BEHAVIOUR OF Nb-Ti-Ta WIRE IN NON-STATIONARY CONDITIONS

Transcription

1 BEHAVIOUR OF Nb-Ti-Ta WIRE IN NON-STATIONARY CONDITIONS M. Asdente, E. Olzi, V. Ottoboni, S. Zannella To cite this version: M. Asdente, E. Olzi, V. Ottoboni, S. Zannella. BEHAVIOUR OF Nb-Ti-Ta WIRE IN NON- STATIONARY CONDITIONS. Journal de Physique Colloques, 1984, 45 (C1), pp.c1-499-c < /jphyscol: >. <jpa > HAL Id: jpa Submitted on 1 Jan 1984 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 JOURNAL DE PHYSIQUE Colioque C1, suppl6ment au no 1, Tome 45, janvier 1984 page C BEHAVIOUR OF Nb-Ti-Ta WIRE IN NON-STATIONARY CONDITIONS M. Asdente, E. ~lzi*, V. Ottoboni and S. Zannella CISE S.p.A., P.O. Box 12081, Milan,.Zl;aZy +CNR-ITM, Via lndun'uno, 10, CiiriseZZo B., ItaZy RElsume - Les perter, d'dnergie en courant alterrlatif et les valeurs critiques du courant ont Bt& n~esurees sur un &chantillon du NbTiTa,pr&c6demment6tudieen conditions stationnaires. L'ensemble des resultats nontre que cet alliage peut en principe Etre utilis6 aussi bien que l'alliage NbTi dans des conditions de champ variable. Abstract - Critical ac currents and losses are measured on a NbTiTa wire previously characterized in dc conditions. The whole of the results show that in principle this alloy could work at least as well as the MbTi onc when time variable conditions are involved. I - INTRODUCTION An increasing interest in Nb-Ti.-Ta alloys/l/2/3/has been promoted in the latest years as a consequence of the forscen possibility that, with superfluid helium, the applications of the ductile alloys could be extended to tesla and above. Until now the Ni-Ti-Ta alloys have been essentially studied and improvcd for dc operative conditions; there are, however, no eats as regards their behaviour in time varying situations. Altough a number of applications of superconductivity are concerned with "a priori" stationary conditions, many of them, such as magnetohydrodynamic generators, supcrconducting cables, alternators, and fusion reactorsimplie situations where time changing components of the magnetic field and/or current are also involved. It seems thercfore worth to have an idea of the Ni-Ti-Ta and generally in time varyina situations. wire behaviour in transient In the aim of giving an insight into this point, principally as far as a comparison with a MbTi alloy is concerned, loss measurements in the same situations as previou- sly considered for a similar RbTi multifilamentary wire /4/, have been performed. I1 - EXPERIMENTAL The sample considered is a Nb-43Wi-25':Ta stabilized multifilamentary wire (61 filaments, um; copper-superconductor ratio = 1.45). For a more - description of this wire see ref. 5. This wire,2 m long, anti-inductively wound as a small coi1,is fcd by a 50 Hz current in the presence of a dc magnetic field perpendi.cular to thc wire itself. The sample is put in grooves on the stumatite support and wrapped with gauze embed- Article published online by EDP Sciences and available at

3 CI-500 JOURNAL DE PHYSIQUE ded with bee wax to minimize the mechanical effect of electrodynamical forces. The experimental apparatus for the measurement of energy losses has been previously described /6/. Owinu to the experimental difficulty of maintaining lower temperatures with relatively high dissipations, and also of havinu a significant comparison with the NbTi wire, the measurement temperature is maintained at 4.2 K although it is surely a worse situation for the NbTiTa wire as regard its typical operative temperature. I11 - RESULTS The loss data as a function of current intensity I at various values of external field B are given in Fig. 1 Fig. 1 - Power losses vs current intensity I at various values of external field B. Tney turn out to be exactly superimposed to those previously found for the NbTi similar wire in the regions where measurements have been performed on both samples (solid line). Also the minimum in losses vs B already noticed /4/ for the MbTi wire at low B and high I is reproduced with the same features (Fig. 2). As far as the current transport capabilities is concerned the trends of dc and ac critical currents (I and I respectively) as a function of B are shown in Fig. 3 PC ac for both samples. Whlle for the >%Ti wire the I values are constantly lower than I ones, for the NbTiTa wire the two values przetically coincide probably because dc of a better stabilization of this wire. The I values for the NbTiTa wire exceed ac the corresponding ones of the NbTi wire at low field values. If we reconsider the curyes in Fig.1 we notice that quite a peculiar trend seems to take place at high fieldsand low I (dashed line): a cross between the curves relevant to 3 and 5 tesla and those at lower field values is shown. Something like this has been already noticed on a monofilamentary NbTi wire /7/ where this fact had turned out to be due to an interchange between the relevant weight of hysteretic and eddy current losses in different fields. Before accepting a similar interpretation,in this case we first prefer to control that no spurious effects due to mechanical

4 . ldc NiTl 'ac.. m I I NbTiTa ware dc ' ac Fig. 2 - Power losses vs magnetic Fig. 3 - Comparison between dc critifield B at different trans- cal current and ac transition port current values (an arbi - current vs magnetic field B trary scale is used). of NbTi and NbTiTa samples. instability are responsible for this trend and if so, to subsequently perform further measurements at different frequencies. IV - CONCLUSIONS Although the results have not been obtained at the best working temperature for the NbTiTa alloy, the whole of them show that in principle this alloy could work at least as well as the NbTi one when time variable conditions are involved, provided an adequate thermo-mechanical production cycle is performed /5/. The most immediate consequence, trivial but interesting from a practical point of view when superconducting apparatus costs are taken into account,is that expensive operation for niobium purification from Ta are unnecessary when this kind of Nb- based alloys are used. REFERENCES /1/ H.R. Segal, T.A. de Winter, Z.J.J. Stekly and K. Hemachalam, IEEE Trans. on Magn., MAG-17, p. 53 (1981). /2/ W.Y. Chen, J.S. Alcorn, Y.H. Hsu and J.R. Purcell, IEEE Trans. on Magn. MAG-17, p. 57 (1981). /3/ D.C. Larbalestier "Superconductors~a~~~i~~Science. Metallurgy, Fabrication and ~pplications", p. 133 Ed. Plenum Press (1981). /4/ M. Asdente, M.C. Pascucci and S. Zannella, Proc. of ICMC, Kobe p. 167 (1982). /5/ E. Olzi, G. Rondelli, G. Turisini and C. Federghini, Proc. of the ICMC p, 49,

5 C1-502 JOURNAL DE PHYSIQUE Kobe (1982). /6/ M. Asdcnte, G. Cavalleri and A.M. Ricca, Proc. of 8th ICEC,p.059,Genova(l980). /7/ M. Asdente, V. Ottoboni, G. Ripamonti and S. Zarlnella, ICMC Conference, Color5 do Sprinp ( 1983). Work performed Inmthe frame of the EMEL-CISE "MACRI" project.