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Superconducting C-shaped magnet for deuteron cyclotron DC-1
ICEC 15 Proceedings
S u p e r c o n d u c t i n g C - s h a p e d m a g n e t for d e u t e r o n c y c l o t r o n DC-1 Yu.G. Alenitckiy, A.F. Chesnov, S.I. Chesnova, N.A. Morozov, V.I. Pryanichnikov, E.V. Samsonov, V.I. Sukhanov, A.T. Vasilenko, N.L. Zaplatin Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia A C-shaped electromagnet with superconducting coils for the foursector deuteron cyclotron of energy about 100 MeV is being developed at the JINR LNP. This cyclotron is the second stage of an accelerating complex for the neutron generator for the electronuclear method of energy generation. The maximum induction in the magnet is 4.5 T, stored energy is 5 MJ, mean current density in a coil is 9.107A/m 2. The heat impulse which shifts the coil to a normal condition is estimated. The status of the manufacturing of the magnetic system elements is considered. INTRODUCTION The cyclotron complex is to include a linear accelerator of Ed = 15 MeV with radiofrequency quadrupole focussing and two cyclotrons with superconducting sector coils, their extracted beam energy being 90 and 1800 MeV respectively [1]. The magnet system of the cyclotron DC-1 consists of four sector magnets. The experimental apparatus described in the present paper is a full-size model of a sector magnet with a cryogenic plant KGU-150/4.5, power supply units, a monitoring and measurement system, and other auxiliary equipment to maintain its operation. 1. Basic parameters of the magnet system Basic parameters of the ferromagnetic and current elements of the DC-1 magnet system were selected by calculating the magnetic field and deuteron beam motion dynamics. Different programs were used for calculation [2, 3]. The magnet system and basic parts of superconducting coils are schematically shown in Fig. 1 and 2 respectively. The basic parameters of a sector magnet for the cyclotron DC-1 are listed in Table 1. Table 1. Basic parameters of a sector magnet Weight (t) Dimensions (m) Yoke aperture (m) Gap between cold poles (m) Ampere-turns per sector (MA) Mean current density ( A / m 2) Maximum magnetic field in gap (T) Stored energy per sector (M J)
35 2.4 x 1.2 x 2.8 1.3 0.14 3.35 9.2 × 106 4.26 5
The required magnetic field along the radius is provided by ferromagnetic plates with a hole along their centre line. Its shape is chosen both experimentally and by calculation. The current winding is chosen to be applied directly on ferromagnetic plates of special shape. This design allows the required magnetic field to be generated at shorter radii. The contribution to the mean magnetic field is about 50% from the main coils, about 42% from the ferromagnetic yoke and about 8% from the cold pole.
Cryogenics 1994 Vo134 ICEC Supplement 667
ICEC 15 Proceedings
2. Cryogenic system Cryostatting of the superconducting of a sector magnet with a cooled mass of 7 tonnes will be provided by circulation of two-phase helium in channels (indirect cooling, Fig. 2). A special precooling block is designed to cool the system to nitrogen temperature. It supplies gaseous helium of temperature from 300 K to 80 K. Further cooling is ensured by a cryogenic helium plant KGU-150/4.5 with a capacity 40 1/h of liquid helium in the liquefying mode or 150 W at a temperature of 4.5 K. The plant ensures removal of heat load from the superconducting system (20-30 W) with a large cooling power margin (about 90 W), simultaneously taking off 0.1 g/s of helium per current input. The total cooling time will be about 7 days [4]. The flow rate of liquid nitrogen in the eryostatting mode will be 12.8 g/s. 3. Superconducting coil safety system Cables with adiabatic stabilization and a safety system with internal energy absorption are used in construction of large magnets . The use of external energy absorbers makes it necessary either to heat some parts of the coil to 400-500 K or to increase the output voltage to 2.5 KV, which is undesirable. If a normal zone appears in a large magnet, the whole coil is shifted to the normal state and the heat energy is distributed over the whole volume. In paper [5] it was shown using the temperature dependence of the conductor enthalpy the maximum coil temperature to be T N 80 K in this case. The whole coil is shifted to the normal state owing to special winding with strong inductive coupling of two coil halves. The coil is wound as a set of two-layer pies, alternate ones being connected together in current. In paper [6] it was shown that at the current rating IT = 830 A after the power supply is switched off the vortex losses in the superconductor matrix shift the coil