Search

A low-energy multipole line cusp ion source with two-grid extraction system has been developed and characterized for studying the role of the charge exchange processes on ion beam extraction, transport, and neutralization. The ion source is operated for extraction of Ar+ ion beam of current 50–240 mA at energies 850–1650 eV. The characterization of the ion beam is carried out at various axial positions along a 200–815-mm beam path with a background pressure of 4– $20\times10$ −5 Torr. An 11-channel Faraday cup array is used to measure the radial profiles of ion current density and angular beam divergence at these positions. The beam divergences are found to be in the range of 6°–15° for beam perveance of 0.50– $3.75\times10$ −9 AV−3/2. The attenuation of ion beam current along the beam path is observed due to the charge exchange neutralization of the energetic ions in the presence of high background pressure. Since ion current density along the beam path can be reduced by both the charge exchange processes and beam divergence, the accounting of beam particles, i.e., energetic ions and neutrals, at larger distances is difficult by the measurements of ion current density using the Faraday cup alone. The flux of energetic particles (energetic ions and fast neutrals) is therefore obtained by a thrust measurements on a beam target fixed at a distance of 800 mm from the ion source. The neutralization of the ion beam obtained by the emission of electrons from a hot filament neutralizer is also investigated in the presence of the charge exchange processes. Space-charge neutralization is provided initially by the secondary electrons emitted from the vessel walls or by the charge exchange processes even without the neutralizer operating at the desired temperature. However, the current neutralization is achieved only by the electrons emitted from the hot filament neutralizer operating in a space-charge-limited mode.

Research in ITER grade magnetic confinement fusion uses high power radio frequency sources and accelerated neutral particles to heat the plasma to fusion temperature. These devices require high voltage DC power supplies in the range of several tens of kilovolts at a power level of few megawatts. Pulse step modulation technique is widely used to generate high voltage by cascading bulk numbers of low voltage switched power modules, offers a minimum ripple with microsecond order transient response and low let-through energy in case of load fault. However, the power quality and reliability of these systems still need enhancement for compatibility with an industrial environment. In a conventional diode rectifier-based switched power module, current drawn from the multisecondary transformer is highly distorted affecting transformer performance, leading to deploy higher capacity with enhanced thermal management. A novel concept of pulsewidth modulated (PWM) rectifiers in pulse step modulated power supplies is attempted for the first time with comparative analysis over conventional diode rectifiers, quoting an example of dual output high voltage power supply. Articles also discuss the development of a laboratory-scale prototype of the switched power supply module utilizing a PWM rectifier.

A solid state High Frequency (HF) 1 MHz, 40 kW source is intended for plasma formation in a neutral beam source by inductive coupling of RF power. An important design feature of such an HF source is its ability to sustain large transient swings of load (due to impedance transition on microsecond time scales). A 40 kW High Frequency Power Supply (HFPS) has been configured with multiple Class-D H-bridge inverters modules by using latest generation switching semiconductors. Each module is capable of delivering 3 kW of power, then magnetic combiners and an LC tuning network provides a 1 MHz sinusoidal output to a 50 Ω standard load. The developed prototype power supply has been coupled to a single-driver RF ion source test bed ROBIN in IPR to characterize the system with actual load conditions. In a recent experimental campaign, tuning of matching network parameters helped to strike and sustain plasma over the pressure range of 1 Pa to 0.42 Pa with forward power of 37 kW to 22 kW. An additional impedance matching network was implemented to map the power supply impedance (50 Ω) with the impedance offered from the source (>90 Ω seen at PS end). A configurable frequency with resolution (∼1 kHz) helped to achieve a power factor close to unity. Experiments helped to study the behavior of the power supply in scenarios of dynamic (plasma) impedance. Auto-tunable frequency for matching the varying load is being implemented in the HF power supply.

