A conduction-cooled, 680-mm-long warm bore, 3-T Nb3Sn solenoid for a Cerenkov free electron laser.

A compact, cryocooler cooled Nb3Sn superconducting magnet system for a Cere nkov Free Electron Laser has been designed, fabricated and tested. The magn et is positioned directly behind the electron gun of the laser system. The solenoidal field compresses and guides a tube-shaped 100 A, 500 kV electron beam. A two-stage G,M. cryocooler, equipped with a first generation ErNi5 regenerator, cools the epoxy impregnated solenoid down to the operating tem perature of about 7.5 K, This leaves a conservative operational margin for the MJR type of Nb3Sn conductor of about 350% (I-c) at 3T, Current leads wi th BTS sections between the first and second stage of the cryo cooler effec tively reduce the conductive heat leak. In the warm bore, 60 mm in diameter and 680 mm long, an operational magnetic field of 2 T has been achieved du ring laser operation without any quench. The field homogeneity is better th an 99.5% over 450 mm axial length, Design details and test results of this magnet system are presented.