Search

• MAST-U NBI beamline re-ionisation modelled for early operation plasma scenarios. • Monte Carlo modelling has derived the heat loading on the beamline duct liners. • New graphite tiles added to catch in-vessel re-ionisation. • ANSYS analysis confirms suitability for initial MAST-U campaigns. • Re-ionisation modelling benchmarked using the fast ion code LOCUST. We describe modelling of neutral beam re-ionization along the MAST-U beamlines and into the MAST-U vessel, within a field envelope applicable to the operational space of the machine. Monte-Carlo simulations using the MAGNET code give the re-ionized power loading on both beamline ducts, which was used to position thermocouples on the duct liners. Thermal and structural analysis of the duct liners has been carried out using ANSYS. The potential for significant amounts of re-ionized power entering the MAST-U vessel has resulted in the installation of graphite tile plating at the end of the ducts, compatible with co-injection. The power loading on these plates and other in-vessel components as modelled by MAGNET has been compared to the LOCUST code. Analysis has confirmed that the graphite tiles are compatible with core scope operation. [ABSTRACT FROM AUTHOR]

The JET Neutral Beam Injection (NBI) system is the most powerful neutral beam plasma heating system currently operating. Optical Interlocks were installed on the beam lines in 2011 for the JET Enhancement Project 2 (EP2), when the heating power was increased from 23 MW to 34 MW. JET NBI has two beam lines. Each has eight positive ion injectors operating in deuterium at 80 kV–125 kV (accelerator voltage) and up to 65 A (beam current). Heating power is delivered through two ducts where the central power density can be more than 100 MW/m 2 . In order to deliver this safely, the beam line pressure should be below 2 × 10 −5 mbar otherwise the power load on the duct from the re-ionised fraction of the beam is excessive. The new Optical Interlock monitors the duct pressure by measuring the Balmer- α beam emission (656 nm). This is proportional to the instantaneous beam flux and the duct pressure. Light is collected from a diagnostic window and focused into 1-mm diameter fibres. The Doppler shifted signal is selected using an angle-tuned interference filter. The light is measured by a photo-multiplier module with a logarithmic amplifier. The interlock activation time of 2 ms is sufficient to protect the system from a fully re-ionised beam—a significant improvement on the previous interlock. The dynamic range is sufficient to see bremsstrahlung emission from JET plasma and not saturate during plasma disruptions. For high neutron flux operations the optical fibres within the biological shield can be annealed to 350 °C. A self-test is possible by illuminating the diagnostic window with a test lamp and measuring the back scatter. We demonstrate an important technology for the protection of high power neutral heating beams and present the design and operational results. [ABSTRACT FROM AUTHOR]

Abstract: The JET neutral beam injection (NBI) system is undergoing an upgrade of both beam power and pulse duration, which will be completed in 2011. In order to obtain an early assessment of the performance of the upgraded injectors, two positive ion neutral injectors (PINIs) with modified ion source and accelerator configuration were installed on Octant 8 Neutral Injector Box and successfully commissioned in summer 2009. Both PINIs were routinely delivering ∼2MW of deuterium neutral beam power during the JET experimental campaign in autumn 2009. These early tests allowed us to predict with confidence that the JET NBI upgrade objective of injecting 34MW of total deuterium neutral beam power into the JET plasma will be achieved. [Copyright &y& Elsevier]

Abstract: The JET neutral beam (NB) heating system is being upgraded as a part of the ongoing JET Enhancement Programme. This is one of the largest upgrades of the JET machine carried out within the EFDA-JET framework. The main goals of the project are to increase the NB power delivered to JET plasma, to increase the beam pulse duration and to improve the availability and reliability of the JET NB system. The upgrade of the system is being carried out through the modification of the two existing neutral injector boxes (NIBs), each equipped with up to eight positive ion neutral injectors (PINIs). Significant changes of the JET NB system will be carried out within the next few years and will include modification of all PINIs, modification or replacement of various beamline components and corresponding instrumentation, procurement and installation of new high voltage power supply (HVPS) units and corresponding control systems and refurbishment of the 36kV power distribution. Various physics, engineering and planning issues related to this project, as well as the current status of the project are discussed in detail. Particular attention is given to the results of a PINI prototype test, which are of crucial importance for the successful completion of the entire enhancement programme. Upon the completion of the project in 2009/2010, JET NB system should be capable of delivering more than 34MW of deuterium beam power into the JET plasma for a duration of up to 20s with improved reliability. This will significantly enhance overall capabilities of the JET machine in support of ITER development. [Copyright &y& Elsevier]