Ion Cyclotron High Voltage Power Supply (IC-HVPS) with dual output (27kV & 15kV, 3MW) is operational at ITER-India lab with a 1.5 MW Diacrode based RF source to be used for ICRF (Ion Cyclotron RF) system. The controller for ICHVPS is designed with LabVIEW Real-time (RT) PXI controller to support all control and monitoring operations of the Pulse Step Modulation (PSM) based power supply. Besides regulation of output voltage, the controller supports all essential features like, fast dynamics, low ripple and protection for source and loads. This is managed by close integration between RT system and FGPA (Field Programmable Gate Array) inside the controller. Two types of data transfers inside the RT controller are implemented, 1) Between FPGAs and RT controller, 2) Between internal algorithms. RT controller and FPGAs are interconnected through PXI bus. Critical functions, signal generations, monitoring & data acquisition and interfaces are assigned to FPGAs. All these processes are managed by Real Time Operating System (RTOS) installed in the controller. Most of the processes initiated by RT controller ends up performing certain task by invoking the algorithm inside FPGA directing some action to outer interfaces. Some of the process routines are implemented for managing the internal algorithms. This paper discusses different techniques used mostly for transfer of information between RT controller and FPGAs. Information includes critical signals, data, measurements, commands and configuration required for internal algorithms. Algorithms use various methods like DMA-FIFOs, local variables, arrays, Trigger lines to transfer information. RT-FIFOs are used to handle bulk data in runtime to improve performance. Methods have been chosen carefully to fulfill critical requirements, balancing the available resources while managing limitations. Discussion also includes some specific choices made for synchronized and asynchronous transmission of parallel and sequential data.

Pulse Step Modulation (PSM) based High Voltage Power Supplies (HVPSs) are widely used in fusion research and other applications viz. broadcast transmitters, particle accelerators and neutral beam injectors because of inherent advantages of modular structure, high accuracy and efficiency, low ripple and fast dynamics. Typical Ion Cyclotron Radio Frequency (IC RF) system composed of cascaded connection of Driver stage (130 kW RF output) and End stage (1500 kW RF Output) would need two power supplies. A novel concept of tapping two outputs from single PSM based HVPS is attempted for the first time. PSM based 3 MW HVPS is developed with dual output to feed anode voltage of Driver (up to 18 kV) and Final Stage (up to 27 kV). Controller for the HVPS is designed to suit requirements during local operation and remote operation. In Local operation mode, protection interlocks with in the HVPS are integrated while remote mode has additional interlocks from IC RF Amplifiers system. Field integration of the controller is achieved through fiber optical links to avoid Electro-Magnetic interferences. Present article discusses initial experience of dual output HVPS with IC RF amplifiers, pre-integration validation campaigns including qualification for energy limits. The paper also presents the performance of HVPS at full rated capacity of 2800 kW continuous duty to support 1.5 MW IC RF system.

A Dual output (27 kV & 15 kV), 3 MW Ion Cyclotron High Voltage Power Supply (IC-HVPS) has been installed and integrated with a Diacrode based RF source to be used for ICRF (Ion Cyclotron RF) system. The IC-HVPS Controller is based on LabVIEW Real-time PXI controller, which supports all control and monitoring operations of the PSM based power supply. The controller supports all essential features like, fast dynamics, low ripple and protection for source and loads. EPICS (Experimental Physics and Industrial Control Systems) is an open source software widely accepted in scientific community as supervisory distributed control system including CODAC (Control, Data Access and Communication) for ITER. However interface with LabVIEW RT systems is not fully mature yet. Evolving interface requirements of platforms like EPICS with IC-HVPS control has been assessed and implemented for monitoring purpose. A test case was implemented to identify compatibility, feasibility, consistency and performance of EPICS server with Input Output Controller (IOCs) implemented in Real-time controller. This paper discusses integration of EPICS IOCs and LabVIEW based Real-time Controller along with an analysis on limitations imposed by such integration.

Mega watt particle accelerators like Neutral Beam Injectors draw electrical power for Plasma formation, Ion Extraction at elevated potential of ~100kV, infact the water cooling lines, gas feed lines are also floating at 100kV. Usually power supplies, hydraulic/gas feed station of typical Injector are placed in a separate building/location. In such a scenario, large coaxial transmission lines are used to support power transport, hydraulic & gas feed lines, providing electrical isolation of 100kV. This paper presents electrostatic analysis for the complex configuration of large transmission line. Specially designed profiles to provide electrical isolation within permissible limits of electric stress. Further HVDC test results showing behaviour of Transmission line over longer exposure of 3600s are also presented.

