CO2 polarimeter system

The tangential CO2 laser interferometer has been installed and operated in the integrated commissioning. To complement the interferometer, the polarimeter using two-color lasers with the wavelength of 10.59 mm and 9.25 mm and Photoelastic Modulators (PEMs) is procured. The target specifications of the CO2 laser polarimeter is shown in Table 1. The CO2 lasers used in the interferometer-polarimeter system have 6 hours stability in wavelength without mode hopping. Moreover, a cavity mode control system has been investigating for the wavelength stability. In the cavity mode control system, a piezo element incorporated in a laser cavity is controlled according to the measured wavelength.

Visible TV camera system

The main role of the visible TV camera system is to monitor the Plasma Wall Interactions (PWIs) at the divertor, limiter and first wall, where is mostly covered by the carbon tiles (1 piece: 12 cm x 7 cm). Thus, the field-of-view (FoV) for each viewing chord is in the order of 80°, covering a wide area of the vacuum vessel, such as inner wall, outer stabilizing plate, and upper/lower divertor regions. The visible TV camera system consists of one endoscope at P6 horizontal port, two periscopes at P15 horizontal port, one periscope at P18 horizontal port and one EDICAM at P18 horizontal port as shown in Figure 1. The light-guide systems is equipped under each port-plug for illuminating inside the vacuum vessel without plasma emission, using a fiber optics connected to the metal halide lamp (375 W).

Infrared TV camera systems

Two types of infrared TV (IRTV) camera systems will be prepared. One having wide-angle FoV covering a wide area in vacuum vessel is used for monitoring the in-vessel components such as inner wall, outer stabilizing plate, and upper/lower divertor regions. The system is installed at P6 horizontal port as a part of the endoscope. The other system having narrow-angle FoV is used for monitoring the divertor tiles and the system is installed at P15 horizontal port. The specifications of the IRTV camera system for wide-angle FoV and narrow-angle FoV (or divertor) are shown in Table 1 and 2, respectively.

Electron cyclotron emission diagnostics system

A port plug with mirror box is installed at P11 horizontal port. The sight line is horizontal and passes the centre of the plasma (Z = 0). To reduce the visual angle, a mirror box containing a pair of parabolic mirrors is installed between the viewing port and the end of the waveguide. Design calculations using the finite-difference time-domain method taking into consideration the size of the ECE port plug showed that the full width at half maximum of a Gaussian beam launched from the ECE port is about 10 cm at the plasma centre (the width is related to the visual angle). The total waveguide length from the diagnostic port to the ECE diagnostic room is about 60 m.

Divertor Langmuir probe system

A divertor Langmuir probe system for the measurement of plasma parameters in the divertor region such as electron density (ne), electron temperature (Te), floating potential (Vf) and ion saturation current (Isat) will be prepared. The divertor Langmuir probes comprise sensor heads, mineral insulated (MI) cables and a data acquisition system. As shown in Figure 1, the sensor heads are installed on the edge of the JT-60SA divertor cassettes to facilitate replacement of those. The sensor heads will be installed in four toroidal sections. Detected current is transported to the data acquisition system by means of MI cables. Figure 2 shows the spatial resolution of the Langmuir probes on the inner and outer divertor target. The Langmuir probe on Section P-3 and 9 are installed 13.5 mm above those on Section P-4 and 15. Simultaneous measurement, for example, Section P-3 and 4, improves the minimal spatial resolution to 13.5 mm. The Langmuir probes on the other position such as the inner and outer baffles, dome and outer cover are installed at the same poloidal position for the different toroidal section. The specifications of the Langmuir probes are shown in table 1.

Bolometer system

A bolometer system for the evaluation of the total of radiation power from the plasma and its spatial distribution will be prepared. The radiation power is also used for real-time feedback control of the plasma. In JT-60SA a 4-channel resistive bolometer system is applied to the radiation power measurement. Two types of bolometer heads are installed at P18 upper and horizontal port, and P16 lower diagnostic slit: one is the head with a thinner absorber for lower energy radiation from the plasma with the electron temperature <7.9 keV and the other is with a thicker absorber for higher energy radiation from the plasma with higher electron temperature <13.5 keV such as Scenario #2. The specifications of the bolometer system are summarized in Table 1.

Visible spectrometer for divertor and Dα emission monitor systems

The visible spectrometer for divertor system measures the two-dimensional distribution of emissions in the visible range from the lower divertor mainly to investigate the behaviour of fuel particles and impurities, particularly from the viewpoint of atomic and molecular processes. Because the spatial distribution of the emission is complicated in the divertor region, a two-dimensional measurement is required. Hence two dimensional arrays of viewing chords will be prepared: one is a vertical array installed at P6 upper vertical port and the other is a horizontal array installed at P6 lower vertical port.

