K.V. Khlopenkov

N. Tamura

S. Sudo

National Institute for Fusion Science (NIFS-Repository)

§59. Preliminary Results of Tracer-Encapsulated Sol id Pellet Injection on LH 0 Khlopenkov, K.V., Sudo, S., Tamura, N. In order to measure the local particle transport, a new diagnostic method has been implemented in LHD experiments, which is based on the concept of tracer-encapsulated solid pellet (TESPEL) [1]. Diffusion coefficient D can be derived from the measured transport motion of tracer particles deposited locally by the injected TESPEL. The TESPEL consists of polystyrene as an outer shell (diameter 0.5-0.6 mm) and LiH as an inner core (80-100 JJ.m size) [2]. The pellet is accelerated pneumatically to the velocity of 300 m/s. The total light emission from the ablating pellet was measured by photo-multipliers (PM) in Ha and Li I lines simultaneously with time resolution of 1 J.ls. Knowing the pellet velocity, the time depend-ence is translated to the pellet position in plasma, and thus tracer location and deposition length can be measured. Figure 1 shows an example of the observed ablation rate. The difference between the pellet with tracer and the reference pellet is obvious, although some background Li I emission is present. The time integrated images of the pellet cloud were obtained through Ha and Li I filters by CCD cameras from two directions (Fig. 2). The obtained images are in good agreement with the PM signals. Background light during ablation of the shell is attributed to a larger spectral width of the Li I filter used (3.6 nm for CCO compared to 1.1 nm for the PM). Both observation methods confirmed that a high localization of the tracer has been achieved (typically, only a few cm in radial direction). Being deposited locally in plasma, the tracer is fully ionized and the Li+3 ions form a toroidal annular domain, which then diffuse in radial direction. The diffusion is measured by observing the Li III light ("-=449.9 nm) originated from charge-exchange with neutral hydrogen of the NBI. For that, two detector arrays are installed at the location of the neutral beam (port 1 0.5L) and at the port without NBI (port 7.5L). The net CXRS signal is obtained by subtracting signals from the corre-sponding detectors. Each detector consists of a lens, optical fiber, and PM equipped with Li III filter. This provides high spatial resolution of 12.5 mm along the minor radius and time resolution of 10 JJ.S. The local value of diffusion coefficient D can be calculated from the measured characteristic time of Li+3 density decay. Due to a low SIN ratio of detected signals achieved up to date, only rough estimations are possible. Preliminary calculations show that for the case of fie = 0.15'10 19 m-3 and Te(O) = 2.9 keY, the average value of Dis 0.13 m2/s, and for fie = 1.1'10 19 m-3, Te(O) = 3.4 keY, D is 3.1 m2/s. The obtained results have demonstrated the potential efficiency of the described diagnostic method for the local transport measurements. ~ #17183 .i" pellet with tracer ~ c o +=> ro :0 « r= 0 370 380 390 ~ #17299 .i" reference pellet ~ c o ~ :0 « 400 410 r=O 370 380 390 400 410 R,cm a) 420 430 440 450 450 Fig. 1. Ablation rate of TESPEL (a) and a reference pellet without tracer (b). The local deposition of the tracer is proved by the upper figure. Fig. 2. ceo images of the ablating TESPEL (a), and reference pellet (b), obtained with Li I filter (Ao = 671. 7 nm). Tracer ablation is clearly seen in the upper image in the area of R = 4.05-4.10 m. References 1) S. Sudo, 1. of Plasma Fusion Research, 69, (1993) 1349. 2) K. Khlopenkov, S. Sudo, Rev. Sci. lnst. 69, (1998) 319. 63 

Preliminary Results of Tracer-Encapsulated Sol id Pellet Injection on LHD

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