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STATIONARY HIGH MAGNETIC FIELDS
N. Chernoplekov
To cite this version:
N. Chernoplekov. STATIONARY HIGH MAGNETIC FIELDS. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-29-C1-33. �10.1051/jphyscol:1984105�. �jpa-00223562�
J O U R N A L DE PHYSIQUE
Colloque Cl,.suppl&ment a u no 1, Tome 45, janvier 1984 page CI-29
STATIONARY HIGH MAGNETIC FIELDS
N . A . Chernoplekov
I . V . Kurchatov I n s t i t u t e o f Atomic Energy, Moscou 123182, U.S.S. R.
R6sum6 - Dans l'article on examine les moyens de production des sources de champ magnetique stationnaire puissant et l'glaboration d'un nouveau systgme hybride dans 1'Institut Kourtchatov dl&nergie atomique.
Abstract
-
Ways of creating stationary high magnetic field sources, as well as development of a new hybrid system at the 1.V.Kurchatov AEI are considered in the report.There is a constant need in physics and other fields of
science for investigations performed under extreme conditions, among them the maximum attainable magnetic fields. If time constants of processes being investigated'in a magnetic field exceed several seconds, this magnetic field should be stationary.
The problem of obtaining strong stationary magnetic fields is one of the most interesting but labour-consuming ones in magnetic technology.
DiIETHODS OF GENERATIlTG STATIONARY HIGH BEIAGMETIC FIELDS
Initially, there existed only one way of producing high stationary magnetic fields, that is the method of resistive water-cooled solenoids. Up till now considerable progress has been made in this way: If a resistive water-cooled solenoid of composite two-section deslgn consisting of the inner polyhelix pert and outer Bitter coil is employed, a field of the 23.4 T at the supply power of 8.7 MW /I/ can be generated in a 5 cm room temperature bore. This
induction turns out to be close to the maximum attainable one for thermal and mechanical limits /2/,
A great number of mostly analytical estimations have been made, which assume that stationary fields of about 40 T are, in prin-
ciple, attainable in resistive water-cooled solenoids. In spite of these interesting calculations there is no practical grounds to expect that a field of more than 25 T can be obtained in actually operating resistive water-cooled stationary magnets in the next 10 years. So far, it is, apparently, a reasonable technical limit of the present-day technology.
In the sixties another method of generating high stationary mag- netic fields, that is a method of superdonducting magnets, began to be developed, It was not an easy way, yet, it produced a number of interesting results. Now, at any laboratory where liquid helium is available it is most likely that a superconducting solenoid will be used for operation in a field of up to 15 T. It is more
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984105
C1-30 JOURNAL DE PHYSIQUE
convenient and, for reasons of maintenance costs, more economical.
The use of niobium-titanlum superconductors makes it possible to produce reliably laboratory solenoids rated for fields up to I 0 T at 4.2 K. Nore than a thousand such solenoids are operating now throughout the world. Only at the 1.V.Kurchatov AEI about a hund- red solenoids of this type were produced for physical investiga- tions /3/. In order to obtain higher fields (up to 15 T and higher) combined solenoids with the outer section made of mb-Ti and the inner one, of 1Bb3Sn are, as a rule, constructed. The two-section (Nb Sn and V Ga) solenoid rated for 17.5 T of the Japan National
~esaarch 1naZitute of Eetals /4/ is a record holder of supercon- ducting solenoids. A record breaker being now in project is a six- section solenoid (three mb-Ti, two I'?b3Sn and one V Ga sections) for a field of 20 T in a 4-cm bore, which is under con&ruction here in Grenoble /5/.
Continuous improvement of superconductors and superconducting mag- net technology allows us to hope that in the next decade super- conducting solenoids with the field of about 20 T will no longer be a unique event. However, we cannot count on making greater progresa in this field during these ten years. So far, we do not have at our disposal either the necessary connnercial superconduc- tors with critical parameters higher than those of Nb Sn and V Ga, or the methods of producing superconducting solenoidgrated fo4 a field of more than 20 T.
