CDC Straw Sag photos

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Gravitational Sag of various tubes

We have tried to compare the gravitational sag of three identical lengths of the straw material. The Lumina mylar straw, the Stone Kapton straw and the Euclid mylar straw. With the straws supported at both ends, the is slightly more sag in the kapton than either of the mylar straws but very hard to measure.

With the 76cm long straws supported it at one end, the katon straw sags about 4-5mm more than either of the mylar straws. One can roughly see this in the pictures below. The left-hand straw is the Stone kapton straw. The middle straw is the Lumina mylar straw and the right-hand straw is the euclid mylar straw. Note that these straws are about 1/2 the length of the final straws in the CDC.

Straw sag 03.jpg
Straw sag 04.jpg

Properties of the Straws

We currently have three straw samples. Mylar tubes manufactured by Euclid, Kapton tubes manufactured by Stone Industrial and Mylar tubes manufactured by Lumina.

  • Euclid Tubes
    • Aluminized mylar wrapped in tape.
    • Mirror surface on Aluminum.
    • Approximately a 4cm tape wrap.
    • Damage very easily when touched.
    • Do not snap back when squeezed.
    • Gravitational sag is minimal.
    • Tolerances worse than 3mil (?)
    • High rejection rate (90+%) of original order.
    • Very inexpensive.
  • Stone Tubes
    • Aluminized Kapton (material from Sheldahl).
    • Mirror surface on Aluminum.
    • Cannot get aluminized kapton with thick Al coating.
    • Approximately 2cm wrap tape.
    • Very Robust.
    • Do not damage when squeezed.
    • Largest gravitational sag.
    • Tolerances at 3mil
    • Not very flat (do not roll well).
    • Most expensive option.
  • Lumina Tubes
    • Mylar
    • Dimples and bubbles on the aluminum surface.
    • Approximately 2cm wrap tape.
    • Very Robust.
    • Do not damage when squeezed.
    • Small gravitational sag.
    • Tolerances to 1mil
    • Short tubes appear very flat (roll well).
    • Relatively inexpensive option.