Electron Cyclotron Heating

Electron Cyclotron Resonance Heating (ECRH) heats the electrons in the plasma with a high-intensity beam of electromagnetic radiation at a frequency of 170 GHz; the resonant frequency of electrons. The electrons in turn transfer the absorbed energy to the ions by collision.

The Electron Cyclotron heating system is also used to deposit heat in very specific places in the plasma, as a mechanism to minimize the build-up of certain instabilities that lead to cooling of the plasma. In comparison to the ICRH system, the ECRH has the advantage that the beam can be transmitted through air which simplifies the design and allows the source to be far from the plasma, simplifying maintenance. Power will be provided by powerful, high-frequency gyrotrons as power sources. The ITER design includes the development of a 1 MW gyrotron operating at 170 GHz with a pulse duration of more than 500 s.

Cryostat

The entire Vacuum Vessel is enclosed within a Cryostat, or cold box, which provides insulation for the superconducting Magnet system and other components.

The Cryostat is a large, stainless steel structure surrounding the Vacuum Vessel and superconducting Magnets, providing a super-cool, vacuum environment. It is made up of a single wall cylindrical construction, reinforced by horizontal and vertical ribs. The Cryostat is 29.3 metres tall and 28.6 metres wide.

The Cryostat has many openings, some as large as four metres in diametre, which provide access to the Vacuum Vessel for Cooling systems, Magnet feeders, auxiliary Heating, Diagnostics, and the removal of Blanket and Divertor parts. Large bellows are used between the Cryostat and the Vacuum Vessel to allow for thermal contraction and expansion in the structures. The Cryostat is completely surrounded by a concrete layer known as the bioshield. Above the Cryostat, the bioshield is two metres thick.

External Systems

Vacuum System

With a volume of 1,400 m³ and 8,500 m³ respectively, the ITER Vacuum Vessel and Cryostat range amongst the largest Vacuum Systems ever built. Sophisticated techniques will be necessary for the monitoring and maintenance of these systems: once in operation, there will no longer be access to the machine.

Vacuum pumping is required prior to starting the fusion reaction to eliminate all sources of organic molecules that would otherwise be broken up in the hot plasma. Vacuum pumping is also required to create low density—about one million times lower than the density of air.

Mechanical pumps and powerful cryogenic pumps evacuate the air out of the Vessel and the Cryostat until the pressure inside has dropped to one millionth of normal atmospheric pressure. Considering the volume of ITER, this operation will take 24 to 48 hours.

The main pumping systems are the eight torus exhaust pumps, the four cryopumps for the Neutral Beam Injection systems used in plasma heating, and the two cryopumps for the ITER Cryostat and the contained superconducting Magnets. They will be cooled with supercritical Helium.

The complex pumps have been tailored for the very specific applications and requirements at ITER.

Remote Handling

Remote handling will have an important role to play in the ITER Tokamak. When operation begins, it will be impossible to make changes, conduct inspections, or repair any of the Tokamak components in the activated areas other than by remote handling. Very reliable and robust remote handling techniques will be necessary to manipulate and exchange components weighing up to 50 tons. The reliability of these techniques will also impact the length of the machine's shut-down phases.

All remote handling techniques developed for ITER operate on the same principle. A remote manipulator is used to detach the component; the component is removed through a port and placed into the docked transport cask; a temporary door is placed over the Vacuum Vessel access port; and the cask is closed to prevent contamination. The cask is moved on air bearings along to the Hot Cell. A similar docking occurs at the Hot Cell and the component is removed to be repaired or replaced. The process is then reversed to bring that component back to the Vacuum Vessel.

Power Supply

Electricity requirements for the ITER plant and facilities will range from 110 MW to up to 620 MW for peak periods of 30 seconds during plasma operation. Power will be provided through the 400 kV circuit that already supplies the nearby CEA Cadarache site—a one-kilometre extension will be enough to link the ITER plant into the network.

ITER will have a steady state distribution system to supply the electricity needed to operate the entire plant, including offices and the operational facilities. The Cooling Water and Cryogenic systems will together absorb about 80% of this supply.

A second pulsed power system will be used during plasma operation to provide the superconducting Magnet coils and the Heating and current drive systems with the large amount of power that they need. Electricity from the 400 kV circuit will be transformed to an intermediate level (69 kV) via 3 step-down transformers.

Emergency backup power for the ITER plant and facilities will be covered by two diesel generators.

Date: 2016-03-03; view: 786