T. Nara

Japan Atomic Energy Agency, Muramatsu, Niigata, Japan

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Publications (29)20.2 Total impact

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    ABSTRACT: A flat distribution of the minimum magnetic field (flat-Bmin) of an electron cyclotron resonance ion source (ECRIS) is expected to perform better in highly charged ion production than classical Bmin. To form a flat-Bmin structure with a liquid helium-free superconducting device, a coil system of seven coils with four current leads has been designed. The lead number was reduced by connecting the plural coils in series to maintain the flat-Bmin structure even when the coil currents are changed for adjustment. This coil system can be operated with a helium-free cryostat, since the estimation of heat from the leads to the coils is nearly equivalent to the existing superconducting ECRIS of a similar type.
    The Review of scientific instruments 02/2014; 85(2):02A917. · 1.52 Impact Factor
  • A. Chiba, T. Nara
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    ABSTRACT: This paper presents a novel method for the localization of a passive radio frequency identification (RFID) tag in a 2-D space. First, we show that the position of the tag can be estimated as the intersection of two orthogonal lines, which are determined by the weighted integrals of the magnetic flux density created by the tag. To measure them, we developed a square magnetic sensor composed of six coils: four rectangular coils, a set of four bow-tie-shaped coils connected in series, and a square coil. Using this sensor with side lengths of 200 mm, an RFID tag was localized in a 180 mm square domain with an average error of 5.1 mm. Using the sensor with side lengths of 400 mm, the RFID tag was also localized in a 300 mm square domain with an average error of 1.8 mm.
    IEEE Transactions on Magnetics 01/2014; 50(9):1-8. · 1.42 Impact Factor
  • A. Chiba, T. Nara
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    ABSTRACT: This paper presents a novel method for the localization of an RFID tag in two-dimensional (2D) space, which can be used in location-aware systems. First, in a 2D square domain inside which an RFID tag is freely placed and moved, we show that a line on which the RFID tag exists can be estimated from the weighted integrals of the magnetic field created by the tag along the boundary of the domain. Then, for measuring them, we develop a square-shaped magnetic sensor composed of three coils only: two pairs of oppositely-wound rectangle coils connected in series on the parallel sides of the squared domain, and four bow-tie-shaped coils connected in series on all sides. The average localization error is 5.9 mm in the 160 mm × 160 mm domain.
    SICE Annual Conference (SICE), 2011 Proceedings of; 01/2011
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    ABSTRACT: A phase bunching effect has been achieved for the first time using a rising slope of the dee voltage waveform produced at the first acceleration gap between the RF shielding cover of the inflector and the puller in the new central region of the JAEA AVF cyclotron. The feasibility of the phase bunching effect in the central region for a two-dee system with a span angle of 86° in three acceleration harmonic modes was assessed by a simple geometrical analysis of particle trajectories and a three-dimensional beam orbit simulation using the calculated electric field and a measured magnetic field. The simulation indicated that the initial beam phase width of 40 RF degrees is compressed to 11 RF degrees (about 28% of the initial phase width) in the second harmonic mode. A phase width of 1.5 RF degrees FWHM for a 260MeV 20Ne7+ beam accelerated in the second harmonic mode was observed when using a 4mm phase slit gap. The phase width reduction was considerably enhanced by the bunching effect, compared with the beam phase width of 7.3 RF degrees FWHM in the same harmonic mode for a 10MeV H+ beam accelerated in the original central region. The ratio of the beam current for the 1.5 RF degrees FWHM phase width with 4mm phase slit gap restriction to the full beam current without the phase slit was drastically improved to 80%, while the beam current was less than 1% of the full beam when narrowing the phase slit gap to obtain the 7.3 RF degrees FWHM phase width in the original central region.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; 636(1):41-47. · 1.14 Impact Factor
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    ABSTRACT: Beam intensity fluctuation was investigated using an electron cyclotron resonance ion source of an all-permanent-magnet type under development for highly stable beam intensity. While the source achieved a stability of better than 3.2% by strict regulation of the coolant temperature change within +/-0.1 degrees C, the intensity varies strongly with intentional changes in the temperature of the plasma chamber coolant. The influence of the temperature on chamber expansion, magnetic field strength, and vacuum was measured or estimated in detail. The result shows that a slight change in vacuum and magnetic field strength has considerable influence on the intensity fluctuation.
