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Dynamic simulations for preparing the acceptance test of JT-60SA cryogenic system
Cryogenics xxx (2016) xxx–xxx
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Research paper
Dynamic simulations for preparing the acceptance test of JT-60SA cryogenic system R. Cirillo ⇑, C. Hoa, F. Michel, J.M. Poncet, B. Rousset Univ Grenoble Alpes, INAC-SBT, F-38000 Grenoble, France
a r t i c l e
i n f o
Article history: Received 6 November 2015 Received in revised form 15 June 2016 Accepted 19 June 2016 Available online xxxx Keywords: Dynamic modelling Pulsed load smoothing Nuclear fusion
a b s t r a c t Power generation in the future could be provided by thermo-nuclear fusion reactors like tokamaks. There inside, the fusion reaction takes place thanks to the generation of plasmas at hundreds of millions of degrees that must be confined magnetically with superconductive coils, cooled down to around 4.5 K. Within this frame, an experimental tokamak device, JT-60SA is currently under construction in Naka (Japan). The plasma works cyclically and the coil system is subject to pulsed heat loads. In order to size the refrigerator close to the average power and hence optimizing investment and operational costs, measures have to be taken to smooth the heat load. Here we present a dynamic model of the JT-60SA’s Auxiliary Cold box (ACB) for preparing the acceptance tests of the refrigeration system planned in 2016 in Naka. The aim of this study is to simulate the pulsed load scenarios using different process controls. All the simulations have been performed with EcosimProÒ and the associated cryogenic library: CRYOLIB. Ó 2016 Published by Elsevier Ltd.
1. Introduction The tokamak JT-60SA (Japan Torus - 60 Super Advanced) is currently under construction in Naka, at JAEA’s Fusion Institute (Ibaraki prefecture, Japan). The project is part of the Broader Approach Agreement concluded between Europe and Japan. The mission of the JT-60SA is to contribute to early realization of fusion energy by addressing key physics issues for ITER and DEMO [1]. CEA is in charge of providing the cryogenic system for this experimental device. Tokamak operation requires several superconducting coils working periodically, meaning that these magnets are facing variable heat loads due to eddy currents, AC losses and neutrons. In order to reduce and optimize the investment cost, there is the need of smoothing the heat pulse arriving at the refrigerator. To better understand how this smoothing strategy impacts the magnet operation, the focus will be on the ‘‘Auxiliary Cold Box” (hereafter referred as ACB), connecting the magnet loops to the Refrigerator Cold Box (RCB) (Fig. 1). JT-60SA’s ACB has been conceived with two distinct parts: a primary circuit composed of 2 closed loops, loop 1 intended to cool the TF magnets (and structures) while Loop 2 is for CS and EF coils, ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (R. Cirillo).
and a secondary circuit which contains the buffer capacity. This latter is a saturated liquid helium bath where the heat pulse is intermittently stored and gradually released during a period of dwell operation. (Fig. 2). In both loops 1 and 2 the helium coolant is driven by a cold circulating pump. The two circuits are thermally coupled via heat exchangers allowing the heat coming from the loops (primary circuit) and from the circulating pumps to be removed by evaporating helium from the thermal buffer (secondary circuit). The pressure inside this thermal buffer is allowed to fluctuate to maintain a quasiconstant vapor mass flow back to the refrigerator. The importance of the thermal buffer to smooth the peak is illustrated in Fig. 3. All the heat load contributions from loop 1, loop 2 as well as static and pump losses have been added. The total represents the power injected in the bath (bath heat injection). For the bath enthalpy balance, the curve shows the power removed from the bath, it is much flatter reflecting the smoothing effect by the energy storage in the bath itself. In order to investigate which will be the behavior of the tokamak, several experimental campaigns took place at CEA-SBT (CEA-Service des Basses Températures) using a 1:20 scaled down mockup of the JT-60SA magnet cryogenic system named: HELIOS [2,3]. The latest experimental campaign was conducted in May 2015 and results are presented in [4] along with a validation of the
http://dx.doi.org/10.1016/j.cryogenics.2016.06.010 0011-2275/Ó 2016 Published by Elsevier Ltd.
Please cite this article in press as: Cirillo R et al. Dynamic simulations for preparing the acceptance test of JT-60SA cryogenic system. Cryogenics (2016), http://dx.doi.org/10.1016/j.cryogenics.2016.06.010
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Fig. 1. Very simplified scheme describing the main components of the cryogenic system along with the temperature evolution.
Fig. 2. JT-60SA’s ACB schematic view of the hydraulic circuit.
HELIOS dynamic modelling with respect to the experimental data. The ACB of JT-60SA’s cryogenic system has been modelled with the same tool: EcosimPro in order to predict the results of the acceptance tests which are planned in 2016. The choice of EcosimPro was mainly influenced by the fact that this tool proved to be adequate for modelling large cryogenics installations at CERN [5]. It was validated against experimental data gathered on HELIOS, and 4C code [6]. Results were consistent [7]. 2. JT-60SA’s ACB model 2.1. Description JT-60SA’s ACB primary circuit is mainly composed by two parallel loops, each one equipped with a circulating pump, supplying
the different coils. (Tables 1 and 2 provide information about geometry). Both loops are thermally coupled with the same saturated bath. The coolant is supercritical helium at about 5 bar while the thermal buffer is filled with saturated liquid helium bath at 4.3 K, 1.1 bar. This secondary circuit is represented by the buffer capacity, a bath of about 7 m3 with 4 heat exchangers (Fig. 4). No coil is represented in the scheme but a heated piping sector (P4 or P4_bis) simulating the loads from the magnets. CV700 is the Joule Thompson valve which allows to fill the bath and CV799 is the bath discharge valve. A flowmeter is placed next to each of them and the two lines link the ACB to the refrigerator. The loops piping has been modelled with 1D pipes, components which incorporate mass, energy and momentum conservation equations in transient operation so that transition time is well simulated along the loop. Dead volumes, on the other end, since they account for non-circulating helium, they are 0D pipes, meaning that mass and energy conservation are enough to describe these components. [8]. The bath has been coded as a 4 heat-exchanger 0D reservoir. Cold Circulators have been coded ad hoc, starting from industrial data provided by Air Liquide Advanced Technology (Fig. 5). The 2 cold circulators are working at different operating points (Table 3), with different speed settings and a different openings of the valve (CV715/725) upstream of each heated sector. The initial conditions (see Table 4) mainly fix the helium inventory. The initial pressure and temperatures along the loop fix the helium mass inside the loop itself (70 kg in total, 35 kg per Loop) and the steady state pressure before pulses are launched. The initial bath temperature and level fix the mass inside the bath (616 kg). The dynamics of the bath are determined by the heat loads and the control parameters. There are two pulse profiles injected at the same time, one per loop Fig. 6. The code calculates the time dependent temperature distribution along the loop as well as the pressure and the position of the actuators used in the implemented controls.
