A. Matsubara

D. Stutman

D.V. Kalinina

Experimental Group LHD

K. Sato

M. Finkenthal

N. Tamura

S. Sudo

National Institute for Fusion Science (NIFS-Repository)

§9. Ultrasoft X-Ray Diagnostic for Impurity Transport Studies with Tracer-Encapsu-lated Solid Pellet Injection on LHD Kalinina, D.V. (Graduate Univ. Advanced Studies), Sudo, S., Tamura, N., Sato, K., Matsubara, A., 'Stutman, D. (JHU), Finkenthal, M. (JHU), LHD Experimental Group The local diffusion properties of impurity tracer ions deposited locally in the core plasma by means of TESPEL injection can be obtained by the observation of the line emission arising from the charge exchange recombination (CXR) of injected impurity nuclei, I (nuclear charge Z) with the neutral hydrogen atoms, H, originated from Neutral Beam Injection (NBI)atoms[I]: 12+ +H1s =>1(2-1)+ +H+ (I). In the TESPEL experiments with low-Z impurities (Li, Mg, F), the signal to noise ratio of the CXR emission was very low, since the charge exchange cross-section decreased substantially due to the high NBI cncrgy on LHD (-180keV) [2). One of the alternatives to increase the charge exchange cross-section of the CXR emission from the TESPEL impurities under LHD plasma condition is a shift of the measurement range from the visible domain to the ultrasoft X-ray (USXR) range. Mg or F is expected to be an optimal tracer for USXR CXR Spectroscopy (CXRS) measurement [3]. The estimated brightness of the CXR emission for F and Mg is more than onc order of magnitude larger than those in the visible domain. However, "the local USXR CXRS measurement using thc TESPEL tracer is still challenging and needs the strong rejection of the background level to distinguish the faint CXRS signal. For such a challenging measurement with the TESPEL tracer, a one-channel USXR polychromator with a high photon throughput has been recently developed by the Johns Hopkins University (JHU) Plasma Spectroscopy Group [4] and tested in a recent LHD experiment. The device consists mainly of a toroidally aligned stacked-grid collimator for the angular collimation of radiation, two planar Ni/C multilayer mirrors (MLM) as a dispersive element, and two high~sensitivity photodetectors. A titanium foil 0.3 ~m in thickness on a Parylene-N film of 0.7 ~m in thickness is applied for reducing scattered VUV and visible lights. The filters are optimized for a maximal background rejection rather than the largest transmission. Such configuration using a grid collimator in combination with MLM and foil filters, which provides a high throughput having 2 cm radial and 0.1-0.2 nm spectral resolution, has been used for the first time in magnetic fusion experiments. The light emissions from the plasma are collimated on the MLM, and the Bragg reflected beam propagates through the filters and is registered by anew, highly sensitive, compact and efficient high-gain micro-channel plate (MCP). The MCP is coated with 150 nm CsI layer that increase the 158 quantum efficiency up to 25% in the spectral range of interest. For the first experiments, the USXR polychromator was optimized for the measurement of the CXR emission of the Mg H-like n = 2-3 (Au", = 4.5 nm). A clear Mg contribution after the TESPEL injection has becn observed. The comparison of the two signals at the Mg H-like line after TESPEL injection at 1.5 sec with and without Mg tracer is show in Fig.l. - with Mg tracer -w/o Mg tracer 1.45 1.50 1.&5 1.60 1.65 1.70 1.7~ 1.110 time, sec Fig.l. Comparison of the signals obtained from the Line channel with (LHD#48640) and without (LHD#48648) the Mg tracer. TESPEL was injected at 1.5 s. Preliminary analysis indicates that the signal obtained from the Line channel with the Mg tracer essentially contains the CXR emissions and other contributions, such as those of electron impact excitation and continuum. Unfortunately, the background measurements at the nearby wavelength 5.1nm installed at the same toroidal location was not useful for obtaining a pure Mg H-like CXR emission, due to the some significant signal contribution after TESPEL injection (conceivably from He-like Mg emission). For a correct background measurement of CXRS, it would be preferable to use a channel with the same wavelength as for the Line MLM but at a different toroidal location without NBI or a shot without NBI at the same toroidal location, that will be carried out during next campaign. This experimental result suggests that the TESPEL technique in combination with the novel USXR polychromator could be a powerful tool for local transport measurement on the LHD. The intermediate Z tracer like Mg injected in the IkeV plasma at the r/a=0.7 tracer deposition cannot be fully ionized before expansion, thus the experiments with another optimal tracer and lower Z, fluorine, will be more interesting for future experiments. References: I) Sudo S. et al., Plasma Phys. Control. Fusion 44 (2002) 129. 2) K. Khlopenkov, S. Sudo, Plasma Phys. Control. Fusion 43 (2001) 1547. 3) D.Kalinina et aI., will be published in JPFR SERIES Vo1.6. 4) D. Stutman et aI., submitted to Proc. 15th Conf. on High Temperature Plasma Diagnostics, San Diego, 2004. 

Ultrasoft X-Ray Diagnostic for Impurity Transport Studies with Tracer-Encapsulated Solid Pellet Injection on LHD

Ultrasoft X-Ray Diagnostic for Impurity Transport Studies with Tracer-Encapsulated Solid Pellet Injection on LHD

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