Anomalous Schottky Signals from a Laser-Cooled Ion Beam

Abstract

Longitudinal Schottky signals from a laser-cooled, spatially dense, ion beam have been studied in the ASTRID storage ring. The fluctuation signals are distorted by the effects of space charge, as is observed in electron cooling experiments.However, the spectra also exhibit previously unobserved coherent components.The ions' velocity distribution, measured by a laser fluorescence technique, suggests that the coherence is due to suppression of Landau damping. The observed behavior has important implications for the attainment of a crystalline ion beam in a storage ring.PACS numbers: 41.75. Ak, 29.20.Dh, 29.27.Bd, 52.25.Wz In this Letter we describe measurements of longitudinal Schottky signals from a unique physical system, a spatially dense, very cold (i.e., having very small velocity spread) ion beam produced by laser cooling. This system has direct relevance to the understanding of the ultimate limits to the quality of a stored ion beam. In particular, the possibility of producing a crystalline ion beam [1] is usually associated with the technique of laser cooling.Schottky signals [2] are used as a powerful diagnostic

Resonance coupling induced enhancement of indirect transverse cooling in a laser-cooled ion beam

“…The layout of the S-LSR with a laser cooling and observation systems for a 40 keV 24 Mg þ ion beam is shown in Fig. 2.…”

“…It is also worth noting that the coasting crystalline string of 24 Mg þ ions with the use of laser cooling was experimentally realized for energy of 1 eV at the tabletop circular ion trap, PALLAS [15], which was also further extended for a bunched beam [16].…”

“…For the past several years, continuous effort has been devoted to attain a three-dimensionally ultracold ion beam circulating in a storage ring. In our present study, we more or less follow the ASTRID approach where a single laser is employed together with an rf voltage to cool a bunched 24 Mg þ ion beam in the longitudinal direction [7]. In case a beam is bunched with an rf field, individual ions execute synchrotron oscillations in the longitudinal phase space, and the rf electric field works as a counter force to the ions in the beam accelerated by copropagating laser with Doppler laser cooling, as shown in Fig.…”

Low-Current, Vertical Blowup in a Stored Laser-Cooled Ion Beam

“…If the above interpretation is correct, laser cooling as implemented in ASTRID may not be suitable for obtaining true one-dimensional order in a storage ring. Schottky diagnostics of the beam could help to clarify the experimental situation, but our earlier experience indicates that the longitudinal Schottky signals are strongly distorted by the effect of the laser [6]. Whether this behavior persists in the regime of one-dimensional beams remains to be determined.…”

“…For diagnostic purposes, copropagating laser light in a second ring section is focused and overlaps the ion beam in the post acceleration tube (PAT) in front of the transverse imaging system. We measure the longitudinal velocity distribution by monitoring the laser-induced fluorescence from the ion beam inside the PAT using a photomultiplier while sweeping the voltage on the PAT [6].…”