    The Review of scientific instruments 02/2010; 81(2):02A312. · 1.52 Impact Factor
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    ABSTRACT: Single-turn extraction from the Japan Atomic Energy Agency AVF cyclotron with a K number of 110 using a flat-top (FT) acceleration system has been achieved to reduce the energy spread of an ion beam for microbeam formation with energy up to hundreds of MeV and to increase extraction efficiency from the cyclotron. In order to generate a FT waveform voltage using the fifth-harmonic frequency on a dee electrode, a FT resonator was designed using MAFIA code to achieve downsizing and low power consumption. The FT resonator, coupled to the main resonator through a coupling capacitor, covered the full range of the fifth harmonic frequency from 55 to 110 MHz. Various ion beams, accelerated using different acceleration harmonic modes of h=1 and 2, such as 220 MeV (12)C(5+) (h=2), 260 MeV (20)Ne(7+) (h=2), and 45 MeV H(+) (h=1), were developed by FT acceleration. A clear turn separation of the beam bunches was successfully observed at the extraction region of the large-scale AVF cyclotron with number of revolutions greater than 200. As a result, high extraction efficiency (over 95%) from the cyclotron was achieved. Single-turn extraction was confirmed by counting the number of beam bunches out of the cyclotron for an injected beam pulsed by a beam chopping system in the injection line. The energy spread of the 260 MeV (20)Ne(7+) beam was measured using an analyzing magnet, and we verified a reduction in the energy spread from DeltaE/E=0.1% to 0.05% by single-turn extraction after FT acceleration.
    The Review of scientific instruments 04/2009; 80(3):033302. · 1.52 Impact Factor
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    ABSTRACT: A heavy-ion microbeam with hundreds of MeV energy is utilized for research in biotechnology and materials science at the JAEA AVF cyclotron facility. Beam users need microbeams providing a wide range of the LET. We have to change ion species and/or energy in order to vary the LET widely. However, it takes much time to develop a new microbeam of different ion species step by step using a flat-top acceleration system. A cocktail beam acceleration technique is frequently used to change the ion species and energy quickly. The cocktail beam acceleration has been first applied to the microbeam formation for quick change of the ion species. As a result, we have succeeded to reduce considerably microbeam changing time to within 30min between a 520MeV 40Ar14+ and a 260MeV 20Ne7+. No deterioration of the microbeam spot size has been confirmed using a SE image of a copper grid.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/2009; 267(12):2024-2027. · 1.27 Impact Factor
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    ABSTRACT: In order to achieve a heavy-ion microbeam with an energy of hundreds of MeV applied to the research fields of biotechnology and materials science, the JAEA AVF cyclotron (K = 110) has been upgraded to provide a high quality beam with a smaller energy spread and a higher current stability. A flat-top (FT) acceleration system of the cyclotron, designed to produce ion beams with an energy spread of ΔE/E ⩽ 0.02%, has been developed to reduce chromatic aberrations in the lenses of the focusing microbeam system. The FT acceleration system provides uniform energy gain of the beam by superimposing a fifth-harmonic voltage on the fundamental one. In addition, stabilization of the acceleration rf voltage and the phase were achieved to accelerate the high quality beam and to provide it stably to the microbeam system connected to a cyclotron beam line. In the latest experiment, we have succeeded to accelerate 260 MeV 20Ne7+ with an energy spread of 0.05% in FWHM using the FT acceleration system.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/2007; · 1.27 Impact Factor
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    ABSTRACT: A magnetic field drift, gradual decrease of the order of 10−4 in several tens of hours, was observed with the beam intensity decrease in an operation of an azimuthally varying field (AVF) cyclotron. From our experimental results, we show that the temperature increase of the magnet iron by the heat transfer from the excitation coils can induce such change of the magnetic field as to deteriorate the beam quality. The temperature control of the magnet iron was realized by thermal isolation between the main coil and the yoke and by precise control of the cooling water temperature of the trim coils attached to the pole surfaces in order to prevent temperature change of the magnet iron. The magnetic field stability of ±5×10−6 and the beam intensity stability of ±2% have been achieved by this temperature control.
