Thermally induced EMF in unirradiated MI cables

A TIEMF model and some implications for ITER magnetic diagnostics

“…A first assumption is that local impurities or physical changes at very small scales (of the order of few millimetres or below) are the most probable causes of TIEMF. This has been validated by all the experimental results obtained so far [7][8]. The second one is that the underlying physical cause is a local change of the Seebeck coefficient.…”

“…In this technique, a small oven is slowly moved along the cable and the e.m.f. is measured at the ends of the cable (see [7][8] for details). Fig.…”

“…Work done in recent years has clearly demonstrated that radiation and temperature induced voltages (RIEMF and TIEMF, respectively) appear in all the cables studied so far (MI coaxial cables, ceramic and enamel coated single cables) [1][2][3][4][5][6][7][8]. TIEMF appears as generation of a voltage along the centre conductor of cables due to temperature gradients, (particularly large for MI Cu cored cables) and cable inhomogeneity.…”

“…A crucial aspect recently established is that the TIEMF voltages (even without irradiation) are generated in well localized regions of the central conductor, suggesting that some inhomogeneity is present [4,7]. Optical and SEM examination indicates that mechanical damage of the inner wire, and/or ceramic incrustation (for MI cables) may be two causes of these inhomogeneities [6].…”

Drift-free magnetic equilibrium reconstruction using the response to plasma position modulation

“…However, inductive magnetic measurements can experience drift during long pulses leading to inaccurate plasma positioning. Two main sources of error have been identified: the drift of electronic integrators, since the field and flux are the time-integral of the inductive magnetic sensor output signals, and a wide diversity of radiation induced effects which induce electromotive forces in the cables [1][2][3][4][5][6]. Significant progress has been made on electronic integrators which now exhibit acceptable drifts for the duration of the ITER plasma discharges [7][8][9][10][11].…”