ITER
The large-scale fusion experiment ITER (Latin for "the way") is currently under construction in Cadarache in the south of France as part of an international cooperation. ITER aims to demonstrate the physical and technological feasibility of fusion energy on a power-plant scale and thus pave the way for the commercial exploitation of fusion. By means of the fusion of heavy hydrogen (deuterium) and super-heavy hydrogen (tritium), up to 500 million watts of fusion power will be produced at ITER for the first time ever.
The following is a summary of ITER's key operating data:
Plasma volume | 840 m3 |
Magnetic field strength | 5.3 Tesla |
Plasma current | 15 Mega-Ampere |
Fusion power | 500 MW |
External heating power | 50 MW |
Power gain | Q = 10 |
Start of operation | approx. 2025 |
The entire body of existing knowledge in fusion research worldwide is being incorporated into the design and construction of ITER. With partners from Europe, the USA, Japan, Russia, China, India, and South Korea, almost all of the world’s major industrial regions are involved in its construction. Jülich also plays a role in ITER’s development with a wide range of research activities and project contributions. Jülich’s studies on plasma-wall interactions, for example, performed essential preliminary work for ITER.
Development of a tritium monitor for ITER
One of the most critical problems for the operation of ITER is the control of the inventory of tritium (abbr. T) stored in the plasma surrounding vessel walls. For the operation of ITER and of a nuclear reactor in general, the determination of the tritium inventory as well as its control is essential. The T-monitor diagnostic system to be developed at Forschungszentrum Jülich should provide information about the tritium content in the deposited layer on the inner divertor.
Within this project, a laser-based T-monitor diagnostic is developed to measure the tritium content in the first wall of ITER. The T-inventory builds up through the interaction of wall erosion and co-deposition of hydrogen isotopes together with the redeposited wall material on the first wall of ITER. It should be emphasized that the limitation of the tritium content in the reactor is an essential safety requirement for the operation of ITER. The measurement concept is based on laser-induced desorption (LID) in conjunction with a mass spectrometer. The heating flux produced by the laser induces a desorption effect and the released tritium is analysed by Residual Gas Analysis (RGA).
In order to monitor the tritium content in the ITER tokamak by laser-induced desorption, the inner divertor baffle is thus illuminated by a means of a high power laser. The 60 kW laser with trains of 3ms pulses is located far away in the tritium building. An optical fibre brings the laser beam to the back of the so-called Port Cell, where the fibre ends. The laser beam is then transported by a series of mirrors through the bioshield and vacuum window to the vacuum vessel where it is focused onto the divertor. This creates an intense light spot with sharp edges and a limited diameter of exactly 5mm, which heats up the surface and desorbs the tritium. The spot can be scanned over an area of 100×500 mm2. An overview of the diagnostic system is shown below.
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