 0.4” diameter coil can be made of low-temperature materials • Is it possible to mount the 0.4” diameter coil inside a tube?

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