Positive Ion Neutral Injectors Research Articles

3D computational fluid dynamics analysis of PINI ion source back plate under high heat flux condition

Neutral Beam Injection (NBI) plays an essential role in Tokamak plasma heating and current drive. A positive ion-based NBI (PNBI) system is adopted in Steady State Superconducting Tokamak- 1 (SST-1). This PNBI system is capable of generating neutral hydrogen beam power of 1.7 MW at 55 keV. This system has a JET PINI (Positive Ion Neutral Injector) type of ion source. The Back Plate (BP) is a component of the PINI ion source. It consists of an SS 304 L magnet positioning & cover plate, and an OFE copper cooling plate. The back plate plays a vital role in removing the high heat load intercepted during beam operation. The present study describes 3D Computational Fluid Dynamics (CFD) analysis of the actual size back plate using the ANSYS version of R121. The 3D CFD analysis has been done under a 2.5 MW/m2 steady heat load incident on the OFE copper plate. Cooling water is provided in the Inlet header of the back plate with a mass flow rate of 1 kg/s at 34 °C. The analysis gives the surface temperature distribution over the OFE copper cooling plate with a maximum surface temperature of 174 °C and the average temperature is 122 °C. This result is in good agreement with High Heat Flux experimental results.

Integration of cryopump instrumentation for SST-1 NBI

A positive ion neutral injector (PINI) capable in delivering 5MW (55kV, 90A) ion beam power is being operated for SST-1 neutral beam injection (NBI). The production and neutralization of the ion beams in the injector require a gas throughput of 20 torr I/s in the plasma box and 50–100 torr I/s in the neutralizer section. It is necessary to maintain operating pressure of vessel at 10−5 torr to reduce the re-ionization loss of beam within tolerable limits. Conventional Turbo molecular pumps cannot maintain this vacuum level at required gas feed rate so two cryo condensation pumps are being operated to achieve require vacuum in vessel. In order to monitor and optimize the performance of cryopumps, it is necessary to measure the temperature at various locations in LN2 and LHe path. It is also required to monitor the level of LHe and LN2 in cryopumps. Several temperature and level sensors are mounted at various places in cryopumps and integrated with PLC and SCADA based control system.

Performance of upgraded JET neutral beam injectors

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 ∼2 MW 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 34 MW of total deuterium neutral beam power into the JET plasma will be achieved.

Overview of the JET neutral beam enhancement project

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 36 kV 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 34 MW of deuterium beam power into the JET plasma for a duration of up to 20 s with improved reliability. This will significantly enhance overall capabilities of the JET machine in support of ITER development.

Commissioning and operation of 130 kV/130 A switched-mode HV power supplies with the upgraded JET neutral beam injectors

The design features, on-site testing, commissioning and operation are described of two new 130 kV/130 A HV power supply units serving four upgraded 130 kV/60 A positive ion neutral injectors (PINIs) on JET. Both units were factory tested at full power and pulse length into dummy resistive load. Following on-site installation, the factory tests were repeated. The transition from dummy-load testing to PINI operation required full integration of the HVPS within the overall JET control system, and rigorous testing of the co-ordinated actions and protections of all PINI power supplies (filament and arc for plasma source and negative suppression grid). The implementation of these functions is described. Extensive use was made of parasitic integrated test pulses, where the other PINIs could be operated normally, with the HVPS energised under full remote control together with the corresponding PINI plasma sources, but with the HVPS connected to dummy load. The amount of NB operation time dedicated to commissioning was thereby minimised, yet gave a high degree of confidence of readiness for HV energisation of the PINI, and first beam operation followed less than 24 h from HV connection to the PINI. The routine operating experience and performance, including load protection characteristics of the new HVPS units are also described.

A review of JET neutral beam system performance 1994–2003

Abstract The operational performance of the JET neutral beam injector (NBI) system during 2003 is presented and compared with NBI operation from 1994 to 2002. The paper also addresses different demands imposed on NBI operation during the JET Joint Undertaking (until the end of 1999) and the European Fusion Development Agreement (EFDA) JET operating contract (from 2000). The material presented shows new operational performance records achieved in 2003, derived from data focused on average and maximum pulse lengths, pulse power and injected pulse energy. Over the last 10 years, the issue of JET NBI positive ion neutral injector (PINI) reliability and availability has also been of significant interest. A discussion is presented where terminology is defined, technical systems causing unreliability and non-availability are analysed and operational practices are reviewed. The performance analysis shows that during the period of JET operation under the EFDA contract, the NBI facility has successfully changed from high power-short pulse to high power-long pulse (10 s) operation. It also shows that the sources of unreliability and non-availability have largely remained constant during this change.