Vacuum Ultra Violet (VUV) spectrometer system

A VUV spectrometer for monitoring the brightness of line emission from light impurities such as carbon and oxygen, and also from metal impurities for safe operation of the JT-60SA device, will be prepared. The VUV spectrometers are installed at P10 horizontal port and view the plasma horizontally without viewing the neutral beams directly. Two grazing incidence spectrometers will be prepared: One spectrometer (high resolution) covers a wavelength range of 0.5  – 5 nm with a holographic grating having 1200 grooves/mm, and the the other spectrometer (survey) covers  a wavelength range of 0.5 – 50 nm with a holographic grating having 300 grooves/mm. The light dispersed by these gratings is focused on a flat plane with a width of ~ 26 mm. On the flat focal planes, a CCD camera with an imaging array of 1340 x 1300 pixels having a size of 20 x 20 mm detects the dispersed light. The object optics with a viewing chord similar to that of the VUV spectrometers, for example, by using zeroth order diffraction (reflection) light, is prepared for an absolutely calibrated visible spectrometer for the purpose of relative calibration with a branching ratio method. The specifications of the VUV spectrometers are shown in Table 1.

 Thomson scattering system

The YAG laser Thomson scattering system consists of core system installed at P2 horizontal port and edge system installed at P1 lower oblique port. Figures 1 and 2 show the schematic of P2 stage and Y3 laser stage for Thomson scattering, respectively. These stages are designed to keep the same stiffness as the stage used in JT-60U.

Charge exchange recombination spectroscopy (CXRS) diagnostics system

The CXRS diagnostics system, for the measurement of the ion temperature, toroidal rotation, poloidal rotation, carbon impurity density profiles based on the Doppler broadening, spectral shift and intensity of the light emitted by charge exchange recombination reaction between the carbon impurity ions and neutral beams, will be prepared.

Soft X-ray intensity measurement system

The soft X-ray intensity measurement system, for the measurement of the line integrated soft X-ray emission, which mainly reflects the electron density and temperature, in order to know the approximate plasma pressure profile, the internal structure of MHD events and the impurity transport, will be prepared. Two sets of 16 channel PIN diode arrays will be installed in the each of the P-14 upper, upper oblique, and horizontal port as shown in Figure 1 in order to measure the soft X-ray intensity profile. The diode arrays with Beryllium filter are fixed in the vacuum condition. Using these profiles from 96 viewing chords, the computer tomographic (CT) reconstruction technique can be applied. The specifications of these spectrometer are shown in Table 1.

Motional Stark effect (MSE) polarimeter system

The MSE polarimeter system for the measurement of pitch angle of magnetic field line to evaluate the safety factor (or current density) profile through equilibrium reconstruction will be prepared. The MSE polarimetry is installed at the P17 horizontal port for viewing the tangential #8B beam (~85keV, P-NB), which is injected slightly off-axis counter (co) direction to the plasma current in lower-single-null configuration. The NB#8B is injected downward. Since the diagnostic beam will pass slightly off-axis, r/a < ~0.15-0.2 cannot be measured in standard configuration, as shown in Figure 1 (a). The sight line becomes almost tangential to the toroidal field when viewing from the P17 horizontal port, which gives the best spatial resolution. The beam radius is about 20cm about the measurement points. Calibration of observed polarization angle will be done by the injection of the diagnostic beam into the machine with D2 gas.

Neutron monitor system

The neutron monitor system for monitoring the fusion performance and measuring neutron yields to meet the requirements from nuclear license will be prepared. The time-resolved volume-integrated neutron-emission rate (neutron yield) will be estimated from a neutron count rate by a detector using a U235 fission chamber (FC). Based on the nuclear license, three identical sets of neutron monitor are installed for redundancy, while two sets should be always active during deuterium plasma operation.

Neutron profile monitor system

The neutron profile monitor system for the measurement of a line-integrated neutron emission profile will be prepared. An NE213 liquid organic scintillator or a stilbene crystal scintillator will be used as a detector because of its better sensitivity and fast response. 

Tracer-encapsulated solid pellet (TESPEL) system

The TESPEL system to provide the known amount of impurities into the core or edge plasmas of JT-60SA for a quantitative study of the impurity transport will be prepared. As a tracer impurity, any element can be embedded if it is solid, and allowed by applicable regulations. The typical amount of the impurity injected into the plasma will be around 3×1018 particles. In the case of tungsten (W), the tungsten ion density in the typical JT-60SA plasma (Vplasma =133 m3) is expected as 2.3×1016 m-3 and consequently the ratio to the bulk ion is estimated as 0.028 % with the averaged bulk ion density of 8×1019 m-3. The electron density sourced from the tungsten injected by the TESPEL is expected as 1.7×1018 m-3 and consequently the ratio to the bulk electron is estimated as 2.1 % with the averaged bulk electron density of 8×1019 m-3. The typical outer diameter of the TESPEL, which can contain the impurity with the particle number of 3×1018 is 1.2 mm. In this case, for the JT-60SA plasma with the averaged bulk density of 8×1019 m-3, the carbon contamination by the TESPEL is estimated as 0.4 %, and the electron density will be increased totally by 4.9 %.

Fast Ion Loss Detectors

In order to identify plasma fluctuations which cause losses of fast ions, Fast Ion Loss Detectors (or FILD) are required. The detectors provide velocity-space measurements of escaping ions with a temporal resolution in the order of milliseconds.