T. Stevenson

The TFTR 40 MW neutral beam injection system and DT operations

Since December 1993, TFTR has performed DT experiments using tritium fuel provided mainly by neutral beam injection. Significant alpha particle populations and reactor-like conditions have been achieved at the plasma core, and fusion output power has risen to a record 10.7 MW using a record 40 MW NB heating. Tritium neutral beams have injected into over 480 DT plasmas and greater than 500 kCi have been processed through the neutral beam gas, cryo, and vacuum systems. Beam tritium injections, as well as tritium feedstock delivery and disposal, have now become part of routine operations. Shot reliability with tritium is about 90% and is comparable to deuterium shot reliability. This paper describes the neutral beam DT experience including the preparations, modifications, and operating techniques that led to this high level of success, as well as the critical differences in beam operations encountered during DT operations. Also, the neutral beam maintenance and repair history during DT operations, the corrective actions taken, and procedures developed for handling tritium contaminated components are discussed in the context of supporting a continuous DT program.

Operation of the TFTR neutral beam injection system which achieved greater than 30 megawatt injection

The Tokamak Fusion Test Reactor (TFTR) neutral beam injection system (NBIS) has performed injection experiments on the TFTR since 1984. During the 1988 run period, the NBIS exceeded the design capability of 27 MW of neutral injection. How the NBIS was operated to yield 30.5 MW of injected neutrals, the equipment upgrades and operational improvements from the 1987 operating experience which contributed to achieving this result, and the techniques used to achieve substantially increased system reliability over the 1987 run period are discussed.<<ETX>>

Long pulse neutral beam system for the Tokamak Physics Experiment

Abstract The Tokamak Physics Experiment (TPX) is planned as a long-pulse or steady-state machine to serve as a successor to the Tokamak Fusion Test Reactor (TFTR). The neutral beam component of the heating and current drive systems will be provided by a TFTR beamline modified to allow operation for pulse lengths of 1000 s. This paper presents a brief overview of the conceptual design which has been carried out to determine the changes to the beamline and power supply components that will be required to extend the pulse length from its present limitation of 1 s at full power. The modified system, like the present one, will be capable of injecting about 8 MW of power as neutral deuterium. The initial operation will be with a single beamline oriented co-directional to the plasma current, but the TPX system design is capable of accommodating an additional co-directional beamline and a counter-directional beamline.

TFTR neutral beam D-T gas injection system operational experiences of the first two years

The TFTR Neutral Beam Tritium Gas Injection System (TGIS) has successfully performed tritium operations since December 1993. TGIS operation has been reliable, with no leaks to the secondary containment to date. Notable operational problems include throughput leaks on fill, exit and piezoelectric valves. Repair of a TGIS requires replacement of the assembly, involving TFTR downtime and extensive purging, since the TGIS assembly is highly contaminated with residual tritium, and is located within secondary containment. Modifications to improve reliability and operating range include adjustable reverse bias voltage to the piezoelectric valves, timing and error calculation changes to tune the PLC and hardwired timing control, and exercising piezoelectric valves without actually pulsing gas prior to use after extended inactivity. A pressure sensor failure required the development of an open loop piezoelectric valve drive control scheme, using a simple voltage ramp to partially compensate for declining plenum pressure.

Neutral beam power system for TPX

The Tokamak Physics Experiment (TPX) will utilize to the maximum extent the existing Tokamak Fusion Test Reactor (TFTR) equipment and facilities. This is particularly true for the TFTR Neutral Beam (NB) system. Most of the NB hardware, plant facilities, auxiliary sub-systems, power systems, service infrastructure, and control systems can be used as is. The major changes in the NB hardware are driven by the new operating duty cycle. The TFTR Neutral Beam was designed for operation of the sources for 2 seconds every 150 seconds. The TPX requires operation for 1000 seconds every 4500 seconds. During the Conceptual Design Phase of TPX every component of the TFTR NB Electrical Power System was analyzed to verify whether the equipment can meet the new operational requirements with or without modifications. The Power System converts 13.8 kV prime power to controlled pulsed power required at the NB sources. The major equipment involved are circuit breakers, auto and rectifier transformers, surge suppression components, power tetrodes, HV Decks, and HVDC power transmission to sources. Thermal models were developed for the power transformers to simulate the new operational requirements. Heat runs were conducted for the power tetrodes to verify capability. Other components were analyzed to verify their thermal limitations. This paper describes the details of the evaluation and redesign of the electrical power system components to meet the TPX operational requirements.

