High precision polarimeter system for atomic polarization and tilted-foil experiments with 1.7 keV/amu N+14 beam

Abstract

A high precision atomic polarimeter system for the use in beam-foil spectroscopy experiments with a few keV/amu heavy-ion beams has been developed. The polarimeter measures the circular polarization of fluorescences from the beam ion in-flight after the beam–foil interaction. The present system has two identical such polarimeters in both sides of the beam axis to reduce the systematic errors such due to the fluctuations of beam current, background and so on. A successful use of an ultrathin carbon foil (1.5 μg/cm2), which was durable for several hours against a few hundred nA beam irradiation, enabled the beam–foil experiments with such low energy heavy-ion beams. A performance test of the polarimeter system was carried out in the tilted foil experiments with a 1.7 keV/amu N+14 beam. The atomic polarization was observed for the transition 1s22s22p3p 1D→1s22s22p3p 1P, whose fluorescence wavelength is 399.5 nm, in the N+ ion (N II). The polarization was approximately −2% for the tilt angle of −40° and showed monotone increasing with increasing tilt angle up to +2% for +40°. The polarization at 0° was (0.002±0.25)%, which is highly consistent with the expected polarization of 0%. This result indicates the high reliability of the present polarimeter system. This is the first tilted-foil experiment at such low beam energy. The present experimental technique will be very useful for studies of the polarization mechanism of the beam–foil interaction.