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在大型托卡马克装置中,各种线圈安装的微小偏差将会引起严重的误差场不稳定性,导致锁模类在大破坏,因此,锁模不稳定性是研究误差场不稳定性的基础。本文分析了H-1M装置锁模不稳定性的产生条件及其特点,并提出抑制锁模不稳定性的参考建议。 相似文献
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本文应用撕裂模理论研究了电流分布对破裂不稳定性的影响。结果表明这种不稳定性由q=2奇异面附近电流梯度的增大引起,因此只要在奇异面附近保持适当的电流梯度就可避免破裂发生,即对电流分布实行局部控制就可实现对破裂的抑制,并不需要去选取某种特定的整体分布。 相似文献
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本文采用统计的方法分析连续工作锁模激光器的不稳定性及扫描电压振幅的不稳定性对同步扫描相机时间分辨率的影响,导出了由这些不稳定性而决定的测量脉宽的表达式,并利用此表达式对实验中观察到的现象进行了解释。 相似文献
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为使光纤激光器在被动谐波锁模状态下实现锁模脉冲高重复频率输出,本文通过激光沉积法制备了一种基于非线性拓扑绝缘体材料碲化铋与侧面抛磨光纤相结合的可饱和吸收体锁模器件,该器件调制深度、非饱和损耗、饱和强度分别为23.96%、37.77%、31.5 MW/cm2。将其应用在掺铒光纤激光器中,通过对整个腔内色散参数的调整,以及利用材料自身良好的非线性可饱和吸收能力,成功实现了锁模自启动,其中心波长为1 555.67 nm,脉冲宽度为487 fs,重复频率为47.87 MHz,信噪比为58 dB。当泵浦功率超过150 mW时出现锁模脉冲的谐波分裂,持续对泵浦功率进行微调,增加直至最高功率250 mW时,出现了11阶谐波锁模脉冲,重复频率最高达到528 MHz,此时的信噪比为41.5 dB。本文结果证明利用侧面抛磨光纤结构的倏逝场,能够辅助材料提升一定的激光抗损伤能力,便于其在基本锁模状态下进一步实现被动谐波锁模,满足锁模脉冲高重频的产生及探究,对材料在高重频超快光纤激光器中的应用具有重要意义。 相似文献
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回顾了短暂时间间隔测量的历史。条纹概念的引入、电光源和电子仪器的使用、激光的出现使能测量到的短暂时间间隔大大缩短。由于对撞脉冲锁模和啁啾脉冲压缩新概念的提出,人们将脉冲宽度压缩到了几个飞秒。介绍了自锁模钛宝石激光器的锁模、放大和调谐的工作原理以及飞秒技术在物理学、生物学、化学控制反应、光通讯等领域中的应用。 相似文献
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Alexeff Igor 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1978,6(4):539-542
Using a model of two interpenetrating ion streams in a background of magnetically immobilized electrons, I obtain a density threshold for separation disruption that agrees with the values observed. The density threshold for disruption is far above that for instability production. The inference is that in ordinary operation a calutron is operating in an unstable mode, but this unstable level is tolerable. 相似文献
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The behavior of magnetohydrodynamic phenomena associated with disruptions of ohmically heated density limit discharges (qa=3.9) in the TEXTOR tokamak has been investigated in detail. A minor disruption is demonstrated to be only due to an tn = 2 mode instability, possibly due to the magnetic reconnection of an m=2 island. When the m = 2 mode oscillations cease, the internal m = 1 kink mode instability is drastically enhanced at once, twisting the plasma core considerably. If the twisting is too strong, the twisted plasma core is inevitably displaced to the outside and brings cold plasma to the central region, leading to the energy quench at a major disruption. 相似文献
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M. I. Patrov Yu. V. Petrov V. K. Gusev G. S. Kurskiev A. N. Novokhatskii S. A. Sakharov S. Yu. Tolstyakov 《Technical Physics》2011,56(9):1259-1265
Experiments with the limiting density of a plasma generated in the Globus-M spherical tokamak operating in the ohmic heating regime show that, when the plasma density reaches a certain value at the center of the plasma filament, snake-type strong magnetohydrodynamic instability exciting the m/n = 1/1 mode arises. A further rise in the density causes an internal disruption of the plasma. Numerical simulation of the instability dynamics is performed, and the results of simulation are compared with experimental and theoretical data. Experimental and theoretical data are in good agreement. It is shown that the instability is associated with an increased amount of impurities in the plasma and that the limit in density is of a “technological,” rather than of a fundamental, character. With the vacuum chamber cleaned more thoroughly, this limit disappears and the snake instability is not observed. Accordingly, a plasma filament density of 1 × 1020 m?3 was attained with a Greenwald number as high as 95%. 相似文献
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Locked particles are defined as those comminuted or particles which contain both gangue and target material. By considering the shape of the comminuted particles and assuming their random distribution in the ore body prior to comminution, it is possible to derive locking profiles which give the frequency of occurrence of particles which have a given fraction of their volume occupied by target material. For most particle shapes (spheres, angular particles, angular plates and rods) the locking profile is a deep U-shaped curve. This suggests that few particles by number contain about 50% target material while a far greater number contain either very little or very much target material. Such a conclusion is important in planning separation processes for locked particles in the mineral industry. 相似文献
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Jiang M Sucha G Fermann ME Jimenez J Harter D Dagenais M Fox S Hu Y 《Optics letters》1999,24(15):1074-1076
We describe an erbium fiber laser that is passively mode locked by a novel, precision antireflection-coated semiconductor saturable-absorber mirror that incorporates an additional two-photon absorber. It is shown that passive mode locking evolves from a Q-switching instability. The results are achieved by use of saturable absorbers that provide a large (15%) nonlinear (saturable) loss. Exploiting two-photon absorption can substantially reduce the peak power of the Q-switched pulses, which results in improved reliability of the laser. Moreover, two-photon absorption can be used to produce an optimal stability range for saturable-absorber mode locking. 相似文献
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Picosecond soliton pulse train has been obtained from a passively mode locked erbium-doped ring fiber laser. The passive mode-locking mechanism that is at play in this laser relies on the modulational instability (MI) theory. By accurately adjusting the polarization setting of the circulating cavity light, the repetition rate can be tuned from 58 to 114 GHz. Theoretical explanations has also been given. 相似文献
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The dispersion equation of the low-freguency flute instability driven by the high-frequency electrostatic eigenmode excited in a plasma slab is studied. If the amplitude of h.f. mode is small the equation is solved and the explicit formula for the maximum growth rate is obtained. As an example we investigate this problem numerically for a slab with the parabolic density profile. In our model we are able to consider the heating only in the frequency band stretching from the lower hybrid frequency to the electron cyclotron frequency. For this case it follows from our calculation that the danger of the low-frequency disruption of a plasma in the process ofheating is serious. 相似文献
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The switching time of an optically switched laser diode between a locked mode and free oscillation mode is studied. By starting with linear stability analysis, analytical expressions are developed to predict the switching time. It is shown that the switching of optical output between the locked and unlocked modes is governed by two relaxation processes with different time constants, and the change in the first relaxation process, dependent on the carrier density in the initial state, gives a strong effect on the total switching time, in contrast to the dynamic behavior of the carrier density dominated by a single relaxation process. Our analytical results show that larger detuning and power of optical input are effective in shortening the switching time and are believed useful to estimate the switching time of an optically switched bistable laser diode. 相似文献