Modeling Quench Evolution and Recovery in Cryogenic Systems without Cold Buffer

1. HL-LHC IT String Cryogenic meeting #2Modeling of quench evolution and recovery with Ecosim and other methods – cases without cold buffer A. Wanninger CERN, 4th April 2019

2. Quench evolution – EcoSIM model • Considered parameters and initial conditions – no quench buffer:

3. Quench evolution – EcoSIM model • Other parameters and modeling choices: • Perfect heat transfer between helium and metal in cold mass • Perfect heat transfer between helium and warm buffer wall (25 mm thick) • All valves are control valves that are controlled by proportional controllers. • QRV is opens at 17 bara and reaches the full lift at 20 bara. It closes again at 16 bara. • Valve to warm buffer is ,opens at 13 bara and reaches the full lift at 14.2 bara. It closes again at 11.8 bara.

4. Quench evolution – Heat load vs time • Development of a correlation to estimate the heat load to the total cold mass over time • 1st step: Exponential correlation for LHC string full quench (15.3 MJ) • Conditions and assumptions: • Quench time of 120s • Isochoric heating to 18 bar within 6 seconds (according to measurements) • Estimated initial heat load in the correlation: Pressure vs time: Measurement (top) and Ecosim model results with developed correlation Developed exponential correlation

5. Quench evolution – Heat load vs time • 2nd step: Extrapolation to HL String full quench (39.07 MJ) • Simple up-scaling by the ratio of energies is not appropriate because heat load from coil to cold mass is proportional to and: • between coil and cold mass does not increase by this factor. Estimation of increase done by Rob van Weelderen. • is likely to be reduced in magnets compared to magnets. • Heat transfer from coils to cold mass will be slower • New approach (assumptions): • Initial heat load in the correlation: 600 kW • Quench time: 180 s • Lower energy quenches are scaled down (energy ratio).

6. Quench evolution – 39 MJ quench simulation: p, T, and ṁ

7. Quench evolution – 39 MJ quench simulation, m and E * Energy fraction values do not sum up exactly to 1 because of a slight difference in the heat capacity data for stainless steel in Ecosim and the correlation used to calculate the indicated value.

8. Quench evolution – 22 MJ quench simulation, summary * Energy fraction values do not sum up exactly to 1 because of a slight difference in the heat capacity data for stainless steel in Ecosim and the correlation used to calculate the indicated value.

9. Focus on warm buffer • Calculation of minimum possible temperature of warm buffer • Assumptions for buffer: • Existing 80 reservoir (1296617_V1_RESERVOIR__80m3_He) • 25 t steel mass • Operating temperature: minimum not to be exceeded after quench • Assumptions for calculations: • Initial temperature of buffer: • Perfect heat transfer between Helium and buffer wall and perfect conduction inside steel wall • No heat external heat source (no heat-up of the reservoir wall or Helium by the atmosphere) • 39 MJ quench • All valves open fully at their respective opening pressures (17 bara and 13 bara) and remain open • Results: • Final temperature in warm buffer is • If all gaseous Helium (220 kg) at 4.5 K was dumped into the buffer, about would be reached.

10. Quench recovery – pumping down to 4.5 K GHe • Analysis of quench recovery time by pumping • Relevant parameters: • Amount of quench energy expelled through quench valve • Temperature of cold mass and GHe after quench • Maximum and best-estimate values • Flush factor included (conservative) • Analytical analysis (excel) * The cooldown is performed with 18 g/s (at 35 mbar including pressure drop in line B) down to 2.1 K , then with 12 g/s (at 25 mbar including pressure drop in line B) down to 2.0 K, and finally with 6 g/s (at 14 mbar including pressure drop in line B) down to 1.9 K.

11. Refill from GHe to LHe at 4.5 K • Limitations: • Total liquid mass flow at 4.5 K provided by cold box: 25 g/s • Maximum pumping capacity: 18 g/s • Refill with LHe at 4.5 K is only possible to a certain liquid level. • Procedure to fully fill cryostat: • After open refill, the magnet cryostat is closed and the remaining GHe is condensed by pumping. • During pumping, the pressure is maintained at 1.3 bar. The density increase must be compensated for by a make-up mass flow of LHe at 4.5K. • The sum of the pumping flow and make-up flow must not exceed 25 g/s optimum can be calculated: 4.6 g/s of pumping flow and 20.4 g/s of make-up flow for any liquid level. • Total time is 2.0 hours. This is equal to the time of a full open refill.

12. Cooldown from 4.5 K LHe to 1.9 K • Limitations: • Total liquid mass flow at 4.5 K provided by cold box: 25 g/s • Maximum pumping capacities: • 18 g/s at 2.04 K and 35 mbar including pressure drop in line B: cooldown to 2.1 K. • 12 g/s at 1.93 K and 25 mbar including pressure drop in line B: cooldown to 2.0 K. • 6 g/s at 1.76 K and 14 mbar including pressure drop in line B: cooldown to 1.9 K. • Procedure to cooldown from LHe at 4.5 K to 1.9 K: • During pumping, the pressure is maintained at 1.0 bar. • The density increase must be compensated for by a make-up mass flow of LHe at 4.5K. The density increase is terminated at about 2.4 K. • The sum of the pumping flow and make-up flow must not exceed 25 g/s optimum can be calculated: 17.5 g/s of pumping flow and 7.5 g/s of make-up flow. Required time to 2.4 K: 1.58 h. • In the further cooldown, the pumping capacity is gradually decreased:

13. 39 MJ quench evolution

14. 22 MJ quench evolution

15. 6.25 MJ quench evolution