Annual report 2000
This year the H-1NF was operated for 103 days over 29 weeks, recording data for 4,600 shots. Of this, approximately 3,100 shots over 67 days of operation were plasma physics shots, the balance being power supply and machine test shots. The new high-precision 12 Megawatt magnet dual power supply was successfully tested into a dummy load to full voltage (900 Volts) and full current (14,000 Amps) individually. The power supply will ultimately increase the magnetic field of the H-1NF device from its original operating value of 0.2T to its design value of 1T.
An interactive but secure control interface was implemented to allow operators to exploit the great flexibility of the programmable power supplies. This allows a range of control by operators with different levels of authorisation, so that the facility can be used safely by a variety of operators. Tests have demonstrated programmable constant or ramping current into H-1NF up to 8,500A, with variations of a small fraction of one ampére. This ensures highly accurate magnetic geometry, avoids interference with measurement systems, and minimises induction of current into this inherently current-free plasma configuration.
Reliability of the motor-generator, an alternative low power source for the magnet system, was enhanced by installation of new switchgear and controls. A secondary supply powers the control windings and allows the plasma shape to be varied, under computer control, over a much wider range than possible in conventional stellarators or tokamaks, with the option of varying the current during a plasma pulse. The connections between these supplies and the five windings of the heliac are made in a very flexible and convenient manner through a `patch panel´. This system is capable of carrying 14,000A for two seconds, and crucial configuration information including total winding inductance, mutual inductance and resistance is passed on to the power supply controller via computer. This enables full exploitation of the wide range of magnetic characteristics accessible to the H-1NF. This ambitious and unique project, combining a power plant similar to that powering a very fast train, with the precision and flexibility of a laboratory instrument, was a product of collaboration between H-1NF staff and a number of Australian and International companies. These include: Walsh & Associates, Consulting Engineers - Sydney, ABB- Melbourne, Technocon AG - Switzerland; TMC Ltd - Melbourne (transformer); CEGELEC - Sydney (AC-DC converter); A-Force Switchboards - Sydney (14kA patch panel) and HOLEC Engineering of Sydney (switchgear).
Plasma operation up to 0.5 Tesla was achieved this year, enabling the first phase of high temperature plasma operation in which the plasma is heated at the second harmonic of the electron cyclotron resonance frequency. Work on the 28GHz, 200kW electron cyclotron heating system continued, as part of the collaboration with Kyoto University and the Japanese National Institute for Fusion Science (NIFS), with testing and enhancing the power electronics, and installing the waveguide and the launching system and associated vacuum window. Work on the ion cyclotron range heating system included installation of DC isolation components, and cabling with high power coaxial cable to the launching port. The electron heating system is now ready for first high-temperature plasma experiments.
A number of the sixteen additional vacuum ports installed last year have been put to use, some for facility collaborators, and others for enhanced diagnostic systems. Development this year included the plasma density tomography system, the optical vector tomography system, the electron cyclotron heating system and the gas injection systems. Experiments for facility users can be quickly connected, without vacuum interruption, via the new gate valves if required. In late 1999 a soft X-ray camera has been installed in collaboration with the University of Canberra, and the University of New England fibre optic interferometer for heat flux and deposition measurements has already been used in several experiments. The modifications to the vessel featured the welding of several large vacuum ports (up to 600mm) by Cowan Engineering of Newcastle, NSW provided excellent vacuum performance. The cryopump, which allows rapid pumpdown after a vacuum break, was remounted, and will be commissioned later in 2000.
As a result of infrastructure upgrades the Facility now has a degree of redundancy in power, heating and vacuum systems. This has allowed a higher level of availability this year, and remaining upgrades to heating and launching systems and bringing the machine up to full magnetic field, that is one Tesla, will result in only minor interruptions to operation over the next two years. A number of new plasma measurement systems have been installed or commissioned.
The Modulated Optical Solid State (MOSS) camera has been operating routinely since early 2000 and has produced a wealth of new information pertaining to the H-1 plasma dynamics. After some early difficulties, the tomographic MOSS (ToMOSS) spectroscopy system is now fully installed and will be commissioned in September 2000. A new multi-channel spectroscopy system for measurement of electron temperature and plasma fluctuations is also operational while a general survey spectrometer completes the spectroscopic diagnostic suite. The far-infrared scanning interferometer has been extensively upgraded this year. The 2mm sweep-frequency interferometer (a standard diagnostic) has been relocated to allow toroidal cross-correlation with the FIR system measurements. A ruby-laser-based Thomson scattering system for electron temperature measurements is also nearing completion. Dr Peter Feng joined the group for laser-induced fluorescence measurements of electric fields in the H-1 plasma edge. His appointment is supported by a Large ARC grant held jointly with the University of Sydney.