J. Graceffa

Status of the ITER heating neutral beam system

The ITER neutral beam (NB) injectors are the first injectors that will have to operate under conditions and constraints similar to those that will be encountered in a fusion reactor. These injectors will have to operate in a hostile radiation environment and they will become highly radioactive due to the neutron flux from ITER. The injectors will use a single large ion source and accelerator that will produce 40?A 1?MeV D? beams for pulse lengths of up to 3600?s.Significant design changes have been made to the ITER heating NB (HNB) injector over the past 4 years. The main changes are: Modifications to allow installation and maintenance of the beamline components with an overhead crane. The beam source vessel shape has been changed and the beam source moved to allow more space for the connections between the 1?MV bushing and the beam source. The RF driven negative ion source has replaced the filamented ion source as the reference design. The ion source and extractor power supplies will be located in an air insulated high voltage (?1?MV) deck located outside the tokamak building instead of inside an SF6 insulated HV deck located above the injector. Introduction of an all metal absolute valve to prevent any tritium in the machine to escape into the NB cell during maintenance. This paper describes the status of the design as of December 2008 including the above mentioned changes.The very important power supply system of the neutral beam injectors is not described in any detail as that merits a paper beyond the competence of the present authors.The R&D required to realize the injectors described in this paper must be carried out on a dedicated neutral beam test facility, which is not described here.

Overview of the design of the ITER heating neutral beam injectors

The heating neutral beam injectors (HNBs) of ITER are designed to deliver 16.7 MW of 1 MeV D0 or 0.87 MeV H0 to the ITER plasma for up to 3600 s. They will be the most powerful neutral beam (NB) injectors ever, delivering higher energy NBs to the plasma in a tokamak for longer than any previous systems have done. The design of the HNBs is based on the acceleration and neutralisation of negative ions as the efficiency of conversion of accelerated positive ions is so low at the required energy that a realistic design is not possible, whereas the neutralisation of H− and D− remains acceptable (≈56%). The design of a long pulse negative ion based injector is inherently more complicated than that of short pulse positive ion based injectors because: • negative ions are harder to create so that they can be extracted and accelerated from the ion source; • electrons can be co-extracted from the ion source along with the negative ions, and their acceleration must be minimised to maintain an acceptable overall accelerator efficiency; • negative ions are easily lost by collisions with the background gas in the accelerator; • electrons created in the extractor and accelerator can impinge on the extraction and acceleration grids, leading to high power loads on the grids; • positive ions are created in the accelerator by ionisation of the background gas by the accelerated negative ions and the positive ions are back-accelerated into the ion source creating a massive power load to the ion source; • electrons that are co-accelerated with the negative ions can exit the accelerator and deposit power on various downstream beamline components. The design of the ITER HNBs is further complicated because ITER is a nuclear installation which will generate very large fluxes of neutrons and gamma rays. Consequently all the injector components have to survive in that harsh environment. Additionally the beamline components and the NB cell, where the beams are housed, will be activated and all maintenance will have to be performed remotely. This paper describes the design of the HNB injectors, but not the associated power supplies, cooling system, cryogenic system etc, or the high voltage bushing which separates the vacuum of the beamline from the high pressure SF6 of the high voltage (1 MV) transmission line, through which the power, gas and cooling water are supplied to the beam source. Also the magnetic field reduction system is not described.

Final design of the beam source for the MITICA injector

The megavolt ITER injector and concept advancement experiment is the prototype and the test bed of the ITER heating and current drive neutral beam injectors, currently in the final design phase, in view of the installation in Padova Research on Injector Megavolt Accelerated facility in Padova, Italy. The beam source is the key component of the system, as its goal is the generation of the 1 MeV accelerated beam of deuterium or hydrogen negative ions. This paper presents the highlights of the latest developments for the finalization of the MITICA beam source design, together with a description of the most recent analyses and R&D activities carried out in support of the design.

