Yoichi Nakai

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.

Cross sections for ionization and fragmentation of by fast impact

Absolute cross sections have been measured for the first time for -impact ionization and fragmentation of at proton energies ranging from 0.2 to 2.0 MeV. The cross sections were in fairly good agreement with other electron-impact data in the high-velocity region, indicating that the charge transfer is negligible in the present energy range. Theoretical cross sections for plasmon excitations were also calculated and compared with the experimental ionization cross sections. Agreement between them was within a factor of two, indicating that the plasmon excitation contributes to the total ionization by about 50%. A careful analysis of the energy dependence of the cross sections for and ions indicates that these ions are produced from the same initial excited states created in collisions with ions.

Compact electron beam ion source with high-Tc bulk superconductors

We have developed an electron beam ion source (EBIS) assembling three rings made of high-TC superconductor as a solenoid coil, which enables us to construct a “table-top” EBIS operated at the liquid N2 temperature with a strong magnetic field. Optimizing a pulse field magnetization procedure, the assembly yielded a magnetic field as high as 0.8 T under a persistent mode, which stably lasted more than two days. An electron beam of 12 keV-50 mA was compressed to a current density of about 300 A/cm2 and guided by the magnetic field along the axis of the drift tube. After exiting the drift tube, the electron beam was decelerated to 2 keV and collected with an electron collector with an efficiency of more than 99%. We have succeeded in extracting highly charged ions such as Ar17+ and Xe42+.

The fragment ion distribution of in close collision with fast carbon ions

We have measured the mass distribution of fragment ions of produced by collisions with 15.6 MeV carbon ions in different charge states. Close collisions were selectively measured using the coincidence method with the change of the projectile charge state. For the electron capture and loss by projectile ions, which are the K-electron processes, the multifragmentation was observed evidently. In L-electron loss channels of the projectile, the peaks of the multiply ionized ions and the multiply ionized fullerene-like fragment ions are more intense or as intense as the small fragment ions. We suppose that we can roughly classify the intermediate states of through the measurement of fragmentation in coincidence with the change of charge state for various projectiles.

High-resolution soft X-ray spectroscopy of slow highly charged ions transmitted through a microcapillary target

Abstract To detect weak X-rays with a high-resolution spectrometer, a charge-coupled device was operated in a single X-ray photon detection mode. A procedure to effectively identify single X-ray was established. In the case of 2.3 keV/u N7+ and Ne9+ incidence, X-rays emitted from ions transmitted through a Ni microcapillary target were measured with the spectrometer using the procedure of the single event mode. The signal-to-noise ratio was improved by using the single photon counting method.

Acoustic emission from fast heavy-ion irradiation on solids

Ultrasonic signals of near-MHz frequencies were observed when solid targets of Al2O3, KCl and metallic aluminum were irradiated with fast heavy-ions. The projectile beam of 26 MeV/u Xe ions were chopped to pulses shorter than 1 ls. Two piezoelectric sensors detected the acoustic signals at the both ends of the target. The signals were analyzed by Fourier transform and several peaks were observed in the frequency range from several hundred kHz. Amplitudes of the frequency components were nearly proportional to the number of the ions in the pulse. ” 2000 Elsevier Science B.V. All rights reserved.

Intercombination transitions in beryllium-like and boron-like iron

Beam-foil spectroscopy techniques have been used to study intercombination transitions in Be-like Fe22+ and B-like Fe21+. The method of time delayed spectroscopy was used to identify the Be-like 2s2 1S0-2s2p 3P1 and B-like 2s22p 2P3/2-2s2p2 4P5/2 transitions. Intensity decay curves for these transitions were recorded and level lifetimes were obtained. The latter were found to be 17.5 ± 1.5 ns for the Be-like 2s2p 3P1 level and 14.8 ± 1.0 ns for the B-like 2s2p2 4P5/2 level.

Molecular orientation effects in CO fragmentation induced by charge-changing collisions of 6 MeV O4+ ions

Ionization and fragmentation of CO molecules have been investigated in chargechanging collisions of 6 MeV O4+ ions. Fragment ions from CO were measured in coincidence with outgoing projectile charge states by means of a momentum 3D imaging technique. Cross sections for the production of fragment ions in electron loss and capture collisions were obtained as a function of the angle between the molecular axis and the beam direction. It was found that double ionization (CO)2+ induces rather isotropic molecular fragmentation for both electron capture and loss collisions. On the other hand, triple ionization (CO)3+ was found to induce highly anisotropic fragmentation during electron loss collisions.

Non‐Neutral Plasma Confinement In A Cusp‐Trap And Possible Application To Anti‐Hydrogen Beam Generation

A new scheme for synthesizing antihydrogen by trapping positrons and antiprotons in a field consisting of a magnetic quadrupole and an electric octupole (cusp ‐trap) is now under investigation. The total electric field of the octupole with the space charge of a nonneutral plasma composed of particles of the same sign of charge, i.e., positrons or mixture of electrons and antiprotons, is expected to form a potential well for particles of the opposite sign of charge. Particles trapped in the well are mixed with the present dense particles, where positrons and antiprotons will combine to produce antihydrogen atoms. A considerable fraction of antihydrogen atoms in low‐field seeking states will be transported outside as a beam.Experiments on electron confinement in the cusp‐trap were carried out in a strong magnetic quadrupole (3.8T at the maximum on the axis). The confinement time reached 400s for the trapped electron number N0= 3.6×107. The time decreased with N0 but it was still about 100s for N0= 1.6×108.A...

Project to produce cold highly charged ions using positron and electron cooling techniques

A project to cool highly charged ions (HCIs) with positron and electron cooling techniques is under way. Trapped 1010 electrons and 107 positrons in a multi-ring trap are used as energy absorbers for HCIs. The detail of the cooling procedure is reviewed.