It is clear from the above-mentioned that either resistive wa-ter- cooled solenoids or superconduoting ones used seperately do not offer the possibility to generate reliably magnetic induction of more than 25 T. The solution was proposed independently by B.Komar
(USSR) and B.Montgomery (USA). Their suggestion was to combine inner resistive and outer superconducting solenoids to form a single system, i.e. a hybrid solenoid. Recently, the technology of creating strong stationary magnetic fields has been developed precisely in this direction. Three hybrid systems /6, 7, 8/ are by now operating throughout the world and some more systems are being constructed and close to completion. It is the main direction of the high stationary magnetic field generation technology develop- ment. Hybrid system generating a stationary magnetic field of about 40 T / 5 / is the goal, which can be achieved i n this direction in the near future due to technical potentialities of the method.
INVESTIGATIONS OF STATIONARY HIGH FIELDS IN THE USSR
In the USSR a number of institutes have laboratories of high mag- netic fields. The most well-known of them are those of the 1.V.Kur- chatov AEI, of the Lebedev Physical Institute of' the Academy of Sciences of the USSR (both in Moscow) and of the L.V.Kirensky
Institute of Physics of the Siberian Department of the USSR Academy of Sciences (in Krasnoyarsk). In these laboratories resistive mag- nets with inductions from 12 to 17 T, as well as superconducting magnets with inductions up to 15 11 are used. Studies on improving resistive water-cooled solenoids are carried out on a large scale at the laboratory of strong magnetic fields of the L.V.Kirensky Institute of Physics. At present a new installation with a Bitter- type water-cooled solenoid rated for a field of more than 20 T is being under construction there. Since this laboratory works in collaboration with the International Laborato of Strong Nagnetic Fields and Low Temperatures in Wroclaw (Polan8 and their joint
report is to be delivered at the Conference, there is no need to go into futher details,
Let us consider thesituationwith the hybrid magnet at the I,V.Kur- chatov AEI. As it is known, the first in the world 25-T hybrid mag- net was successfully put into operation at the 1.V.Kurchatov AEI exactly ten years ago /6/. B.Nontgomery was one of the first to visit the Institute and offer us his congratulations upon the suc- ces. Let us recollect the system design and parameters. They are represented in fig. I and table I, respectively.
A rather curious episode took place when the hybrid system was put into operation for the first time. The water prgotection system of the ripple suppressor trans- former of the water-cooled sole- noid failed. As a result, the transformer burned out, the 25-kA circuit broke and the magnetic equilibrium of the two parts of the h y b r l d system was destroyed.
a All that caused a great electro-
6
magnetic and thermal shock in the superconducting solenoid, It passed into the normal state and the energy was withdrawn from it with the time constant of 5 s.This incident shows that a hybrid system is highly reliable and safe if protection is properly arranged. Our ten-year experience
i n operating the hybrid magnet confirms this statement.
Fig. 1. Layout of the 25 Tesla hybrid magnet system at the 1,V.Kurchatov AEI.
Table 1.
Description of parameter Water-cooled Superconduc t ing
system eolenoid
Diameter of turns, cm:
inner 4.8 and 16.4 37.6
outer 15.6 and 27.5 70,O
number of turns 75 and 65 4000
Power consumption, MW 3.1 a d 2.5
-
Specific volume heat
release, w/cm3 1200 and 300 Contribution into
induction, T 18.3 at 25 kA 6.3 at 1 kA Our hybrid solenoid is in operation during one week in a month, as a rule. 'Phis restriction is due to the supply source of the resi-
CI-32 JOURNAL DE PHYSIQUE
stive solenoid, which is also used in plasma physics experiments according to the operating schedule. The use of the hybrid system al-
lowed us to make a large number of studies on semiconductors and metals, and superconductors as well as commercial superconducting materials. In that seemingly complicated hybrid system it is pos- sible to carry out such delicate experiments as the measurement of temperature dependence within the interval of 1
-
300 K of heatcapacity of samples which mass is less than 1 g in the field of more than 20 T or the high-precision measurements of the Hall con- ductivity in the inverse layers within the ultraquantum limit.
