Observation of simultaneous oscillations of bunch shape and position caused by odd-harmonic beam loading in the Japan Proton Accelerator Research Complex Rapid Cycling Synchrotron

Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Sugiyama, Yasuyuki*; Yoshii, Masahito*

Progress of Theoretical and Experimental Physics (Internet), 2017(11), p.113G01_1 - 113G01_24, 2017/11

AA2017-0469.pdf:2.78MB

https://doi.org/10.1093/ptep/ptx141

Two proton bunches circulates the accelerator ring in the J-PARC 3GeV synchrotoron (RCS). The accelerating voltage is also generated in twice of the revolution frequency. The major Fourier component of the wake voltage should become even harmonics. However, the odd harmonics grow and cause a large number of beam loss. The beam measurement suggests that the odd harmonic wake voltages promote oscillations of not only the bunch position but also the bunch shape. The oscillations continue because they amplify the odd harmonic beam components. A particle tracking simulation can reproduce these simultaneous oscillations. It is found that the odd harmonic wake voltages lead to severe rf bucket distortion that results in beam loss. As a result, introducing a beam loading compensation system for the minor harmonics can prevent the beam loss and it would contribute the stable accelerator operation with the reduction of the activation.

Suppression of neoclassical tearing modes towards stationary high-beta plasmas in JT-60U

Isayama, Akihiko; JT-60 Team

Plasma Science and Technology, 8(1), p.36 - 40, 2006/01

https://doi.org/10.1088/1009-0630/8/1/9

no abstracts in English

MHD instabilities leading to disruptions in low beta JT-60U reversed shear plasmas

Takechi, Manabu; Fujita, Takaaki; Ishii, Yasutomo; Ozeki, Takahisa; Suzuki, Takahiro; Isayama, Akihiko; JT-60 Team

Nuclear Fusion, 45(12), p.1694 - 1699, 2005/12

https://doi.org/10.1088/0029-5515/45/12/025

High performance reversed shear discharges with strong internal transport barrier (ITB) and flat pressure profile in the plasma core region disrupt frequently even with low beta. We analyzed MHD instabilities leading to low beta disruption with measuring fluctuations and current profile with MSE measurement. We mainly observed two type of disruptions. One is the disruption without precursor at . The other is the disruption with n=1 precursor of 100 ms. To explain these characteristics of disruption, we introduce the simple model such as, disruption occurs when the both MHD instabilities at plasma surface and at safety factor being equal to surface mode are unstable. This simple model can explain almost all observed disruption by two process. One is the surface mode triggered disruption, which occurs when qeff change, corresponding q surface at ITB layer changes discretely. The other is the internal mode triggered disruption, which occurs when corresponding q surface become unstable gradually.

Nonlocal energetic particle mode in a JT-60U plasma

Todo, Yasushi*; Shinohara, Koji; Takechi, Manabu; Ishikawa, Masao

Physics of Plasmas, 12(1), p.012503_1 - 012503_7, 2005/01

https://doi.org/10.1063/1.1828084

Energetic-ion driven instability in a JT-60U plasma was investigated using a simulation code for magnetohydrodynamics and energetic particles. The spatial profile of the unstable mode peaks near the plasma center where the safety factor profile is flat and the spatial profile consists of a single primary harmonic m/n = 2/1. The real frequency of the unstable mode is close to the experimental starting frequency of the fast frequency sweeping mode. Simulation results demonstrate that energetic ion orbit width and energetic ion pressure significantly broaden radial profile of the unstable mode. For the smallest value among the investigated energetic ion orbit width, the unstable mode is localized within 20% of the minor radius. This gives an upper limit of the spatial profile width of the unstable mode which the magnetohydrodynamic effects alone can induce. For the experimental condition of the JT-60U plasma, energetic ions broaden the radial width of the unstable mode spatial profile by a factor of 3. The unstable mode is primarily induced by the energetic particles.

Stabilization of neoclassical tearing mode by electron cyclotron current drive and its evolution simulation on JT-60U tokamak

Nagasaki, Kazunobu*; Isayama, Akihiko; Hayashi, Nobuhiko; Ozeki, Takahisa; Takechi, Manabu; Oyama, Naoyuki; Ide, Shunsuke; Yamamoto, Satoshi*; JT-60 Team

Proceedings of 20th IAEA Fusion Energy Conference (FEC 2004) (CD-ROM), 8 Pages, 2004/11

http://www-naweb.iaea.org/napc/physics/fec/fec2004/datasets/EX_7-4.html

no abstracts in English

Numerical stability analysis of the Gaussian filtered Navier-Stokes equations

Ida, Masato; Taniguchi, Nobuyuki*

Nihon Ryutai Rikigakkai Nenkai 2004 Koen Rombunshu, p.122 - 123, 2004/08

The numerical stability of the Gaussian filtered Navier-Stokes equations is studied theoretically. Our recent theoretical results showed that for a large filter width, the linear shears in the time-averaged velocity fields numerically destabilize the fluctuation components because a numerically unstable term is derived by the Gaussian filtering operation. In this report we extend that numerical stability analysis based on an exact expansion series for the subgrid-scale stress terms and a numerical stability analysis of arbitrary-order spatial derivatives. The present investigation shows that numerically unstable terms can appear in many situations.

Recent progress in magnetic measurement

Sakakibara, Satoru*; Kurihara, Kenichi

Purazuma, Kaku Yugo Gakkai-Shi, 80(5), p.364 - 371, 2004/05

http://ci.nii.ac.jp/naid/110003827689

This article presents recent progress in magnetic measurements at magnetic confinement systems. The drift-problem of the integrator used in magnetic measurements is one of the major problems for plasma control and estimation of equilibrium parameters in long-pulse operation. In addition, the durability of the sensors such as a magnetic probe, a flux loop, etc., under fusion neutron irradiation environments is also important. The present status of the developments of a long-pulse integrator and a magnetic sensor are reported.

Study of HOM instability of the JAERI ERL-FEL

Sawamura, Masaru; Hajima, Ryoichi; Kikuzawa, Nobuhiro; Minehara, Eisuke; Nagai, Ryoji; Nishimori, Nobuyuki

Free Electron lasers 2003, p.II_31 - II_32, 2004/00

no abstracts in English

Comparative study of MHD instabilities in LHD and JT-60U; Instability at during counter NB

Isayama, Akihiko; Oyama, Naoyuki; Fujita, Takaaki; Inagaki, Shigeru*; Watanabe, Kiyomasa*; Toi, Kazuo*

Annual Report of National Institute for Fusion Science; April 2003 - March 2004, P. 23, 2003/10

http://www.nifs.ac.jp/report/annrep04/00000001.pdf

no abstracts in English

HOM properties of the JAERI ERL-FEL

Sawamura, Masaru; Nagai, Ryoji; Kikuzawa, Nobuhiro; Hajima, Ryoichi; Nishimori, Nobuyuki; Minehara, Eisuke

Proceedings of 28th Linear Accelerator Meeting in Japan, p.384 - 386, 2003/08

no abstracts in English