A model of a central superconducting solenoid has been successfully proved
in dynamical experiments in Japan. The superconducting coil to be inserted
into the solenoid is under way in Russia. One ton of the Nb3Sn
superconducting material was already reported to have been produced at the
Bochvar All-Russian Research Institute of Inorganic Materials (BARRIIM).
The assistant director of the BARRIIM, a member of the International
Technical Advisory Committee on ITER (International Thermonuclear
Experimental Reactor) Alexander Shikov answered a number of questions
about the current state of the process and explained that a spiral
superconducting current-carrying Nb3Sn element designed for the coil is to
be inserted into the solenoid after the corresponding thermal treatment.
- Not so long ago our institute received an order for the delivery
of 1 ton of Nb3Sn superconductor for the coil-insertion in accordance with
the ITER project. This amount was produced at the experimental and
industrial base of our institute 2 years ago. After that the material was
transfered to the All-Russian Research Institute of Cable Industry
(ARRICI), Moscow, where the preparation was proceeded by A.Rychagov and
A.Taran under V.Sytnikov. The superconductor was twisted in a tight plait
and pulled into a titanium tube with the diameter of 42.7 mm and longer
than 100 m. The current-carrying conductor was subsequently curved in a
helicoidal spiral and transfered to the Yefremov Research Institute of
Electrical and Physical Equipment (YRIEPE), Saint Petersburg, for the coil
to be produced. It is worth mentioning how large is the size of the coil
having 5 m height and approximately 2 m in diameter.
So, for the past 2 years we have worked very hard being in charge of
creating equipment assigned for the thermal treatment of this
coil-insertion. To begin with, we had no furnace of a needed size for
precise conditions to be maintained in an uninterrupted cycle for more
than 20 days long during the thermal treatment. The unique furnace was
developed at the experimental base of the YRIEPE itself. The technical
instructions were elaborated by the YRIEPE and the
BARRIIM in collaboration. The BARRIIM, being in charge of the
thermal treatment process, elaborated and
provided all so called thermal treatment regulations.
Three vital requirements provided the great challenge of the task: first,
it was necessary to attain a large voluum of vacuum to within 0.0005 torr;
second, a multi-stepped regime of thermal treatment was needed, with
possible temperature deviations less than 5 degrees Centigrade throughout
the voluum; third, the regime was to be observed round-the-clock for 22
days long. The last requirement was not only a technical problem, but
might also be an organization failure: water, electric power were to be
fed continuously, neither cutting off in feeding was permittable. Other
non-regular situations were out of question either. The stepped thermal
annealing was to be applied in order to remove gases occuring in vacuum
while treating the current-carrying element of the coil. An additional
challenge was connected with the fact that, on the one hand, the spiral
was to be held in vacuum and, on the other hand, it was necessary to
remove impurities with the help of gaseous helium flowing inside the tube
pumped out. By common efforts the furnace was constructed on the base of
the YRIEPE, the scheme of spiral arrangement was worked out and
substantiated, the whole control of the process being effected by means of
a computer. First tests have been carried out using a prototype, a so
called DUMI spiral involving copper instead of superconductor that is too
much expensive to take any risks (it costs some 1000 $/kg). At the ARRICI
a copper plait was twisted up, which contained 1152 wires, and was pulled
up into a titanium tube. It was for the first time that using titanium
tubes to provide an outer casing for protection of a current-carrying
element was suggested by us. Titanium is of special interest when cooling
till helium temperatures because it compresses less as compared to steel
or other materials; thus, its deforming effect on the superconductor is
not so great. This DUMI spiral was undergone to the whole technological
chain: a tube was twisted in a spiral, the spiral was put into the furnace
to be treated thermally. In the end the spiral was unloaded from the
furnace.
After all the procedures having been completed successfully, with the
required temperature and vacuum regimes maintained in the furnace, the
annealing of the regular coil-insertion was initiated at the end of the
December. Any failure was out of permittance: an extra-expensive coil was
to be unique. The specialists from the BARRIIM were leaving for Saint
Petersburg in a shifting regime. To control the fundamental parameters
(i.e. critical current, wastes, etc.) there existed special
witness specimens placed along the whole perimeter of the spiral: short
wire duplicating the superconductive material of the spiral.
And finally, as short ago as January 17, the furnace was unloaded. The
greatest anxiety was due to possible formation of cracks in the casing
material. But the very first test under the pressure of
helium which was pumped up inside the casing showed the casing to remain
totally hermetic.
Today I am so glad to tell that the complex trials of witness specimens
have been completed and the results are ready to be sent off to the ITER
headquarters to Japan. The superconductor properties have been shown not
only to correspond to the sample ones in every aspect but also to have
certain safety margin as compared to them. It is worth mentioning also
that thermal treatment of the coil-insertion was performed after a short
sample of a current-carrying element had been modelled and tested in
Switzerland at the SULTAN equipment. Our superconductors posessed all
required parameters, in particular, the capability needed to carry the
current, the absence of damages, and showed persistent properties under
twisting.
By the present moment, the current-carrying element has been completely
covered by insulating material. The element is going to be placed into a
solid steel case, that has been produced at the Izhorsk works, to be
compounded and furnished with all required supply leads. After having
performed the control trials, the coil-insertion will be sent to Japan by
a special international flight at the end of February or at the beginning
of March.
All the specialists to have participated in the coil-insertion production
and those to perform its testing are going to meet in Saint Petersburg at
the large consultation on March 1/2. The purpose of the meeting is to
co-ordinate a final testing program of the coil inserted in the central
solenoid. Thus, the collective 10-year hard work of the three Russian
institutes - BARRIIM, ARRICI, YRIEPE - and their colleagues from other
scientific and technological branches is anticipated to come to its
successful end.
At the BARRIIM the project has been under laboratory head A.Vorobiova's
and my guidance; the most active efforts in its elaboration have been made
by V.Pantsyrny, A.Silaev, and Dergunova's group. The great part taken by
our young specialists - K.Mareev, I.Abdyukhanov, and I.Siniyn n - is worth
mentioning as well, and I do this with pleasure. On behalf of Saint
Petersburg all the current guidance was realised by O.Filatov, ing g at
the same time the manager of the ITER project in Russia and the assistant
director of the YRIEPE, and by V.Beliakov. Moreover, S.Egorov, I.Rodin,
and V.Trofimov participated deeply in the work. They worked in the
twenty-four-hour shifting regime having sometimes planning meetings by
telephone at nights especially when changing temrature e regimes. By the
way, an hour before the New Year approach O.Filatov and V.Beliakov came to
congratulate operators on duty at the working furnace and I wished them a
happy New Year by telephone from Moscow.
The thermal treatment process which began in 2000 and finished in 2001 is
of great symbolic significance: the large-scale operations dealing with
superconductivity that began in the past century are to be proceeded in
the century to come. Granting that the decision on the ITER construction
is taken what is the hope of all project members, we can aspire at the
delivery of more than 240 tons of the (Nb-Ti alloy/Nb3Sn compound)-based
Russian superconductors. A number of home industrial works have already
begun preparing for output of these materials.
Advanced Technologies, Superconductors, Nanotubes, Fullerans
Translated by Nataliya Lipunova
