C-AD Accelerator Physics Seminar

""Lengthening the Spin Coherence Time: A Progress Report from COSY""

Presented by Dr. Edward Stephenson, Indiana University

Wednesday, July 18, 2012, 4:00 pm — Bldg 911B, Rm A202, Large Conf. Rm

A requirement for using a storage ring in the search for an electric dipole moment on charged particles is that the beam be polarized along the beam velocity and remain that way for times up to 103 seconds. This seminar will report on progress made in May of this year using a vector polarized, 0.97-GeV/c deuteron beam at the Cooler Synchrotron (COSY) located at the Forschungszentrum-Jülich in Germany to study the evolution of the horizontal-plane polarization under a variety of conditions. Beam polarization measurements were made continuously during the beam store by slowly extracting the beam onto a thick, 1.5-cm target and observing scattered, charged particles in the EDDA scintillator array. Asymmetries in the count rates provided information on the two transverse components of the beam polarization. The polarization was rotated from the vertical (stable) direction into the ring plane using an RF solenoid operated on the 1‒Gγ harmonic of the spin tune frequency. A system was commissioned to time-stamp each polarimeter event so that the revolution of the polarization in the horizontal plane (120 kHz) could be unfolded and measured directly. By the use of electron cooling and selective beam heating through white noise applied to stripline plates, the vertical and horizontal emittances of the beam were adjusted separately. Horizontal polarization measurements showed that the polarization lifetime fell as the square of the width of the horizontal beam profile. By adjusting a family of sextupole magnet currents, it was possible to cancel the spread of the spin tunes responsible for the depolarization and achieve lifetimes of hundreds of seconds. Similar large polarization lifetimes were observed using beam that was continuously electron cooled.

Hosted by: Chuyu Liu

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