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Journal Articles

Development of real-time rotating waveplate Stokes polarimeter using multi-order retardation for ITER poloidal polarimeter

Imazawa, Ryota; Kawano, Yasunori; Ono, Takehiro; Itami, Kiyoshi

Review of Scientific Instruments, 87(1), p.013503_1 - 013503_7, 2016/01

AA2015-0219.pdf:1.34MB

 Times Cited Count:2 Percentile:14.5(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Meshless method for solving fixed boundary problem of plasma equilibrium

Imazawa, Ryota; Kawano, Yasunori; Itami, Kiyoshi

Journal of Computational Physics, 292, p.208 - 214, 2015/07

 Times Cited Count:5 Percentile:41.4(Computer Science, Interdisciplinary Applications)

no abstracts in English

Journal Articles

Profile measurement of current density, electron density and electron temperature using laser polarimetry on burning plasma

Imazawa, Ryota; Kawano, Yasunori; Itami, Kiyoshi

Purazuma, Kaku Yugo Gakkai-Shi, 90(11), p.743 - 747, 2014/11

no abstracts in English

Journal Articles

Multi-parameter measurement using finite electron temperature effect on laser polarimetry for burning plasma reactor

Imazawa, Ryota; Kawano, Yasunori; Itami, Kiyoshi

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 6 Pages, 2014/10

no abstracts in English

Journal Articles

Linearity-independent method for a safety factor profile

Imazawa, Ryota; Kawano, Yasunori; Itami, Kiyoshi; Kusama, Yoshinori

Nuclear Fusion, 54(1), p.013012_1 - 013012_8, 2014/01

 Times Cited Count:0 Percentile:0.01(Physics, Fluids & Plasmas)

This paper proposes a new method to calculate a safety factor, $$q$$, profile from gridded data of a poloidal flux, $$Psi$$, efficiently and accurately. Difficulties of calculating $$q$$ are derived from a difficulty of specifying a contour line of $$Psi$$ and a singularity at a magnetic axis. In order to solve the first difficulty, the proposed method interpolates knots, which are located on a target $$Psi$$, by utilizing a normalized arc length and constraints expressed by a magnetic field. Regarding the second difficulty, the proposed method identifies $$q_0$$ by extrapolating $$q$$ profile around a magnetic axis with a constraint of $$mathrm{d}q/mathrm{d}rho=0$$ at the magnetic axis. Accuracy assessments of the proposed method are carried out by utilizing Solov'ev type equilibrium. The results show the validity and high performance of the proposed method.

Journal Articles

Separation of finite electron temperature effect on plasma polarimetry

Imazawa, Ryota; Kawano, Yasunori; Kusama, Yoshinori

Review of Scientific Instruments, 83(12), p.123507_1 - 123507_5, 2012/12

 Times Cited Count:4 Percentile:24.65(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Highly accurate approximate solutions of the stokes equation for high electron density and long laser-wavelength

Imazawa, Ryota; Kawano, Yasunori; Kusama, Yoshinori

Plasma Physics and Controlled Fusion, 54(5), p.055005_1 - 055005_7, 2012/05

 Times Cited Count:7 Percentile:33.8(Physics, Fluids & Plasmas)

Journal Articles

A New approach of equilibrium reconstruction for ITER

Imazawa, Ryota; Kawano, Yasunori; Kusama, Yoshinori

Nuclear Fusion, 51(11), p.113022_1 - 113022_8, 2011/11

 Times Cited Count:21 Percentile:70.43(Physics, Fluids & Plasmas)

