Duan Yanmin

Compact Continuous-Wave Nd:YVO 4 Laser with Self-Raman Conversion and Sum Frequency Generation

Low threshold and compact cw Nd:YVO4 self-Raman lasers at 1176 nm and sum-frequency mixing of fundamental and first-Stokes wavelengths are demonstrated. A 20-mm Nd:YVO4 crystal is adopted in a compact plane-concave resonator. The results show that the cw Raman conversion is sensitive to cavity length. At an incident pump power of 22.5 W, output power of 1.53 W at 1175.6 nm is achieved, corresponding to the threshold of only 0.8 W and the slop efficiency of 8.1%. Intra-cavity sum-frequency generation is realized in a type-II phase-matching cut KTP crystal, 480 mW at 558.6 nm is obtained at incident pump power of 12 W.

Soft X-ray PHA Diagnostic for the Electron Temperature Measurements on EAST

Two soft X-ray pulse height analysis (PHA) systems, based on silicon drift detector (SDD), were established on the experimental advanced superconducting tokamak (EAST) to measure spectrum of soft X-ray emission. In this paper, the soft X-ray PHA systems on EAST are introduced and some experimental results of electron temperature in EAST obtained from the soft X-ray PHA diagnostic are presented.

Soft X-ray Tomography on HT-7

The soft X-ray imaging system on HT-7 is introduced. Fourier–Bessel expansion method is used to reconstruct the soft X-ray emission distribution. Simulation results show that the inversion accuracy is associated with the angular expansion limit and the hot core displacement. In addition, tomographic results of sawtooth oscillations in a typical low hybrid current drive (LHCD) plasma are presented. It is shown that the reconstructions are reliable to analyze the perturbative mode and the evolution.

Nd:YAG/Cr 4+ :YAG/YAG键合晶体调 Q 激光输出特性研究

对激光二极管端面抽运Nd：YAG/Cr4+：YAG/YAG键合晶体的1 064 nm被动调Q激光性能进行了研究.对比分析了Cr4+：YAG晶体初始透过率分别为84.9%和90.6%的调Q激光输出特性，以及不同耦合输出镜透过率对调Q性能的影响.结果表明，在特定抽运功率下，各输出特性参数的优化（高输出功率，高重复频率，窄脉冲宽度）分别对应一个最佳的输出镜透过率；随着抽运功率增加，对应最佳的输出镜透过率越大.对比两种初始透过率的Cr4+：YAG晶体对应的激光输出特性，84.9%初始透过率的晶体获得相对较低的平均输出功率，但相应的重复频率较小，脉冲宽度窄，使得调Q激光的峰值功率明显提高.采用30%透过率的耦合输出镜和10.4 W入射抽运功率下，获得了3.2 W平均输出功率、9.7 ns脉冲宽度和52 kHz重复频率的激光输出，经计算可知峰值功率达6.3 kW.

Observation of Electron Energy Pinch in HT-7 ICRF Heated Plasmas

Inward energy transport (pinch phenomenon) in the electron channel is observed in HT-7 plasmas using off-axis ion cyclotron resonance frequency (ICRF) heating. Experimental results and power balance transport analysis by TRANSP code are presented in this article. With the aids of GLF23 and Chang-Hinton transport models, which predict energy diffusivity in experimental conditions, the estimated electron pinch velocity is obtained by experimental data and is found reasonably comparable to the results in the previous study, such as Song on Tore Supra. Density scanning shows that the energy convective velocity in the electron channel has a close relation to density scale length, which is qualitatively in agreement with Wangs theoretical prediction. The parametric dependence of electron energy convective velocity on plasma current is still ambiguous and is worthy of future research on EAST.

Characteristic Optimization of 1.3 μm High-Speed MQW InGaAsP-AlGaInAs Lasers

We investigate 1.3 ?m multi quantum-well (MQW) lasers with InGaAsP (well) and InGaAlAs (barrier) on InP for high speed application, compared to the typical structures of InGaAsP (well)-InGaAsP (barrier)/InP and InGaAlAs (well)-InGaAlAs (barrier)/InP with the same quaternary in the well and barrier. We calculate the characteristics of band offset and gain of InGaAsP-AlGaInAs quantum wells (QWs). The advances of the new QW design are mainly rooted in the large ratio between conduction-band and valence-band offsets (?Ec:?Ev = 7:1), higher than the typical value of 4:6 in InGaAsP-InGaAsP and 7:3 in InGaAlAs-InGaAlAs for 1.3 ?m lasers. Due to the low confinement energy of holes, non-uniformity of carrier distribution over multi-InGaAsP-AlGaInAs QWs is significantly reduced. The enhancement of high-speed performance of InGaAsP-AlGaInAs MQW lasers is investigated in terms of turn-on oscillation.

AC operation and runaway electron behaviour in HT-7 tokamak

Operation of HT-7 tokamak in a multicycle alternating square wave plasma current regime is reported. A set of AC operation experiments, including LHW heating to enhance plasma ionization during the current transition and current sustainment, is described. The behaviour of runaway electrons is analysed by four HXR detectors tangentially viewing the plasma in the equatorial plane, within energy ranges 0.3–1.2 MeV and 0.3–7 MeV, separately. High energy runaway electrons (~MeV) are found to circulate predominantly in the opposite direction to the plasma current, while the number of low energy runaway electrons (~tens to hundreds of keV) circulating along the plasma current is comparable to that in the direction opposite to the plasma current. AC operation with lower hybrid current drive (LHCD) is observed to have an additional benefit of suppressing the runaway electrons if the drop of the loop voltage is large enough.