Runaway-limiter interaction in the FTU tokamak during disruptions

Photoneutron production during disruptions was monitored on the FTU machine by a set of calibrated BF3 proportional counters. Both hydrogen and deuterium discharges covering a wide density range were examined. The functional dependence of the photoneutron production on n(e), Z(eff) and I-p is in agreement with the Dreicer generation, being the main source of runaway electrons during disruptions in FTU. No detectable photoneutron production was observed at a plasma density higher than 1.4 x 10(20) m(-3), corresponding to Z(eff) values close to 1. The typical runaway energy was evaluated from the curve of the photoneutron yield per electron vs. energy for disruptions characterized by a hesitation in the plasma current decay. Damage by disruption generated runaways was found to be concentrated around the inboard equatorial plane as suggested by temperature and activation measurements. (C) 1999 Elsevier Science B.V. All rights reserved.