Sadayoshi Fukumoto

Further evaluation of the high intensity plasma sputter heavy negative ion source

In this report, we provide more detailed information on the high intensity heavy negative ion source described previously. Intensity vs time spectra, mass distribution data and source operational data are presented for Au, Cu, Ni and CuO sputter probes. Sputter probe voltage limited beam intensities of 10.2, 8.2, 5.1 and 4.5 mA, respectively have been realized from these sputter probes. The results of emittance measurements for Au and Ni probes indicate a rather strong dependence on beam intensity, as expected from space charge considerations. The source, when operated in pulsed mode, holds considerable promise for use in conjunction with tandem electrostatic accelerator/synchrotron injection applications. The high intensity capabilities of the source make it a viable candidate for generating mA intensity level, cw ion beams for a variety of other applications, including ion implantation.

A versatile high intensity plasma sputter heavy negative ion source

Abstract A multicusp magnetic field plasma surface ion source, normally used for H − ion beam formation, has been utilized for the generation of high intensity, pulsed, heavy negative ion beams suitable for a variety of uses including tandem electrostatic accelerator/synchrotron injection applications. Sputter probe voltage limited total ion currents of 5.5, 8.2, 5.1 and 4.5 mA (peak intensity) have been produced from Au, Cu, Ni and CuO sputter probes, respectively. The mass distributions of these ion beams are found to be dominated by Au − , Cu − , Ni − and O − atomic species, respectively. The source offers the interesting prospect of providing cw negative ion beams at mA intensity levels of the commonly used semiconducting material dopants (e.g. B − , P − , As − and Sb − ) as well as O − for isolation barrier formation. Illustrative examples of intensity versus time and the mass distribution of ion beams extracted from a Ni sputter probe, along with brief descriptions of the source, experimental apparatus and procedures followed during the course of these investigations, are presented in this report.

Measurement of electron polarization of optically pumped sodium atoms

Abstract The electron-spin polarization of optically pumped sodium atoms for a polarized H− ion source was measured by a Faraday rotation method. This paper presents the theory of this scheme and some experimental results which have been obtained so far. When two pumping lasers were used, a sodium electron-spin polarization of about 90% was obtained at a target thickness of 1 × 1013n/cm2.

The cusp H− ion source at KEK

A cusp H− ion source has been operated at the 12 GeV proton synchrotron at KEK. The ion source is pulsed (200 μsec×20 Hz) and provides 15–20 mA H− beams to the linac. The long lifetime of the LaB6 cathodes resulted in stable operation.

Polarization measurement of atomic hydrogen beam spin-exchanged with optically oriented sodium atoms

The spin-exchange reaction between hydrogen atoms and optically oriented sodium atoms was used to produce a polarized atomic hydrogen beam. The electron-spin polarization of the atomic hydrogen beam, which underwent the spin-exchange reaction with the optically oriented sodium atoms, was measured. A beam polarization of −(8.0 ± 0.6)% was obtained when the thickness and polarization of the sodium target were (5.78 ± 0.23) × 1013 atoms/cm2 and −(39.6 ± 1.6)%, respectively. The value of the spin-exchange cross section in the forward scattering direction, whose scattering angle in the laboratory system was less than 1.0°, was obtained from the experimental results as Δσex=∫dσdωdωθlab=0 →1.0°=(3.39±0.34)×−15cm2. This value is almost seven times larger than the theoretical value calculated from the NaH potential. The potential was computed quantum mechanically in the space of the appropriate wave functions of the hydrogen and the sodium atoms.

Radiation trapping in an optically pumped thick sodium target

Abstract The effect of radiation trapping in an optically pumped sodium target was measured with a Faraday rotation method. The experimental results were compared with calculations based on recent theoretical work, and good agreement was found between the two.

Dc beam operation of the CUSP negative heavy ion source

Abstract Dc mode operation was tried in the cusp-magnetic-field negative heavy ion source, which has been successfully operated in the pulsed mode recently to obtain intense negative heavy ion beams. In a preliminary experiment, a dc beam of more than 1.5 mA for negative copper ions has been obtained easily at the relatively low are current of 3.5 A

Recent progress on the optically pumped polarized H− ion source at KEK

Recent progress on the optically pumped polarized H− ion source is described. Beam current of 50 μA with nuclear polarization of 56±5% has been obtained with an intense pulsed dye laser. Experimental results for radiation trapping are also described.

Intense negative heavy ion sources

Negative ion sources based on plasma‐surface interactions (BLAKE ion source) have been developed at KEK for producing negative heavy ions. The first negative heavy ion source (BLAKE‐II) was developed by modifying the ordinary negative hydrogen ion source with converter (BLAKE‐I) placed into the plasma. It generates various species of negative heavy ions with intense beam currents. For example, a more than 10 mA Au− ion beam was obtained from the ion source. Recently, the large scaled negative heavy ion source (BLAKE‐III) has been developed and in the preliminary test experiment, more than 100 mA Cu‐ ion beam has been stably obtained with a 10% duty factor in pulsed operation. The BLAKE‐II ion source was attached to the BNL 15 MV and Tsukuba University TANDEM accelerators and large current negative heavy ion beams were successfully accelerated in pulsed mode operation. Also, it was found that the space charge effect should be carefully considered for such a large current acceleration in a tandem accelerato...

Faraday rotation of optically pumped sodium vapour in a weak magnetic field

Abstract Faraday rotation of optically pumped sodium atoms in a weak magnetic field, which is lower than the critical field of hyperfine splitting, was obtained theoretically. The estimated rotation angles were compared with the experiments for various magnetic fields. The measured values showed good agreement with the values calculated from the theory.