Overview of the negative ion based neutral beam injectors for ITER

The ITER baseline foresees 2 Heating Neutral Beams (HNBs) based on 1 MeV 40 A D(-) negative ion accelerators, each capable of delivering 16.7 MW of deuterium atoms to the DT plasma, with an optional 3rd HNB injector foreseen as a possible upgrade. In addition, a dedicated diagnostic neutral beam will be injecting ≈22 A of H(0) at 100 keV as the probe beam for charge exchange recombination spectroscopy. The integration of the injectors into the ITER plant is nearly finished necessitating only refinements. A large number of components have passed the final design stage, manufacturing has started, and the essential test beds-for the prototype route chosen-will soon be ready to start.

Heating neutral beams for ITER: Present status

The heating neutral beam (HNB) systems at ITER are designed to inject a total of 33 MW of either 1 MeV D0 or 870 keV H0 beams into the ITER plasma using two injectors with a possible addition of a third injector later to increase the injected power to ~50 MW. The injectors become radioactive due to the neutron flux from ITER and, in order to avoid the resulting complex remote maintenance, the design, choice of materials and the manufacturing process of each component of the injector is, wherever possible, such that they survive the life time of ITER. To ensure a smooth operational phase of neutral beams at ITER a neutral beam test facility (NBTF) is under construction at Consorzio RFX, Padova, (hereinafter referred to as RFX), which consists of 2 test beds, the 100 kV “SPIDER”, and a 1 MV “MITICA” facilities, which will be used to optimize the source operation for H and D beams. MITICA is essentially a full scale ITER prototype injector for the ITER beam parameters. The manufacturing and operation of the facility will allow validation of the operational space of the injectors and provide valuable information about the manufacturing processes applicable to HNB components. Operation of the two facilities is expected to begin in 2016 and 2019 respectively. Currently experiments on the ELISE facility with a half ITER sized RF beam source are underway. ITER relevant parameters for the H beams have almost been achieved. Efforts are underway to optimise the same with D beams. The experimental database from ELISE will be an important input for establishing the ITER relevant parameter space on the SPIDER source. This paper discusses the present status of the design and development of the injectors for ITER and the progress on the test facilities.

Heating Neutral Beams for ITER: Present Status

The heating neutral beam (HNB) systems at ITER are designed to inject a total of 33 MW of either 1 MeV D0 or 870 keV H0 beams into the ITER plasma using two injectors with a possible addition of a third injector later to increase the injected power to ~50 MW. The injectors operate in a radioactive environment and should survive the life time of ITER, placing thereby stringent requirements on material and manufacturing choices. To ensure a smooth operational phase of neutral beams at ITER, a neutral beam test facility is under construction at Consorzio RFX, Padova, (hereinafter referred to as RFX), and consists of two test beds. The 100-kV SPIDER test bed will be used to optimize the source operation for H and D beams. The 1-MV MITICA test bed is essentially a full scale ITER prototype injector. The manufacturing and operational experiences at MITICA will not only establish the manufacturing processes of ITER HNB components but will also allow validation of the operational space of the injectors for ITER HNB. Operation of the two facilities is expected to begin in 2016 and 2019, respectively. Currently, the experiments on the ELISE facility, IPP Garching, with a half ITER sized RF beam source are underway. The ITER relevant parameters for the H beams have been achieved. Efforts are underway to optimize the same with D beams. The experimental database from ELISE will be an important input for establishing the SPIDER operation. This paper discusses the present status of the design and development of the injectors for ITER and the progress on the test facilities.

