The cathode foil tension is 660n/m

[Eugene Chudakov <gen@jlab.org>]

Micah and I measured the foil tension of the tight copper
plated sample, used for the flatness measurements, to be 660+/-30 n/m.

We put a 1.9 kg aluminum disk, 266mm diameter on the top of the foil,
at its center and measured the foil sagging with the laser, in 2 radial
positions "r". The internal radius of the fiberglass ring is R=503 mm.
The measurement was done along the copper stripes.

  r          sagging           T
 221+/-5mm     3.73+/-0.05mm  650+/-20 n/m
 347+/-5       1.53+/-0.05    720+/-40 n/m

The formula used: sagging=m*g/(2*pi*T)*ln(r/R)

The Young modulus of kapton is 2.5 GPa. The relative elongation of the 25-um foil
(neglecting the copper plating) is 1%.

Eugene