Fig. 3. Thermal buffer effect. The sum of all the contributors to the power injected in the saturated helium bath compared with the enthalpy balance computed at the bath inlet and outlet valves to show the buffer effect.
Please cite this article in press as: Cirillo R et al. Dynamic simulations for preparing the acceptance test of JT-60SA cryogenic system. Cryogenics (2016), http://dx.doi.org/10.1016/j.cryogenics.2016.06.010
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R. Cirillo et al. / Cryogenics xxx (2016) xxx–xxx Table 1 Geometrical data. Volumes Bath Piping Loop 1
Piping Loop 2
6700 liters (l) P1 = 73.8 l P2 = 47.2 l P3 = 70.3 l P4 = 6.9 l P5 = 51.2 l Tot = 249.4 l Dead Volume_1 = 4.9 l P1_bis = 66.3 l P2_bis = 42.2 l P3_bis = 61.5 l P4_bis = 6.9 l P5_bis = 55.3 l Tot = 232.1 l Dead Volume_2 = 19.7 l
Table 2 Valves characteristic. Valves parameters Control valves parameters
CV700 CV799 CV720/CV710 CV725/CV715 CV729/CV719
Cv = 5 Cv = 186 Cv = 120 Cv = 30 Cv = 120
2.2. Control strategy As presented in [4] the control strategy consists in limiting the variation of the mass flow at the bath outlet during the pulses. In the meantime, it is important to avoid a level drift in between one pulse and the subsequent one, but the level is allowed to fluctuate during one pulse duration (one single cycle). During the initialization process, the bath level is controlled. During the pulsed regime, the level is not controlled directly anymore, but the inlet mass flow is imposed at a value correspond-
ing to the time averaged mass consumption over one cycle by means of CV700. In case of drift after a cycle, value of JT valve CV700 is re-adapted. The goal is to operate the refrigerator close to the average loads, with the lowest fluctuations of the inlet and outlet mass flows from the bath.
Initialization Pulsed regime
Variable to control
Variable to regulate (set point)
Actuators
Bath level Power to be removed at constant bath Temperature Maximum return mass flow
Bath level Bath inlet mass flow
CV700 CV700
Bath outlet mass flow
CV799
Once the level is not controlled anymore, its stability depends on the equilibrium in between the inlet and outlet mass flow set points. Equilibrium does not imply same value for inlet and outlet set points as the former has a fixed value corresponding to the time averaged consumption value while the latter is limited to a maximum value. The inlet mass flow set point is a boundary condition which aims to compensate for the evaporation taking place as a consequence of the bath heat injection at a given bath temperature. The outlet mass flow set point is an upper limit: the outlet mass flow cannot exceed this value. If it is set too high, the regulation will never be active, all the heat will immediately be converted to vapor, and hence there will be no buffer effect. If the outlet set point is too close to the inlet mass flow rate, the temperature (and consequently the pressure) will rise due to the thermal load without having enough margin to restore the initial conditions before the next pulse arrives. To determine the two set point values, an average power is estimated first and the corresponding mass flows are calculated.
Fig. 4. JT-60SA’s ACB circuit hydraulic scheme.
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Fig. 5. JT-60SA’s cold circulator characteristic; m and dP are calculated at 5 bar and 4.5 K. Thermal-hydraulic input parameters of the ACB model are listed in Table 4.
implemented in the model are PID (Proportional Integral Derivative) controllers.
Table 3 Cold circulator characteristic. Cold circulator nominal operating points Loop 1 Loop 2
876 g/s 1.3 bar 960 g/s 0.8 bar
The focus of the analysis is the range of temperatures and pressures following a pulse. The controls outputs (bath level and outlet mass flow) are also checked to judge the control parameters.
Table 4 Model input parameters. All pressures are absolute pressures. Initial conditions Loop 1
Loop 2
Bath High Pressure Line – HP Low Pressure Line – LP Boundary conditions Bath mass flow control Loop fixed settings
2.3. Results
4.4 K, 6.5 bar (coils interface – after the HX downstream the pump) 4.4 K, 5.1 bar (pump inlet) 4.4 K, 6.0 bar (coils interface – after the HX downstream the pump) 4.4 K, 5.2 bar (pump inlet) 4.3 K, 71% liquid level 4.7 K, 6 bar 4.3 K, 1.16 bar 340 g/s inlet – FE700 367 g/s outlet – FE799 164.2 W – Estimated Heat Leaks [9] 2 Time dependent heat profiles applied to the loops [10]
The outlet mass flow set point, since it is an upper limit only, is taken with an arbitrary margin, typically about +10%. All controls
2.3.1. Bath As Fig. 7 shows, the pressure in the bath is expected to rise to 1.51 bar (i.e. 4.67 K) when starting at 1.16 bar (at 4.37 K), with the given outlet mass flow set point at 367 g/s. Hence there is an increase of 0.35 bar (Fig. 7) corresponding to 0.31 K, which is below the 0.4 K maximum temperature increase specified for the acceptance tests. The control on the outlet mass flow is effective: there is synchronism between the closing of the valve and the limitation of the mass flow.
2.3.2. Loop The simulation is able to keep the cold circulators at their operational points (Table 3). The fluctuations in pressure drop and mass flow are relatively small, while the requirements for the acceptance tests limit the fluctuations of the mass flow to below 20% (see Table 5).
5000
Power (W)
4000 3000 2000 1000 0
0
300
600
900
1200
1500
1800
me (s) LOOP 2
LOOP 1
Fig. 6. JT-60SA pulses; the full line describes the pulse applied on Loop 2 and the dashed line describes the pulse applied on Loop 1.
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Fig. 7. Bath pressure and outlet mass flow control. Controls are effective and the valve closing is synchronized with the outlet mass flow limitation.
