C. Schultheiss

Status of the R&D towards electron cooling of RHIC

The physics interest in a luminosity upgrade of RHIC requires the development of a cooling-frontier facility. Detailed calculations were made of electron cooling of the stored RHIC beams. This has been followed by beam dynamics simulations to establish the feasibility of creating the necessary electron beam. The electron beam accelerator will be a superconducting Energy Recovery Linac (ERL). An intensive experimental R&D program engages the various elements of the accelerator, as described by 24 contributions to the 2007 PAC.

Progress in tune, coupling, and chromaticity measurement and feedback during RHIC run 7

Tune feedback was first implemented in RHIC in 2002, as a specialist activity. The transition of the tune feedback system to full operational status was impeded by dynamic range problems, as well as by overall loop instabilities driven by large coupling. The dynamic range problem was solved by the CERN development of the Direct Diode Detection Analog Front End [1]. Continuous measurement of all projections of the betatron eigenmodes made possible the worlds first implementation of coupling feedback during beam acceleration [2,3], resolving the problem of overall loop instabilites. Simultaneous tune and coupling feedbacks were utilized as specialist activities for ramp development during the 2006 RHIC run. At the beginning of the 2007 RHIC run there remained two obstacles to making these feedbacks fully operational in RHIC - chromaticity measurement and control, and the presence of strong harmonics of the power line frequency in the betatron spectrum [4]. We report on progress in tune, coupling, and chromaticity measurement and feedback, and discuss the relevance of our results to LHC commissioning.

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.

Beam-Based Alignment in the RHIC E-Cooling Solenoids

Accurate alignment of the electron and ion beams in the RHIC electron cooling solenoids is crucial for well-optimized cooling. Because of the greatly differing rigidities of the electron and ion beams, to achieve the specified alignment accuracy it is required that transverse magnetic fields resulting from imperfections in solenoid fabrication be down by five orders of magnitude relative to the pure solenoid fields. Shimming the solenoid field to this accuracy might be accomplished by survey techniques prior to operation with beam, or by methods of beam-based alignment. We report on the details of a method of beam-based alignment, as well as the results of preliminary measurements with the ion beam at RHIC.