to the normal state in time 3T1 -----0.05 s. 4. Mechanical stresses in the superconducting coil The superconducting coil consists of the upper and lower halves symmetrical about the median plane of the magnet. The coil is installed in the vacuum chamber of the cryostat shaped as a regular triangular prism 1.3 m high, with sides 1.8 m long (Fig. 2). It is fixed with 6 vertical supports (3 from the above and 3 from the below) and 4 horizontal ones. All structure elements are made of stainless steel 12X18H10T. Mechanical stresses in structural elements of the coil were cMculated by a computer program where the problem of the theory of elasticity is solved by the final elements method on a two-dimensional triangular grid [7]. The initial conditions were calculated distributions of pondermotive forces acting on the coil and temperature deformations. The main structural element of the coil is a section whose view in plan and section are shown in Fig. 2. Stresses arise from the fact that the heat shrinkage of the frame material is larger than that of steel plate on which the coil is wound. The pondermotive forces acting on the current elements make an insignificant contribution. The maximum values are el = 230 M N / m 2 and Tm~= = 120 M N / m 2, which is tolerable. 5. Thermodynamic calculations Heat perturbations capable of shifting part of the superconductor to a normal state arise in the superconducting magnet coil due to some causes, and Joule heat is released in this part of the coil due to resistance of the copper matrix. The results of the numerical study of the relation between the heat impulse shifting the coil to the normal state and the transport current in the conductor are given in Fig. 3. A nonstationary heat conductance equation was solved on the three-dimensional rectangular irregular grid. Heat of density Q0 and duration 0.2 s is released in a heater of volume 30 cm 3. Joule heat Q j is released at the conductor temperature above 7.5 K. For current rating I = 830 A Qj is 2.9 × 105 J / m 3.
668
Cryogenics 1994 Vol 34 ICEC Supplement
ICEC 15 Proceedings
6. Fabrication of magnet system By now all the main elements of the magnet system have been fabricated. They are the magnet yoke, vacuum chamber, nitrogen screen, supports, current inputs, frames of coil segments, steel pole discs. Also, a technological bay is set up for winding and compounding the superconducting coil. The chosen shape of steel plates for the cold pole is such that all sides of the coil have a positive curvature radius. It ensures uniform tension of the current wire under the winding and over all the coil perimeter under operational conditions. The temperature deformation ratio of the internal steel plates, superconducting coils and stainless steel frame ensures outside and inside compression of the coil. The procedure of coil winding and compounding was successfully tested with two experimental segments of 4 pies each. Examination of the coil section showed that compound densely fills all cavities between the superconductor [8]. This procedure is now used to wind segments of DC-1 coils. Their parameters are given in Table 2. Table 2. Parameters of wind segment Wire Number of segments in coil Number of modules in segment Number of pies in module Number of turns in pie Total number of turns Wire insulation Wire insulation thickness Frame insulation Interpie insulation Segment cross section
SPNT-50-2x3.5-2970-0.35 8 2 6 42 4032 80% glass + 20% lavsan 0.15-0.17 m m fibre glass fabric (1-4) m m fibre glass fabric 0.3 m m 50 x 56 mm 2
At present an experimental coil segment is fabricated and compounded by hot-hardened resin. Two more segments are under fabrication for experiments on their cooling and energizing. Simultaneously, work is going on to install the nitrogen screen, external service lines, vacuum system, diagnostics systems, and other auxiliary devices. REFERENCES 1 2 3 4 5 6 7 8
Glazov A.A. et al, J1NR, 9-81-734, Dubna (1981) (in Russian) Vorozhtsov S.B. et al., JINR, 9-83-608, Dubna(1983); Proc. of MT-8, Grenoble, France (1983) Alenitsky Yu.G. et al., JINR, E9-85-608, Dubna (1985) Alenitsky Yu.G. et al., Proc.of MT-10 IEEE Trans.on Mag.(1988) vol. 24, num. 2, p. 1125 Alenitsky Yu.G. et al., JINR, P9-85-707, Dubna, (1986) (in Russian) Zaplatin N.L., Samsonov E.V., JINR, P9-85-707 (1986) (in Russian), p. 113 Segerlind J. "Applied Finite Element Analysis", New York, 1976, p. 122 Alenitsky Yu.G. et al., Proc.of MT-12, IEEE Trans.on Mag. (1992) vol. 28, num. 1, p. 554
Cryogenics 1994Vol 34 ICEC Supplement
669
I C E C 15 P r o c e e d i n g s
~.~o Co~l~ Po~e
Hote ¢ortLetd form •" p
/
i ", eace~"Jz-t'esonator"~,efd
i , i i i~ CH
x
Figure 1
DC-1 magnet system.
