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(γ , 2e) triple differential cross sections are presented for helium at 60 eV above the photodouble ionization threshold with energy-sharing ratios (R = E 2 /E 1) for the two ejected electrons of R = 1, 5 and 11. The measurements were taken using a toroidal spectrometer and linearly polarized light from an undulator beamline (SU6) at the Super-ACO storage ring. Good agreement is found with TDCSs obtained by the CCC method and by the length gauge of 3C theory.

Helium double photoionization (␥,2e) triple differential cross sections ͑TDCSs͒ were measured at an excess energy of 60 eV using a dual toroidal spectrometer and synchrotron radiation from a helical undulator ͑BL-28A, Photon Factory, Japan͒. Energy-sharing ratios (RϭE 2 /E 1 ) for the two ejected electrons of 5 and 11 are studied with both right-and left-handed elliptically polarized light. The TDCSs are found to be in good agreement with those obtained using the hyperspherical R matrix with semiclassical outgoing waves theory. The circular dichroism for a limited mutual angular range ( 12 Ϸ110°-200°) is determined from the experimental data for both Rϭ5 and 11, and compared to theoretical calculations performed over the complete range of mutual angles. No dynamic nodes are found in either the experimental ͑within the explored 12 range͒ or theoretical circular dichroism for these R values at this excess energy.

Precision measurement and control of the betatron tunes and betatron coupling in RHIC are required for establishing and maintaining both good operating conditions and, particularly during the ramp to high beam energies, high proton beam polarization. While the proof-of-principle for simultaneous tune and coupling feedback was successfully demonstrated earlier, routine application of these systems has only become possible recently. Following numerous modifications for improved measurement resolution and feedback control, the time required to establish full-energy beams with the betatron tunes and coupling regulated by feedback was reduced from several weeks to a few hours. A summary of these improvements, select measurements benefitting from the improved resolution and a review of system performance are the subject of this report.

Beam profiles in the two storage rings of the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Lab (BNL) are measured with ionization profile monitors (IPMs). Each ring has a vertical and horizontal detector. An IPM measures the distribution of electrons produced in the beam line by beam ionization of background gas. These detectors have been developed at BNL in a program that began in 1996. The current detectors are a design that was based on a prototype built in 2007 and used in RHIC from 2007 to 2012. During the 2012 shutdown we refurbished this prototype and installed it into the Alternating-Gradient Synchrotron (AGS). This paper describes the new AGS IPM and shows data from the detector commissioning.