    Review of Scientific Instruments 02/2005; 76(3):033301-033301-6. · 1.60 Impact Factor
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    ABSTRACT: A flat-top acceleration system appropriate to minimization of energy spread in an ion beam was investigated for the JAERI AVF cyclotron. A combination of the fundamental- and the fifth-harmonic voltages to obtain a homogeneous energy gain distribution of accelerated particles is ideally suited to a variable-energy multiparticle cyclotron using acceleration harmonics of 1, 2, and 3. The flat topping of the energy gain distribution using the fifth harmonics has the advantages of minimizing amplifier power, reducing power dissipation in a resonator, and increasing the energy gain per turn. The flat-top acceleration system was designed to reduce the energy spread to 0.02%, which fulfills a beam focusing condition for production of a microbeam with a beam spot diameter of 1 μm. Tolerable fluctuations of acceleration voltages, required to achieve the energy spread of 0.02%, were 2.0×10<sup>-4</sup> for the fundamental voltage and 1.0×10<sup>-3</sup> for the fifth-harmonic voltage. Both fundamental- and fifth-harmonic phases were required to be stabilized within 0.2 rf degrees. The tolerance of the magnetic excitation was 1.9×10<sup>-5</sup>. In order to enhance compactness of the flat-topping cavity and to make a substantial saving of the amplifier power, optimum geometric parameters of the flat-topping cavity were determined by a cold model test and a calculation using the MAFIA code. A full range of the fifth-harmonic frequency, 55–110 MHz, was covered by the flat-top system, which enables us to apply the flat-top acceleration to a wide range of energy. © 2003 American Institute of Physics.
    Review of Scientific Instruments 05/2003; · 1.60 Impact Factor
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    ABSTRACT: A heavy-ion microbeam with energy of hundreds of MeV is a significantly useful probe for research in biology and biotechnology. A single-ion hit technique using the heavy-ion microbeam is being developed at the JAERI AVF cyclotron facility for elucidation of biofunctions. For production of a microbeam with a spot size of one micro-meter in diameter, the energy spread in the beam is required to be reduced to 0.02% to minimize the effect of chromatic aberrations in the focusing lenses. The energy spread in the cyclotron beam depends on a waveform of the acceleration voltage and beam phase acceptance of the cyclotron. The typical energy spread of the cyclotron beam is around 0.1% in the ordinary acceleration mode using a sinusoidal voltage waveform. The energy spread can be reduced by superimposing a fifth-harmonic voltage waveform on the fundamental one to generate a flat-top waveform for uniform energy gain. The flat-top acceleration system has been designed for the variable-energy multi-particle AVF cyclotron with acceleration harmonic mode of 1, 2 and 3. An additional coaxial cavity has been installed to generate the fifth-harmonic voltage, coupled to the main resonator. The frequency range of the fifth harmonics, 55–110 MHz, was fully covered by the flat-top acceleration system.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/2003; 210:33-36. · 1.27 Impact Factor
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    ABSTRACT: A flat-top acceleration system for the JAERI AVF cyclotron has been designed. The fifth harmonic of the fundamental frequency is used to obtain uniform energy gain. To determine optimum parameters of the flat-top system, a cold model test was carried out and flat-top waveforms of the voltages were observed successfully in the whole range of the fundamental frequency. An rf power required for generating a flat-top dee voltage of 30 kV was estimated to be about 1 kW. The design of the flat-top cavity is being modified using the MAFIA code. © 2001 American Institute of Physics.
    AIP Conference Proceedings. 12/2001; 600(1):303-305.
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    ABSTRACT: A new project aiming for a breakthrough in biotechnology and materials science has been proposed at TIARA (Takasaki Ion Accelerators for Advanced Radiation Application) facilities of JAERI. Heavy ion beams with an energy of more than a hundred MeV/n will contribute to remarkable progress in breeding of plants and development of new materials. We have started designing a new superconducting AVF cyclotron with a bending limit of 900 and a focusing limit of 300. The cyclotron magnet is being designed to cope with acceleration of both the heavy ions and 300 MeV protons. .
    12/2001;
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    ABSTRACT: The AVF cyclotron system at JAERI Takasaki has been smoothly operated without serious troubles since the first beam extraction of 50 MeV 4He2+ in March 1991. A yearly operation time is about 3200 hours on an average for past several years. In the last three years, we performed some improvements and developments as follows: stabilization of the cyclotron beam, renewal of computers and basic programs for the control system, installation of a new ECR ion source and reconstruction of the rotary shutter. Furthermore, two series of M/Q=4 and M/Q=2 cocktail beams have been developed continuously. Now we are modifying the RF cavities for the flat-top acceleration by superimposing the fifth-harmonic frequency on the fundamental one. .
    12/2001;
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    ABSTRACT: Frequent corrections of the magnetic field of the JAERI AVF cyclotron were required for keeping a beam current constant during long time operation. We observed correlation between the magnetic field and the temperature of the cyclotron magnet yoke by measuring the magnetic field with an NMR probe and the temperature with platinum resistance thermometers. As a result, this instability of a cyclotron beam was induced by temperature-change of the magnet yoke caused mainly by thermal conduction from the main coil. To restrain the thermal conduction to the yoke, we have inserted temperature-controlled copper plates between the yoke and the main coil. In addition, a temperature control system for the cooling water of the trim coils has been installed, which is independent of the total cooling system for controlling the pole tip temperature. An optimum condition of the temperature control systems for stabilizing the magnetic field has been investigated. .