Table 5 Fluctuations around the nominal operation points.
Loop 1 Loop 2
Nominal mass flow
Max fluctuation
Nominal pressure head
Max fluctuation
876 g/s 960 g/s
0.4% 1.6%
1.3 bar 0.8 bar
0.5% 2%
2.3.3. Parametric study on the outlet mass flow Figs. 8–10 show the impact of the outlet mass flow set point (SP) on the bath level, the bath pressure and the opening of the outlet control valve. The inlet mass flow set point is always the same (340 g/s). The outlet mass flow set point is equal to 367 g/s or it can be too high: 600 g/s, or equal, to the inlet mass flow set point of 340 g/s. The evolution of the bath level allows to judge (Fig. 8), whether the drift is sufficiently low to be considered acceptable during subsequent pulses. The evolution of the bath pressure (Fig. 9) shows immediately when the outlet mass flow set point is too high and hence, there is no buffer effect: there is, in that case, no pressure rise. If the outlet mass flow is too low or too close to the inlet mass flow set point, there is a drift in the pressure which is not acceptable during the acceptance tests. Finally, a parametric study (Fig. 10) on the outlet mass flow versus the opening of the outlet control valve was performed. If the outlet set point is chosen too high the valve never closes (dashed lines), since the control on the mass flow is never effective. On the other hand, if the set point is the same as the inlet, the mass flow is constant which implies that the valve closes and then reopens but without starting from the same value (dotted lines). If
the value is appropriate instead, both the valve and the mass flow come back to the same value after each pulse. The evolution of the two variables is synchronized. It can be noted that different bath pressures imply different peak pressures in the loop. This effect is shown in Fig. 11. One disadvantage of this method is that the mean value of the mass flows has to be determined ‘‘a priori”. For the acceptance tests, powers injected inside the bath and on the loop are set by the operator and the corresponding time dependent values are well known. With this information, the time averaged value and the evaporated mass flow can be calculated. This result provides information about the averaged inlet mass flow set point. So the set points for inlet and outlet mass flow can be set a priori. During real operation of the tokamak, however, the power deposited will not be known in advance and another control strategy need to be adopted to control the valves. This is explained in the next section. 2.4. Mass control strategy The alternative control strategy tries to control the level drift after consecutive pulses (as the previous strategy) but this time controlling the mass in the bath continuously and directly, not via the level control or giving an inlet mass flow set point to balance the outlet. There is no more need to estimate the injected power. The only mass flow set point to give in the outlet one because the inlet will follow due to the fact that the regulation on the mass inventory is active all the time. Furthermore with this alternative strategy, inlet and outlet mass flows should remain equal at any time, thus increasing the efficiency of refrigerator heat exchangers.
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Fig. 8. Bath level evolution if the outlet mass flow set point changes.
Fig. 9. Bath pressure evolution if the outlet mass flow set points changes.
Fig. 10. Bath outlet mass flow and outlet control valve opening evolution if the outlet mass flow set point changes.
Initialization Pulsed regime
Variable to control
Variable to regulate
Actuators
Bath mass inventory Bath mass inventory Maximum return mass flow
Bath mass inventory Bath mass inventory Bath outlet mass flow
CV700
The following equation has to be verified.
CV700 CV799
mbath ¼ qLiq V Liq þ qgas V gas
ð1Þ
where mbath is the helium mass inside the bath; qLiq and V Liq are respectively the density and the volume of the amount of liquid helium; qgas and V gas refer to the gaseous phase.
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Fig. 11. Loops pressure evolution if the outlet mass flow set points changes. Loop 1 on the left and Loop 2 on the right.
80 76
660
72 640 68 620
64
600 0
1800
3600
Liquid level (%)
Mass inventory (kg)
680
60 5400
me (s) Mass inventory
Level
Fig. 12. Mass inventory and liquid level when the mass control is active. The mass (dashed line) remains constant along the transient while the level (full line) fluctuates but goes back to the same value periodically.
Fig. 13. Inlet and outlet mass flows with the previous approach.
Fig. 14. Inlet and outlet mass flows with the alternative approach (mass control strategy).
From the experimental point of view, bath temperature (or bath pressure) has to be used to calculate vapor and liquid densities whereas level measurement (associated with the knowledge of the reservoir geometry) gives access to liquid and vapor volumes. Numerical results are as follows: the mass inside the bath is kept constant while the level bounces but goes through the same point at the end of each cycle (Fig. 12), in other words there is no drift and the level is recovered at the end of each pulse. It is interesting to check the mass flows for the two different control strategies. With the previous approach, two different values were input (inlet as a set point, outlet as an upper limit), hence
the two mass flows were distinguishable (Fig. 13). In the case of the mass control approach, the two mass flows variations are almost the same (Fig. 14). With the previous approach a regulation on the inlet bath mass flow was active. This means that the average mass in the bath remains constant but the transient value experiences large variations. The refrigerator heat exchangers might be not well balanced because the inlet mass flow set point and mass flow rate differ in time. Furthermore, the level fluctuates and goes back to the same value periodically but a small change in the thermal load would imply a drift.
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The alternative control approach, hereafter referred as ‘‘mass control strategy”, is simpler to implement: it is active all the time while, in the previous case, what was controlled during the initialization (the bath level) stops to be controlled during the pulsed regime. Hence, in this case, there is no need to give 2 mass flow values, also because the inlet mass flow would need to be regulated using the same actuator CV700 which is still set on the mass inventory control. The only mass flow to control is the outlet one. The inlet will follow this latter. To conclude, a last parametric study is presented, to show that the mass control can be quite effective. As a start, three different mass set points were investigated to check the resulting variations of the loop pressure.
In the ‘‘reference” case the reservoir is filled up to 71% (Table 4) corresponding to 616 kg of helium. In addition 420 kg and 700 kg helium inventories have been tested. These values represent the minimum (heat exchanger still fully immersed) and maximum filling levels of the buffer. With 700 kg as set point, the bath is in average filled at 83% but reaches 90% during the pulses. With 420 kg the bath starts at 42% during the initialization time and the variations of the level are very small (about 1%) during the pulse transients. In the reference case the pressure in the bath increases by 0.39 bar (Fig. 15). For the higher mass case, the pressure rises only by 0.37 bar as more helium can store more energy. In the lower mass case the pressure rises by 0.43 bar. The loops pressure
Fig. 15. Parametric study of the mass inventory set point. Bath pressure evolution.
