Abstrtlct-The Crenoble High Magneiic Field Lriborrrinryis developing n 4 k T Hybrid Mugiief System io srtpporl resefireh irr sfeody, high nmgneticJelds. Oxford Instruments has bee!] selected tu supply the superconiiticlilrg orifsert system for !he hybrid mngtwl. The scope of siipply includes flie sirpercandtiding magnet, the Iiquejler, a 1.8 IC refrigemtor, ,Ire ttyasrrrt, the poww siipp& nnd the coiriroi-pmtectiolt ,rysietn. Tfic srrpercnnrlrrcfini: magne! is II 8-r, 1.8 m lotig nnd 1.1 m bore NBTi solenoid. It will be operaied in n 1.8 K superfluid keliim hnth (11 IilmospReric presstire. 111 order to deveiop the mngfiet, n speciflc R&Dprogr#m has been curried ofif. This pnper will rlescrihe the prirrclpn/ nsprcls vf the project iricluding the mnin results obfnined fo dflte.This paper describes the main features of the superconducting magnet system to be installed at the Grenoble High Magnetic Picld Laboratory (GHMFL) as part of thc 40 T new Hybrid Magnet. The GHMFL Hybrid Mngnet will produce o field of 40 T in a 34 inm bore; the superconducting magnet outsert itself will producc 8 T iii an 1100 m m cold bore while the 24 MW resistive insert will contribute 32 T. Oxford Instruments (0.1.) has been selected as supplier for the siiperconducting magnet system; thc scope of supply includes:Design and construclion ($the superconducting magnet, clyostuf and cryogenic system Refig~rudion-liy~e~er system 1500 A power supply with +/-I ppm sfabiliQ over 30 minutes Control andprotection sy.stemThe main requirements of the system are the following:Cupubilily of the magnet to with.Ttand a resistive inserf trip wilhout ylrmching, When a powcr failure occurs, the current in the resistivc insert decays with a 0.6 s time constant producing up to 3 T / s magnetic field variation on the outscrt. The fast field variation will produce at the same time current iiicrease and AC loss in the superconducting magnct. As a power 19R3 A.Nijliuis et al., 'I Coupling loss timc caiistaiits in iiill4zc Nb,Sn CIC modcl coltducton for fiision magnets ", ICMC '95 Procccdings M.Ohl ct al.,
The superconducting magnet for the Grenoble 40-T Hybrid system has been tested, up to its guaranteed value of 7 T, on its own and together with the resistive magnet. Although the superconducting magnet has been consistently operated at 7 T several times, it has shown ramp-rate limitations. In particular, when trying to ramp to field in less than 1 hour, premature quenches have been observed. Subsequent measurement of the voltages across the sections of the superconducting coil has revealed the presence of anomalous voltage spikes during ramp-up and ramp-down of the magnet. These spikes have been attributed to the presence of a shorted turn in the superconducting magnet. A theoretical model simulating the shorted turn has been developed and used to reproduce the observed magnet behavior. In particular, by analyzing the relative amplitude of the voltage spikes, we have determined the likely position of the short in the magnet and the amplitude of the current induced in the shorted turn during ramping. In this paper, both theoretical and experimental aspects of the analysis are presented. Finally, the plan of actions to fix the problem is reported.
A high field, large free bore (more than 100 mm at 4.2 K ) solenoid for the LASA lab of INFNMilan is almost completed. The NbsSn insert, constituted by two coils independently supplied, is designed to provide a central field in excess of 18 tesla when immersed in the background field of 8 tesla generated by a NbTi solenoid of 550 mm room temperature bore (this last solenoid already being in operation). The construction technique-W & R followed by vacuum impregnation-is described and the results of tests and measurements carried out on models wound with the real conductor (a NbSn/Cu Rutherford flat cable) are reported.
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