RIEMF in MgO and Al 2 O 3 insulated MI cable ITER magnetic diagnostic coils R. Vila * , E.R. Hodgson Euratom/CIEMAT Fusion Association, Inst. Investigacion Basica, Avenida Complutense 22, 28040 Madrid, Spain Abstract Radiation induced currents and voltages, generally termed RIEMF, have recently been the object of discussion due to inconsistent results. The problem is due to a possible RIEMF generated along the centre conductor of a coil in a radiation field. To address this, two representative ITER coils have been made from 1 mm diameter MI cable with copper and stainless steel inner conductors. Measurements were made of the radiation induced voltage and current between the centre and outer sheath, as well as the voltage across the two ends of the centre conductor during 60 Co gamma irradiation at 10 Gy/s. While putting an upper limit on the radiation-induced part, it has been demonstrated that, within the measurement capability, no significant RIEMF is produced along the central conductor. However, the measurements have highlighted other potential problems due to temperature and pressure gradients for the use of MI cable magnetic coils in ITER. Ó 2004 Elsevier B.V. All rights reserved. 1. Introduction It has become evident that the use of mineral insu- lated (MI) coaxial cables in the expected ITER radiation field must accommodate radiation induced currents and voltages, generally termed RIEMF (radiation induced electromotive force), which represent additional noise in the cables. The problem is of particular concern for the sensitive magnetic coil diagnostics, a prime candidate for plasma current and position control. The existence of RIEMF between the central con- ductor and outer sheath which can generate potentials of the order of volts and microamps of current, has been known and employed for many years. However in recent experiments orientated towards ITER diagnostic needs, tentative evidence has been found for the possible gen- eration of a small voltage along the central conductor itself. Such an RIEMF is of serious concern. Due to experimental difficulties in measuring small voltages and currents in a radiation environment at the end of long cables, no definite conclusions could be drawn [1,2]. The difficulty arises because at the 100 nV level, thermal voltage effects, as well as possibly temperature/ pressure and movement induced polarization effects in the insulator itself become important. 2. Experimental procedure 2.1. Coils To perform the task two separate coils were wound using different MI cables, see Table 1. The coil dimen- sions were calculated from the recommendations taken for ITER relevant conditions [3]. These may be sum- marized as follows: The coil diameter including case should be less than 0.025 m to avoid large blanket cut-outs and large ther- mal gradients. Here to perform the gamma irradiations this size limitation is required in order to avoid large dose rate gradients due to the localized radiation field. The sizes relevant for ITER-FEAT of the MI cable should be about 1.6 mm (outer) and 0.75 mm (inner) diameter, and the coil should have an NA value of about * Corresponding author. Tel.: +34-1 346 6580; fax: 34-1 346 6068. E-mail address: rafael.vila@ciemat.es (R. Vila). 0022-3115/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2004.04.253 www.elsevier.com/locate/jnucmat Journal of Nuclear Materials 329–333 (2004) 1524–1528