Heating neutral beam (HNB) injectors, necessary to achieve burning conditions and to control plasma instabilities in ITER, are characterized by such demanding parameters that a neutral beam test facility (NBTF) dedicated to their development and optimization is being realized in Padua (Italy) with direct contributions from the Italian government (through Consorzio RFX as the host entity) and the ITER international organization (with kind contributions from the ITER domestic agencies of Europe, Japan and India) and technical and scientific support from various European laboratories and universities. The NBTF hosts two experiments: SPIDER, devoted to ion source optimization for the required source performance, and MITICA, the full-size prototype of the ITER HNB, with an ion source identical to SPIDER. This paper gives an overview of the progress towards NBTF realization, with particular emphasis on issues discovered during this phase of activity and on solutions adopted to minimize the impact on the schedule and maintain the goals of the facilities. The realization of MITICA is well advanced; operation is expected to start in 2023 due to the long procurement time of the in-vessel mechanical components. The beam source power supplies, operating at 1 MV, are in an advanced phase of realization; all high-voltage components have been installed and the complex insulation test phase began in 2018. At the same time, construction and installation of SPIDER plant systems was successfully completed with their integration into the facility. The mechanical components of the SPIDER ion source were installed inside the vessel and connected to the plants. Integrated commissioning with the control, protection and safety systems ended positively and the first experimental phase has begun. The first results of the SPIDER experiment, with data from operational diagnostics, and the plans for the 1 MV insulation tests on the MITICA high-voltage components are presented.

Controlled fusion is the huge energy source and able to cater the future electricity needs. To achieve controlled fusion, wide variety of power supplies are being used at experimental level, mainly categorized as converters for supplying superconducting magnets and converters for plasma heating and current drive (H&CD) systems. Power converters for supplying super conducting coils are generating very high dc current (in kA range) while high dc voltage (∼ 30–1000 kV) is required for heating and current drive systems. Present article describes stringent performance requirements demanded by H&CD system and reason for adopting Pulse Step Modulation (PSM) based or modular inverter based High Voltage Power Supply (HVPS). Article also discuss case study of PSM based HVPS along with associated challenges appearing at operation modes. A glimpse of few important behavior of H&CD load and possible solution also discussed at the end.

The realization of the ITER Neutral Beam Test Facility (NBTF) and the start the experimental phase are important tasks of the fusion roadmap, since the target requirements of injecting to the plasma a beam of Deuterium atoms with a power up to 16.5 MW, at 1MeV of energy and with a pulse length up to 3600s have never been reached together before. The ITER NBTF, called PRIMA (Padova Research on ITER Megavolt Accelerator), is hosted in Padova, Italy; it includes two experiments: MITICA, the full-scale prototype of the ITER injector and SPIDER, the full-size negative ion source. The realization promoted by the ITER organization is carried out with the contribution of the European Union, channeled through the Joint Undertaking for ITER (F4E), of the Consorzio RFX which hosts the Test Facility, the Japanese and the Indian ITER Domestic Agencies (JADA and INDA) and several European laboratories, such as IPP-Garching, KIT-Karlsruhe, CCFECulham, CEA-Cadarache. The early start of operation of PRIMA experiments is urgent because sufficient experimental time is necessary to face and solve the issues related to the achievement of the desired performance in time for the ITER operation, requiring NBI since the beginning. Substantial progresses have been recently achieved: the buildings construction, begun in October 2012, has been completed by the end of 2015 and the installation of some components has been started since the end of 2014. The SPIDER realization is well advanced: the installation phase is proceeding in good agreement with the general plan; it is expected to be almost completed by the end of 2016. In parallel, the commissioning of the SPIDER power supply (PS) and auxiliary plant systems is being proceeding. Tests at full power and remote control are planned, including also those addressed to reproduce the grid breakdowns and to test the relevant protections. The design of the MITICA injector components was completed in 2015their procurement is being made through a number of tenders, some of them already launched. The HV Power Supply system of the MITICA 1MV accelerator, provided by JADA, was delivered on site in December 2015. The challenging installation of these components, including the step-up transformers and the SF6 gas insulated transmission line, started soon after and will go on throughout 2016. The present phase, with the PRIMA buildings continuously filled with new components, with the installation activities progressing and with also the commissioning and testing phase starting represents a substantial step forward toward the main target. The paper will describe the main challenges the Project Team has dealt during this phase and the important feedback derived for the ITER HNB systems both from the technical and the organizational standpoints.

