Takeshi Kasai

A highly efficient neutron time-of-flight detector for inertial confinement fusion experiments

We have developed the highly efficient neutron detector system MANDALA for the inertial-confinement-fusion experiment. The MANDALA system consists of 842 elements plastic scintillation detectors and data acquisition electronics. The detection level is the yield of 1.2×105 for 2.5 MeV and 1×105 for 14.1 MeV neutrons (with 100 detected hits). We have calibrated the intrinsic detection efficiencies of the detector elements using a neutron generator facility. Timing calibration and integrity test of the system were also carried out with a 60Co γ ray source. MANDALA system was applied to the implosion experiments at the GEKKO XII laser facility. The integrity test was carried out by implosion experiments.We have developed the highly efficient neutron detector system MANDALA for the inertial-confinement-fusion experiment. The MANDALA system consists of 842 elements plastic scintillation detectors and data acquisition electronics. The detection level is the yield of 1.2×105 for 2.5 MeV and 1×105 for 14.1 MeV neutrons (with 100 detected hits). We have calibrated the intrinsic detection efficiencies of the detector elements using a neutron generator facility. Timing calibration and integrity test of the system were also carried out with a 60Co γ ray source. MANDALA system was applied to the implosion experiments at the GEKKO XII laser facility. The integrity test was carried out by implosion experiments.

Formation of an intense pulsed beam of CH3Cl in the ‖111≳ state using a 2‐m electrostatic hexapole field

An intense pulsed beam of CH3Cl in the ‖111≳ state without velocity selection was focused using a 2‐m electrostatic hexapole field. The beam intensity was estimated to be ∼1×1013 molecules pulse−1, which is much greater than the similar beams in the earlier study of Gandhi et al. by at least two orders of magnitude. The beam had a 3‐ms pulse width and was focused with an angular divergence of 0.7 mrad. The improvements in beam intensity and in the divergence of the beam can be mainly ascribable to the efficient pumping of the hexapole field through the cylindrical electrodes, which enables us to employ the helium seeding to have the fast stream velocity, the narrow distribution of velocity, and the aerodynamic effects. Those factors altogether made the velocity selection of the beam unnecessary.

Multidimensional steric effects for the XeI∗ (B, C) formations in the oriented Xe∗ (P32,MJ=2)+oriented CF3I reaction

Steric effects for the XeI(*) (B) and XeI(*) (C) formations in the oriented Xe(*) ((3)P(2),M(J)=2)+oriented CF(3)I reaction have been observed as a function of the mutual configuration between molecular orientation and atomic alignment in the collision frame. The mutual configuration exercises the significant influences on the stereoanisotropy for both the reactivity and the branching to the XeI(*) (B) and XeI(*) (C) channels.

Full characterization of an intense pulsed hyperthermal molecular beam

A molecular beam technique for generating an intense pulsed hyperthermal molecular beam (pulsed HTMB) was developed. The beam source consists of a pulse valve, a cooling-water bottle that protects the pulse valve from heat transfer of the high temperature nozzle, and a nozzle with a heater. The point was a pulse-valve operation with the high temperature nozzle which was 30-mm long and was made of pyrolytic boron nitride. The pulsed HTMB of HCl was practically generated. The total beam intensity of the pulsed HTMB was measured by a quadrupole mass spectrometer. It was determined that the beam intensity of the pulsed HTMB was two orders of magnitude larger than that obtained in continuous-HTMB conditions. The pulsed HTMB of HCl was fully characterized by means of (2+1) resonance-enhanced multiphoton ionization and ion time-of-flight techniques. We found that the velocity distribution of the pulsed HTMB was well expressed as supersonic molecular beams. At the highest nozzle temperature of 1400 K, the mean tr...

Development of multi channel neutron spectrometer at GEKKO XII laser fusion facility

A high efficiency time‐of‐flight neutron spectrometer is under construction at the GEKKO XII laser fusion facility. Neutron spectra measured with this system is used for diagnosing fuel areal density and ion temperature of inertial‐confinement‐fusion targets. This system consists of 960 plastic scintillation detectors and a data acquisition electronics. Fuel areal density is deduced from DT neutron spectra produced in initially pure deuterium fuel. Ion temperature is also deduced from primary DD neutron energy spread. The spectrometer was designed to measure relatively rare secondary neutrons from neutron yield as low as 7×105 (100 detector hits). It is also capable to measure 2.45 MeV neutron spectra in lower neutron yield experiment as low as 5×105 neutron. We have constructed a 1/10 module for testing performance of the system, established calibration technique and used it in implosion experiment at the GEKKO XII laser fusion facility to demonstrate ion temperature measurement.

Balloon borne optical particle counter for stratospheric observation

This article presents the ambient air pressure effects on a balloon borne optical particle counter (an aerosol sonde: AS) equipped with a laser as the light source, and the relevant measures to overcome these effects. To investigate the effects of ambient air pressure varying from 1013 to 10 hPa (from ground level to an altitude of about 30 km) and estimate the general performance of the AS, a novel versatile pressure-variable test chamber was constructed equipped with a built-in nebulizer system. To overcome the direct effect of ambient air pressure on the sensing zone occurring when an open cavity laser (an external mirror-type laser) is used, a flat parallel window was adopted in place of the Brewster window, and in addition, only the laser tube was sealed in an aluminum tube under normal atmospheric pressure. Consequently, the laser power change was suppressed to within ±0.5% for the pressure variation range. To overcome the large dependence in the aerosol sampling flow rate on the ambient air pressur...

Does the vestibular (otolith) system contribute to stabilizing vision during linear transient head movement

When the head is suddenly translated, eye movement of the vestibular (otolith) system and of the visual (smooth pursuit) system possibly contribute to stabilization of vision. To investigate how these two systems work together, we compared the eye velocity while fixating on a visual target (LVORv) or a remembered target (LVORr) during head translation with that of smooth pursuit (SP). Latency of LVORv and LVORr responses proved much shorter than that of pursuit. The eye velocity of LVORv response was close to the addition of those in LVORr and SP responses until 216 ms from motion onset. These findings suggest that the neural command signal of the otolith system is linearly added to those of the pursuit system.

Contribution of vestibular (otolith) and pursuit system to stabilizing vision during sinusoidal head movement

The purpose of this study was to investigate how the vestibular (otolith) system and the visual pursuit system contribute to stabilizing vision during head translation. Eye velocity when fixating a stationary target with sinusoidal head movement (visually enhanced LVOR, VLVOR) was compared to that of smooth pursuit (SP) with the same relative target velocity (20 to 180 deg/s) as in the case of VLVOR. The eye velocity during VLVOR was much higher than that during SP with increasing relative target velocity. The gain of the SP (eye velocity/target velocity) markedly decreased with increasing stimulus frequency (0.6 1.2 Hz) while the gain of the VLVOR decreased only slightly. The eye velocity during VLVOR depended on the target velocity, not on the velocity of head motion, and was not associated with the state of vergence. These findings suggest that the command signal of the VLVOR is generated mostly by the visual pursuit system, and that the signal from the otolith system modifies the command signal of the pursuit system to improve the target tracking performance.

System Analysis of the Vestibularly Induced Eye Movement System at Neuronal Level

Abstract The eye movement system induced by head rotation was investigated in cats at neuronal level along the major portions of the signal pathway, the primary vestibular nerve, vestibular nucleus and abducens nucleus Unitary discharges were analyzed by the help of an on-line data processing system. At least 5 types of units were found based on the frequency and transient responses. A mathematical model incorporating these units were sought with reasonably satisfactory simulation results.