z r , ~ ~"
0.1
,,.z 0.2
Z~)I
.
I
~
_.~
/'(M) .
.
.....
r(.~')
.
i-i
~
,-,-
F i g u r e 2 Cold pole of the magnet, a) I-IV - segments, b) View in plan. c) Segment I enlarged (1 - - coil, 2 - - steel plates, 3 - - stainless steel serving, [] - - cooling channels). Y
QO (W/M3)I
x
\ 104
f
\\l
i
\ f 2xi0 4
i
i
i
i
i
i
lO 4
,
, i l l
105
f i
.
.
.
.
Q/ {W/M3}
F i g u r e 3 Thermodynamic stability boundary of the coil. Q0 is the heat impulse (At = 0.2 s), Q j is the Joule heat in the normal phase region (1 - - stainless steel serving, 2 - - cooling channels, 3 - coil, 4 - - volume of heat perturbation).
670
Cryogenics 1994 Vol 34 ICEC S u p p l e m e n t
S u p e r c o n d u c t i n g C - s h a p e d m a g n e t for d e u t e r o n c y c l o t r o n DC-1 Yu.G. Alenitckiy, A.F. Chesnov, S.I. Chesnova, N.A. Morozov, V.I. Pryanichnikov, E.V. Samsonov, V.I. Sukhanov, A.T. Vasilenko, N.L. Zaplatin Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia A C-shaped electromagnet with superconducting coils for the foursector deuteron cyclotron of energy about 100 MeV is being developed at the JINR LNP. This cyclotron is the second stage of an accelerating complex for the neutron generator for the electronuclear method of energy generation. The maximum induction in the magnet is 4.5 T, stored energy is 5 MJ, mean current density in a coil is 9.107A/m 2. The heat impulse which shifts the coil to a normal condition is estimated. The status of the manufacturing of the magnetic system elements is considered. INTRODUCTION The cyclotron complex is to include a linear accelerator of Ed = 15 MeV with radiofrequency quadrupole focussing and two cyclotrons with superconducting sector coils, their extracted beam energy being 90 and 1800 MeV respectively [1]. The magnet system of the cyclotron DC-1 consists of four sector magnets. The experimental apparatus described in the present paper is a full-size model of a sector magnet with a cryogenic plant KGU-150/4.5, power supply units, a monitoring and measurement system, and other auxiliary equipment to maintain its operation. 1. Basic parameters of the magnet system Basic parameters of the ferromagnetic and current elements of the DC-1 magnet system were selected by calculating the magnetic field and deuteron beam motion dynamics. Different programs were used for calculation [2, 3]. The magnet system and basic parts of superconducting coils are schematically shown in Fig. 1 and 2 respectively. The basic parameters of a sector magnet for the cyclotron DC-1 are listed in Table 1. Table 1. Basic parameters of a sector magnet Weight (t) Dimensions (m) Yoke aperture (m) Gap between cold poles (m) Ampere-turns per sector (MA) Mean current density ( A / m 2) Maximum magnetic field in gap (T) Stored energy per sector (M J)
35 2.4 x 1.2 x 2.8 1.3 0.14 3.35 9.2 × 106 4.26 5
The required magnetic field along the radius is provided by ferromagnetic plates with a hole along their centre line. Its shape is chosen both experimentally and by calculation. The current winding is chosen to be applied directly on ferromagnetic plates of special shape. This design allows the required magnetic field to be generated at shorter radii. The contribution to the mean magnetic field is about 50% from the main coils, about 42% from the ferromagnetic yoke and about 8% from the cold pole.
