1. MANUFACTURING OF MAGNETS FOR SST-1 TOKAMAK
Y.C. Saxena1, S. Pradhan1, R. Bahl1,V. Bedkihale1, V. Jain1, K.J. Thomas1, S. Karthikeyan2, K.N.Das2, C..V. K. Ecka2 and BHEL Team2
1Institute for Plasma Research, Bhat, Gandhinagar, INDIA
2Bharat Heavy Electricals Limited, Piplani, Bhopal , INDIA
The Magnet System of the Steady State Superconducting Tokamak, SST-1 consists of both the superconducting and resistive magnets. The manufacturing of the magnet system has been carried out at the Bharat Heavy Electricals Limited, Bhopal, India, under design and supervision of Institute for Plasma Research.
Several technology and processes involving the winding of large size superconducting magnets have been developed. The cryo-compatible insulation systems. used in the superconducting magnets has been developed and tested. All superconducting PF coils, nearly half of the TF coils and all resistive coils have been manufactured. Manufacturing of precisely machined TF cases, outer inter-coil support structures and other associated support structures are in an advanced stage of fabrication.

2. SST1 MACHINE PARAMETERS
MAJOR RADIUS : 1.1M
MINOR RADIUS : 0.2 M
ELONGATION : 1.7-2
TRIANGULARITY :
TOROIDAL FIELD : 3T
PLASMA CURRENT : 220 kA.
ASPECT RATIO : 5.2
SAFETY FACTOR : 3
AVERAGE DENSITY : 1X 1013cm-3
AVERAGE TEMP : 1.5 keV
PLASMA SPECIES : HYDROGEN
PULSE LENGTH : 1000S
CONFIGURATION : DOUBLE NULL
: : POLOIDAL DIVERTER
HEATING & CURRENT DRIVE:
LOWER HYBRID : 1.0 MW
NEUTRAL BEAM : 0.8 MW
ICRH : 1.0 MW
TOTAL INPUT POWER : 1.0 MW
FUELLING : GAS PUFFING
3-D Cut View of SST-1

3. Supercondcting Magnets: Toroidal Field (TF) Coils : 16 Nos.
SST-1 MAGNET SYSTEM
Requirements:
Confinement, Shaping and Equilibrium Fields
Ohmic Flux Storage
Feed-Back Control
Supercondcting Magnets:
Toroidal Field (TF) Coils : 16 Nos.
Poloidal Field (PF) Coils : 9 Nos.
Copper Magnets (Water Cooled) :
Ohmic Transformer (TR) Coils : 7 Nos.
Poloidal Field (PF ) Coils ( in-Vessel): 2 Nos.
Position Control Coils ( in-Vessel) : 2 Nos.

4. SST-1 TOROIDAL FIELD COILS
Design Drivers for TF coils:
3 Tesla Field at Plasma Center
< 2% ripple at plasma edge
Large Radial Ports
Tangential access for NBI
Human Entry in Vacuum Vessel
TF COIL Winding Pack:
Modified D-Shape
Base Conductor: NbTI based CICC
6 # of Double pancakes (Joint less) assembly consolidated by VPI.
Cross-section : 194x144 mm2
Encased in SS316L casing.
PARAMETERS OF TF COILS:
Total No. of Coils :
Turns per Coil :
6 Double Pancakes with 9 turns per pancake
Current per turn (3T Field at Plasma Center): 10 kA
Maximum Field at Conductor: T
Maximum Field Ripple : %
Total Inductance (16 Coils in series) : H
Total Stored Energy: MJ
Dump Time Constant: s
Peak Dump Voltage: ±600V

5. TF MAGNETS’ CASINGS
TF winding packs are encased in casings made of SS316L
Each of the Casing consist of Inner ring, outer rings & two side plates
Inter coil supports are provides on inner and outer legs

6. Assembly of TF coils
TF coils nosed and bolted on in-board side to form a toroidal vault
Outer Inter coils supports (2 #each ) provided between adjacent coils
Coil Casings insulated from each other.
Casings and inter-coils structures support PF coils

