The Upgrade of MA.RI.S.A. Facility from 6.5 to 10 Tesla Design, Construction and Preliminary Test

Abstract

The facility MA.RI.S.A. is based on a superconducting solenoid (MARISA I) with a maximum attanaible central field of 6.5 Tesla at 4.2 K and 1080 A supply current in a quite large bore: 500 mm I.D. The facility is upgraded by inserting into the basic solenoid a second one (MARISA II), that rises the field up to 8 Tesla at 4.2 K and 10 Tesla at 1.8 K in a bore 380 mm I.D. Mechanical stresses are the main problems of the inner solenoid; the hoop stress is 200 MPa so that a structure shrinking the solenoid is required. Using a stainless steel cylinder the maximum hoop stress can be reduced to 130 MPa without a significative reduction of the clear bore. A further problem is the interaction between the winding and the outer stainless steel cylinder; the friction due to relative axial motion, after the cool-down or under stress, of the two structures can cause premature quenching. To avoid this occurence, the banding structure of the inner solenoid was designed to be unisotropic i.e. composed by stainless steel and fiber glass thick strips, wound onto the solenoid and vacuum impregnated with epoxy resin. This structure behaves circumferentially like stainless steel but axially like the solenoid winding, so that no thermal stresses take place and, on charging the solenoid, the relative stress are reduced of a factor 2. In the paper these design guidelines are discussed together with the description of the technical solutions, adopted during the construction.