Hadron monitor (HM) plays an important role in inferring or estimating the properties of a neutrino beam by measuring the secondary hadrons in the beam. The HM is also used for the alignment of the primary beam on the production target and for the beam status monitoring during operation. Since HM is permanently placed in the beam line, it has to be robust enough to endure high-level radiation when beam is on. Considering very large dynamic ranges for the beam size and current in different machine modes at the Long Baseline Neutrino Facility (LBNF), an HM in multi-strip secondary electron emission (SEM) type was proposed to meet all the requirements. This paper presents a simulation study of several key issues related to the multi-strip HM, such as energy deposition, signal level estimation and vacuum in a long pipe. A test stand has been setup for measuring the sag in the strips at different temperature that imitates the energy deposition of beam in the strips. The measurements show that with appropriate tension applied, the sag can be easily controlled within a few micrometers.

Original article: EPL , 129 (2020) 35001 .

The Chinese First Quasi-axisymmetric Stellarator (CFQS) is now under design and construction. It will be the first quasi-axisymmetric (QA) configuration device to be operated in the world. The main parameters of the CFQS are as follows: the toroidal periodic number N-p = 2, major radius R = 1.0 m, aspect ratio A(p) = 4.0 and magnetic field strength B-t = 1.0 T. The low A p makes it quite challenging to design a supporting structure because of the limited space and strong electromagnetic (EM) force. In this paper, a cage-like supporting structure is proposed for the CFQS modular coil (MC) system to sustain the EM force and the weight of entire device. A finite element analysis is carried out for ensuring the reliability of the supporting structure. The analysis results of the CFQS global model indicate that the cage-like supporting structure can basically satisfy the requirement.

The world's first quasi-axisymmetric stellarator CFQS (China First Quasi-axisymmetric Stellarator) will be constructed as the joint project of National Institute for Fusion Science (NIFS) in Japan and Southwest Jiaotong University (SWJTU) in China [1]. Physics design of CFQS plasma was completed [2, 3], and numerous efforts are now being made to finalize engineering design of CFQS [4]. The CFQS vacuum vessel (VV) will be made of thin plates of SUS316L with thickness of 6 mm. The thickness is determined by considering fabricability and manufacturing cost. In this report, analyses have been performed to confirm the structural reliability of VV and evaluate the influence of eddy current using finite element method software ANSYS/Mechanical (TM) and ANSYS/Maxwell (TM). (C) 2020 The Japan Society of Plasma Science and Nuclear Fusion Research

To date, almost all coil-design codes, e.g. NESCOIL, COILOPT, FOCUS codes, etc, have been primarily attributed to the optimization of filament coils for stellarators. However, evolving to a practical/finite-sized coil from a filament coil, the finite-size effect of coils significantly constrains the fabrication tolerances of a coil system. This paper presents a novel approach that emphasizes the optimization of practical modular coils to reduce sensitivity to fabrication tolerances and to achieve the expected magnetic configurations precisely. A new evaluation parameter, surface twist, is defined in this paper and applied to the optimization sequence in addition to the practical coil line torsion and curvature. The approach has been applied to the framework of the filament coil scheme in the Chinese first quasi-axisymmetric stellarator. This practical coil system without surface twists has been accomplished. Compared to the original finite-sized coil design, the new result is a more considerable simplification of coil shapes, such that in a certain direction view each finite-sized coil becomes a planar-like one. Moreover, this method can also be implemented for the estimation of stochastic deviations of practical coils during the fabrication and assembly of the coil system.

The effects of misalignment of modular coils on various physical properties in the Chinese first quasi-axisymmetric Stellarator (CFQS) are discussed in this study. To estimate the effects quantitatively, simple assumptions are made regarding the structure of coil displacement. We consider the following three cases: displacement in radial direction (Case A), displacement in the vertical direction (Case B), and displacement by tilting (Case C). In all cases, we assume that the displacement structure has a stellarator symmetry. These assumptions are employed to calculate the change in the magnetic surfaces, rotational transform profile, magnetic well depth profile, and the effective helical ripple. Calculation results show that if the magnitude of displacement is less than 10 mm, the effects on these physical properties are small, and the good neoclassical transport property is retained. (C) 2019 The Japan Society of Plasma Science and Nuclear Fusion Research

1 Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, China 2 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan 3 SOKENDAI (The Graduate University for Advanced Studies), Toki, Japan 4 Physics Department, Sichuan University, Chengdu, China 5 Hefei Keye Electro Physical Equipment Manufacturing Co., Ltd, Hefei, China