7. SST-1 Poloidal Field Coils
Design Drivers:
Support single & double null equilibria with wide range of Triangularity ( ), Elongations ( ), li ( ), p ( ) & slot divertor configuration
Limiter operation during Plasma current ramp up
Parameters of PF Coils

8. Conductor for SST-1 Superconducting Magnets
Conductor Characteristics
Conductor type : CICC
Dimensions : 14.8×14.8 mm2
No. of Strands : 135
Cabling Pattern : 3335
Last stage wrapped (half overlap) with 25 m thick SS304 tape.
Twist Pitches:
I stage : 40 mm;
II stage : 75 mm
III stage: 130 mm;
IV stage: 290 mm
Conduit Material : SS 304L
Conduit thickness : 1.5 mm
Void Fraction :  36 %
5T, 4.2K : 36 kA
5T, 4.5K : 10 kA
Strand Specifications
Material : NbTi in Cu
Strand Dia : 0.86 mm
Filament Dia. : 10 µm
Filaments
per strand : 1272
Cu : NbTi : : 5 : 1
Cu RRR : 100
Hysterisis
Losses : <100 mJ cm-3 Cu
NbTi Cu
Strand Cross-section
Strand Characteristics:
5T : 232A
Index ‘n’ : 45
(0.1 V / cm criteria)
Hysterisis
loss : 33.5 mJ cm-3
(±3T; 4.2K)
CICC Cross-section

9. SST-1 OHMIC TRANSFORMER
Design Drivers:
Stress limited maximum flux storage
Matching to existing power supply
Plasma Break down and initial plasma current ramp up
TR2
Characteristics:
Water cooled copper coils
Copper (OFHC) conductor
19 22.7 mm2 cross-section
8 mm dia. hole for water flow
Stored Flux : kA per turn
Maximum Field in plasma Volume : 18 G
TR1
TR3
TR2
Coils #
Radius (m)
Turns
(#)
X-section (mm2)
Center
(m)
TR1 1
0.20
672
1202600
0.00
TR2 2
0.49 40
195  95
 1.40
TR3
2.42 3
58  23
0.73

10. Constructional Features and Type of Winding of SST-1 Magnets
PF1, PF2, PF3 and TR1 coils are layer wound on epoxy glass winding spools. Winding packs are vacuum pressure impregnated.
TR2, TR3 and VF are single pancake wound. Consolidated and cured with internal heating

11. Constructional Features and Type of Winding of SST-1 Magnets
TF, PF4 and PF5 are wound as double pancake (DP). Typical DP winding for TF is illustrated above.

12. Superconducting coils
CICC Spool
CICC Shaping
Take-up spool for double pancakes winding
TF Double-pancake winding machine

13. Superconducting coils
Dummy TF double pancake
VPI Mould for TF coils

14. Superconducting coils
Winding machine for PF1,P2 and PF3 coils
Winding of PF1 in progress
Winding of PF5 in progress
Winding former for PF4 and PF5 coils

15. Insulation System for Superconducting magnets
A specially developed glass fibre based (BHELMAT-G) insulation with Bisphenol-A epoxy resin system has been used for SCMS.
An extensive pre-qualification of this insulation system on CICC samples have been carried out.
Test samples (length > 500 mm) :
CICC bend samples of radii 200,300,400 and 500 mm
CICC 4 X 4 array of straight conductors
CICC S-bend samples

16. Insulation System for Superconducting magnets
Electrical tests :
Inter-turn insulation at 1 kV DC
Insulation resistance between turns
Insulation resistance on main insulation
2 kV AC 50 Hz proof resistance for 1 min.
Thermal cycling test:
10 cycles of Heating at 1600 C for 15 minutes in an electrical oven followed by quenching in liquid Nitrogen at minus 1960 C for 5 minutes. After thermal cycling all electrical tests were done.
The samples passed all the electrical tests with degradation in performance below 5% after the thermal cycling. No mechanical cracks were observed.

17. Water Cooled Copper Coils
TR1 winding in progress
Winding set up for VF coil