Refurbishing tritium contaminated ion sources

Extended tritium experimentation on TFTR has necessitated refurbishing Neutral Beam Long Pulse Ion Sources (LPIS) which developed operational difficulties, both in the TFTR Test Cell and later, in the NE Source Refurbishment Shop. Shipping contaminated sources off-site for repair was not permissible from a transport and safety perspective. Therefore, the NE source repair facility was upgraded by relocating fixtures, tooling, test apparatus, and three-axis coordinate measuring equipment; purchasing and fabricating fume hoods; installing exhaust vents; and providing a controlled negative pressure environment in the source degreaser/decon area. Appropriate air flow monitors, pressure indicators, tritium detectors and safety alarms were also included. The effectiveness of various decontamination methods was explored while the activation was monitored. Procedures and methods were developed to permit complete disassembly and rebuild of an ion source while continuously exhausting the internal volume to the TFTR Stack to avoid concentrations of tritium from outgassing and minimize personnel exposure. This paper presents upgrades made to the LPIS repair facility, various repair tasks performed, and discusses the effectiveness of the decontamination processes utilized.

Facilities for quasi-axisymmetric stellarator research

The quasi-axisymmetric (QA) stellarator, a three-dimensional magnetic configuration with close connections to tokamaks, offers solutions for a steady-state, disruption-free fusion system. A new experimental facility, QUASAR, provides a rapid approach to the next step in QA development, an integrated experimental test of its physics properties, taking advantage of the designs, fabricated components, and detailed assembly plans developed for the NCSX project. A scenario is presented for constructing the QUASAR facility for physics research operations starting in 2019. A facility for the step beyond QUASAR, performance extension to high temperature, high pressure sustained plasmas is described. Operating in DD, such a facility would investigate the scale-up in size and pulse length from QUASAR, while a suitably equipped version operating in DT could address fusion nuclear missions, with operation starting in 2027.

NSTX-U Vacuum Vessel design modification

The NSTX-U requirements will double the Toroidal Field (TF), Plasma Current (Ip), Beam Injection Power, and extend pulse length. The larger centerstack requires re-aiming of the Multi Pulse Thomson Scattering (MPTS) lasers and Vacuum Vessel (VV) modifications at Bay L. The second neutral beam requirements include larger tangency radii and thus a VV modification at Bay K and Bay J. A cap design for a new weldment was developed to achieve these larger beam trajectories without losing the utility of the Bay J port for diagnostics. Analyses of loads indicated the need for reinforcements of the vessel at the midplane. NSTX has 6 picture frame type Resistive Wall Mode (RWM) coils around the exterior circumference of the vacuum vessel; each coil surrounds pairs of ports. The modifications needed for the upgrade were intended to minimize the impact to the RWM fields at the plasma. A Pro E global model segment was used to model the vacuum vessel. ANSYS was used to apply loads and investigate reinforcement configurations. A focused effort and analysis produced a design capable of achieving the desired performance of the upgrade while maintaining utility and continuity of RWM coil physics pre- and post-upgrade physics performance. The installation of the Bay J-K and Bay L Port Caps was completed and the reinforcing weldments have been partially installed.

TPX Neutral Beam injection system design

The existing Tokamak Fusion Test Reactor (TFTR) Neutral Beam system is proposed to be modified for long pulse operation on the Tokamak Physics Experiment (TPX). Day one operation of TPX will call for one TFTR beamline modified for 1000 second pulse lengths oriented co-directional to the plasma current. The system design will be capable of accommodating an additional co-directional and a single counter directional beamline. For the TPX conceptual design, every attempt was made to use existing Neutral Beam hardware, plant facilities, auxiliary systems, service infrastructure, and control systems. This paper describes the moderate modifications required to the power systems, the ion sources, and the beam impinged surfaces of the ion dumps, the calorimeters, the various beam scrapers, and the neutralizers. Also described are the minimal modifications required to the vacuum, cryogenic, and gas systems and major modification of replacing the beamline-torus duct in its entirety. Operational considerations for Neutral Beam subsystems over 1000 second pulse lengths will be explored including proposed operating scenarios for full steady state operation.

Expansion of the TFTR neutral beam computer system for D-T operations

The TFTR neutral beam computer system has expanded to provide an easy-to-use windowing and graphics environment for running the TFTR neutral beam injection system for D-T operations. Two SUN workstations are used for interactive analysis and display of neutral beam diagnostic and operational data. These systems are interfaced via Ethernet to another SUN computer which is used for data transfer and real-time analysis. The real-time analysis computer is linked to the TFTR Encore computer system via a DMA interface. Data acquisition and device control is performed on the Encore computers, and raw data is transferred via a memory-mapped approach to memory partitions and files on the SUN Analysis computer. Real-time analysis programs provide numerous displays to operators and engineers of operational data every 150 seconds. Physicists use X-window and OSF/MOTIF-based graphical user interfaces (GUIs) on the Diagnostic workstation to display interactive analysis of diagnostic data. These include X-window graphical displays of thermocouples, OMA, waterflow calorimetry, H-alpha duct and ion gauge data to the workstation. Neutral beam operations engineers also use a similar GUI to display interactive summary, power and ion source waveforms on the Operations workstation. In addition, these engineers have access to INGRES databases, which contain operational and analyzed data for the past several TFTR run periods. The Operations computer has a hard disk drive, which contains these INGRES databases and a database of restored analysis and raw data files. These files can be restored on demand from the TFTR computer system VAX cluster. The real-time Analysis computer also has a hard disk drive, which contains a database of the most recent analysis and raw data files.