    12/2001;
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    ABSTRACT: An 18 GHz electron cyclotron resonance ion source under development since. 1994 has a solenoid coil between a pair of mirror coils to vary the mirror ratio over a wide range. The solenoid coil of the original design formed a small bump in the bottom of the mirror field profile when the source parameters were optimized for high charge states. Source performance in generating highly charged ions improved with a number of minor changes on the vacuum, the gas feed, and the beam extraction system. The maximum beam current of Ar16+ was 2 enA, which was much lower than that expected from the microwave frequency and the magnetic field strength. Little effect of a biased disk on intensities of highly charged ions and dependence of the charge state distribution on the solenoid coil current suggested that the bump divided plasma into two regions and limited the source performance. The bump was removed by halving the solenoid coil length, and the beam current of Ar16+ increased to 1.3 eμA as a result. © 2000 American Institute of Physics.
    Review of Scientific Instruments 01/2000; 71(2):906-908. · 1.60 Impact Factor
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    ABSTRACT: The ion species and energy of a cyclotron beam can be quickly changed using a cocktail acceleration technique. Cocktail beams of mass-to-charge (M/Q) ratio of 4 and 5 have been developed at the JAERI AVF cyclotron. Purity of the beam depends on the M/Q resolution of the cyclotron. The resolution has been estimated theoretically and experimentally. A radial spread of an internal beam bunch caused by phase slip of particles with a different M/Q value has been observed using a pulsed incident beam. For practical operation, some methods have been devised for avoiding intermixture of different ion species in a beam extracted from the cyclotron
    Particle Accelerator Conference, 1999. Proceedings of the 1999; 02/1999
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    ABSTRACT: A beam chopping system for a cyclotron is in operation at the JAERI cyclotron facility. A combination of a pulse voltage chopper in the injection line and a sinusoidal voltage chopper after the exit of the cyclotron is adopted to produce beam pulses spaced at 1 μs–1 ms intervals from natural cyclotron beams. The chopping system was designed according to a simple formulation of the chopping process in which the multiturn extraction was taken into account. Performance of the chopping system was experimentally proved to satisfy requirements of the design. In actual operation to produce beam pulses at long intervals, however, the number of the multiturn extraction is usually larger than the assumed value in the design because of a large phase acceptance of the cyclotron. Careful tuning of the acceleration phase width or the base magnetic field of the cyclotron is necessary to reduce it. It is essential to strictly define the acceleration phase of injected beams in the central region of the cyclotron to improve this situation. © 1997 American Institute of Physics.
    Review of Scientific Instruments 03/1997; 68(4):1714-1719. · 1.60 Impact Factor
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    ABSTRACT: Metallic ion generation from eight kinds of ceramic rods such as Al2O3, Mo2C, BN was examined by an ECR ion source with a direct insertion method, and stable ion beams were observed from six. Vapor pressure of possible products from a solid phase or a solid-liquid condensed phase of the examined materials was evaluated by thermodynamic calculation and ranged over more than nine orders of magnitude at high temperatures. A clear correlation was found between the beam stability of metallic ions and the surface condition of the rod ends exposed to the plasma, and it is completely explained by the magnitudes of the calculated vapor pressure. This indicates that the vaporization process can be understood as sublimation. Sputtering of the ceramic rods by ECR-plasma ions is considered not to be able to provide sufficient vapor pressure of metallic elements because of the low ion energy close to the sputtering threshold energy.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/1997; 122(1):141–148. · 1.27 Impact Factor
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    ABSTRACT: An 18 GHz electron cyclotron resonance ion source for multiply charged ions was constructed and is now in operation. A new distribution of the mirror field was adopted, and minimum strength is varied by a solenoid coil installed between the mirror coils. The measured mirror field distribution is close to the designed distribution and its maximum strength exceeds 1.4 T. The source is now being tuned by use of Ar ion generation. The relatively high base pressure in the plasma chamber has been improved by installing an additional vacuum pump. The source performance has been maturing gradually with the vacuum and Ar ions with charge states of up to 13+ have been observed so far. © 1996 American Institute of Physics.
    Review of Scientific Instruments 04/1996; · 1.60 Impact Factor