A large solid-angle secondary-beam collector using an axially symmetric superconducting magnetic field

A new type of beam collector for light secondary charged particles (“Large ω” beam course) was designed and constructed at the RIKEN Ring Cyclotron (RRC). It makes use of the focusing properties of an axially symmetric magnetic field produced by three short superconducting coils. The system sees the target at right angles to the primary beam, and covers a solid angle of about 600 msr. It has been used mainly to transport surface muons from the decay of pions produced in nucleus-nucleus collisions. The large collection efficiency of surface muons by this collector helped us to obtain valuable data on the production cross section of low-energy pions (below 10 MeV) in reactions of 135 MeV/u ¹⁴N beam with various target nuclei. Its future development will also be discussed.     

Steady axially symmetric three-dimensional thermoelastic stresses in fuel rods

Steady axially symmetric three-dimensional thermoelastic stresses in solid rods having space dependent energy generation are given in terms of the Goodier and the Love-Galerkin or the Boussinesq-Papkovich potentials. Results find applications in nuclear technology.     

Equilibrium and stability of plasma in axially symmetric toroidal systems

Conclusions In the case when the magnetic surfaces have circular normal cross sections in the neighborhood of a magnetic axis (=1), the stability criterion reduces to a limitation on the ratio of the current density to the magnetic field on the magnetic axis j₀R/B₀<2. On the assumption of a uniform axial current, this criterion is equivalent to the Shafranov-Kruskal stability condition RB (a)/aB(a)<1/m for the first mode of oscillation m=1. If the current density falls off on going away from the magnetic axis, the stability criterion when written in the form of the Shafranov-Kruskal condition will correspond to m>1. For example, in the case of the parabolic current density distribution j=j₀ (1–₂/a ²), it turns out that m=2.To investigate the effect of the ellipticity of the magnetic surface cross sections, a study was made of the two cases when the external magnetic surface had an elliptical or semielliptical cross section. As can be seen from Figs. 2 and 4, the limiting value of j₀R/B₀ decreases rapidly when the semi-axis ratio is decreased below unity and decreases more smoothly when is increased above unity: (=l _z/l _r).In the case when toroidal aspects of the problem are very strongly expressed, when the external boundary of the plasma has a semi-elliptical cross section with a semi-axis ratio =1/2 (which corresponds to =1), the limiting ratio of the axial current in the plasma to the current in the windings of the solenoid producing the axial magnetic field amounts to J/I1/3, which corresponds to a ratio of plasma pressure to magnetic pressure 1/2.To investigate the effect of the toroidal geometry on the stability, we also investigated the case of a plasma torus in which the external magnetic surface was of rectangular cross section. As can be seen from Fig. 6, in the case when the axial magnetic field decreases on moving away from the magnetic axis (b/a>0) the limiting value of the ratio N=j₀R/B₀ is reduced somewhat with increasing toroidality, this reduction in N being associated with a corresponding increase in .In summary, as far as the conditions of hydromagnetic stability for a prescribed magnetic field are concerned, an increase in toroidality should lead to an increase in the limiting plasma current and pressure.Translated from Atomnaya Énergiya, Vol. 24, No. 5, pp. 453–459, May, 1968.     

Calibration method for electrode gains in an axially symmetric stripline BPM

The four electrodes in the stripline beam position monitor(BPM) for Hefei Light Source(HLS II) storage ring are of axially symmetric type. We have derived a new calibration method of electrode gains for this type stripline BPM. The gain fit error of different data grids was analyzed, and the ±5 mm by ±5 mm grid is the best.The electrode gains of two stripline BPMs(HLS II SR-BD-STLB1 and HLS II SR-BD-STLB2) were obtained based on offline calibrated data. The results show that data after fitting gains are improved, with the electrode gains being between 0.94 and 1.15.     

