Recent progress of the design activity for the poloidal field coil system in JT-60SA

Tsuchiya, Katsuhiko; Kizu, Kaname; Murakami, Haruyuki; Asakawa, Shuji; Kuramochi, Masaya; Yoshida, Kiyoshi; Tomarchio, V.*

IEEE Transactions on Applied Superconductivity, 20(3), p.525 - 529, 2010/06

https://doi.org/10.1109/TASC.2009.2039780

The programme of constructing JT-60SA device is progressing under the framework of the Broader Approach (BA) agreement decided by Japan (JA) and European Union (EU). The magnet system for JT-60SA consists of 18 toroidal field (TF) coils, a central solenoid (CS) with four modules, six equilibrium field (EF) coils. It is decided in the agreement between JA and EU that the poloidal field magnet system, CS and EF coils, shall be procured by JA. The CS consists of independent winding pack modules, which is hung from the top of the TF coils through its pre-load structure. The six EF coils are attached to the TF coil cases through supports that include flexible plates allowing radial displacements. In the procurement arrangement (PA) for CS and EF coils that was recently agreed by JA and EU, basic mechanical designs of CS and EF coils are prescribed in the basis of structural analysis. The equipment for the mass-production of conductors for CS and EF coils is prepared by JAEA. And JAEA also prepare the equipment for the fabrication of EF coils in the field of JAEA Naka site because these coils have large bores. In this paper, we describe the recent mechanical design of poloidal field coils, and evaluation result for the support structure.

A Gas-based neutron imaging detector with individual read-outs

Nakamura, Tatsuya; Tanaka, Hiroki; Yamagishi, Hideshi; Soyama, Kazuhiko; Aizawa, Kazuya; Ochi, Atsuhiko*; Tanimori, Toru*

Nuclear Instruments and Methods in Physics Research A, 573(1-2), p.187 - 190, 2007/04

https://doi.org/10.1016/j.nima.2006.10.238

We have been developing a neutron imaging gas detector with a high spatial resolution and with a high temporal response for the neutron scattering instruments at the pulsed neutron source in the Japan proton accelerator research complex. The gas detector system with individual read-outs was developed to meet the requirements for the instruments for neutron reflectometry or for small angle neutron scattering. The performances of the prototype detector using a multi-wire (MW) or micro-strip (MS) detector head were evaluated using a collimated neutron beam, and we confirmed the MS detector exhibiting a spatial resolution of 1.5 mm and a pulse-pair resolution of about 100 ns with a gas pressure of 6 atm helium with a mixture of 30% CF. The performances for the MS detector were also evaluated up to the total gas pressure of 8 atm.

Development of 2D position sensitive neutron detector with a high spatial resolution, 3

Yamagishi, Hideshi; Nakamura, Tatsuya; Tanaka, Hiroki; Soyama, Kazuhiko; Aizawa, Kazuya; Ochi, Atsuhiko*; Tanimori, Toru*

no journal, , 

no abstracts in English

Characteristics of 2-dimensional micro-pixel gas chamber under Cf-252 neutron irradiation

To, Kentaro; Yamagishi, Hideshi; Soyama, Kazuhiko; Ochi, Atsuhiko*; Tanimori, Toru*

no journal, , 

Neutron scattering experiments using high intensity pulsed neutrons will be carried out in Materials and Life Science Facility at J-PARC. Detectors using in the facility require features such as a good spatial resolution, high detection efficiency, fast response, etc. We have developed a 2D position sensitive neutron detector system consist of micro-pattern detector array such as microstrip and miltiwire detector array. In this presentation, characteristics of the 2D micro-pixel gas chamber system under Cf-252 neutron irradiation are reported. Detection area used in this experiment is 5050 mm and pitches of both axes, anodes and cathodes, are 0.4 mm. Irradiation were carried out with a mixture gas of helium-3 and carbon tetrafluoride. It can be seen that signal pulse peaks of neutrons can be identified and these pulse peaks is discriminated easily from background noises. Here, degradation of gas gain arisen from a charge up effect was not observed in our system.