We have developed the new method for identifying the $$q$$-profile from data, whose accuracy is determined in ITER, in order to assess the necessary measurement accuracy of the poloidal polarimeter. We have adopted the finite element method to calculate the ideal MHD equilibrium. Assuming that all measurement data has no error, we have shown the Importance of using the measurement data of the electron temperature, $$T_e$$, and the ellipticity angle, $$epsilon$$, of the polarization state in the inductive operation scenario II (S2), and the non-inductive operation scenario IV (S4). $$T_e$$ is used to calculate the relativistic effect on the polarization state. When the relativistic effect has not been included in the $$q$$-profile identification, the error of $$q$$-profile identification has exceeded 7.7 ${%}$ and 15 ${%}$ in S2 and S4, respectively. $$epsilon$$ is mainly related to the Cotton-Mouton effect, which is an obstacle in measurement of a pure Faraday effect. Taking into account $$epsilon$$ reduced the error of $$q$$-profile identification by 0.5 ${%}$. Finally, we have assessed the necessary accuracy of the orientation angle, $$Deltatheta$$, and the ellipticity angle, $$Deltaepsilon$$. The polarimetric measurements with accuracy of $$(Deltatheta, Deltaepsilon)=(0.5^circ, 3^circ)$$ have satisfied the measurement requirement for the $$q$$-profile identification ($$pm5$$ ${%}$) in case of that viewing chords are via both equatorial and upper ports.

Journal Articles

Neutronic analysis of the ITER poloidal polarimeter

Ishikawa, Masao; Kawano, Yasunori; Imazawa, Ryota; Sato, Satoshi; Vayakis, G.*; Bertalot, L.*; Yatsuka, Eiichi; Hatae, Takaki; Kondoh, Takashi; Kusama, Yoshinori

Fusion Engineering and Design, 86(6-8), p.1286 - 1289, 2011/10

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

The nuclear heating rates of the optical mirrors of the poloidal polarimeter installed in the equatorial port plug of ITER are calculated. Since the system cannot have a sufficiently labyrinthine structure and the second mirrors are located nearly as close to the plasma as the first mirrors due to limited space, the nuclear heating rate of the second mirrors is as high as that of the first mirrors. However, it is possible to reduce the nuclear heating rates of the mirrors if the blanket shield module provides a sufficient degree of neutron shielding.

Journal Articles

Thermal and optical analyses of retro-reflector for poloidal polarimeter on ITER

Imazawa, Ryota; Kawano, Yasunori; Ono, Takehiro; Kusama, Yoshinori

Plasma and Fusion Research (Internet), 6(Sp.1), p.2402032_1 - 2402032_5, 2011/08

This paper describes results from the first integrated analysis on the feasibility of a retro-reflector (RR) installed in the ITER vacuum vessel. We make thermal and structural analyses of passively-cooled RR and terrace retro-reflector array (TERRA) by using heat load conditions on ITER. In the case of RR, the temperature reaches over 600$$^{circ}$$C, and the flatness of deformed mirror surface forming RR is approximately 80 $$mu$$m. Although the maximal displacement of mirror surface is large, 69% of the incident-laser power returns to a diagnostic room, disturbance of phase is $$pi/4$$ and rotation angle of polarization plane is less than 0.06 $$^{circ}$$. On the other hand, the temperature of TERRA is approximately 350$$^{circ}$$C, and the flatness of the deformed mirror surface is less than 10 $$mu$$m. The flatness of the mirror surface of the deformed TERRA is much smaller than laser wavelength (118 $$mu$$m), but the global shape is curved to ruin the coherent phase of laser light. The curvature radius of TERRA is 21 m, and 49% of the incident-laser power returns to the diagnostic room, disturbance of phase is $$pi/5$$, and rotation angle of polarization plane is less than 0.06$$^{circ}$$. Since the optimized incident angles of flat and curved TERRA are different, a real-time feedback control of the incident angle is necessary for applying TERRA to ITER poloidal polarimeter.

