Status and activity on LIF-technique development in NFI. I.Moskalenko, N.Molodtsov, D.Shcheglov.

Divertor plasma diagnostics by Laser-Induced Fluorescence method in program of ITER LIF-technique is based on detection of fluorescence radiation of atom or ion excited by laser beam. The diagnostic gives opportunity to perform measurements with good spectral, temporal and spatial resolution. Helium is ash of thermonuclear reactions, the measurement of helium density and temperature in divertor plasmas is a problem of importance. Another inert gases (Ne, Ar, Kr) are also is targets for LIF- technique application because of idea to inject these extrinsic impurities in order to run experiments using RI-discharges. A priory estimation of signal and signal-to-noise ratios were carried out by making use of real laser parameters; this laser considered to be a prototype of laser transmitter for measurements on ITER. Parameters of laser system give a possibility to perform Doppler measurements of temperature by laser spectroscopy method (by scanning narrowband laser line over absorption spectral line profile). A large series of such measurements have been carried out on plasma machine in Kurchatov Institute (T-10, HELLA, PNX-U). Integral part of activity on development of LIF-technique is work on interpretative (CRM). The activity includes development of methods to measure parameters of electron component with help of LIF-method.

The field of LIF-technique activities Helium Temperature T (He I) Task of priority Helium density in divertor plasmas CRM-modernizing (Non-stop activity) -new databases for HeI and etc. Electron density n e (R,Z)=f I( 1 )/I( 2 ) New scheme Extrinsic impurities CRM n(Ar II) Doppler measurements of f(v i ) Ar II Modelling experiments on PNX-U Targets for T i (R,Z) measurements Supplementary functions Additional opportunities Supplementary function

He I spectroscopic scheme for LIF measurements in ITER divertor This scheme permit to avoid stray light problem. The application of laser spectroscopy gives possibility to measure three plasma parameters simultaneously. Local measurement of Doppler temperature by Laser Spectroscopy Method is based on scanning of pumped spectroscopic transition with radiation of narrow band tunable laser and detection of fluorescence light. After making the correction on laser line width, Zeeman splitting and etc. the atom temperature can be calculated using Doppler width. Helium temperature at nm has been also measured on T-10 tokamak. Temperature was (4-5) eV. Measurements of helium concentration The sum of fluorescence signals gives input data for He I density estimates via CRM. Estimates of local electron density by LIF-technique The ratio of fluorescence signals at nm and nm lines depends on electron density. The modeling experiments have been performed on PNX-U and results demonstrated good agreement with electric probes measurements. 3 3 P S 3 3 D 2 3 P 2 3 S

Alternative spectroscopic scheme of helium atom measurements S 3 3 P 3 3 D 2 3 P 2 3 S N e This scheme also provides avoiding the stray light problem. Detuninig FLU - L is large for both fluorescence lines. From point of view of application to divertor plasma diagnostic, this scheme is preferable in case when transmission of optics in the near UV became low.

- pm Ar II ion. Spectral profile of nm line. The next step was to apply LIF technique to diagnosis of extrinsic impurities. Doppler profiles of Ar II have been measured on plasma neutralizer PNX-U. Narrow band ( L 3.6 pm) dye laser was scanning across nm absorption line. T i range was (4-25 eV). It correspond for helium temperatures (588 nm absorption line) to range values of 0.5 – 2.7 eV because width of Doppler- broadened intensity distribution D 0 (T i /M i ) 1/2, M(Ar) = 40 and M(He) = 4. Helium Doppler temperature was measured to be (1.5-2) eV in PNX-U plasma.

Ar II measurements on PNX-U

Comparison of ITER Measurement Requirements and performance of LIF-technique. Parameter Parameter range Spatial Resolution Accuracy ITER (Level 1) T i,a 0.3 – 200 eV 5 сm "along legs " 3 mm "across legs " 20% PNX--U T i, (Ar 1+ ) 4 – 25 eV (experiments) Δl || = 4 cm Δl = 3 mm % (depending on discharge)

Schematic diagram of Laser Module for LIF-Diagnostic Pump laser Wavelength, nm 308 Repetition rate, Hz 100 Output energy, mJ 200 – 240 Pulse duration, ns28 – 32 Dye laser Output energy, mJ 15 – 20 Pulse duration, ns 18 – 20 Tuning range, nm 340 –800 Bandwidth, pm 3.5 Output beam size, mm 2 x 2

3-level schemes for Ne I LIF-technique probing 2p22p2 1s 2 1s 3 1s s 3, 1s 5 – metastable levels (Paschens notation) Possible scheme for electron density measurements on Ne I 1s j LCIF 2pi2pi e-e- λLλL 1s m 1s l LIF 2pk2pk Spectroscopic schemes for LIF on Ne I

LIF system in zone A right divertor leg is shown. The probing laser beam is transmitted trough labyrinth mirrors and windows in closure plates and then directed with the help of large plane mirror M1 to cylindrical laser mirror ML. Changes of angle beam direction can be provided observe all zone A of investigation. Fluorescence light from part of laser beam equal ~ 40 mm and plasma light in zone A is collected by scanning mirror MS, transmitted by large mirror M1 to Cassegrain telescope and is directed to spectrometer. Using this configuration, it is possible to achieve the spatial resolution, equal to ~ 40 mm along leg and ~30 mm across leg.

Conclusions Making use of LIF-technique in experiments on plasma devices has demonstrated the ability of the system to measure density, temperature (atoms, ions) and electron density in real physical experiments. The laser diagnostic system is occurred to be reliable from technical point of view and can be considered as to be the prototype of LIF transmitter for ITER. The work on development of Collisional Radiative Models is integral part of LIF program activity It is necessary to develop diagnostics by LIF-technique based on new targets (trace elements) for measurements.