However, the need for further development of studies on stationary high magnetic fields made us commence devising a new hybrid magne- tic system, This work is done in two stages. At the first stage a new superconducting solenoid for a hybrid system rated for a 12-1 field at 4.2 K is developed. At the second one, a new water-cooled polyhelix solenoid for a field of 20 T will be devised, and the hybrid system will be essentially a combination of these two parts, which will make it possible to take measurements in the fields of about 30 T in addition to the opportunities provided by our pre- vious hybrid system.
Apparently, the first stage, i.e. the construction of a supercon- ducting solenoid for a field of 12 T, should be discussed in detail. One can see from table 1 that the contribution of the superconducting solenoid in our previous hybrid magnet is only 6.3 T, The progress made recently i n developing multifilament noi- bium-tin superconductors and the respective magnets /9/ allows us to increase the contribution of superconducting solenoid up to 12 T thus raising the total induction of the hybrid system up to 30 T even with the resistive solenoid at the same level of power consumption, We believe that this way is more correct than that of increasing the power of supply sources.
A new superconducting so enoid will be wound with a niobium-tin conductor of the '20x3-mm3 cross section. The main parameters of this solenoid are presented in table 2 and its layout is given in fig. 2.
Table 2.
Description of parameter Value of parameter
Winding inner diameter, cm 39
Outer diameter, cm 9 5
Height, cm 88
Induction in the centre, T 12.5
Operating current, kA 3.45
Number of double pancakes 20
Stored energy, IUJ 16
The solenoid will be placed into a cryostat with a warm bore of 30 om. The cryostat is not too high, which is more convenient in performing investigations. In this case the main supply of liquid helium is provided f ~ r by a aupply tank with current leads arranged above the cryostat. The current leads may be disconnected in the
storage condition in order to save liquid helium. The cryostat will be equipped with a self-contained liquefier
-
a refrigerator withequivalent li uid helium capacity
He &9ue/e~ of about 20 1%. At ppreant,
theae operations are carried out together with the studies on de- veloping a new resistive magnet supply source of 7.5 W .
We look forward to completion of the new hybrid system development in the near 1 . 5 - 2 y e a r s .
In conclusion I would like to Thank my colleagues P.A.Cherem- nykh, V.E.Keilin, V.I.Ozhogin and B.P.E[hmrstalev for stimulating discussion of the stationarg high magnetic field generation prob- lems and their assistance in preparing the report.
Fig, 2. Layout of a new 30 Tesla hybrid system at the 1,V.Kurchatov A . 1 . Refereno es
/I/ SCHIiEIDER %.Ye, D E E Transactions on Magnetics, MJa'gl- (1981) 1775.
/2/ KATRUKHIN Yu.K,, PTE No,2 (1977) 199 (in Russian).
/3/ ANASHKIN O.P., KEILIM V.E., SURIN M.10, SHLEIFEBAN VoKh., Cryogenics, July 1979,.405.
/4/ TACHIKAWA K. in: "Physics in high magnetic fields". CHIKAZU-
gdI S. and MIURA B. eds. Springer Verlag, 1981
,
1 2./5/ LAKDWEHR C,, IEEE Transactions on m e t i c s &fag-17 (1981) 1768.
/6/ CHEREMHYKEI P.A.
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CHURAKOV Gel?., POZHDETVEXSKY B O X , SAMOI- WIV B.X., CHERmOPLEKOV N.A., IEEE Transactions on Magnetics Mag-11 (1975) 519./7/ Kvan HULST, IEEE Transaction8 on Magnetics Mag-1 7 (1981 ) 1790, /8/ LEUPOLD M,Y.
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HALF Y.R., IWASA Y,,
RUBIN L.G., ~ G G E L R.Y.,IEEE Transactions on Magnetics PBeg-17 (1981) 1779.
/9/ CHEIWOPZEKOV N.A., Superconducting -te- systems for plasma physics research in the USSR, Sixth International Coaference on Magnet Technology XT-6, Bratislava, 1977,
