A Quercia, N Pomaro, C Visone (ENEA/CREATE-RFX)

Presented by A.Murari

Many thanks to: R Albanese, S Gerasimov

Nonlinear Effects inNew Magnetic Pick-up Coils for JET

International Tokamak Physics ActivityDiagnostics Meeting

Moscow 10-14 Apr 2006, http://itpa.ipp.mpg.de

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

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Normal and Tangential JET EP Upper Coils

The Coil Formers are made of Nickel Alloy Inconel® 600The Coil windings consist of Mineral Insulated Cable

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

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Calibration with Solenoid @ RFX

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

Photo 1

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Calibration with Helmholtz Coil @ JET

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

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Cross CalibrationNew Upper Coils Calibrated at RFX and at JET

The calibration of a set of new JET EP Upper Normal and Tangential Coils was performed using the two different calibration systems at RFX and at JET The corrispondent measured Magnetic Sections were different in the order of 3%, ten times the calibration procedures accuracy

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

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Cross Validation of the two Calibration Systems

A plastic former coil with a geometrically known magnetic section (uncertainty better than 0.1%) was used to evaluate the actual accuracy of the two different calibration systems at RFX and at JET Sine wave magnetic field in the ranges 0.03-2 mT and 100-1000 Hz was used No relevant dependence from field amplitude and frequency was observed, and the two calibration systems gave results in very good agreement, within 0.2%

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

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Cross Calibration of a Normal Coil with Copper winding

A Normal Upper Coil was calibrated at RFX and at JET To make possible a precise calculation of the magnetic section, the Mineral Insulated Cable multi-layer winding was substituted with a single layer copper enamelled wire winding The calculated magnetic section is in this case known within about 0.12% uncertainty

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

The data showed on this plot were obtained by demagnetizing the Inconel former before each measurement The measured Magnetic Section results strongly field dependent It is larger than the calculated one (more than +5 % around 1 mT) Accordingly with the expected filtering effect of the conductive former, a small frequency dependence is also observed

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Relative Permeability of the Inconel former

An Inconel specimen taken from the former of a new Upper Tangential Coil was analyzed by means of a Magnetometer The relative permeability plot shows a nonlinear ferromagnetic behaviour at low field amplitude levels, with an increment on the rel value up to nearly 50 % Outside of this low field level region, the behaviour is linear, and rel=1.01, as reported in the literature The Magnetic Sections (NA) of the coils are measured at low field and so are affected by the non-linearity The ferromagnetic behaviour is thought to be due to the mechanical and thermal treatments performed on the former during probes manufacturing and testing

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

Conclusions The Magnetic Section (NA) of the Coils significantly depends nonlinearly from field intensity

At low level field, the Inconel 600 former shows a ferromagnetic behaviour

The ferromagnetic behaviour is tought to be due to the mechanical and thermal treatments performed on the former during probes manufacturing and testing

Both RFX and JET calibration procedures were unable to provide with acceptable accuracy the effective magnetic section of the new probes

Investigations are in progress in order to relate the measured Magnetic Sections to the nonlinear behaviour of the Inconel, and to develop a method to correct the calibration constants

The results will be presented at the HTPD 2006 Conference

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

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References

[1] A Quercia, N Pomaro, C Visone, Nonlinear Effects in New Magnetic Pick-up Coils for JET, to be submitted for the HTPD 2006 Conference, Williamsburg USA, 7-11 May 2006.

[2] S Gerasimov, UKAEA Memorandum, JET Magnetic Pick-up Coils Calibration – Measurement of the NA, Issue 6, 8 Nov 2005.

[3] N Pomaro, SM_PR_001_CA, Operational Procedure for Calibration of Magnetic Sensors to be used in JET Experiment, rev. 0, 28 Feb 2005.

[4] N Pomaro, EP-DIA-MAG-T-007, JET EP Magnetic Probes Calibration, 3 Feb 2004.

[5] EP-DIA-MAG-S-004, JET EP on Magnetic Diagnostics, Subsystem Upper Coils, Technical Specification for the procurement of the Electromagnetic Transducers, Issue 2, 22 Sep 2003.

[6] S Takahashi, Y Yato, Y Kamada, T Abe, Study of chromium depletion by magnetic method in Ni-based alloys, Jurnal of Magnetism and Magnetic Materials 269 (2004) 139-149.

[7] V Coccorese, R Albanese, Design of the new magnetic sensors for Joint European Torus, Review of scientific instruments, Vol 75, Nr 10, Oct 2004.

ITPA Diagnostics Meeting, Moscow 10-14 Apr 2006 A Quercia, N Pomaro, C Visone

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