Update on CAST CFD Simulations

Ideas for coherence length parameterizationand

Tuning Windows Temperatures

06.08.2013 – 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 0.1-0.5m– We can always fine tune temperatures to reach

the experimental data, but is there a point?