H. Kuramoto

K. Sato

K. Toi

N. Hiraki

T-IIU Group JIPP

National Institute for Fusion Science (NIFS-Repository)

§24. Measurement of Poloidal Magnetic Field Profile with Zeeman Polarimeter Kuramoto, H., Hiraki, N. (Kyusyu lnst. Tech.) Toi, K., Sato, K., JIPP T-IIU Group We have developed a single-channel Zeeman polarimeter and measured the poloidal magnetic field in JIPP T-IIU. The poloidal magnetic field is deduced from polarization analysis of a Hell 4686A spectral lines emitted from a He-doped deuterium plasma. The polarization modulation is estimated as a ratio of the difference between left-hand and right-hand circular polarized line profiles to the sum of them, from which the magnetic field strength along the line of sight is directly estimated. Figure 1 shows a schematic of the polarimeter designed for JIPP T-IIU. The output signals from the system have been analyzed through the procedure based on FFT technique as shown in Fig.2. The magnetic field strength averaged along the line of sight is derived as follows, B8(z) = C X Max(/L- IR) X ~A, (1) Io where Iv IR and Io denote the left- and right-hand circularly polarized line proftles and the maximum intensity of a profile respectively and z is a tangency radius of a line of sight. A local poloidal field is estimated through Abel inversion from the above field expressed by eq.(1) Be(r) = __ r_ fa !!_(B8 (z)I(z)J dz (2) ne(r) J, dz z ~ z2 - r 2 A where a is the plasma minor radius, I(z) is a measured line brightness, and E(r) is a local emissivity obtained from Abel inversion ofl(z). The poloidal field proftle is shown in Fig.3, where open circles denote experimentally obtained data and two curves correspond to the poloidal field profiles for the current density profile assumed as Mr)=joxfl-(:rJ. (3) We have performed calibration of an absolute value, measuring the toloidal magnetic field and poloidal field at the plasma surface. This system has achieved good time resolusion of -1.5 ms in He-doped plasmas(nHe"ne> 10%) with a newly developed fast scanning Fabry-Perot interferometer. PMTI PMTl Fig.1. Schematic of a polarimeter on JIPP T-IIU. CL:condenser lense,PH:pinhole,FL:field lense, PEM:photoelastic modulator ,BF: bandpass filter, PBS:polarized beam splitter,F-P:the scanning Fabry-Perot interferometer,PMT:photomultipliers fromPMfl fran .FMT2 Y+v_ (V+-V J+(~-v-_) 5 (kHz "ii'<i'Se Bandpass Filter (50±10)kHz fromPEM si ncomt reference &gnal (S(kHz) Fig. 2. Block diagram of data analysis sequence 2000 .- lSOO flj flj = ~ 1000 -Q. ~ soo o measured --m=2,n=3 ---- -m=2,n=2 oL-L......I__.__.---'--'-_.__.__.__._....___._~.1..-.L._j__.__.---'--'-_.__._--'--' 0 S 10 lS 20 25 radius( em) Fig.3. Poloidal field proftle measued with the polarimeter in the JIPP T-llU plasmas, where Br2.6T, IP=150kA, and q(a)=6.0. 191 

Measurement of Poloidal Magnetic Field Profile with Zeeman Polarimeter

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