Cryogenics 1994 Vo134 ICEC Supplement 667
ICEC 15 Proceedings
2. Cryogenic system Cryostatting of the superconducting of a sector magnet with a cooled mass of 7 tonnes will be provided by circulation of two-phase helium in channels (indirect cooling, Fig. 2). A special precooling block is designed to cool the system to nitrogen temperature. It supplies gaseous helium of temperature from 300 K to 80 K. Further cooling is ensured by a cryogenic helium plant KGU-150/4.5 with a capacity 40 1/h of liquid helium in the liquefying mode or 150 W at a temperature of 4.5 K. The plant ensures removal of heat load from the superconducting system (20-30 W) with a large cooling power margin (about 90 W), simultaneously taking off 0.1 g/s of helium per current input. The total cooling time will be about 7 days [4]. The flow rate of liquid nitrogen in the eryostatting mode will be 12.8 g/s. 3. Superconducting coil safety system Cables with adiabatic stabilization and a safety system with internal energy absorption are used in construction of large magnets . The use of external energy absorbers makes it necessary either to heat some parts of the coil to 400-500 K or to increase the output voltage to 2.5 KV, which is undesirable. If a normal zone appears in a large magnet, the whole coil is shifted to the normal state and the heat energy is distributed over the whole volume. In paper [5] it was shown using the temperature dependence of the conductor enthalpy the maximum coil temperature to be T N 80 K in this case. The whole coil is shifted to the normal state owing to special winding with strong inductive coupling of two coil halves. The coil is wound as a set of two-layer pies, alternate ones being connected together in current. In paper [6] it was shown that at the current rating IT = 830 A after the power supply is switched off the vortex losses in the superconductor matrix shift the coil to the normal state in time 3T1 -----0.05 s. 4. Mechanical stresses in the superconducting coil The superconducting coil consists of the upper and lower halves symmetrical about the median plane of the magnet. The coil is installed in the vacuum chamber of the cryostat shaped as a regular triangular prism 1.3 m high, with sides 1.8 m long (Fig. 2). It is fixed with 6 vertical supports (3 from the above and 3 from the below) and 4 horizontal ones. All structure elements are made of stainless steel 12X18H10T. Mechanical stresses in structural elements of the coil were cMculated by a computer program where the problem of the theory of elasticity is solved by the final elements method on a two-dimensional triangular grid [7]. The initial conditions were calculated distributions of pondermotive forces acting on the coil and temperature deformations. The main structural element of the coil is a section whose view in plan and section are shown in Fig. 2. Stresses arise from the fact that the heat shrinkage of the frame material is larger than that of steel plate on which the coil is wound. The pondermotive forces acting on the current elements make an insignificant contribution. The maximum values are el = 230 M N / m 2 and Tm~= = 120 M N / m 2, which is tolerable. 5. Thermodynamic calculations Heat perturbations capable of shifting part of the superconductor to a normal state arise in the superconducting magnet coil due to some causes, and Joule heat is released in this part of the coil due to resistance of the copper matrix. The results of the numerical study of the relation between the heat impulse shifting the coil to the normal state and the transport current in the conductor are given in Fig. 3. A nonstationary heat conductance equation was solved on the three-dimensional rectangular irregular grid. Heat of density Q0 and duration 0.2 s is released in a heater of volume 30 cm 3. Joule heat Q j is released at the conductor temperature above 7.5 K. For current rating I = 830 A Qj is 2.9 × 105 J / m 3.