ITER neutral beam Vacuum Vessel design

The Vacuum vessel of the ITER Heating Neutral Beam injector is a key component of the neutral beam system. It supports the injector components and is also an extension of the ITER Vacuum Vessel. This paper presents the status of the design of the vessel. In the first part of this paper we present the main design requirements. Besides the pressure and thermal loads, the various interfaces with other components are important constraints for the design. Some have specific requirements concerning displacement, or require specific features for their maintenance. Indeed all maintenance involving opening of the vessel needs to be performed using remote handling systems. The second part aims at presenting the present design of the NB vessel. Various concepts were studied before coming to the present design. Structures were optimised to satisfy the chosen design code (RCC-MR) under the various loading scenarios applied to the vessel, both for normal and accidental cases. In addition, the vessel incorporates two sets of long lip seals which tolerate limited displacements. Limiting the displacement is a real challenge considering the size of the flange and the forces involved. An innovative solution has been developed to improve the mechanical connection between the lids and the vessel walls in order to fulfil the requirements. The vessel displacement is also important for the alignment of the Beam Line Components with respect to the neutral beam and for the cryopumps interfaces. The geometry of the vessel was optimised to reduce the electric field stresses and to increase the voltage holding of the Beam Source, which is at 1 MV potential.

An alternative design concept for the DNB calorimeter motion mechanism

Calorimeter for Diagnostic Neutral Beam (DNB) consists of two movable panels, forming V-shaped configuration with an included angle of 45 Deg. w.r.t. neutral beam axis. Panels closing and opening motion will be achieved through Calorimeter Motion Mechanism (CMM). The DNB calorimeter design has evolved after analyzing several design proposals serving the basic functionality of the component, but these designs had compatibility issues for the ITER Remote Handling (RH) scenarios, operational maintenance, ITER Vacuum Handbook (IVH) compliance for hydraulic integration, design of flexible elements for large displacements, neutron irradiation susceptibility and joint materials for Vacuum Quality Class 1 (VQC1) application. In the design concept the movement mechanism and hydraulic line flexible element have been deliberately kept outside the DNB vessel, hence there is no sliding and complicated links inside the vessel which cannot be maintained through available RH tools. The paper proposes to present state of the art design of the ITER-DNB Calorimeter.

Overview of the iter negative-ion-based neutral beam injector and its development

The ITER fusion device is intended to demonstrate the viability of magnetically confined deuterium-tritium plasma as an energy source. One of the principal methods of heating and driving current in the plasma will be energetic beams of neutral atoms of D° at up to 1 MeV and of H° at up to 870 KeV, with a total injectable neutral beam power after transit through the neutralizer and downstream beamline elements of 16.5 MW from each ion source for pulse lengths of up to 3600 seconds. These requirements far exceed those of any previous positive or negative ion source, thus spawning a substantial development program to ensure that they will be met with a robustly reliable system. The ion source will consist of a large plasma expansion region fed by 8 RF driver units, and will be cesiated to enhance surface production of negative ions, followed by a multi-aperture multi-grid extractor and electrostatic accelerator. The plasma portion of the source is derived from a line of RF sources developed at IPP Garching,1 and the extractor/accelerator from development work at JAEA2, with the integrated design of the ITER source being done at Consorzio RFX. Unlike the first generation of high power negative hydrogen ion isotope sources, the ITER source will have the major advantage of a succession of progressively more comprehensive test facilities, culminating in a full power and pulse length test bed at Consorzio RFX. This talk will discuss the major beamline components, including the ion source and accelerator, the neutralizer cell that converts a portion of the negative ions to neutrals, the residual ion deflection system, and the tokamak field compensation system. Some remaining physics and engineering issues, along with their expected resolution, will be discussed, as well as the development and testing strategy.

Status of the 1 MeV Accelerator Design for ITER NBI

The beam source of neutral beam heating/current drive system for ITER is needed to accelerate the negative ion beam of 40A with D− at 1 MeV for 3600 sec. In order to realize the beam source, design and R&D works are being developed in many institutions under the coordination of ITER organization. The development of the key issues of the ion source including source plasma uniformity, suppression of co‐extracted electron in D beam operation and also after the long beam duration time of over a few 100 sec, is progressed mainly in IPP with the facilities of BATMAN, MANITU and RADI. In the near future, ELISE, that will be tested the half size of the ITER ion source, will start the operation in 2011, and then SPIDER, which demonstrates negative ion production and extraction with the same size and same structure as the ITER ion source, will start the operation in 2014 as part of the NBTF. The development of the accelerator is progressed mainly in JAEA with the MeV test facility, and also the computer simulation ...