Simultaneous Tune And Coupling Feedback During Rhic Run 6

The Relativistic Heavy Ion Collider (RHIC) is a versatile facility, capable of operating with both polarized protons and a variety of ion species over a broad range of energies. Acceleration ramp requirements change frequently to meet the needs of the physics experiments. There has been an ongoing effort at RHIC to implement reliable betatron tune feedback as a tool for ramp development, and possibly to control tune during routine operations. Vertical orbit fluctuations in the chromaticity correction sextupoles during ramping are sufficient to fully couple the tunes. This complicates tune control, and with tune feedback causes the basis in which tune errors are reported to not match the basis used to correct the quadrupole currents, leading to feedback instability. This problem has been overcome by using realtime measurements of the coupling projections of both betatron eigenmodes to close feedback loops onto two skew quadrupole families. This minimizes coupling and matches the tune and coupling reporting basis to the correction basis. We report on successful simultaneous tune and coupling feedback during RHIC ramp development and implications of this effort for the LHC[1].