668
Cryogenics 1994 Vol 34 ICEC Supplement
ICEC 15 Proceedings
6. Fabrication of magnet system By now all the main elements of the magnet system have been fabricated. They are the magnet yoke, vacuum chamber, nitrogen screen, supports, current inputs, frames of coil segments, steel pole discs. Also, a technological bay is set up for winding and compounding the superconducting coil. The chosen shape of steel plates for the cold pole is such that all sides of the coil have a positive curvature radius. It ensures uniform tension of the current wire under the winding and over all the coil perimeter under operational conditions. The temperature deformation ratio of the internal steel plates, superconducting coils and stainless steel frame ensures outside and inside compression of the coil. The procedure of coil winding and compounding was successfully tested with two experimental segments of 4 pies each. Examination of the coil section showed that compound densely fills all cavities between the superconductor [8]. This procedure is now used to wind segments of DC-1 coils. Their parameters are given in Table 2. Table 2. Parameters of wind segment Wire Number of segments in coil Number of modules in segment Number of pies in module Number of turns in pie Total number of turns Wire insulation Wire insulation thickness Frame insulation Interpie insulation Segment cross section
SPNT-50-2x3.5-2970-0.35 8 2 6 42 4032 80% glass + 20% lavsan 0.15-0.17 m m fibre glass fabric (1-4) m m fibre glass fabric 0.3 m m 50 x 56 mm 2
At present an experimental coil segment is fabricated and compounded by hot-hardened resin. Two more segments are under fabrication for experiments on their cooling and energizing. Simultaneously, work is going on to install the nitrogen screen, external service lines, vacuum system, diagnostics systems, and other auxiliary devices. REFERENCES 1 2 3 4 5 6 7 8
Glazov A.A. et al, J1NR, 9-81-734, Dubna (1981) (in Russian) Vorozhtsov S.B. et al., JINR, 9-83-608, Dubna(1983); Proc. of MT-8, Grenoble, France (1983) Alenitsky Yu.G. et al., JINR, E9-85-608, Dubna (1985) Alenitsky Yu.G. et al., Proc.of MT-10 IEEE Trans.on Mag.(1988) vol. 24, num. 2, p. 1125 Alenitsky Yu.G. et al., JINR, P9-85-707, Dubna, (1986) (in Russian) Zaplatin N.L., Samsonov E.V., JINR, P9-85-707 (1986) (in Russian), p. 113 Segerlind J. "Applied Finite Element Analysis", New York, 1976, p. 122 Alenitsky Yu.G. et al., Proc.of MT-12, IEEE Trans.on Mag. (1992) vol. 28, num. 1, p. 554
Cryogenics 1994Vol 34 ICEC Supplement
669
I C E C 15 P r o c e e d i n g s
~.~o Co~l~ Po~e
Hote ¢ortLetd form •" p
/
i ", eace~"Jz-t'esonator"~,efd
i , i i i~ CH
x
Figure 1
DC-1 magnet system.
z r , ~ ~"
0.1
,,.z 0.2
Z~)I
.
I
~
_.~
/'(M) .
.
.....
r(.~')
.
i-i
~
,-,-
F i g u r e 2 Cold pole of the magnet, a) I-IV - segments, b) View in plan. c) Segment I enlarged (1 - - coil, 2 - - steel plates, 3 - - stainless steel serving, [] - - cooling channels). Y
QO (W/M3)I
x
\ 104
f
\\l
i
\ f 2xi0 4
i
i
i
i
i
i
lO 4
,
, i l l
105
f i
.
.
.
.
Q/ {W/M3}
F i g u r e 3 Thermodynamic stability boundary of the coil. Q0 is the heat impulse (At = 0.2 s), Q j is the Joule heat in the normal phase region (1 - - stainless steel serving, 2 - - cooling channels, 3 - coil, 4 - - volume of heat perturbation).
670
Cryogenics 1994 Vol 34 ICEC S u p p l e m e n t