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Nr 16: Optimization accounting for the field angle dependence on the critical current density

Goal

Optimize the conductor position with respect to the magnet operational point in the load line in a background field of 8 T.

Description

Info

It is recommended to follow the [Use case 15](use_case_15.md) before proceeding with this case.

  • 2D options:

    • Fields & forces = TRUE makes ROXIE calculate the magnetic field and Lorentz forces in the position of every line current in the model. The conductor is discretized by a number of line currents defined by N1 and N2.

    • Margin to Jc-fit = TRUE triggers the calculation of the position of each block on the load line. For low temperature superconductors, this is the position of the strand in the block that is exposed to the highest field. In the case of superconductors where the critical current depends on the field direction, this is the position of the strand in the block that is closer to the critical surface. The margins are calculated by bisection w.r.t. the Jc-fit function that is specified in the .cadata file. The parametrization of the critical surface is described in [1]. The operational temperature is defined in the cadata file.

    • Margin to linear Jc-approx. = FALSE. This option would calculate the margin w.r.t. to a linear approximation of the Jc-fit.
      • Enthalpy margins: = FALSE. This option triggers the calculation of enthalpy margins to quench, that is to say, we determine how much energy can be deposited in the coils to raise the temperature above the critical level. The material properties of the conductor ar specified in the .cadata file but they are only available NbTi and Nb3Sn superconductors.
      • Optimization = TRUE.
    • Design variables:
    • Optimization algorithm: different algorithms are available. One can be insterested in performing a parametric study between given boundaries study the variation of the objectives as a function of the design variable. In this particular case, we go for the Genetic Algorithm, setting as design objective minimizing the percentenge on the load line of each block. In addition to the operation point, field quality requirements can be set as objectives in order to optimize the block position in order to minimize the harmonic content.
    • We select as optimization variables the tilt angle of each block.
    • A background field of 8 T is also set in this widget. As this is not an optimization variable it shall be placed at the end of the design variables list.
    • Block restriction: This field is a list of those blocks, in which we want to calculate the fields, forces, and margins. We select only the two blocks in the first quadrant, since all other blocks feature equivalent data by symmetry in order to save time for the optimization.

Output:

  • In the “run” menu, we can select “Open cockpit view” in order to follow the optimization process.
  • The optimal solution can be uploaded in the design variable widget The results of an optimization can be read into the data file from the 'Design Variables' widget. Click on the symbol in the top-right corner of the table and select 'Read in design set ...'. Select the .scan file with the same filename as the .data file. If you aborted the optimization, the .scan file is called 'roxie.scan'. Now you can load the last design set which should correspond to the best design.

REFERENCES

  1. J. Fleiter and A. Ballarino. Parameterization of the critical surface of REBCO conductors from Fujikura. EDMS Nr: 1426239

Files

use_case_16.zip

  • opt_REBCO.data
  • REBCO.cadata
  • usercase_REBCO_optimization.pdf