Neutral Beam Injection in the JET Trace Tritium Experiment

Operation of the JET Neutral Beam Injectors with tritium is described. Supplying the tritium feed via the special electrically grounded gas feed compromised the performance of the up-graded high current triode Positive Ion Neutral Injectors (PINI) due to gas starvation of the source and the methods adopted to ameliorate this effect are described. A total of 362 PINI beam pulses were requested, circulating a total of 4.73g tritium, of which 9.3mg was injected into the torus. Safety considerations required a continuous, cumulative total to be maintained of the mass of tritium adsorbed onto the cryo-pumping panel; a daily limit of 0.5g was adopted for the Trace Tritium Experiment (TTE). A subsequent clean up phase using 115keV deuterium beams completed the isotopic exchange of components in the beamline.

MAST neutral beam long pulse upgrade

Abstract Until summer 2003 two Neutral Beam Injectors (NBI), each equipped with one duopigatron ion source on loan from Oak Ridge National Laboratory (ORNL), were delivering up to 3 MW of deuterium neutral beam power into the Mega Amp Spherical Tokamak (MAST) plasma for a duration of up to 300 ms. The two ORNL injectors are now being replaced with JET type Positive Ion Neutral Injectors (PINIs). The MAST PINI design is a modification of the JET high current tetrode injector, with nominal deuterium beam voltage and current of 75 kV and 65 A, respectively. Each injector will deliver up to 2.5 MW of deuterium neutral beam power (in excess of 1 MW in hydrogen) for pulse lengths of up to 5 s. In addition to the replacement of the two injectors, many other components of the MAST NBI system are being replaced or modified. The various design issues of the upgraded MAST NBI system are addressed.

130 kV 130 A High voltage switching mode power supply for neutral beam plasma heating: design issues

The company JEMA has designed and manufactured two High Voltage Switching Mode Power Supplies (HVSMPS), rated at 130 kV dc and 130 A, each of which will feed the accelerator grids of two Positive Ion Neutral Injector (PINI) loads, to be installed at the Joint European Torus (EFDA-JET facility located at Culham, UK). The solution designed by JEMA includes two matching transformers which adapt the 36 kV of the JET AC power distribution network to the required 670 V at the secondary side. Additionally, such transformers provide a 30° phase shift which is required by a 30 000 A 12 pulse thyristor rectifier. The obtained and stabilised 650 V feed 120 IGBT invertors, which operate at 2778 Hz with modulated square waveform. Each invertor feeds a High Insulation High Frequency Transformer. The 120 transformers corresponding to one power supply are arranged in three oil filled tanks and provide the main insulation from the low voltage to the high voltage side. The square waveform obtained at the secondary of each transformer is rectified by means of a diode bridge. The connection in series of the 120 diode bridges provides the required 130 kV d.c. at the output. In order to protect the load, a redundant solid state crowbar has been designed. Such short circuiting device is composed of 26 Light Triggered Thyristors (LTTs), connected in series. Electrical simulations have been carried out in order to ensure that the system complies with the requirements of high accuracy and adequate protection of the load. The critical design of the High Voltage-High Frequency Transformers has also required electrostatic simulations of the electric field distribution

Effect of accelerating electrode rotation on ion beam optics

The effect of a rotation of the electrode used to accelerate a positive ion beam is treated analytically for the Joint European Torus (JET) Positive Ion Neutral Injector (PINI) tetrode accelerator. The rotation is taken to be about an axis in the plane of the electrode and perpendicular to the beam axis, so the effect is that of a tilt in the alignment of the affected electrode. The effect of such a tilt in either of the two multiaperture accelerating electrodes is to introduce an additional steering of the beam, the magnitude of which depends upon the ratio of the potentials across the first and second accelerating gaps and the position of the beamlet with respect to the tilt axis. The direction of the steering is dependent upon which electrode is displaced. Steering angles of the order 10 mrad can be generated by this effect, which is significant compared to the alignment precision required from high power neutral injectors such as those on JET. The presence of a grid rotation also affects the total perveance of a multiaperture system and this can be used to obtain information on the position of the tilt axis. Typical values are calculated for the JET PINI geometry and compared to observation.