J.H. Kamperschroer

Measurements of tritium retention and removal on the Tokamak Fusion Test Reactor

Recent experiments on the Tokamak Fusion Test Reactor have afforded an opportunity to measure the retention of tritium in a graphite limiter that is subject to erosion, codeposition, and high neutron flux. The tritium was injected by both gas puff and neutral beams. The isotopic mix of hydrogenic recycling was measured spectroscopically and the tritium fraction T/(H+D+T) transiently increased to as high as 75%. Some tritium was pumped out during the experimental run and some removed in a subsequent campaign using various clean‐up techniques. While the short term retention of tritium was high, various conditioning techniques were successful in removing ≊8000 Ci and restoring the tritium inventory to a level well below the administrative limit.

The neutral beam heating system for the tokamak fusion test reactor

Abstract A neutral beam injection system will be the principal heat source for the plasma of the Tokamak Fusion Test Reactor. This system will use twelve positive ion sources (developed by Lawrence Berkeley Laboratory) on four beamlines (designed by Lawrence Livennore Laboratory) to deliver up to 27 MW of neutral power to the plasma as D0 at a maximum energy of 120 keV. The first two beamlines are becoming operational in 1984.

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.

Gas utilization in the Tokamak Fusion Test Reactor neutral beam injectors

Measurements of gas utilization were performed using hydrogen and deuterium beams in the Tokamak Fusion Test Reactor (TFTR) neutral beam test beamline to study the feasibility of operating tritium beams with existing ion sources under conditions of minimal tritium consumption. (i) It was found that the fraction of gas molecules introduced into the TFTR long‐pulse ion sources that are converted to extracted ions (i.e., the ion source gas efficiency) was higher than with previous short‐pulse sources. Gas efficiencies were studied over the range 33%–55%, and its effect on neutralization of the extracted ions was studied. At the high end of the gas efficiency range, the neutral fraction of the beam fell below that predicted from room‐temperature molecular gas flow (similar to observations at the Joint European Torus). (ii) Beam isotope change studies were performed. No extracted hydrogen ions were observed in the first deuterium beam following a working gas change from H2 to D2. There was no arc conditioning ...

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.

D-T gas injection system for TFTR neutral beams

The authors describe the design of the TFTR (Tokamak Fusion Test Reactor) NB (neutral beam) D-T Gas Injection System and the results of tests conducted to confirm its functionality. Detailed design is progressing for a NB TGIS (tritium gas injection system) which includes the option of injecting either H/sub 2/, D/sub 2/, or T/sub 2/ into each of the 12 neutralizers at ground potential based on limited experiments to date. Most commercial components have been ordered and fabrication of special hardware is underway. Additional tests are planned to confirm LPIS (long pulse ion sources) operations compatibility with neutralizer gas injection, to inject the gas through shorter tubes which would simplify installation and interactions in LPIS parameters with alternating gases between pulses from H/sub 2/ to D/sub 2/ /sup 3/He. Tests of piezoelectric valves operated with the plenum pressure feedback controller will be conducted and a prototype NB TGIS will be installed and tested on TFTR during the September 91 to May 92 operational period. Installation of the complete system will take place during the pre-tritium shutdown presently scheduled for 1992-3.<<ETX>>

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.

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.

Operations with tritium neutral beams on the tokamak fusion test reactor

Abstract In November of 1993 the tokamak fusion test reactor began operating with a deuterium-tritium fuel mixture instead of the pure deuterium which it had used heretofore. The major portion of this tritium has been supplied as energetic neutral particles injected by the neutral beams. After an initial run in which some ion sources used a mixture of 2% T and 98% D to test tokamak systems, full tritium beam operations commenced, with some of the ion sources run on pure tritium and some on deuterium to optimize the fuel mixture in the core plasma. Hundreds of tritium source shots have now occurred, with reliability which is better than that typical of deuterium operation. The maximum power injected with deuterium and tritium beams was 39.6 MW. D-T fusion power levels of up to 10.7 MW have been produced. Energy confinement in D-T plasmas of the “supershot” variety appears to be better than in similar deuterium plasmas.

TPX/TFTR neutral beam energy absorbers

The present beam energy absorbing surfaces on the TFTR neutral beams such as ion dumps, calorimeters, beam defining apertures, and scrapers, are simple water cooled copper plates which were designed to absorb (via their thermal inertia) the incident beam power for two seconds with a five minute cool down interval between pulses. These components are not capable of absorbing the anticipated beam power loading for 1000 second TPX pulses and will have to be replaced with an actively cooled design. While several actively cooled energy absorbing designs were considered, the hypervapotron elements currently being used on the JET beamlines were chosen due to their lower cooling water demands and reliable performance on JET. The authors summarize the size, location (relative to the source) and the peak power requirements of the various beam components.