Journal Articles

Terrace retro-reflector array for poloidal polarimeter on ITER

Imazawa, Ryota; Kawano, Yasunori; Ono, Takehiro; Kusama, Yoshinori

Review of Scientific Instruments, 82(2), p.023116_1 - 023116_5, 2011/02

 Times Cited Count:1 Percentile:7.72(Instruments & Instrumentation)

Oral presentation

Design and analysis of retro-reflector according to thermal distortion

Imazawa, Ryota; Kawano, Yasunori; Kusama, Yoshinori

no journal, , 

no abstracts in English

Oral presentation

Neutronic analysis for ITER poloidal polarimeter

Ishikawa, Masao; Kawano, Yasunori; Imazawa, Ryota; Sato, Satoshi; Vayakis, G.*; Bertalot, L.*; Yatsuka, Eiichi; Hatae, Takaki; Kondoh, Takashi; Kusama, Yoshinori

no journal, , 

The nuclear heating rates of the optical mirrors of the poloidal polarimeter installed in the equatorial port plug of ITER are calculated. Since the system cannot have a sufficiently labyrinthine structure and the second mirrors are located nearly as close to the plasma as the first mirrors due to limited space, the nuclear heating rate of the second mirrors is as high as that of the first mirrors. However, it is possible to reduce the nuclear heating rates of the mirrors if the blanket shield module provides a sufficient degree of neutron shielding.

Oral presentation

Progress in the design of the ITER poloidal polarimeter

Kawano, Yasunori; Ishikawa, Masao; Sato, Kazuyoshi; Imazawa, Ryota; Kusama, Yoshinori; Hayashi, Toshimitsu; Ono, Takehiro; Ebisawa, Katsuyuki*; Wakabayashi, Kuniaki*; Hiramatsu, Miho*; et al.

no journal, , 

Oral presentation

Current profile measurement by poloidal polarimeter, 2

Imazawa, Ryota; Kawano, Yasunori

no journal, , 

no abstracts in English

Oral presentation

Progress in ITER diagnostics development in Japan

Kusama, Yoshinori; Kondoh, Takashi; Ishikawa, Masao; Hatae, Takaki; Yatsuka, Eiichi; Hayashi, Toshimitsu; Ono, Takehiro; Kawano, Yasunori; Imazawa, Ryota; Ogawa, Hiroaki; et al.

no journal, , 

no abstracts in English

Oral presentation

Safety factor profile identified by poloidal polarimeter during plasma start-up and at start-of-burn phase in ITER

Imazawa, Ryota; Kawano, Yasunori; Kusama, Yoshinori

no journal, , 

no abstracts in English

Oral presentation

Progress in ITER diagnostics development in Japan

Kawano, Yasunori; Kondoh, Takashi; Ishikawa, Masao; Hatae, Takaki; Yatsuka, Eiichi; Imazawa, Ryota; Ogawa, Hiroaki; Sugie, Tatsuo; Takeuchi, Masaki; Sato, Kazuyoshi; et al.

no journal, , 

Recent progress in development of ITER diagnostic systems in Japan is presented as briefly shown below. (1) Microfission Chamber: A prototyping of vacuum feedthrough showed that the vacuum leak rate satisfies that of ITER requirement. (2) Thomson scattering (edge): A new method proposed for the measurement of anisotropic electron temperature was presented. (3) Poloidal Polarimeter: Measurement accuracy of the poloidal polarimeter was evaluated so that the accuracy of resultant current profile can satisfy the ITER measurement requirement. (4) Impurity influx monitor (divertor): By improvement of the design of equatorial port optics, expected detected light was 16 times increased in comparison with that of the previous design. (5) Divertor thermocouples (outer target): Investigation was started about the fixation method of the thermocouple on the side of divertor outer target. (6) Divertor IR thermography: Conceptual design activity was started for equatorial port optics.

Oral presentation

Highly accurate approximate solutions of stokes equation for polarimetry of ITER-like plasmas

Imazawa, Ryota; Kawano, Yasunori; Kusama, Yoshinori

no journal, , 

no abstracts in English

Oral presentation

Progress in design study of ITER poloidal polarimeter

Kawano, Yasunori; Imazawa, Ryota; Ono, Takehiro; Ishikawa, Masao; Hayashi, Toshimitsu; Sato, Kazuyoshi; Kusama, Yoshinori; Ebisawa, Katsuyuki*; Wakabayashi, Kuniaki*; Katsumata, Takahito*

no journal, , 

no abstracts in English

42 (Records 1-20 displayed on this page)