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.
Supplementary functions method in program of ITER
T (He I)
Task of priority
in divertor plasmas
of f(vi) Ar II
Modelling experiments on PNX-U
-new databases for HeI and etc.
Targets for Ti(R,Z)
measurementsThe field of LIF-technique activities
3 method in program of ITER3D
2 3SHe 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 parameterssimultaneously.
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 l 587.6 nm has been alsomeasured 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 388.9-nm and 706.5-nm lines depends on electron density. The modeling experiments have been performed on PNX-U and results demonstrated good agreement with electric probes measurements.
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.
( method in program of ITERl-l0) pm
Ar II ion. Spectral profile of 611.5-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 611.5 nm absorption line. Ti 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 DlD0(Ti/Mi)1/2 , M(Ar) = 40 and M(He) = 4.
Helium Doppler temperature was measured to be (1.5-2) eV in PNX-U plasma.
Parameter method in program of ITER
0.3 – 200 eV
5 сm "along legs "
3 mm "across legs "
4 – 25 eV
Δl|| = 4 cm
Δl┴ = 3 mm
10 - 20% (depending
Comparison of ITER Measurement Requirements and performance of LIF-technique.
Schematic diagram of Laser Module for LIF-Diagnostic method in program of ITER
Output energy, mJ
15 – 20
Repetition rate, Hz
Pulse duration, ns
18 – 20
Output energy, mJ
200 – 240
Tuning range, nm
Pulse duration, ns
28 – 32
Output beam size, mm
2 x 2
1s3 , 1s5 – metastable
levels (Paschen’s notation)
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”.