نقش JET برای آماده سازی و بهره برداری ITER

The JET programme is devoted to the consolidation of ITER design choices and the qualification of ITER integrated regimes of operation. During the experimental campaigns carried out in 2008 and 2009 attention focussed on the test of the ITER-like ICRH antenna, the ITER scenario preparation, the verification of the adequacy of the ITER poloidal field coil design and the test of disruption mitigation methods such as massive gas injection. From 2011 the new ITER-like wall with all beryllium and tungsten plasma facing components, the neutral beam power upgrade and the enhanced control and diagnostic capability will allow key questions on plasma-wall interactions, fuel retention and plasma impurity control with the foreseen ITER wall materials to be addressed. Finally, feasibility studies have confirmed the option of installing an ITER-technology based 170 GHz/10 MW electron cyclotron resonance heating system for the control of MHD activity and the development of advanced tokamak scenarios, and 32 in-vessel coils for ELM control capable of producing magnetic perturbation spectra with a Chirikov parameter above unity for plasma currents up to 5 MA. During the ITER construction phase, JET will be the only device of its class in operation and will therefore play a key role in the preparation of ITER operations – saving time and reducing risk from the ITER programme.

The efficient exploitation of ITER will depend crucially on the scientific and technical preparatory work performed in present day devices to optimize those aspects of the ITER design that are not yet frozen and to develop safe and effective operating scenarios. The Joint European Torus, JET, is ideally positioned to advance the state of ITER preparations by virtue of its size, ITER-like geometry, large plasma current and unique capability to operate with tritium fuel and beryllium plasma facing components. In the last couple of years, these features have allowed significant progress in the understanding of key ITER physics issues and in testing and validating the performance of new technologies. As examples of this work, this paper presents results from studies on the ITER integrated scenario preparation and ITER-like Ion Cyclotron Resonance Heating (ICRH) antenna and on the effect and mitigation of disruptions. To take full advantage of the scientific opportunities offered by the JET facilities a series of strategic upgrades are an integral part of the ongoing JET programme in support of ITER [1] and will also be reported on here. The JET ITER-like wall (ILW) [2] will provide the first experience of tokamak operation with a beryllium (Be) first wall and tungsten (W) divertor, as is planned for the activated phase of ITER. Compared to carbon, the new wall materials should demonstrate a major beneficial impact on fuel retention and on the lifetime of plasma facing components (PFCs). The Neutral Beam Injection (NBI) system is being upgraded with the routinely available total injected power in deuterium being increased from the present 20 MW to 30 MW, while the maximum NBI pulse length is doubled to 20 s, or 40 s at half power [3]. Finally, to address the limitations of the JET Vertical Stabilisation (VS) system in controlling high current plasmas at the ITER-relevant collisionalities (ν*) that will be achievable with the increased heating power [4] the JET plasma control system has recently been upgraded and successfully commissioned on plasma [5], using a model-based approach to minimise the time and risk to the main JET programme. A number of new diagnostics have also come to fruition. With these enhancements, the JET programme in the coming years will provide an unequalled opportunity for advancing ITER preparations in conditions as close to those foreseen in ITER as is possible in any present fusion device. The main objectives of the JET programme now being elaborated for the 2011–2014 period are to: • Demonstrate sufficiently low fuel retention for a Be/W wall to meet ITER requirements. • Study the formation of Be–W mixed layers, their impact on W erosion, material migration and resistance to melting damage. • Develop control strategies for detecting and limiting damage to Be and W plasma facing components by steady state and transient heat loads. • Develop fully integrated scenarios for an all-metal machine, demonstrating the required confinement for ITER with impurity seeding strategies to replace the intrinsic carbon radiation and active mitigation of Edge Localised Modes (ELMs) for acceptable wall and divertor power loads. The possibility of further improving the JET capability of preparing ITER operation has also been investigated. Specifically, two feasibility studies have been conducted for a 170 GHz/10 MW Electron Cyclotron Resonant Heating (ECRH) system and a set of Resonant Magnetic Perturbation (RMP) coils.

By virtue of its main characteristics (large size, ITER-like geometry, large plasma current capability) and new enhancements nearing completion (ITER-like wall, neutral beam and diagnostics enhancements) JET is an ideal machine to advance the state of ITER preparations. In the near term, these capabilities will be fully exploited in characterising the plasma-wall interactions and plasma compatibility of the Be/W first wall and in developing and optimising safe operational scenarios for all-metal walls in ITER-relevant conditions. This work is planned to lead up to a full deuterium–tritium campaign in the 2015 time frame for fully integrated tests of the Q = 10 ITER baseline scenario, including the required active techniques for plasma-wall compatibility (impurity seeding, active ELM mitigation) in a metallic machine. In the longer term, recent feasibility studies have confirmed the option of installing a 170 GHz/10 MW Electron Cyclotron Resonance Heating system based on ITER technology and 32 in-vessel RMP coils for ELM control. If realized these upgrades would allow JET to significantly advance preparations for ITER operations – saving time and reducing risk from the ITER programme.