Coil TQ 36 size measurements F. Nobrega/ R. Bossert

TQ coil 36 contains 54/61 cable made at LBNL and has 2 layers of butt lap 3 mil e-glass insulation. The purpose is to test the e-glass insulation system, both mechanically and electrically, for the future LQ coils. Azimuthal measurements of the coil were taken after curing, in a small measuring fixture as shown below. (impregnated coil section shown in fixture). Measurements of the coil at various pressures (5, 10, 15 and 20 MPa) are taken and compared to a steel master of the coil design size. 2

A plot of the measurements (size with respect to nominal coil size), together with all previously measured TQ coils, is shown below. 3 * All coils except were measured at four pressures. Coils were only measured at 10 MPa, because this is the measurement used to determine reaction cavity size. Measurements at other pressures for these coils were derived from average MOE of the other coils. x *

The most relevant point on the plot is that of coil TQ36 at 10 MPa. We expect to shim the reaction mold cavity to mils ( microns) larger than the coil azimuthal size at 10 MPa. This allows the coil to grow by that amount in the reaction mold without exceeding a pressure of 10 MPa. TQ cured coils varied between -150 and -475 microns at this pressure, (as can be seen from the plot) and the mold cavity was always set at zero, so many of the TQ coils were probably subjected to higher pressures during reaction. A study showed no significant correlation between the cured size and performance, although coil 19, which reached the highest %SSL of any TQ coil, was in fact the smallest after curing. 4 x 10 MPa TQ19

Coils 34 and 35, which were used in the last two mirrors, were significantly larger than the previous two coils due to the double overlap e-glass on coil 34 and the core on coil 35. The reaction molds on both these coils were shimmed by 20 mils larger than their respective cured coil measurement at 10 MPa, and both coils performed very well. (Incidentally, note that there are two measurements for coil 34, "TQ34" and "TQ34r". This is because we cured coil 34 twice, the second time at a higher pressure of approximately 45 MPa, as opposed to the normal 35 MPa, and the TQ34r measurement is after the re-curing.) 5 x 10 MPa TQ34 TQ34r

We were hoping that TQ36 would fall in the normal range of TQ coils, but unfortunately, it looks similar to coil 34. It measures +55 microns at 10 MPa. This means, if we are to use our mil rule, we need to shim the mold cavity to be about 20 mils larger than nominal. This works for a mirror coil, but will make the coils too big for use in a real magnet unless something else is removed which would change the field components. So this is not good news for the LQ coils. The current plan is to react and pot coil TQ36, section it and do electrical tests to qualify it for the next LQS. There are several options: 1.Still use this insulation system, but find a way to reduce other areas of the cross section, for example: a)removing the extra insulation currently placed at the poles (5 mils) b)reduce poles and or wedge size 2.Manufacture the cable smaller by an amount equivalent to the mil difference (this is about 1 mil per turn). 3.A combination of 1 and 2. 4.Consider a different insulation system, either the braided S-2 glass supplied by Arup, or a version of the e-glass with a 40% or less overlap. (needs qualification) Option 4 will require more ten-stack insulation tests, with the alternate systems. This can begin soon with either system. Fermilab has about meters of cable with the braided insulation supplied by Arup. 6