[en] Glassy carbon (GC) possesses excellent thermal resistance but is apt to oxidation. This significantly limits its potential applications in high-temperature environments. This paper investigates the surface deterioration mechanisms of three types of GCs prepared at different heat treatment temperatures (HTT) and/or machining conditions. After cyclic heating-cooling, the polished GC made under a higher HTT (GC-G) demonstrated better anti-deterioration performance than that under a lower HTT (GC-K). In the GC-K, oxidation readily proceeds along the depth direction during the heating-cooling process, leading to the reduction of Young’s modulus and catastrophic surface cracks; whereas in the GC-G, the more ordered graphite sites provide resistance to the thermal oxidation induced surface deterioration. Cutting-induced defects can significantly reduce Young’s modulus and accelerate the deterioration. (paper)

[en] This paper presents the first investigation of the effect of lithium coating on the optics of Doppler backscattering. A liquid lithium limiter has been applied in the Experimental Advanced Superconducting Tokamak (EAST), and a Doppler backscattering has been installed in the EAST. A parabolic mirror and a flat mirror located in the vacuum vessel are polluted by lithium. An identical optical system of the Doppler backscattering is set up in laboratory. The power distributions of the emission beam after the two mirrors with and without lithium coating (cleaned before and after), are measured at three different distances under four incident frequencies. The results demonstrate that the influence of the lithium coating on the power distributions are very slight, and the Doppler backscattering can work normally under the dosage of lithium during the 2014 EAST campaign

[en] A Zr_47.7Cu₃₁Ni₉Al_12.3 bulk metallic glass was irradiated directly by KrF excimer laser pulses with wavelength 248 nm and duration 10 ns. Scanning electronic microscope photographs indicated that many ripples in micro-nano scale would be generated on the edge of the irradiated area under the action of the higher intensity laser pulse. Detailed observation demonstrated that the ripples exhibited fluidity and became closer and closer out from interior. Theoretical analysis revealed the formation mechanism of the ripples, including melting, subsequent propagation of capillary waves and final solidification.

[en] A Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ bulk metallic glass (BMG) was welded to a crystalline aluminum by the parallel plate explosive welding method. Experimental evidence and numerical simulation show that atomic-scale bonding between the BMG and the crystalline aluminum can be achieved, and the weldment on the BMG side can retain its amorphous state without any indication of crystallization in the welding process. Nanoindentation tests reveal that the interface of the explosive joints exhibits a significant increase in hardness compared to the matrix on its two sides. The joining of BMG and crystalline materials opens a window to the applications of BMGs in engineering

[en] A 384 channels (24 vertical × 16 radial) Electron Cyclotron Emission Imaging (ECEI) system has been installed on Experimental Advanced Superconducting Tokamak (EAST). With the aid of advanced front optics, high spaital resolution around 1.1cm and flexible vertical coverage 30 ∼ 70 cm have been realized. The well-designed optics also provides a long Rayleigh length up to 70 cm even with an object length larger than 2.6 m. The electronic system has a wide immediate frequency (IF) bandwidth 2 ∼ 16.5 GHz, which enables a continuous radial coverage up to 25 cm. Benefited from advanced optics design and the wide IF bandwidth, the ECEI system with high spatial resolution can provide a large and continuous view field, especially in the radial direction, which is enough for the observation of the whole q = 1 surface. The comprehensive details of the ECEI system will be presented in this paper, along with some experimental results.

[en] We study stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) in shock ignition by comparing fluid and particle-in-cell (PIC) simulations. Under typical parameters for the OMEGA experiments [Theobald et al., Phys. Plasmas 19, 102706 (2012)], a series of 1D fluid simulations with laser intensities ranging between 2 × 10"1"5 and 2 × 10"1"6" W/cm"2 finds that SBS is the dominant instability, which increases significantly with the incident intensity. Strong pump depletion caused by SBS and SRS limits the transmitted intensity at the 0.17n_c to be less than 3.5 × 10"1"5" W/cm"2. The PIC simulations show similar physics but with higher saturation levels for SBS and SRS convective modes and stronger pump depletion due to higher seed levels for the electromagnetic fields in PIC codes. Plasma flow profiles are found to be important in proper modeling of SBS and limiting its reflectivity in both the fluid and PIC simulations.