8
pressure (bar)
pressure (bar)
8
7
6
5
0
1800
3600
me (s)
5400
7
6
5
0
1800
3600
5400
me (s)
Mass SP = 616 kg (Reference)
Mass SP = 616 kg (Reference)
Mass SP = 700 kg
Mass SP = 700 kg
Mass SP = 420 kg
Mass SP = 420 kg
Fig. 16. Loops pressure evolution. Parametric study of the mass inventory set point. Loop 1 on the left and Loop 2 on the right.
Fig. 17. Bath pressure evolution. Parametric study on the outlet mass flow set point. The configuration is thermal buffer plus mass control strategy.
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Fig. 18. Loops pressures evolution. Parametric study on the outlet mass flow set point. The configuration is thermal buffer plus mass control strategy. Loop 1 on the left and Loop 2 on the right.
Table 6 Recap of pressure rises in the bath and in both loops. 616 kg (Reference) Bath
420 kg Bath
Loop 1
Loop 2
Bath
Loop 1
Loop 2
Mass SP variation with fixed mass flow SP = 367 g/s 0.39 bar 1.66 bar 2.04 bar
0.43 bar
1.81 bar
2.17 bar
0.37 bar
1.61 bar
1.95 bar
367 g/s (Reference)
400 g/s
Bath
Loop 1
Loop 1
Loop 2
700 kg
Loop 2
Outlet mass flow SP variation with fixed Mass SP = 616 kg 0.39 bar 1.66 bar 2.04 bar
450 g/s
Bath
Loop 1
Loop 2
Bath
Loop 1
Loop 2
0.29 bar
1.34 bar
1.74 bar
0.16 bar
0.88 bar
1.41 bar
Table 7 Results of the model for the mass control strategy compared to the requirements in the technical specifications.
Technical specifications requirements [11] Simulations with SP = 367 g/s Initialization (end) Pulsed regime (peak)
Pressure head (dP)
_ Mass flow (m)
Loop 1
Loop 2
Loop 1
P1.3 bar 1.36 bar 1.37 bar
P0.8 bar 0.80 bar 0.81 bar
P876 g/s 877 g/s 880 g/s
evolution is shown in Fig. 16, the pressure in Loop 1 increases by 1.81 bar in the 420 kg case, but only by 1.61 bar for the 700 kg case. In loop 2 the pressure increases between 2.17 bar and 1.95 bar. For the reference case the pressure in loop 1 increases by 1.66 bar and for loop 2 by 2.05 bar. Finally, the outlet mass flow set point was changed to see its impact on the buffering effect. This case may be investigated also during the acceptance tests, to see the operation possibilities of the cryogenic system. As shown in Fig. 17, stable operation can be achieved with a flow of 367 g/s while below this value the pressure drifts, since the bath cannot recover its previous state. As for outlet mass flows higher than 500 g/s there is no control, there is no point in going farther or there will be no effective limitation. The effect is the same described in Fig. 9, case 600 g/s. The pressure rise in the bath and in the two loops (Fig. 18) are indicated in Table 6.
3. Conclusions Table 7 compares the results of the simulation following the ‘‘mass control strategy” with the requirements of the technical specifications. After validating the modelling tool EcosimPro on the HELIOS experimental set-up [4], there is confidence in using this simula-
Coils interface Pressure
Coils interface Temperature
Loop 2
Loop 1
Loop 2
Loop 1
P960 g/s 963 g/s 980 g/s
P5.3 bar 6.5c bar 8.2 bar
P4.8 bar 6.0 bar 8.0 bar
4.4 6 T 6 4.8 K 4.4 K 4.4 K 4.7 K 4.7 K
Loop 2
tion tool also to model the JT-60SA ACB. The isochoric operation has been modelled and analyzed. To simulate the conditions during acceptance tests, where no coils will be connected, the thermal buffer operation with the outlet bath mass flow control has been studied as well. Finally a control strategy for long term operation has been studied in the form of ‘‘mass control strategy” (CEA patent [12]) and first results have been presented and analyzed. Following the successful application to JT-60SA ACB operation, the model could be expanded to consider other parts of the cryogenic system or different operation modes like isobaric.
Acknowledgements The authors wish to thanks M. Wanner (F4E, Fusion for Energy) for the fruitful discussion and François Bonne (CEA) for sharing his idea with us.
References [1] Kamada Y, Barabaschi P, Ishida S. The JT-60SA team and the JT-60SA Research Plan Contributors 2013, Progress of the JT-60SA project, Nuclear Fusion 53, Number 10 – IAEA. [2] Hoa C, Lagier B, Rousset B, Michel F, Roussel P. Experimental and numerical investigations for the operation of large scale helium supercritical loops subjected to pulsed heat loads in tokamaks. Phys Procedia 2015;67:54–9.
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[3] Lagier B et al. Validation of an EcosimPro model for the assessment of two heat load smoothing strategies in the HELIOS experiment. Cryogenics 2014;62:60–70. [4] Cirillo R, Hoa C, Michel F, Poncet JM, Rousset B. Dynamic simulations of the cryogenic system of a tokamak. IOP conf. series: materials science and engineering, 101. p. 012158. http://dx.doi.org/10.1088/1757-899X/101/1/ 012158. [5] Bradu B. Modélisation, simulation et contrôle des installations cryogéniques du CERN [Ph.D. thesis], Université Paris Sud – Paris XI. [6] Guelfi F, Bonifetto R, Hoa C, Savoldi L, Zanino R. 4C modeling of the supercritical helium loop HELIOS in isobaric configuration. Cryogenics 2014;64:51–62.
[7] Cirillo R. Dynamic modelling of the cooling circuits of the Japanese tokamak JT60SA, Master degree report, Grenoble INP – Phelma, unpublished results. [8] Empresarios Agrupados 2012, CRYOLIB 1.0 Reference Manual. [9] Heat Inleaks General Thermal Calculation, Air Liquide internal calculations, unpublished results. [10] Lamaison V et al. Conceptual design of the JT-60SA cryogenic system. AIP Conf Proc 2014;1573:337. [11] Michel F, et al. Technical Specifications for the cryogenics system of JT-60SA tokamak, JT-60SA internal document; 2012, unpublished results. [12] Bonne F, et al. Procédé de régulation d’un système de refroidissement cryogénique, Patent n° FR 15 59773; 2015, unpublished results.
