BNL, Upton, Long Island, New York, USA
The head-on beam-beam interaction is the dominant luminosity limiting effect in polarized proton operation in RHIC. To mitigate this effect two electron lenses were installed in the two RHIC rings. We summarize the hardware and electron beam commissioning results to date, and report on the first experience with the electron-hadron beam interaction. In 2014 RHIC is operating with gold beams only. In this case the luminosity is not limited by head-on beam-beam interactions and compensation is not necessary. The goals of this year’s commissioning efforts are a test of all instrumentation; the demonstration of electron and gold beam overlap; the demonstration of electron beam parameters that are sufficiently stable to have no negative impact on the gold beam lifetime; and the measurement of the tune footprint compression from the beam overlap. With these demonstrations, and a lattice with a phase advance that has a multiple of 180 degrees between the beam-beam interaction and electron lens locations, head-on beam-beam compensation can be commissioned in the following year with proton beams.
BNL, Upton, Long Island, New York, USA
This paper describes the development and demonstration of a novel technique of adjusting measured field quality at the design field in superconducting magnets. The technique is based on placing iron shims of variable stack thicknesses, variable width and/or variable length on the outer surface of the stainless steel shell at strategic locations. Since the shims are placed outside the helium vessel, adjustments can be made without involving major operations such as opening the helium vessel. It is a simple and economical technique which is suitable for long magnets with a fast turn-around. This allows one to reduce field errors well beyond the normal construction errors. The technique has recently been successfully applied in two 3.8 T, 80 mm aperture, 9.45 m long dipoles. These magnets were built at Brookhaven National Laboratory (BNL) for the APUL project (Accelerator Project to Upgrade the LHC) as a part of US contribution to LHC. The paper will present the design, measurement and adaptation of this technique which, when used in combination with the coil shims, produced near zero sextupole harmonic at high fields and small harmonics throughout the range of operation.