[en] Significant progress has been made in the imaging and visualization of magnetohydrodynamic and microturbulence phenomena in magnetic fusion plasmas. Of particular importance has been microwave electron cyclotron emission imaging (ECEI) for imaging T_e fluctuations. Key to the success of ECEI is a large Gaussian optics system constituting a major portion of the focusing of the microwave radiation from the plasma to the detector array. Both the spatial resolution and observation range are dependent upon the imaging optics system performance. In particular, it is critical that the field curvature on the image plane is reduced to decrease crosstalk between vertical channels. The receiver optics systems for two ECEI on the J-TEXT device have been designed to ameliorate these problems and provide good performance with additional field curvature adjustment lenses with a meniscus shape to correct the aberrations from several spherical surfaces

[en] Millimeter-wave imaging diagnostics, with large poloidal span and wide radial range, have been developed on the EAST tokamak for visualization of 2D electron temperature and density fluctuations. A 384 channel (24 poloidal × 16 radial) Electron Cyclotron Emission Imaging (ECEI) system in F-band (90-140 GHz) was installed on the EAST tokamak in 2012 to provide 2D electron temperature fluctuation images with high spatial and temporal resolution. A co-located Microwave Imaging Reflectometry (MIR) will be installed for imaging of density fluctuations by December 2016. This “4th generation” MIR system has eight independent frequency illumination beams in W-band (75-110 GHz) driven by fast tuning synthesizers and active multipliers. Both of these advanced millimeter-wave imaging diagnostic systems have applied the latest techniques. A novel design philosophy “general optics structure” has been employed for the design of the ECEI and MIR receiver optics with large aperture. The extended radial and poloidal coverage of ECEI on EAST is made possible by innovations in the design of front-end optics. The front-end optical structures of the two imaging diagnostics, ECEI and MIR, have been integrated into a compact system, including the ECEI receiver and MIR transmitter and receiver. Two imaging systems share the same mid-plane port for simultaneous, co-located 2D fluctuation measurements of electron density and temperature. An intelligent remote-control is utilized in the MIR electronics systems to maintain focusing at the desired radial region even with density variations by remotely tuning the probe frequencies in about 200 μs. A similar intelligent technique has also been applied on the ECEI IF system, with remote configuration of the attenuations for each channel.

[en] Low-frequency zonal flow (ZF) has been observed in a linear magnetic plasma device, exhibiting significant intermittency. Using the conditional analysis method, a time-averaged fluctuation-induced particle flux was observed to consistently decrease as ZF increased in amplitude. A dominant fraction of the flux, which is driven by drift-wave harmonics, is reversely modulated by ZF in the time domain. Spectra of the flux, together with each of the related turbulence properties, are estimated subject to two conditions, i.e., when potential fluctuation series represents a strong ZF intermittency or a very weak ZF component. Comparison of frequency-domain results demonstrates that ZF reduces the cross-field particle transport primarily by suppressing the density fluctuation as well as decorrelating density and potential fluctuations

[en] With the application of a four-tip Langmuir probe, the anomalous transport contributed by the turbulence and its impact on particle decay length in the scrape-off layer (SOL) has been studied on HL-2A tokamak. A high-frequency electromagnetic mode (HFM, 100 kHz < f _HFM < 400 kHz) is reported, which can both be observed in the pedestal region and the SOL during the type-III ELMy H-mode discharge. In SOL, the HFM propagates in the electron diamagnetic direction in both the laboratory frame (22 km s⁻¹) and plasma frame (24 km s⁻¹) with m ≃ 28, n ∼ 8 and k _θ ρ _i ∼ 0.04. Direct measurement shows that the HFM can drive inward particle flux, which can be explained by the electron diamagnetic rotation of the HFM. The time evolutions of particle flux driven by the low frequency turbulence (LFT, ‘blobby’ structures) and the HFM as well as the typical decay length of divertor particle flux suggest that the decay length in SOL can both be modified by the outward particle transport of the ‘blobby’ structures (Γ_r,LFT, <40 kHz) and inward particle transport by the HFM (Γ_r,HFM). The decay length of the particle flux is mostly suppressed when a significant inward flux by the HFM bursts under the condition of a low-level outward flux by ‘blobby’ events, suggesting the important role of anomalous transport on the decay length in the SOL. (paper)