A Quantum Diaries Survivor

In an attempt to find out more about the recent problem experienced with a triplet of low-beta quadrupoles at the Large Hadron Collider, I dug a bit into the technical publications related to the design and test of those structures.

There is not a lot online on the issue. Many of the papers are not accessible freely… But I found a paper that describes the choice of material for the support structures (the so-called G11, a glass cloth-epoxy laminate which was the part which broke in the triplet at point P5 in the LHC ring. The paper also discusses several of the tests performed to study the mechanical stresses under quench conditions. Here are the conclusions of the paper:

The HGQ [short fully instrumented model magnets - TD] mechanical design has been refined and improved through a combination of analytical, computational, and empirical studies. Quench performance has improved substantially, and is well reproduced among magnet assembiles. The essential design details leading to achievement of the performance goals are being finalized. Two additional model magnets will be fabricated in order to refine production techniques and test minor modifications to cable desing, in preparation for full-scale prototype fabrication.

Not very illuminating. Let’s see another paper titled “Quench performance of Fermilab high-gradient quadrupole short models for the LHC interaction regions“. It is a 1999 publication, so it is an earlier one than the one quoted above. In it, one reads that the supports were still designed to be made of G-10. It said:

Model HGQ05 included a set of changes which addressed the issues raised by previous models. The most important of the changes from the base-line design included n HGQ05 are:

• Use of G10 as end part material
• Re-cure of inner coil at higher pressure, resulting in a higher inner layer elasticity modulus and more uniform inner/outer coil mechanical properties
• A continuous body/end transition, including elimination of key extension
• …

In the conclusions, one learns that

…Significant improvement in magnet training at 4.5K and 1.9K was achieved in last model (HGQ05) as a result of the optimization of design details of magnet support structure. Test of HGQ05 in a second termal cycle continues. Although the results obtained demonstrate that the magnet desing can provide the required quench performance some further optimization is desirable…

Interesting. It looks like these support structures were understood as critical points early on, as demonstrated by the attention they received and the changes - from an earlier design to G-10, and then G-11. And one also infers that the quality of the support is instrumental in preventing the quenches.

Is any expert willing to elaborate on these issues ? My comments column is always open.