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Research paper
Dynamic simulations for preparing the acceptance test of JT-60SA cryogenic system R. Cirillo ⇑, C. Hoa, F. Michel, J.M. Poncet, B. Rousset Univ Grenoble Alpes, INAC-SBT, F-38000 Grenoble, France
a r t i c l e
i n f o
Article history: Received 6 November 2015 Received in revised form 15 June 2016 Accepted 19 June 2016 Available online xxxx Keywords: Dynamic modelling Pulsed load smoothing Nuclear fusion
a b s t r a c t Power generation in the future could be provided by thermo-nuclear fusion reactors like tokamaks. There inside, the fusion reaction takes place thanks to the generation of plasmas at hundreds of millions of degrees that must be confined magnetically with superconductive coils, cooled down to around 4.5 K. Within this frame, an experimental tokamak device, JT-60SA is currently under construction in Naka (Japan). The plasma works cyclically and the coil system is subject to pulsed heat loads. In order to size the refrigerator close to the average power and hence optimizing investment and operational costs, measures have to be taken to smooth the heat load. Here we present a dynamic model of the JT-60SA’s Auxiliary Cold box (ACB) for preparing the acceptance tests of the refrigeration system planned in 2016 in Naka. The aim of this study is to simulate the pulsed load scenarios using different process controls. All the simulations have been performed with EcosimProÒ and the associated cryogenic library: CRYOLIB. Ó 2016 Published by Elsevier Ltd.
1. Introduction The tokamak JT-60SA (Japan Torus - 60 Super Advanced) is currently under construction in Naka, at JAEA’s Fusion Institute (Ibaraki prefecture, Japan). The project is part of the Broader Approach Agreement concluded between Europe and Japan. The mission of the JT-60SA is to contribute to early realization of fusion energy by addressing key physics issues for ITER and DEMO [1]. CEA is in charge of providing the cryogenic system for this experimental device. Tokamak operation requires several superconducting coils working periodically, meaning that these magnets are facing variable heat loads due to eddy currents, AC losses and neutrons. In order to reduce and optimize the investment cost, there is the need of smoothing the heat pulse arriving at the refrigerator. To better understand how this smoothing strategy impacts the magnet operation, the focus will be on the ‘‘Auxiliary Cold Box” (hereafter referred as ACB), connecting the magnet loops to the Refrigerator Cold Box (RCB) (Fig. 1). JT-60SA’s ACB has been conceived with two distinct parts: a primary circuit composed of 2 closed loops, loop 1 intended to cool the TF magnets (and structures) while Loop 2 is for CS and EF coils, ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (R. Cirillo).
and a secondary circuit which contains the buffer capacity. This latter is a saturated liquid helium bath where the heat pulse is intermittently stored and gradually released during a period of dwell operation. (Fig. 2). In both loops 1 and 2 the helium coolant is driven by a cold circulating pump. The two circuits are thermally coupled via heat exchangers allowing the heat coming from the loops (primary circuit) and from the circulating pumps to be removed by evaporating helium from the thermal buffer (secondary circuit). The pressure inside this thermal buffer is allowed to fluctuate to maintain a quasiconstant vapor mass flow back to the refrigerator. The importance of the thermal buffer to smooth the peak is illustrated in Fig. 3. All the heat load contributions from loop 1, loop 2 as well as static and pump losses have been added. The total represents the power injected in the bath (bath heat injection). For the bath enthalpy balance, the curve shows the power removed from the bath, it is much flatter reflecting the smoothing effect by the energy storage in the bath itself. In order to investigate which will be the behavior of the tokamak, several experimental campaigns took place at CEA-SBT (CEA-Service des Basses Températures) using a 1:20 scaled down mockup of the JT-60SA magnet cryogenic system named: HELIOS [2,3]. The latest experimental campaign was conducted in May 2015 and results are presented in [4] along with a validation of the
http://dx.doi.org/10.1016/j.cryogenics.2016.06.010 0011-2275/Ó 2016 Published by Elsevier Ltd.
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Fig. 1. Very simplified scheme describing the main components of the cryogenic system along with the temperature evolution.
Fig. 2. JT-60SA’s ACB schematic view of the hydraulic circuit.
HELIOS dynamic modelling with respect to the experimental data. The ACB of JT-60SA’s cryogenic system has been modelled with the same tool: EcosimPro in order to predict the results of the acceptance tests which are planned in 2016. The choice of EcosimPro was mainly influenced by the fact that this tool proved to be adequate for modelling large cryogenics installations at CERN [5]. It was validated against experimental data gathered on HELIOS, and 4C code [6]. Results were consistent [7]. 2. JT-60SA’s ACB model 2.1. Description JT-60SA’s ACB primary circuit is mainly composed by two parallel loops, each one equipped with a circulating pump, supplying
the different coils. (Tables 1 and 2 provide information about geometry). Both loops are thermally coupled with the same saturated bath. The coolant is supercritical helium at about 5 bar while the thermal buffer is filled with saturated liquid helium bath at 4.3 K, 1.1 bar. This secondary circuit is represented by the buffer capacity, a bath of about 7 m3 with 4 heat exchangers (Fig. 4). No coil is represented in the scheme but a heated piping sector (P4 or P4_bis) simulating the loads from the magnets. CV700 is the Joule Thompson valve which allows to fill the bath and CV799 is the bath discharge valve. A flowmeter is placed next to each of them and the two lines link the ACB to the refrigerator. The loops piping has been modelled with 1D pipes, components which incorporate mass, energy and momentum conservation equations in transient operation so that transition time is well simulated along the loop. Dead volumes, on the other end, since they account for non-circulating helium, they are 0D pipes, meaning that mass and energy conservation are enough to describe these components. [8]. The bath has been coded as a 4 heat-exchanger 0D reservoir. Cold Circulators have been coded ad hoc, starting from industrial data provided by Air Liquide Advanced Technology (Fig. 5). The 2 cold circulators are working at different operating points (Table 3), with different speed settings and a different openings of the valve (CV715/725) upstream of each heated sector. The initial conditions (see Table 4) mainly fix the helium inventory. The initial pressure and temperatures along the loop fix the helium mass inside the loop itself (70 kg in total, 35 kg per Loop) and the steady state pressure before pulses are launched. The initial bath temperature and level fix the mass inside the bath (616 kg). The dynamics of the bath are determined by the heat loads and the control parameters. There are two pulse profiles injected at the same time, one per loop Fig. 6. The code calculates the time dependent temperature distribution along the loop as well as the pressure and the position of the actuators used in the implemented controls.
