Update on CAST CFD Simulations Ideas for coherence length parameterization and Tuning Windows Temperatures – Cenk Yildiz

Part 1: Coherence Length Parametrization

Problem1: Short length for tilted sims Tilted Simulations can have very short length due to hydrostatic pressure difference

Problem1: Short length for tilted sims One should be able to use the rest of the profile (with different photon mass)

Solution Remove effect of hydrostatic pressure from the profile(remove the tilt) Calculate coherence length for DST=1E-3 Use the coherence length, P_CB and Peng-Robinson equation(or Refprop) to calculate the density at any point inside this length. Calculate conversion probability integrating through the whole length. (effective photon mass will be a function of length) The cost will be computing time.

Problem 2: How to find length for any angle How can we parametrize the length for (pressure, angle)? How can we chose model for intermediate angles: – The horizontal simulations use laminar model on both MFB,MRB – Tilted simulations use half Laminar model (MFB:laminar, MRB:turbulent)

Comparing different models: Problem 2: How to find length for any angle Big difference in laminar side Tiny difference in turbulent side Very big difference from tilted to horizontal simulation

Comparing different models: Problem 2: How to find length for any angle Note that for angles < 1deg, half Laminar simulations doesn’t converge! (under investigation)

Solution Simulating -6,-3,-1,0 degree for all pressures, and do a 2 dimensional fit for pressure – angle?

Part 2: Tuning Windows Temperatures

Reminder… Laminar horizontal, and Half Laminar tilted simulations gives the closest pressure difference when tilting, thus is the model we chose for cold windows. Windows Temperature values and change in windows temperature while tilting is worse.

Reminder: Comparison of Pressure Change

Reminder: Comparison of Change in TMFB

Reminder: Comparison of Change in TMRB

Update: Changing CW Boundary Condition Set to 130K instead of 90K With this change, simulated temperatures are closer to experimental temperatures

Comparison of Temperatures (only laminar/half Laminar models) T-MFB T-MRB Horizontal(Laminar) Tilted(Half Laminar)

Comparison of Change in TMFB BC=130K

Comparison of Change in TMRB BC=130K

Pressures and Coherence Length Pressure change is within 0.03mbar of old boundary condition(Only for 98 mbar change in pressure is 0.13mbar higher) Gas is pushed more to inside, the coherence length is smaller – Around 0.5m for horizontal cases(laminar) – Around 0.2m for tilted cases(half laminar)

Conclusion Coherence length: – We need to use a new method to be able to use the whole length in the tilted cases. With new Temperature boundary condition: – Temperatures are closer to experimental values. – Temperature change during tilting is worse. – Coherence length differs in order of m – We can always fine tune temperatures to reach the experimental data, but is there a point?