Phase I Plasma Diagnostics

Some limited diagnostics will be prepared for IC for machine protection and confirmation of the controllability of plasma. They are summarized in Table 1.

CO2 Laser interferometer (tangential), Visible spectroscopy (tangential)P1 and P8Horizontal
Soft X-ray detector arraysP14Horizontal
Visible TV cameras (+ two light guide)P15Horizontal
Langmuir probesP2, P8 and P14upper divertor
Table 1: Diagnostics to be installed for IC

Laser interferometer (tangential)

The tangential CO2 laser interferometer is used for measurement of line-integrated electron density along a tangential chord. The measured line-integrated density will be used not only for plasma physics, but also for real-time feedback of plasma control. Its major components, e.g. lasers, Acousto-Optic modulators (AOM) and detectors, will be installed in “Laser Room 1” where the FIR laser system for an interferometer of JT-60U was installed. The apparatus in the torus hall, e.g. vacuum windows and laser transmission optics, are newly fabricated to match JT-60SA. Figure 1 shows the system configuration of CO2 tangential interferometer/polarimeter. Figure 2 shows a schematic view of the system. The target specification is shown in Table 2.

Visible spectroscopy

The purpose of this system is to measure the intensities of Ha emission, Bremsstrahlung emission and other spectral lines. The viewing chord is tangential between the P1 horizontal port and the P8 horizontal port as shown in Figure 3. Two identical optical systems, each of which consists of a vacuum window (with an effective diameter of 43 mm), a lens (with a focal length of 100 mm) and a bundle of 19 optical fibers (core and clad diameter of 200 mm and 250 mm, respectively and a numerical aperture of 0.2), are installed at the P1 and the P8 port. An image of the central optical fiber is mapped onto the vacuum window of the other optics system (distance ~ 13700 mm) with a diameter of less than 40 mm. The layout of the optic allows to calibrate the sensitivity of the whole spectroscopic system including the vacuum window without in-vessel work: a standard light source just outside the vacuum window can be used to calibrate the sensitivity of the other optical system through the two vacuum windows. In addition, simultaneous measurement from the two ports enables to improve the accuracy through comparison and provide redundancy.

Soft X-ray detector arrays

The purpose of this system is to observe the last closed flux surface (LCFS), the magnetic axis and the electron temperature profile by measuring the intensities of soft X-ray emission through a  pinhole. For IC, only soft X-ray detector arrays is available for the electron temperature profile measurement. The system consists of two detectors. Each detector has an Absolute X-ray and UV (AXUV) sensor, a pre-amplifier and thin beryllium films. The detectors are put on the end of a port plug and the port plug is inserted at the P14 horizon port. Both detectors have a similar measuring range set at a poloidal angle of ~15 degrees downwards which allows to measure the lower half of the plasma as shown in Figure 4. The outputs of the pre-amplifiers are transferred to digitizers installed inside the electromagnetic shield box located at the PIG room (underground floor). Since Be films work as band pass filters, the electron temperature can be evaluated by the ratio of the intensities from two detectors with different film thickness. Table 4 shows the specification of the system.

Event Detection Intelligent Camera (EDICAM)

The EDICAM diagnostic is located in port P18, having a tangential view into the torus (see  Figure 6). Equipped with wide-angle optics, the field-of-view (FoV) is in the order of 80°, thus the camera view can cover about 1/5 of the plasma vessel. A fast wide-angle visible video diagnostic system, based on the Event Detection Intelligent Camera (EDICAM) can also measure, in addition to recycling and impurity influx, the visible light emission associated with fast phenomena such as plasma start up, disruptions, gas injection or even edge filaments.

Langmuir probes (upper divertor)

The primary purpose of the Langmuir probes is the detection of the divertor leg during its sweeping. The position of the divertor leg evaluated from the Langmuir probes is compared with that evaluated by the Plasma Control System (PCS) or equilibrium solver (Meudas). This comparison shall confirm the controllability of the plasma position and shape. To evaluate the position of the divertor leg, four Langmuir probe heads (two is the inner divertor region and two the outer divertor region) are installed at the P2, P8 and P14 toroidal sections of the upper divertor. Additional three heads are installed around the outer divertor region at the P8 toroidal section to evaluate the position of the divertor leg for various plasma configurations. The Langmuir probe head is mounted on the structure of the upper divertor as shown in Figure 7. The Langmuir probe head is composed of a corrector, insulators, a connector and bolts. A mineral insulated (MI) cable is connected to the collector with the connector. The Langmuir probe head on the plasma side is dome shaped with a dimeter and a height of 6.0 mm and 1.2 mm, respectively. A DC voltage is supplied by a power supply installed in the tokamak hall and passed by the MI cables through vacuum feedthroughs installed on the P1, P8, P14 horizontal ports. An ion saturation current (Iis) for detection of the divertor leg position is measured at a time resolution of ≤ 50ms with the data acquisition system installed on the tokamak hall. Evaluation of electron temperatures (Te), electron densities (ne) and floating potential (Vf) can be evaluated by sweeping the applied voltage. The specifications of the Langmuir probes are shown in Table 7.

Phase I diagnostic gallery