Propagation of surface magnetoplasmon polaritons in a symmetric waveguide with two-dimensional electron gas

The properties of surface magnetoplasmon polaritons(SMPPs) in a symmetric structure, composed of two semi-infinite regions of high-density two-dimensional electron gas(2DEG) separated by a thin film in Voigt configuration, are investigated. The normal and absorption dispersion relations for the transverse magnetic polarization are derived by correlating Maxwell’s equation and the boundary conditions. It is demonstrated that the features of SMPPs are greatly influenced by the external magnetic fi...     

非均匀填充束团纵向不稳定性的模拟计算

为精确计算储存环中高频腔等高Q值元件引起的耦合束不稳定的增长率，我们通过分析束团和高频腔高次模的相互作用，编制了能计算非均匀填充束团纵向不稳定性增长率的程序－SLIAB程序，在束团均匀分布这种特例情况下，该程序与常用的ZAP程序计算得到的结果基本一致，作为一个应用实例，本文给出了高能物理研究所BEPC改进方案BEPC－Ⅱ上束腔耦合不稳定性的增长率的计算结果。     

Tokamak field error measurements with an electron beam in KSTAR

It is possible to detect the presence of small field errors in a tokamak with an electron beam. This was demonstrated earlier on T-15 and TEXTOR. This paper discusses the concept, past experience on these tokamaks, calculations for the Korea Superconducting Tokamak Advanced Research (KSTAR) device, an electron beam source, measurement devices for these measurements, and some results. It is shown that small toroidally averaged field errors can be detected by this method. A low voltage electron beam (e-beam) gun and fluorescent screen were mounted in a vertical port and inserted into the vacuum vessel at the end of the KSTAR 2nd campaign plasma experiments. A camera with a narrow field of view was mounted in midplane port in a tube tangent to the field lines at R ∼ 1.3 m and photographed the beam striking the screen. The poloidal field (PF) currents were held constant during the camera exposure period. Many shots with various PF coils energized were made and the deflections of the e-beam were measured. The measurements were made with a camera integration time of 300 ms because of the low light intensity. The results show that there are large field errors that diminish as the PF currents are raised. There appears to be no significant up-down asymmetry for static fields. Measurements with a 7 PF coil scenario with a calculated field null located at e-beam radial position show much larger fields than calculated. KSTAR was constructed with Incoloy 908 conduit using cable-in-conduit conductors (CICC) in 10 of the 14 PF coils and all 16 of the toroidal field (TF) coils. Incoloy 908 has a relative magnetic permeability, μ, of about 10. The field errors appear to be largely due to Incoloy 908.     

Constraints on the skewness coefficient of symmetric nuclear matter within the nonlinear relativistic mean field model

Within the nonlinear relativistic mean field(NLRMF) model, we show that both the pressure of symmetric nuclear matter at supra-saturation densities and the maximum mass of neutron stars are sensitive to the skewness coefficient, J_0, of symmetric nuclear matter. Using experimental constraints on the pressure of symmetric nuclear matter at supra-saturation densities from flow data in heavy-ion collisions and the astrophysical observation of a large mass neutron star PSR J0348+0432, with the former favoring a smaller J_0 while the latter favors a larger J_0, we extract a constraint of -494 MeV≤J_0≤-10 MeV based on the NL-RMF model. This constraint is compared with the results obtained in other analyses.     

Effects of magnetic field on electron power absorption in helicon fluid simulation

In this study, a code, named Peking University Helicon Discharge(PHD), which can simulate helicon discharge processes under both a background magnetic field greater than 500 G and a pressure less than 1 Pa, is developed. In the code, two fluid equations are used. The PHD simulations led to two important findings:(1) the temporal evolution of plasma density with the background magnetic field exhibits a second rapid increase(termed as the second density jump),similar to the transition of modes in helicon plasmas;(2) in the presence of a magnetic field, the peak positions of electron power absorption appeared near the central axis, unlike in the case of no magnetic field. These results may lead to an enhanced understanding of the discharge mechanism.