SPIDER is one of two projects of the ITER Neutral Beam Test Facility under construction in Padova, Italy, at the Consorzio RFX premises. It will have a 100 keV beam source with a full-size prototype of the radiofrequency ion source for the ITER neutral beam injector (NBI) and also, similar to the ITER diagnostic neutral beam, it is designed to operate with a pulse length of up to 3600 s, featuring an ITER-like magnetic filter field configuration (for high extraction of negative ions) and caesium oven (for high production of negative ions) layout as well as a wide set of diagnostics. These features will allow a reproduction of the ion source operation in ITER, which cannot be done in any other existing test facility. SPIDER realization is well advanced and the first operation is expected at the beginning of 2018, with the mission of achieving the ITER heating and diagnostic NBI ion source requirements and of improving its performance in terms of reliability and availability. This paper mainly focuses on the preparation of the first SPIDER operations - integration and testing of SPIDER components, completion and implementation of diagnostics and control and formulation of operation and research plan, based on a staged strategy

The ITER Neutral Beam Test Facility (NBTF), called PRIMA (Padova Research on ITER Megavolt Accelerator), is hosted in Padova, Italy and includes two experiments: MITICA, the full-scale prototype of the ITER heating neutral beam injector, and SPIDER, the full-size radio frequency negative-ions source. The NBTF realization and the exploitation of SPIDER and MITICA have been recognized as necessary to make the future operation of the ITER heating neutral beam injectors efficient and reliable, fundamental to the achievement of thermonuclear-relevant plasma parameters in ITER. This paper reports on design and R&D carried out to construct PRIMA, SPIDER and MITICA, and highlights the huge progress made in just a few years, from the signature of the agreement for the NBTF realization in 2011, up to now - when the buildings and relevant infrastructures have been completed, SPIDER is entering the integrated commissioning phase and the procurements of several MITICA components are at a well advanced stage

High voltage power supply (HVPS) based on pulse step modulation (PSM) topology has already demonstrated its ability for broadcast transmitters, accelerators using radio frequency (RF) source and neutral beam injectors. Typical ion cyclotron resonant heating (ICRH) system composed of cascaded connection of driver stage and end stage would need two power supplies. A novel concept of tapping two outputs from single PSM based HVPS is attempted for the first time. A PSM based HVPS is developed with dual output to feed driver and end stages of a high power RF amplifier. This article discusses the development of a HVPS, capable to provide 14–18 kV, 250 kW to driver stage and 16–27 kV, 175–105 A, 2800 kW to end stage RF amplifier chain. Here dual output are controlled independently by single FPGA based PXI controller which support all pros of PSM based HVPS like low ripple, fast dynamics and very short time to turn-off. Discussed HVPS supports non-linear demand from ICRH system i.e. lower current (105 A) at higher voltage (27 kV) and higher current (175 A) at lower voltage (18 kV), which developed as indoor compact solution. As an add-on specification, HVPS facilitates 1 kHz RF power modulation. The HVPS is composed of two cast resin multi-secondary transformers (CRT), 48 numbers of switched power supply (SPS) modules; FPGA/real time based controller and other auxiliaries including passive protection devices. Present article describes technical details of HVPS components which are manufactured to IEC standards. HVPS with dual output is an effective replacement to conventional solutions, as it offers optimized solution for equipment bulk as well as economy.

The Indian Test Facility (INTF) for Neutral Beams is designed with the objective to not only test the performance of an ion source but also to characterize the transmission of the Neutral Beam to a length of 20.66 m and thereby generate adequate database on the quality of the beam that is required for the CXRS diagnostics for measurement of Helium ash content in the fusion plasma.

High Frequency Power supply (HFPS) is used for various applications like AM Transmitters, metallurgical applications, Wireless Power Transfer, RF Ion Sources etc. The Ion Source for a Neutral beam Injector at ITER-India uses inductively coupled power source at High Frequency (~1 MHz). Switching converter based topology used to generate 1 MHz sinusoidal output is expected to have advantages on efficiency and reliability as compared to traditional RF Tetrode tubes based oscillators. In terms of Power Electronics, thermal and power coupling issues are major challenges at such a high frequency. A conceptual design for a 200 kW, 1 MHz power supply and a prototype design for a 600 W source been done. The prototype design is attempted with Class-E amplifier topology where a MOSFET is switched resonantly. The prototype uses two low power modules and a ferrite combiner to add the voltage and power at the output. Subsequently solution with Class-D H-Bridge configuration have been evaluated through simulation where module design is stable as switching device do not participate in resonance, further switching device voltage rating is substantially reduced. The rating of the modules is essentially driven by the maximum power handling capacity of the MOSFETs and ferrites in the combiner circuit. The output passive network including resonance tuned network and impedance matching network caters for soft switching and matches the load impedance to 50ohm respectively. This paper describes the conceptual design of a 200 kW high frequency power supply and experimental results of the prototype 600 W, 1 MHz source.