NCSX

David Johnson

August 18, 2004

Discussion of Co-Wound Flux Loops

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Motivation and Issues

• PAC recommended test of flux loop concept with twisted racetrack prototype at recent review

• Project schedule calls for CDR for co-wound flux loops at end of FY04.

• Issues for today’s discussion– Loop location– Type of cable– Termination strategy– Prototype tests

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ICD - Flux Measurement Requirements

• Each magnet that could be independently powered should have a Rogowski coil or shunt to measure its current and a co-wound sensor to detect the flux through it. This sensor should be on the plasma-facing side of the magnet wherever possible and redundancy is required. The design should be at a level where failure of the sensor is no more likely than failure of the magnet. We expect the control signal to the coil to be the error in this flux measurement.

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ICD - Co-Wound Loops for Modular Coils

The co-wound sensor loops shall be installed during winding of the modular coils. This installation, as part of coil manufacture, shall include lead termination at the coil casing (or boundary). The leads are to be terminated in a heavy duty structure, rigidly attached to the coil and capable of protecting the leads from breakage for the coil lifetime. The dual sensors are for redundancy and the terminating structures should be appropriate to this function.

The sensor loops shall be laid on top of the winding pack before epoxy impregnation and held in place by the winding clamps (grooves on the inside of each clamp are required). The epoxy will hold the sensor loops in place after impregnation. The sensor loops shall be made of suitable thin cable such as mineral insulated cable (diameter: 0.061” or less). The two leads for each loop shall be brought out through holes in the center leg of the winding form tee. The reliability of the sensor loops shall be at the same level as the reliability of the modular coils. The loops shall be positioned within 1/16” of the design position and their positions shall be known to the same accuracy as that of the modular coils themselves.

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Flux Loop Location

From sensor standpoint:• Two loops are needed

for redundancy.• For protection, loops

should be inside epoxy• Any of the three

locations shown are acceptable

Other considerations affecting location:

• Assembly issues• Mechanical fatigue due

to thermal cycling

From sensor standpoint:• Two loops are needed

for redundancy.• For protection, loops

should be inside epoxy• Any of the three

locations shown are acceptable

Other considerations affecting location:

• Assembly issues• Mechanical fatigue due

to thermal cycling

2.043

4.086

Possible Flux Loop Locations

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POSSIBLE WIRELOCATIONS

AB

C

A – tee web, under chill plate, shown as 1-mm dia

B – wp corner, between chill plate and vpi bag, shown as 1.6-mm dia

C – tee relief, shown as 1.6-mm

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Flux Loop Termination

Coil Type A

Type B

• Flux loops could be terminated on same terminal area as main coil leads.

• How to incorporate into impregnation?

• Electrical isolation?

Flux loop and termination

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Another Lead Design Without Support Bracket

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Alternate Wire Types

• Mineral insulated coax– Less flexible, self

supporting– Minimum bend radius – More difficult to terminate– OK at low temperature

• Glass-insulated, shielded copper – Twisted pair shown with double

glass insulation– Used for flux loops on NSTX– Flexible, easy to terminate– Diameters down to 1/16”– Should be compatible with

impregnation– Cryogenic operation?

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ICD - Co-Wound Loops for Conventional Coils

• The co-wound sensor loops will be installed as part of the fabrication of the TF, PF (including solenoid),and external trim coils. The sensor loops will be held in place by either the epoxy impregnation or insulating tape used in the coil fabrication.

• This installation, as part of coil manufacture, shall include lead termination at the coil casing (or boundary). The leads are to be terminated in a heavy duty structure, rigidly attached to the coil and capable of protecting the leads from breakage for the coil lifetime. The dual sensors are for redundancy and the terminating structures should be appropriate to this function. All other work related to these sensor loops (e.g., connections to instrumentation) will be the responsibility of WBS3.

• Cable type for sensor loops to be determined. The reliability of the sensor loops shall be at the same level as the reliability of the TF, PF, and trim coils.