Cryogenic Heat loads Analysis from SST-1 Plasma Experiments N. Bairagi, V. L. Tanna and S. Pradhan SST-1 Mission Institute for Plasma Research, Bhat, Ganhinagar. INDIA.

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]2 Outline  Introduction  Cryogenics for SST-1 Superconducting Magnets System (SCMS)  Methodology for cryogenic heat loads calculation  Cryogenic Heat loads on SCMS during plasma shots  Results  Summary

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]3 Actual image of the SST-1 assembled machine 3D cut view of the SST-1 machine The Steady State Superconducting Tokamak (SST-1)

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2] 4  16 numbers of modified ‘D’ shaped Toroidal field (TF) coils  9 Poloidal field (PF) superconducting coils  Both TF and PF magnets are fabricated using same NbTi/Cu based cable-in conduit conductor (CICC)  All 16 TF coils tested at rated 10 kA in either single phase or double phase cooling conditions prior to assembly Cross-sectional view of SST-1 CICC SST-1 TF coil pair SST-1 Superconducting Magnets System (SCMS)

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2] 5 Cryogenics for Superconducting Magnets System (SCMS) Helium refrigerator cum liquefier (HRL) of equivalent nominal power: K 400 W for SCMS W for Cold Circulator 200 l/h Liquefaction for Current leads (10 pairs) 2500 l capacity Main Control Dewar (MCD) Forced flow supercritical helium cooling up to 300 g/s at 4 bar, 4.5 K Process flow diagram of HRL system with connection of SCMS

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]6 Glimpse of the SST-1 Cryogenic subsystems

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]7 HRL Parameters during plasma experiments

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2] 8 TF current leads parameters during plasma experiments  All TF, PF and Case are cooled from 300 K to ~ 24 K.  Then PF and case are isolated from HRL to mitigate additional heat loads on TF system by PF system and conduction cooled passive structures within SST-1  TF magnets cooled by two-phase helium to 5 K and operating successfully at 1.5 T toroidal field for plasma experiments.

 Energy loss (E) can be calculated by specific heat at constant pressure using: E = ṁ C p 0 ∫ t ∆T (t) dt where ṁ is mass flow rate of helium in the coil, ∆T is temperature difference between inlet and outlet helium in CICC, C p is the specific heat of helium at constant pressure and temperature and t is the time.  This energy term can also be expressed in terms of helium enthalpy as: E = 0 ∫ t ṁ [ h o (t) –h i (t) ] dt where h i and h o are specific enthalpy of inlet and outlet helium stream in CICC.  In our experiments C p does not remain constant, so we use helium enthalpy data to evaluate gross heat loads on TF system. Methodology for cryogenic heat loads calculation N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]9 Toroidal field magnets Helium inlet T i, P i, ṁ Helium outlet T o, P o Schematic diagram showing helium flow in TF magnets  Helium mass flow rate is recorded from cryoplant outlet which supplies cold helium to TF coils during the entire current ramp-up and ramp-down cycle.  Helium stream temperature and pressure are measured at the inlet and outlet of TF coils supply / return end.

Transport current profiles and corresponding temperature/pressure profile of TF system during plasma experiments N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]10

TF Coils charging details Supply helium parameters Mass flow rate ṁ (in g/s) Return helium parameters Enthalpy change ∆H (J/g) Gross load from ∆H (in W) 4.6 kA with dI/dt = 5 A/s T i = 5.5 K, P i = 1.6 B, H i = J/g 61.3 T o = 4.8 K, P o = 1.41 B, H o = J/g kA with dI/dt = 5 A/s T i = 5.5 K, P i = 1.62 B, H i = J/g 57.7 T o = 4.8 K, P o = 1.44 B, H o = J/g kA with dI/dt = 5 A/s T i = 5.55 K, P i = 1.7 B, H i = 36.9 J/g 58.9 T o = 4.9 K, P o = 1.41 B, H o = J/g kA with dI/dt = 5 A/s T i = 5.5 K, P i = 1.63 B, H i = 36.9 J/g 60.4T o = 4.8 K, P o = 1.44 B, H o = J/g  Table above shows gross heat loads for SST-1 TF coils during TF current of 4.6 kA / 1.5 T  Average heat load for SST-1 TF system from enthalpy data is around K at 1.5 T (TF field).  Remaining cold capacity is utilized for balancing the heat loads of PF and Case system along with the cryo distributions and feeders ducts as well as production of liquid helium for current leads.  As the PF and Case systems are isolated at intermediate temperature of ~ 24 K, the additional heat loads other than the TF system would be a function of time.  Over a days, this contribution keeps increasing and after few days of operation it exceeds even the cold capacity available with the HRL system. N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2] 11 Calculated gross heat loads for SST-1 TF coils for toroidal field (B T ) of 1.5 T

Summary  SST-1 TF magnets system successfully operates under two-phase helium flow conditions 4.8 K - 5 K at 1.4 bar (a) – 1.65 bar (a) regularly for plasma experiments. This is one of the unique regime of operation in case of CICC wound SCMS.  Enthalpy change data is more suitable compared to specific heat method for estimating heat loads in present experimental conditions.  Gross heat loads are found to be about 275 W from helium enthalpy change data for integrated TF magnets of SST-1 during plasma experiments  These heat loads include steady state as well as pulsed losses from PF coils, Case and conduction cooled passive structures within the SST-1 machine.  Experiments have shown that the transient losses are smoothly absorbed by HRL during plasma experiments.  These results are very useful reference for heat loss analysis for PF coils and provides database for future operation of SST-1 machine N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]12

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]13 References: [1] Pradhan S et al., The first experiments in SST-1, Nuclear Fusion [2] Bonneton M et al., W at 4.5 K and 200 l/h refrigeration plant for IPR Tokamak SST-1 project supplied by Air Liquide, Proceedings of the Eighteenth International Cryogenic Engineering Conference (ICEC18), Mumbai, India [3] Sharma A N et al., Thermo hydraulic and quench propagation characteristics of SST-1 TF coil, Fusion Engineering and Design 89, 115 – 121. [4] Patel R et al., Cool down experiences with the SST-1 helium cryogenics system before and after current feeders system modification, Physics Procedia 67, 170 –175. [5] Tanna V et al., Recent progress and development of cryogenics system towards the refurbishment of SST-1, Proceedings of the Twenty fourth International Cryogenic Engineering Conference (ICEC24), Fukuoka, Japan [6] Tan Yunfei et al., Analysis and calculation of AC losses Test of EAST PF model coil, Plasma Science & Technology, Vol. 8, No.4, 488–490 [7] Filina N N and Weisend II J G 1996 Cryogenic Two-Phase Flow (Cambridge University Press) Acknowledgements: I would like to acknowledge significant contributions by all the members of the SST-1 Mission specially Cryogenics and Magnets division for their efforts to realize the plasma experiments in the SST-1 machine.

N. Bairagi, ICEC26-ICMC26 New Delhi 09/03/2016 [9-O-4B-2]14 Thank you