HOME PROGRAM REGISTRATION HOTEL TRANSPORTATION SUBMIT ABSTRACT ABSTRACT LIST PROGRAM COMMITTEE MORE ON MADISON	The Multi-Pinch experiment Author: Micozzi Paolo Coauthor: F. Alladio, A. Mancuso, F. Rogier, S. Papastergiou Institution : Associazione Euratom-ENEA Abstract text: The PROTO-SPHERA machine aims to study the properties of a Spherical Torus (ST), where a Hydrogen force-free Screw Pinch (SP) replaces the central rod of the standard ST experiments. PROTO-SPHERA, with a longitudinal pinch current Ie=60 kA, will produce an ST of diameter 2Rsph=75 cm, aspect ratio A=1.2-1.3, carrying a toroidal current Ip=120-240 kA. The plasma will be magnetically shaped as a disk near each modular annular electrode. Theoretical calculations show that such a configuration should be ideally stable up to a total beta ranging between 15-25%, depending upon the ratio Ip/Ie. The ST toroidal current should be sustained by Helicity Injection from the Screw Pinch. In order to prove the feasibility of the Screw Pinch, the experimental set-up Multi-Pinch will be built. It will produce a stabilized SP having the same linear dimensions of the PROTO-SPHERA pinch, but with reduced electrodes and PF coils currents. Its main task will be to explore the breakdown conditions and the pinch stability of PROTO-SPHERA before the formation of the ST. The vacuum vessel of the START experiment (Culham Euratom-UKAEA Association) will be transferred to Frascati and used for Multi-Pinch. It will have a limited number of cathode wires (18 Vs. 378), but each of them will be of the nominal size and will capable of delivering the PROTO-SPHERA design current (150 A). Therefore the cathode structure will be the one designed for PROTO-SPHERA but only a total limited current (2.7 kA Vs. 60 kA) will be driven between the electrodes. The first phase of the experiment will have a provisional single anode (not mushroom-shaped). In this phase the uniformity of emission from multiple cathodes, in presence of a mushroom-shaped cathode guide field, will be investigated. In the second phase, corresponding to the full PROTO-SPHERA mushroom-shaped hollow anode, the breakdown between two annular electrodes with mushroom-shaped guiding fields and the occurrence of anode arc anchoring will be investigated. Sufficient space is available near the electrodes, should additional tools (such as rotating magnetic fields) be added inside the vacuum vessel to overcome difficulties with current channelling and guide field instabilities.