Two-dimensional neutron gas detector using micro-pixel detector head and individual readout method

To, Kentaro; Yamagishi, Hideshi*; Sakasai, Kaoru; Nakamura, Tatsuya; Soyama, Kazuhiko; Ochi, Atsuhiko*; Tanimori, Toru*

no journal, , 

Neutron scattering experiments involving high-intensity and wide-energy pulsed neutrons are expected to be conducted at the MLF in the J-PARC. These experiments require neutron detectors with features such as a two-dimensional detection area, good spatial resolution, high detection efficiency, and a fast response time. In this study, a gas-based neutron detection system with individual readout method and consisting of a micro-pixel detector head was developed, and preliminary experiments were conducted under neutrons irradiation. To examine the operation of the detector system, the total projection ranges of the secondary particles emitted by the nuclear reaction between neutrons and He nuclei are measured and compared with the values obtained from a Monte Carlo simulation. Since the measured projection ranges of the secondary particles agree with the ranges obtained from the Monte Carlo simulation, it is concluded that the operation of the developed system is satisfactory.

Simulating gamma spectrometers with PHITS; Examples of LaBr(Ce) airborne detector and shielded HPGe detector inside a vehicle

Malins, A.; Ochi, Kotaro; Sanada, Yukihisa; Yamaguchi, Ichiro*; Sato, Tatsuhiko

no journal, , 

Measurement and analysis of radiation distribution images in the Hamadori area of Fukushima Prefecture using a Compton camera

Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*

no journal, , 

In this study, the distribution of radioactive materials was measured in the Hamadori area of Fukushima prefecture using a Compton camera. Compton cameras are lightweight and capable of visualizing radiation distribution, which makes them useful for in-situ measurements. This time, in addition to the Compton camera, several instruments, such as a survey meter, were used to measure radiation and compare them. As a result, the radiation distribution (2D image) in the environment was clarified by the Compton camera. However, the distance to the hot spot cannot be grasped in the 2D image. Therefore, in order to grasp the radiation source in detail, we aim to create a 3D map of radiation source position and its intensity. Since the Compton camera requires the dose rate for each nuclides, we believe that it will lead to the prediction of the dose rate distribution in the future.

Compton camera measurements of radiation distribution images at Hamadori, Fukushima Prefecture

Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*

no journal, , 

As a result of the Fukushima Daiichi Nuclear Power Station accident, radioactive materials were dispersed into the environment from inside the nuclear reactor. Now that the difficult-to-return zone is being lifted, it is important to understand the radiation distribution in the surrounding area. At two locations in the difficult-to-return zone (Okuma Town), measurements were taken with a Compton camera and video was recorded with an optical camera. The locations of radionuclides were confirmed by combining the measurement data and video. The measurement equipment used included a Compton camera using a CZT (CdZnTe) semiconductor (H420 manufactured by H3D), a survey meter with a wand-type GPS (Gamma Plotter H manufactured by Japan Radiation Engineering Co., Ltd.) and an optical camera. Air dose rates at 1 m above ground level ranged from 4 to 46 Sv/h at the first location and from 6 to 12 Sv/h at the second location. By photographing the high-dose points from various positions and angles, the three-dimensional spatial extent of the radiation source could be confirmed.

Imaging of gamma-rays by nuclides at Hamadori, Fukushima

Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*

no journal, , 

A Compton camera can only provide two-dimensional radiation information, and it is impossible to determine the distance to hot spots. In this study, in order to obtain more detailed radiation source distribution, we combined a Compton camera and an optical camera to create a three-dimensional distribution map of source locations and their intensities. The survey was conducted at two locations in the difficult-to-return zone: a park parking lot and the area around a private house in the difficult-to-return zone (Okuma Town). The distribution of air dose rates was ascertained by measurement with a survey meter with a stick-type GPS (Gamma Plotter H manufactured by Japan Radiation Engineering Co. Measurements were taken with a Compton camera (H420, H3D, USA) at different positions and angles toward the hot spots. The software (Application Programming Interface Example (APIE)) was used to check the radiation incident information (incident time, energy, x, y, z) obtained by the Compton camera in real time. In the future, we will use the incident radiation information obtained with APIE to estimate the position of the radiation.

Estimating source location and spread using Compton cameras

Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*

no journal, , 

Radiation distribution maps based on Compton cameras make it possible to identify hotspots where radioactive material has accumulated locally. However, the radiation distribution obtained is two-dimensional and the distance to the hotspot cannot be confirmed. In this study, a combination of a Compton camera and an optical camera was used to integrate the radiation distribution with optical images and to confirm the radiation source position and its spread, aiming at a detailed understanding of the radiation distribution. Field tests using a Compton camera (H3D, H420, USA) with a CZT (CdZnTe) semiconductor and an optical camera (GoPro) were carried out in the difficult-to-return zone, approximately 3.6 km away from the Fukushima Daiichi NPP. By taking images of the hotspot at different positions and angles, the location of the radiation source and its three-dimensional extent could be confirmed.