Fig. 3. Thermal buffer effect. The sum of all the contributors to the power injected in the saturated helium bath compared with the enthalpy balance computed at the bath inlet and outlet valves to show the buffer effect.
Please cite this article in press as: Cirillo R et al. Dynamic simulations for preparing the acceptance test of JT-60SA cryogenic system. Cryogenics (2016), http://dx.doi.org/10.1016/j.cryogenics.2016.06.010
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R. Cirillo et al. / Cryogenics xxx (2016) xxx–xxx Table 1 Geometrical data. Volumes Bath Piping Loop 1
Piping Loop 2
6700 liters (l) P1 = 73.8 l P2 = 47.2 l P3 = 70.3 l P4 = 6.9 l P5 = 51.2 l Tot = 249.4 l Dead Volume_1 = 4.9 l P1_bis = 66.3 l P2_bis = 42.2 l P3_bis = 61.5 l P4_bis = 6.9 l P5_bis = 55.3 l Tot = 232.1 l Dead Volume_2 = 19.7 l
Table 2 Valves characteristic. Valves parameters Control valves parameters
CV700 CV799 CV720/CV710 CV725/CV715 CV729/CV719
Cv = 5 Cv = 186 Cv = 120 Cv = 30 Cv = 120
2.2. Control strategy As presented in [4] the control strategy consists in limiting the variation of the mass flow at the bath outlet during the pulses. In the meantime, it is important to avoid a level drift in between one pulse and the subsequent one, but the level is allowed to fluctuate during one pulse duration (one single cycle). During the initialization process, the bath level is controlled. During the pulsed regime, the level is not controlled directly anymore, but the inlet mass flow is imposed at a value correspond-
ing to the time averaged mass consumption over one cycle by means of CV700. In case of drift after a cycle, value of JT valve CV700 is re-adapted. The goal is to operate the refrigerator close to the average loads, with the lowest fluctuations of the inlet and outlet mass flows from the bath.
Initialization Pulsed regime
Variable to control
Variable to regulate (set point)
Actuators
Bath level Power to be removed at constant bath Temperature Maximum return mass flow
Bath level Bath inlet mass flow
CV700 CV700
Bath outlet mass flow
CV799
Once the level is not controlled anymore, its stability depends on the equilibrium in between the inlet and outlet mass flow set points. Equilibrium does not imply same value for inlet and outlet set points as the former has a fixed value corresponding to the time averaged consumption value while the latter is limited to a maximum value. The inlet mass flow set point is a boundary condition which aims to compensate for the evaporation taking place as a consequence of the bath heat injection at a given bath temperature. The outlet mass flow set point is an upper limit: the outlet mass flow cannot exceed this value. If it is set too high, the regulation will never be active, all the heat will immediately be converted to vapor, and hence there will be no buffer effect. If the outlet set point is too close to the inlet mass flow rate, the temperature (and consequently the pressure) will rise due to the thermal load without having enough margin to restore the initial conditions before the next pulse arrives. To determine the two set point values, an average power is estimated first and the corresponding mass flows are calculated.
Fig. 4. JT-60SA’s ACB circuit hydraulic scheme.
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Fig. 5. JT-60SA’s cold circulator characteristic; m and dP are calculated at 5 bar and 4.5 K. Thermal-hydraulic input parameters of the ACB model are listed in Table 4.
implemented in the model are PID (Proportional Integral Derivative) controllers.
Table 3 Cold circulator characteristic. Cold circulator nominal operating points Loop 1 Loop 2
876 g/s 1.3 bar 960 g/s 0.8 bar
The focus of the analysis is the range of temperatures and pressures following a pulse. The controls outputs (bath level and outlet mass flow) are also checked to judge the control parameters.
Table 4 Model input parameters. All pressures are absolute pressures. Initial conditions Loop 1
Loop 2
Bath High Pressure Line – HP Low Pressure Line – LP Boundary conditions Bath mass flow control Loop fixed settings
2.3. Results
4.4 K, 6.5 bar (coils interface – after the HX downstream the pump) 4.4 K, 5.1 bar (pump inlet) 4.4 K, 6.0 bar (coils interface – after the HX downstream the pump) 4.4 K, 5.2 bar (pump inlet) 4.3 K, 71% liquid level 4.7 K, 6 bar 4.3 K, 1.16 bar 340 g/s inlet – FE700 367 g/s outlet – FE799 164.2 W – Estimated Heat Leaks [9] 2 Time dependent heat profiles applied to the loops [10]
The outlet mass flow set point, since it is an upper limit only, is taken with an arbitrary margin, typically about +10%. All controls
2.3.1. Bath As Fig. 7 shows, the pressure in the bath is expected to rise to 1.51 bar (i.e. 4.67 K) when starting at 1.16 bar (at 4.37 K), with the given outlet mass flow set point at 367 g/s. Hence there is an increase of 0.35 bar (Fig. 7) corresponding to 0.31 K, which is below the 0.4 K maximum temperature increase specified for the acceptance tests. The control on the outlet mass flow is effective: there is synchronism between the closing of the valve and the limitation of the mass flow.
2.3.2. Loop The simulation is able to keep the cold circulators at their operational points (Table 3). The fluctuations in pressure drop and mass flow are relatively small, while the requirements for the acceptance tests limit the fluctuations of the mass flow to below 20% (see Table 5).
5000
Power (W)
4000 3000 2000 1000 0
0
300
600
900
1200
1500
1800
me (s) LOOP 2
LOOP 1
Fig. 6. JT-60SA pulses; the full line describes the pulse applied on Loop 2 and the dashed line describes the pulse applied on Loop 1.
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Fig. 7. Bath pressure and outlet mass flow control. Controls are effective and the valve closing is synchronized with the outlet mass flow limitation.
Table 5 Fluctuations around the nominal operation points.
