I'm using COMSOL to simulate the effect of cavity sagging to find the optimum suspension points. The answer is not yet ready, I'm still working around COMSOL.

• Problem with point like contact: First I tried to simulated 4-fixed-point support, however the result was asymmetric along beam line. It might be the result from the point-like contacting areas between the support and the cavity. You can see the tilting along the beam line in the figure below. Note the constrained area  of the support effect the sagging slightly as well [add ref].

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fig1: cavity sagging, on 4 point suspension. The cavity is not symmetric on left and right.

     So, as a start, I switched to half line support. As my cavity support will be rods placed perpendicular to the refcav, the simulation might not be off by much. Then I checked the displacement at the center of the mirrors. The result was, the further to the ends of the spacer, the less displacement of the mirrors. I think this is strange. I also remember a paper about this and their cavity dimension is similar to what we have, and their result is slightly away from the ends [ref]. I'll have to double check the result again.

Note: I think what is wrong is how I use the displacement of the mirrors along the beamline as differential length of the cavity, I have not taken into account tilting of the mirrors yet. Also, I'll try to position the venting hole downward to see if there is any differences in the result or not.