Fueling characteristics of supersonic gas puffing applied to large high-temperature plasma in LHD
Fueling characteristics of supersonic gas puffing applied to large high-temperature plasma in LHD
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发表时间：
2011
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通讯作者：
A. Murakami;J. Miyazawa;C. Suzuki;I. Yamada;T. Morisaki;R. Sakamoto;H. Yamada
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作者：
A. Murakami;J. Miyazawa;C. Suzuki;I. Yamada;T. Morisaki;R. Sakamoto;H. Yamada
超音速充气(SSGP)已应用于大型高温等离子体，并在大型螺旋装置(LHD)上对其加注特性进行了研究。SSGP喷射方法，即高压氢气通过配备拉瓦尔喷嘴的快速电磁阀喷射，已被开发为铲运机的一种新的燃料方法[1，2]。该电磁阀的特点是比用于普通充气的压电阀具有更短的响应时间(1ms)和更高的工作压力(<；8 Mpa)。在SSGP中安装了三个不同拉瓦尔喷嘴的电磁阀，喉部直径分别为0.1、0.3和0.6 mm。通过选择喷嘴和真空室压力，可以调节喷嘴的流量，流量范围为1~1000Pam-3/S。为了研究喷嘴的加注特性，对三种喷嘴进行了密度上升实验。典型的穿透深度为ρ~0.9，其中ρ为归一化小半径，与流量无关。在注入前电子密度较低(<；1.0×1019m-3)的情况下，SSGP的效率约为40%。而当注入前电子密度大于5.0×1019m-3时，效率约为10%。随着SSGP注入前电子密度的增加，SSGP的效率降低。SSGP注入后，形成了中空的电子密度分布。在ρ~0.7时，dNe/dρ与dNe/dt之间有较好的线性关系。高dne/dρ意味着形成了陡峭的中空剖面。由于扩散作用，从等离子体边缘带出的粒子增加了核心等离子体区域的电子密度。已经证明，SSGP以毫秒量级的脉冲向边缘等离子体提供大量粒子，从而控制边缘密度梯度。
Supersonic gas puffing (SSGP) has been applied to large high-temperature plasma and its fueling characteristics have been investigated in the Large Helical Devise (LHD). The SSGP injection method, where a high-pressure hydrogen gas is ejected through a fast solenoid valve equipped with a Laval nozzle, has been developed as a new fueling method for LHD [1, 2]. The solenoid valve is characterised by the shorter response time of < 1 ms and higher working pressure of < 8 MPa than those of piezoelectric valves used in ordinary gas puffing. Three solenoid valves with different Laval nozzles of 0.1, 0.3 and 0.6 mm throat diameter, respectively, are installed in the SSGP. By selecting the nozzles and the plenum pressure, the flow rate of SSGP can be adjusted and range from 1 to 1000 Pa*m -3 /s. In order to investigate the fueling characteristics, density ramp-up experiments have been carried out using the three nozzles. Typical penetration depth of the SSGP is ρ ~ 0.9, where ρ is the normalized minor radius, and independent of the flow rate. In the case of low electron density before injection (< 1.0 × 10 19 m -3 ), the efficiency of SSGP is ~40 %. On the other hand, when the electron density before injection is larger than 5.0 × 10 19 m -3 , the efficiency is ~10 %. As the electron density before SSGP injection increases, the efficiency of the SSGP decreases. After the SSGP injection, hollow electron density profile is formed. A linier relationship between dne/dρ and dne/dt at the position of ρ ~ 0.7 is observed. High dne/dρ means that steep hollow profile is formed. The particles carried from plasma edge region due to diffusion increase electron density at the core plasma region. It has been demonstrated that SSGP supplies a large number of particles to the edge plasma in a pulse in the order of msec and consequently controls the edge density gradient.