title: An arc control and protection system for the JET lower hybrid antenna based on an imaging system.
abstract: Arcs are the potentially most dangerous events related to Lower Hybrid (LH) antenna operation. If left uncontrolled they can produce damage and cause plasma disruption by impurity influx. To address this issue an arc real time control and protection imaging system for the Joint European Torus (JET) LH antenna has been implemented. The LH system is one of the additional heating systems at JET. It comprises 24 microwave generators (klystrons, operating at 3.7 GHz) providing up to 5 MW of heating and current drive to the JET plasma. This is done through an antenna composed of an array of waveguides facing the plasma. The protection system presented here is based primarily on an imaging arc detection and real time control system. It has adapted the ITER like wall hotspot protection system using an identical CCD camera and real time image processing unit. A filter has been installed to avoid saturation and spurious system triggers caused by ionization light. The antenna is divided in 24 Regions Of Interest (ROIs) each one corresponding to one klystron. If an arc precursor is detected in a ROI, power is reduced locally with subsequent potential damage and plasma disruption avoided. The power is subsequently reinstated if, during a defined interval of time, arcing is confirmed not to be present by image analysis. This system was successfully commissioned during the restart phase and beginning of the 2013 scientific campaign. Since its installation and commissioning, arcs and related phenomena have been prevented. In this contribution we briefly describe the camera, image processing, and real time control systems. Most importantly, we demonstrate that an LH antenna arc protection system based on CCD camera imaging systems works. Examples of both controlled and uncontrolled LH arc events and their consequences are shown.
authors.affiliation: Associação EURATOM/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal and EFDA-CSU, Culham Science Centre, Abingdon OX14 3DB, United Kingdom.
authors.forename: J
authors.initials: J
authors.lastname: Figueiredo
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: J
authors.initials: J
authors.lastname: Mailloux
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Kirov
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Kinna
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Stamp
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Devaux
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Arnoux
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: J S
authors.initials: JS
authors.lastname: Edwards
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: A V
authors.initials: AV
authors.lastname: Stephen
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: P
authors.initials: P
authors.lastname: McCullen
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Hogben