Finn O’Shea August 03, 2016 Construction of the Non-linear Insert for the IOTA Ring

Short motivation for Integrable Optics and the IOTA project. 3-year SBIR project to build the prototype non-linear insert for the IOTA project. RadiaBeam’s Insert: General overview Magnet modules Vacuum chamber Contents FHO - IOTA magnets - AAC August 03, 2016

Linear lattices are nice because they are easy to understand. They are also unstable to perturbations and suffer from chromaticity. Both of these can be corrected by non-linear elements (sextupoles and octupoles). But these elements limit dynamic aperture because the systems are far from integrable. These problems can be ameliorated if the system is both non-linear and integrable from the very beginning. This requires a magnetic element in which the magnetic field depends on x, y and s. V. Danilov and S. Nagaitsev, PR ST-AB 13, (2010). Integrable Optics Background FHO - IOTA magnets - AAC August 03, 2016

IOTA is a project at FermiLab to perform a proof-of-principle experiment on the integrable optics concept. Scale: 32 m circumference, 150 MeV electron ring, β = cm, eventually ~3 MeV protons Integrable Optics Test Accelerator FHO - IOTA magnets - AAC August 03, 2016

2-meter long device where the field strength varies quadratically with s. Alignment goal of r = 100 um, 0.5 deg for all the modules Field required a set of specific harmonics RadiaBeam’s Insert FHO - IOTA magnets - AAC August 03, 2016

Sent the Phase I prototype to Argonne for measurement on a rotating coil. We were not thrilled with the results. The motion of the reluctance gaps was not repeatable, so it was very hard to tune the whole device at once. It is kind of hard to see how good or bad the harmonic content is with typical harmonic content chart. Phase I measurements Upright Harmonic Content Skew Harmonics FHO - IOTA magnets - AAC August 03, 2016

Optical stages are used to position the modules Magnetic Modules FHO - IOTA magnets - AAC August 03, 2016 B’ max = 2.5 T/m, B max = 400 G

Vibrating wire for locating the centers Others have proven the technique to the μ m level, which is well more than we need. Current results show: (repeatability) X-location: ±2 μ m (auto) Y-location: ±5 μ m (auto) Pitch: <1 deg Yaw: <1 deg Roll: ±0.2 deg (auto) Axis finding FHO - IOTA magnets - AAC August 03, 2016

Nearly 2-meters long but requires 0.25 mm features to fit magnets. Cannot be extruded because of the quadratic growth in diameter. Requires a complex schedule of alternating machining and e-beam welding to maintain the <0.005” dimensions needed for good welds. Use 2219 Al at the request of the e-beam welder. Vacuum chamber FHO - IOTA magnets - AAC August 03, 2016

Test Chamber Pump-Down Pump: Pfeiffer HiPace 80 (67 L/s) Pressure Gauge: Pfeiffer PKR 261 Minimum Pressure: 3.74 * Pressure measurements began after a three day bake at 150°C and four days of vacuum pumping RGA partial pressure measurements taken concurrent to pressure and temperature measurements FHO - IOTA magnets - AAC August 03, 2016

Test Chamber Data Internal Volume [V]: L Internal Surface Area [A]: cm 2 Initial Pressure [P]: 5.78*10 -9 torr Final Pressure [P]: 1.02*10 -6 torr Average outgassing rate 6.54* torr*L/s/cm 2 = 8.71 W/m 2 Estimated ultimate pressure of the final chamber P = 6* torr FHO - IOTA magnets - AAC August 03, 2016

We have performed extensive prototyping of the critical features: the magnets and the vacuum chamber. The results have been promising on both fronts, no major issues. Fabrication work is ongoing and we expect to deliver in late September Thanks to C. Doose at ANL for the magnetic measurements. Thanks to Jacob McNevin, David Martin, Ronald Agustsson and the RadiaBeam shop for all of their work on this project. Further information on the insert: F. H. O’Shea, NA-PAC 2013, p 922. F. H. O’Shea, AAC 2014, Working Group 7. F. H. O’Shea, IPAC 2015, p 724. Summary FHO - IOTA magnets - AAC August 03, 2016 Funding: DOE DE-SC