K.E. Wright

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.

Experiments with high‐voltage insulators in the presence of tritium

During the final deuterium‐tritium phases of the TFTR and JET tokamaks half of the neutral injectors will be used to produce tritium neutral beams to maintain an equal mix of deuterium and tritium in the core plasma, and such requirements may also occur in future devices. This will require that the voltage hold off capabilities of the high voltage insulators in the accelerators be unimpaired by any charge buildups associated with the beta decay of adsorbed layers. We report tests in which we measured the drain currents under high dc voltage of TFTR and JET accelerator insulators while they were successively exposed to vacuum, deuterium and tritium. There did not appear to be any substantial reduction in hold‐off capability with tritium, although at some voltages there was a small increase in the leakage current. We also compared the breakdown properties of a plastic tubing filled with deuterium and then tritium at varying pressures, since such tubing has been considered as a high‐voltage break in the gas ...

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>>

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.

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.

Conceptual design of the neutral beamline for TPX long pulse operation

The Tokamak Physics Experiment (TPX) will require a minimum of 8.0 megawatts of Neutral Beam heating power to be injected into the plasma for pulse lengths up to one thousand (1000) seconds to meet the experimental objectives. The Neutral Beam Injection System (NBIS) for initial operation on TPX will consist of one neutral beamline (NBL) with three ion sources. Provisions will be made for a total of three NBLs. The NBIS will provide 5.5 MW of 120 keV D/sup 0/ and 2.5 MW of partial-energy D/sup 0/ at 60 keV and 40 keV. The system also provides for measuring the neutral beam power, limits excess cold gas from entering the torus, and provides independent power, control, and protection for each individual ion source and accelerating structure. The Neutral Beam/Torus Connecting Duct (NB/TCD) includes a vacuum valve, an electrical insulating break, alignment bellows, vacuum seals, internal energy absorbing protective elements, beam diagnostics and bakeout capability. The NBL support structure will support the NBL, which will weigh approximately 80 tons at the proper elevation and withstand a seismic event. The NBIS currently operational on the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory (PPPL) is restricted to injection pulse lengths of two (2) seconds by the limited capability of various energy absorbers. This paper describes the modifications and improvements which will be implemented for the TFTR Neutral Beamlines and the NB/TCD to satisfy the TPX requirements.

Operation of large ‘‘field‐free’’ ion sources in the presence of magnetic fields

Large area 10×40‐cm Lawrence Berkeley Laboratory ‘‘field‐free’’ ion sources were used during the first 2.5 yr of the neutral beam injection heating experiment on the tokamak fusion test reactor. Although these ion sources were located inside magnetic shielding structures, interference from tokamak magnetic fields prevented beam operation under certain conditions when using hydrogen. The fields causing this interference have been studied, and modifications which allow operation of such sources in these fields have been made.

Neutral beam heating system for TFTR

The first two neutral injection beamlines have been installed on TFTR and are now operational. The operation of six ion sources producing either hydrogen or deuterium beams at energies up to 80 kilovolts has produced notable plasma heating results. Eventual neutral beam capability on TFTR should provide the energy necessary to demonstrate breakeven.