R. Newman

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.

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 control and monitoring for DT operations

Record fusion power output has recently been obtained in TFTR with the injection of deuterium and tritium neutral beams. This significant achievement was due in part to the controls, software, and data processing capabilities added to the neutral beam system for DT operations. Chief among these improvements was the addition of SUN workstations and large dynamic data storage to the existing Central Instrumentation Control and Data Acquisition (CICADA) system. Essentially instantaneous lookback over the recent shot history has been provided for most beam waveforms and analysis results. Gas regulation controls allowing remote switchover between deuterium and tritium were also added. With these tools, comparison of the waveforms and data of deuterium and tritium for four test conditioning pulses quickly produced reliable tritium setpoints. Thereafter, all beam conditioning was performed with deuterium, thus saving the tritium supply for the important DT injection shots. The lookback capability also led to modifications of the gas system to improve reliability and to control ceramic valve leakage by backbiasing. Other features added to improve the reliability and availability of DT neutral beam operations included master beamline controls and displays, a beamline thermocouple interlock system, a peak thermocouple display, automatic gas inventory and cryo panel gas load monitoring, beam notching controls, a display of beam/plasma interlocks, and a feedback system to control beam power based on plasma conditions.

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.

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.

Operation of TFTR neutral beams and heavy ions

Moderate atomic number neutral atoms have been injected into TFTR (Tokamak Fusion Test Reactor) plasma in an attempt to enhance plasma confinement through modification of the edge electric field. TFTR ion sources have extracted 9 A of 62-keV Ne/sup +/ for up to 0.2 s during injection into deuterium plasmas, and for 0.5 s during conditioning pulses. Approximately 400 kW of Ne/sup 0/ have been injected from each of two ion sources. Operation under these conditions was at full bending magnet current, with the Ne/sup +/ just contained on the ion dump. Modifications to permit operation up to 120 keV with krypton and/or xenon are described. Such ions are too massive to be deflected up to the ion dump with the beamlines as designed. The plan is to procure a 3600-A power supply and pulse it into the magnet for initial Kr/Xe experiments. Information relevant to heavy ion operation was acquired during the course of ion source operation with small water leaks. Spectroscopic analysis of certain pathological pulses indicates that up to 6% of the extracted ions were water. After dissociation in the neutralizer, water produces oxygen ions which, as with Ne/sup +/, Kr/sup +/, and Xe/sup +/, are underdeflected by the magnet. Damage to a calorimeter scraper, due to the focal properties of the magnet, resulted. A power density of 6 kW/cm/sup 2/ for 2 s, from approximately 90 kW of O/sup +/, is the probable cause.<<ETX>>

The 33 MW TFTR neutral beams

The TFTR (Tokamak Fusion Test Reactor) neutral beam injection system (NBIS) has performed injection experiments on TFTR since 1984. During the 1990 run period the NBIS exceeded previous levels, reaching a record 48 MJ (24 MW for 2 s) of neutral injected energy and, at a later date, a record neutral power of 33 MW, which produced a record plasma neutron source rate. The operation of the NBIS resulting in this performance, the equipment changes and operational improvements from the 1989 operating experience which contributed to achieving this result, and the techniques used to analyze the effects of these changes are discussed.<<ETX>>