The RHIC IR Quadrupoles (The best field quality magnets ever built)
At first glance, a very unlikely cross-section for building the best field quality magnet
- Doesn’t have the basic 4-fold quadrupole symmetry (large non-allowed harmonics).
- Close-in iron (large saturation-induced allowed harmonics).
- Uses RX630 spacers -large errors in parts (large geometric harmonics).
Moreover, it started out with ~ 1 mil uncertainty in insulation thickness (or effective cable thickness).
- Total ~27 mils (order of magnitude more than the typical 2 mil) in overall coil dimensions for 27 turns.
- Conventional thinking : Fix cable first.
- Done here : A flexible design which can absorb such large differences. This approach was used during production also for several adjustments in harmonics.
Cross section of the 130 mm aperture
RHIC insertion quadrupole