Loop 1 Loop 2
Nominal mass flow
Max fluctuation
Nominal pressure head
Max fluctuation
876 g/s 960 g/s
0.4% 1.6%
1.3 bar 0.8 bar
0.5% 2%
2.3.3. Parametric study on the outlet mass flow Figs. 8–10 show the impact of the outlet mass flow set point (SP) on the bath level, the bath pressure and the opening of the outlet control valve. The inlet mass flow set point is always the same (340 g/s). The outlet mass flow set point is equal to 367 g/s or it can be too high: 600 g/s, or equal, to the inlet mass flow set point of 340 g/s. The evolution of the bath level allows to judge (Fig. 8), whether the drift is sufficiently low to be considered acceptable during subsequent pulses. The evolution of the bath pressure (Fig. 9) shows immediately when the outlet mass flow set point is too high and hence, there is no buffer effect: there is, in that case, no pressure rise. If the outlet mass flow is too low or too close to the inlet mass flow set point, there is a drift in the pressure which is not acceptable during the acceptance tests. Finally, a parametric study (Fig. 10) on the outlet mass flow versus the opening of the outlet control valve was performed. If the outlet set point is chosen too high the valve never closes (dashed lines), since the control on the mass flow is never effective. On the other hand, if the set point is the same as the inlet, the mass flow is constant which implies that the valve closes and then reopens but without starting from the same value (dotted lines). If
the value is appropriate instead, both the valve and the mass flow come back to the same value after each pulse. The evolution of the two variables is synchronized. It can be noted that different bath pressures imply different peak pressures in the loop. This effect is shown in Fig. 11. One disadvantage of this method is that the mean value of the mass flows has to be determined ‘‘a priori”. For the acceptance tests, powers injected inside the bath and on the loop are set by the operator and the corresponding time dependent values are well known. With this information, the time averaged value and the evaporated mass flow can be calculated. This result provides information about the averaged inlet mass flow set point. So the set points for inlet and outlet mass flow can be set a priori. During real operation of the tokamak, however, the power deposited will not be known in advance and another control strategy need to be adopted to control the valves. This is explained in the next section. 2.4. Mass control strategy The alternative control strategy tries to control the level drift after consecutive pulses (as the previous strategy) but this time controlling the mass in the bath continuously and directly, not via the level control or giving an inlet mass flow set point to balance the outlet. There is no more need to estimate the injected power. The only mass flow set point to give in the outlet one because the inlet will follow due to the fact that the regulation on the mass inventory is active all the time. Furthermore with this alternative strategy, inlet and outlet mass flows should remain equal at any time, thus increasing the efficiency of refrigerator heat exchangers.
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Fig. 8. Bath level evolution if the outlet mass flow set point changes.
Fig. 9. Bath pressure evolution if the outlet mass flow set points changes.
Fig. 10. Bath outlet mass flow and outlet control valve opening evolution if the outlet mass flow set point changes.
Initialization Pulsed regime
Variable to control
Variable to regulate
Actuators
Bath mass inventory Bath mass inventory Maximum return mass flow
Bath mass inventory Bath mass inventory Bath outlet mass flow
CV700
The following equation has to be verified.
CV700 CV799
mbath ¼ qLiq V Liq þ qgas V gas
ð1Þ
where mbath is the helium mass inside the bath; qLiq and V Liq are respectively the density and the volume of the amount of liquid helium; qgas and V gas refer to the gaseous phase.
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Fig. 11. Loops pressure evolution if the outlet mass flow set points changes. Loop 1 on the left and Loop 2 on the right.
80 76
660
72 640 68 620
64
600 0
1800
3600
Liquid level (%)
Mass inventory (kg)
680
60 5400
me (s) Mass inventory
Level
Fig. 12. Mass inventory and liquid level when the mass control is active. The mass (dashed line) remains constant along the transient while the level (full line) fluctuates but goes back to the same value periodically.
Fig. 13. Inlet and outlet mass flows with the previous approach.
Fig. 14. Inlet and outlet mass flows with the alternative approach (mass control strategy).
From the experimental point of view, bath temperature (or bath pressure) has to be used to calculate vapor and liquid densities whereas level measurement (associated with the knowledge of the reservoir geometry) gives access to liquid and vapor volumes. Numerical results are as follows: the mass inside the bath is kept constant while the level bounces but goes through the same point at the end of each cycle (Fig. 12), in other words there is no drift and the level is recovered at the end of each pulse. It is interesting to check the mass flows for the two different control strategies. With the previous approach, two different values were input (inlet as a set point, outlet as an upper limit), hence
the two mass flows were distinguishable (Fig. 13). In the case of the mass control approach, the two mass flows variations are almost the same (Fig. 14). With the previous approach a regulation on the inlet bath mass flow was active. This means that the average mass in the bath remains constant but the transient value experiences large variations. The refrigerator heat exchangers might be not well balanced because the inlet mass flow set point and mass flow rate differ in time. Furthermore, the level fluctuates and goes back to the same value periodically but a small change in the thermal load would imply a drift.
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The alternative control approach, hereafter referred as ‘‘mass control strategy”, is simpler to implement: it is active all the time while, in the previous case, what was controlled during the initialization (the bath level) stops to be controlled during the pulsed regime. Hence, in this case, there is no need to give 2 mass flow values, also because the inlet mass flow would need to be regulated using the same actuator CV700 which is still set on the mass inventory control. The only mass flow to control is the outlet one. The inlet will follow this latter. To conclude, a last parametric study is presented, to show that the mass control can be quite effective. As a start, three different mass set points were investigated to check the resulting variations of the loop pressure.
In the ‘‘reference” case the reservoir is filled up to 71% (Table 4) corresponding to 616 kg of helium. In addition 420 kg and 700 kg helium inventories have been tested. These values represent the minimum (heat exchanger still fully immersed) and maximum filling levels of the buffer. With 700 kg as set point, the bath is in average filled at 83% but reaches 90% during the pulses. With 420 kg the bath starts at 42% during the initialization time and the variations of the level are very small (about 1%) during the pulse transients. In the reference case the pressure in the bath increases by 0.39 bar (Fig. 15). For the higher mass case, the pressure rises only by 0.37 bar as more helium can store more energy. In the lower mass case the pressure rises by 0.43 bar. The loops pressure
Fig. 15. Parametric study of the mass inventory set point. Bath pressure evolution.
