1508 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 13, NO. 2, JUNE 2003 Tests of Prototype Quadrupole Magnets for Heavy Ion Fusion Beam Transport Chen-yu Gung, Joseph V. Minervini, Joel H. Schultz, Rainer B. Meinke, Carl L. Goodzeit, GianLuca Sabbi, and Peter Seidl Abstract—Four NbTi superconducting prototype quadrupole magnets have been built for the High Current Transport Experi- ment (HCX) as part of the multi-beam heavy-ion fusion research activity, led by the Lawrence Berkeley National Laboratory (LBNL). MIT performed quench training and ramp rate tests of the two prototype magnets that were designed and built by the Advanced Magnet Lab, Inc. (AML), based on a novel concept featuring cable-in-groove and multi-layer stacking. Both magnets are splice-free without inter-layer or inter-quadrant joint. Each coil was wound with a continuous NbTi round cable, placed in precise grooves machined in G-11 plates. The two magnets differ in their cable construction and their coil and yoke configuration. Each magnet was tested more than once in liquid helium bath with a room temperature thermal cycle between cold tests. This paper describes the results of the performance tests as well as the instrumentation and the quench protection system. Possible improvements for future coil winding are discussed. Index Terms—Heavy ion fusion (HIF), quadrupole magnets, quench training, superconducting magnets. I. INTRODUCTION T HE HIGH Current Experiment in the heavy-ion fusion (HIF) program is being built at Lawrence Berkeley National Laboratory (LBNL) to explore driver-scale beam transport [1], [2]. Beyond the present beam experiment using electrostatic quadrupoles (ESQ), both resistive and supercon- ducting quadrupole magnets have been built and tested aiming at magnetic transport experiment as an extension to the HCX [3], [4]. The resistive quadrupole pulse magnets provide a flexible and low-cost alternative to initiate magnetic transport experiment. For fusion driver application, the steady state superconducting quadrupole magnets will be the best approach to achieve break-even between the required and the extractable power. Two magnet design concepts were respectively adopted by Lawrence Livermore National Laboratory (LLNL) and AML to construct the first series of four NbTi superconducting prototype quadrupoles based on the magnet parameters defined by LBNL [5], [6]. Manuscript received August 6, 2002. This work was supported by the U.S. Department of Energy under Grant DE-FC02-93ER54186 Task 01E. C. Gung, J. V. Minervini, and J. H. Shultz are with the MIT Plasma Sci- ence and Fusion Center, MA 02420 USA (e-mail: gung@psfc.mit.edu; min- ervini@psfc.mit.edu; jhs@psfc.mit.edu). R. B. Meinke and C. L. Goodzeit are with Advanced Magnet Lab, Inc., Palm Bay, FL 32905 USA (e-mail: rmeinke@magnetlab.com; cgoodzeit@mag- netlab.com). G. Sabbi and P. Seidl are with the Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (e-mail: glsabbi@lbl.gov; paseidl@lbl.gov). Digital Object Identifier 10.1109/TASC.2003.812762 The first series of the cold tests was to characterize the performance of the prototype quadrupole magnets from their virgin state by investigating the quench training process and comparing the achievable current with the short sample limit current, . The operating current is defined as 85% of the along the load line of the peak field [5]. II. AML PROTOTYPE QUADRUPOLE MAGNETS AML uses a recently developed technique [7] of placing con- ductor in pre-machined grooves in a G-11 plate to wind single pancake. The position of the groove is determined by the re- sults from 3D FEM field analysis with field error optimized. The calculated data are used as input to control the programmable high precision milling machine to fabricate the grooved plate. The random error of local field in both straight and end turn re- gions of a multipole magnet can easily be controlled by using this well-defined process. Small round superconducting cable is used in this winding technique for the advantage of easy to bend in all directions. In the AML prototype quadrupoles, the cable is insulated with thin Kapton tape, which has one side coated with cryogenic epoxy. The pre-machined grooves are painted with epoxy before the placement of the conductor. Six layers of single pancake wound in G-11 plate, with both faces painted with epoxy, are stacked together and cured under pressure to form a quadrant of mono- lithic subcoil. The quadrupole consists of four subcoils, which is surrounded by laminated iron yoke and pre-loaded with alu- minum frames. The quadrupole magnet, composed of 24 pancake windings, is continuously wound without internal joints. Continuous winding in a subcoil is achieved by allowing a cutout on each grooved plate for the layer transition. The turns in the cutout are supported by a matching insert plate, which is bonded to the subcoil with epoxy. The lengths of the interconnections between subcoils are preserved during subcoil winding, and routed to their final positions on a grooved G-10 flange after the subcoils are cured. A. First AML Prototype Magnet A 6 around 1 round conductor made of 7 SSC outer NbTi wires, is used to wind the first AML prototype quadrupole. The conductor parameters are listed in Table I. The short sample limit current was calculated as the number of strands multiplied by the measured single strand critical current [8] at the design peak field of 4.7 T and 4.2 K. The is estimated as 2450 A, 1051-8223/03$17.00 © 2003 IEEE