Shunsuke Ohtani

Slow RI-beams from projectile fragment separators

Abstract The projectile fragment separator provides a wide variety of short-lived RI-ions with less restrictions on their chemical property or lifetime limit. The beam energy and quality is, however, not adequate for low-energy beam experiments, in particular for trapping experiments. Recently, one has proposed to obtain a low-energy beam from an energetic RI-beam leaving a projectile fragment separator by using a large gas-catcher and an rf ion-guide system. In off-line and in on-line test experiments, the principle of the rf ion-guide was proven. An overall efficiency of 0.2% for 70 MeV/u 8 Li from the RIKEN projectile fragment separator (RIPS) was obtained so far.

A new cooling and focusing device for ion guide

Abstract A highly efficient focusing device which uses a RF multipole field (sextupole-ion-beam guide (SPIG)) has been developed for the ion guide isotope separator on-line (IGISOL). The SPIG, placed after the nozzle, consists of six circular rods uniformly distributed on a circle in the plane perpendicular to the axis of symmetry. Under the combined action of the sextupole RF electric field produced by the rods and helium gas flow, well focused ion beams with low energy spread can be transmitted efficiently by use of the SPIG. The experimental results, using a discharge ion source, show that almost nearly 90% of the ions which leave the nozzle can be transported through the SPIG, and that the width of the kinetic energy distribution after the SPIG is about 0.8 eV (FWHM). These experimental results agree with the results of Monte Carlo simulations; the simulation studies also indicate that the size of the spatial distribution in the plane perpendicular to the symmetry axis is less than 1 mm in diameter at the end of the SPIG.

A New Versatile Electron-Beam Ion Trap

We have constructed an electron-beam ion trap (EBIT) to facilitate the creation and study of highly charged ions. After a brief introduction to EBITs in general, we describe the design of the new device, highlighting its unique features. Some preliminary results are presented which demonstrate the devices capability to produce and study highly charged ions.

Scanning tunneling microscopy and atomic force microscopy study of graphite defects produced by bombarding with highly charged ions

The defects produced on a graphite surface by single ion impact using highly charged Ar ions (charge state q⩽8) is investigated by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The defect looks like a protrusion in the STM image, while it is flat in the AFM image. From these two contrasting images, the defects are considered to be due to the increase in the local charge density of state at the surface caused by carbon atom sputtering. The average value for the defect size increases remarkably with the charge state of incident Ar ions. This is explained by the enhancement of potential sputtering due to the Coulomb repulsion between surface holes which are generated by the neutralization of highly charged Ar ions.

Space-charge effects in the catcher gas cell of a rf ion guide

Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities.

Characteristics of the Tokyo Electron-Beam Ion Trap.

We have constructed a new Electron Beam Ion Trap (EBIT). Over recent months, we have operated this device and obtained some experimental results. In this paper, we show the performance of this EBIT by illustrating these results.

Accumulation of ions from a recoil mass separator in a new type of linear ion trap

Abstract A new type of linear ion trap system in combination with a sextupole ion beam guide (SPIG) has been developed for the accumulation of a continuous ion beam. An axial trapping potential is generated by three cylindrical electrodes mounted outside, but concentric to, the SPIG. The ions in a continuous beam are trapped in the potential well via collisions with He gas. This linear ion trap is called the “SPIG-trap”. The properties of the SPIG-trap were tested off-line with a discharge ion source in a gas cell. Up to 106 ions were trapped and extracted as a bunch with an efficiency of 10% for 10 ms of accumulation. The SPIG-trap system was then connected to a gas filled recoil mass separator (GARIS) and tested with an energetic primary beam from a cyclotron (16O, 107 MeV). The overall efficiency of the SPIG-trap including ion losses in an energy degrader, which was placed in front of the He cell, was measured to be of the order of 10−5 for 10 ms accumulation.

Double charge transfer spectroscopy for N22+ and CO2+ at vibrational resolution

Abstract Doubly charged molecular ions (dications) of N 2 and CO have been studied using a double charge transfer (DCT) spectrometer capable of resolving vibrational levels. The vibrational structures of low-lying singlet states are observed in the translational energy spectra of H − ions produced by double electron capture collisions of H + projectiles. The observed spectra are well reproduced using the theoretical Franck–Condon (FC) profiles calculated from the best available ab initio potential curves. This suggests that the DCT process obeys the FC principle, i.e., the vertical transition from a neutral molecule to the corresponding dication.

An overview of the Tokyo electron beam ion trap

A new Electron Beam Ion Trap has recently been completed in Tokyo. The general features of the apparatus, design and operation are given. This paper also surveys the planned and ongoing experimental program.

The measurement of the dielectronic recombination in He-like Fe ions

We have studied the dielectronic recombination process in He-like Fe ions and have obtained the resonant strengths of the KLn (3 n 5) resonances. This measurement was performed with the use of an electron beam ion trap by measuring the x-ray energy emitted from highly charged ions simultaneously with the electron beam energy scanned during the measurement. The total resonant strengths obtained are 5.0×10 −19 ,2 .1×10 −19 and 1.1×10 −19 cm 2 eV, for KLM, KLN and KLO, respectively.