8
pressure (bar)
pressure (bar)
8
7
6
5
0
1800
3600
me (s)
5400
7
6
5
0
1800
3600
5400
me (s)
Mass SP = 616 kg (Reference)
Mass SP = 616 kg (Reference)
Mass SP = 700 kg
Mass SP = 700 kg
Mass SP = 420 kg
Mass SP = 420 kg
Fig. 16. Loops pressure evolution. Parametric study of the mass inventory set point. Loop 1 on the left and Loop 2 on the right.
Fig. 17. Bath pressure evolution. Parametric study on the outlet mass flow set point. The configuration is thermal buffer plus mass control strategy.
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Fig. 18. Loops pressures evolution. Parametric study on the outlet mass flow set point. The configuration is thermal buffer plus mass control strategy. Loop 1 on the left and Loop 2 on the right.
Table 6 Recap of pressure rises in the bath and in both loops. 616 kg (Reference) Bath
420 kg Bath
Loop 1
Loop 2
Bath
Loop 1
Loop 2
Mass SP variation with fixed mass flow SP = 367 g/s 0.39 bar 1.66 bar 2.04 bar
0.43 bar
1.81 bar
2.17 bar
0.37 bar
1.61 bar
1.95 bar
367 g/s (Reference)
400 g/s
Bath
Loop 1
Loop 1
Loop 2
700 kg
Loop 2
Outlet mass flow SP variation with fixed Mass SP = 616 kg 0.39 bar 1.66 bar 2.04 bar
450 g/s
Bath
Loop 1
Loop 2
Bath
Loop 1
Loop 2
0.29 bar
1.34 bar
1.74 bar
0.16 bar
0.88 bar
1.41 bar
Table 7 Results of the model for the mass control strategy compared to the requirements in the technical specifications.
Technical specifications requirements [11] Simulations with SP = 367 g/s Initialization (end) Pulsed regime (peak)
Pressure head (dP)
_ Mass flow (m)
Loop 1
Loop 2
Loop 1
P1.3 bar 1.36 bar 1.37 bar
P0.8 bar 0.80 bar 0.81 bar
P876 g/s 877 g/s 880 g/s
evolution is shown in Fig. 16, the pressure in Loop 1 increases by 1.81 bar in the 420 kg case, but only by 1.61 bar for the 700 kg case. In loop 2 the pressure increases between 2.17 bar and 1.95 bar. For the reference case the pressure in loop 1 increases by 1.66 bar and for loop 2 by 2.05 bar. Finally, the outlet mass flow set point was changed to see its impact on the buffering effect. This case may be investigated also during the acceptance tests, to see the operation possibilities of the cryogenic system. As shown in Fig. 17, stable operation can be achieved with a flow of 367 g/s while below this value the pressure drifts, since the bath cannot recover its previous state. As for outlet mass flows higher than 500 g/s there is no control, there is no point in going farther or there will be no effective limitation. The effect is the same described in Fig. 9, case 600 g/s. The pressure rise in the bath and in the two loops (Fig. 18) are indicated in Table 6.
3. Conclusions Table 7 compares the results of the simulation following the ‘‘mass control strategy” with the requirements of the technical specifications. After validating the modelling tool EcosimPro on the HELIOS experimental set-up [4], there is confidence in using this simula-
Coils interface Pressure
Coils interface Temperature
Loop 2
Loop 1
Loop 2
Loop 1
P960 g/s 963 g/s 980 g/s
P5.3 bar 6.5c bar 8.2 bar
P4.8 bar 6.0 bar 8.0 bar
4.4 6 T 6 4.8 K 4.4 K 4.4 K 4.7 K 4.7 K
Loop 2
tion tool also to model the JT-60SA ACB. The isochoric operation has been modelled and analyzed. To simulate the conditions during acceptance tests, where no coils will be connected, the thermal buffer operation with the outlet bath mass flow control has been studied as well. Finally a control strategy for long term operation has been studied in the form of ‘‘mass control strategy” (CEA patent [12]) and first results have been presented and analyzed. Following the successful application to JT-60SA ACB operation, the model could be expanded to consider other parts of the cryogenic system or different operation modes like isobaric.
Acknowledgements The authors wish to thanks M. Wanner (F4E, Fusion for Energy) for the fruitful discussion and François Bonne (CEA) for sharing his idea with us.
References [1] Kamada Y, Barabaschi P, Ishida S. The JT-60SA team and the JT-60SA Research Plan Contributors 2013, Progress of the JT-60SA project, Nuclear Fusion 53, Number 10 – IAEA. [2] Hoa C, Lagier B, Rousset B, Michel F, Roussel P. Experimental and numerical investigations for the operation of large scale helium supercritical loops subjected to pulsed heat loads in tokamaks. Phys Procedia 2015;67:54–9.
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R. Cirillo et al. / Cryogenics xxx (2016) xxx–xxx
[3] Lagier B et al. Validation of an EcosimPro model for the assessment of two heat load smoothing strategies in the HELIOS experiment. Cryogenics 2014;62:60–70. [4] Cirillo R, Hoa C, Michel F, Poncet JM, Rousset B. Dynamic simulations of the cryogenic system of a tokamak. IOP conf. series: materials science and engineering, 101. p. 012158. http://dx.doi.org/10.1088/1757-899X/101/1/ 012158. [5] Bradu B. Modélisation, simulation et contrôle des installations cryogéniques du CERN [Ph.D. thesis], Université Paris Sud – Paris XI. [6] Guelfi F, Bonifetto R, Hoa C, Savoldi L, Zanino R. 4C modeling of the supercritical helium loop HELIOS in isobaric configuration. Cryogenics 2014;64:51–62.
[7] Cirillo R. Dynamic modelling of the cooling circuits of the Japanese tokamak JT60SA, Master degree report, Grenoble INP – Phelma, unpublished results. [8] Empresarios Agrupados 2012, CRYOLIB 1.0 Reference Manual. [9] Heat Inleaks General Thermal Calculation, Air Liquide internal calculations, unpublished results. [10] Lamaison V et al. Conceptual design of the JT-60SA cryogenic system. AIP Conf Proc 2014;1573:337. [11] Michel F, et al. Technical Specifications for the cryogenics system of JT-60SA tokamak, JT-60SA internal document; 2012, unpublished results. [12] Bonne F, et al. Procédé de régulation d’un système de refroidissement cryogénique, Patent n° FR 15 59773; 2015, unpublished results.
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