I have been looking at the feasibility of an alternative heater element design for FROSTI that replaces the original ring-like heater elements with n rectangular elements with straight edges. They form an n-sided regular polygon that could well approximate the original annular ring if n is large enough. This eliminates curved surfaces requirement for the heater elements, which was the source of the many month production delay for the prototype parts.

This design was implemented in COMSOL, shown in the attached. From the face on view, each element has a trapezoid shape with straight edges. The edges between neighboring elements are parallel, with a space of 2 mm in between them.

The ray tracing and thermal analysis obtained from COMSOL are shown in the attached pdf.

In particular, the 2D irradiance profiles were obtained from the ray tracing (so far from the front heating surfaces only). The 1D radial profiles were integrated and shown in the attached. The power delivery efficiency for the original ring-like heater element design is integrated to be roughly 65%, for comparison. The plot also shows the radial irradiance profiles for three different straight-edge designs, which correspond to 16 edges, 18 edges, and 24 edges. We see that with the straight-edge designs, the irradiance profiles stay in a good Gaussian shape. In addition, with a larger number of edges, the power efficiency increases, but is always less than the case for the optimized ring-like design.

The thermal distortions for the TM were also obtained from COMSOL, using the irradiance profiles at the TM HR. As shown in the attached, with the straight-edge design, the effects on the thermal lens OPD and the HR surface deformation are similar to the ring design, but with less severe edge roll-off for instance.