H-1NF: The National Plasma Fusion Research Facility

1. 24 pulse 2kHz PWM switchgear rectifier + H-1 + + 800VDC 14,000A f 11kV 3 11kV :: 10 ea. 1MW 800V DC-DC convertor transformer SVC switched permanent power factor critical accuracy harmonic filter adjustment time window (11kV, 2.5MVAr) 1-4MVAr, 800V 1 second 2-4 2-4 Mostly 0-3 4-5, 7-8 3-8 4-5, 7-8 H-1NF: The National Plasma Fusion Research Facility B.D. Blackwell , D.G. Pretty, J.H. Harris, T.A.S.Kumar, D.R. Oliver, J. Howard, M.G. Shats, S.M. Collis,C.A. Michael and H. Punzmann Magnetic Fluctuations high temperature conditions: H, He, D; B ~ 0.5T; ne ~ 1e18; Te<50eV i,e<< a, mfp >> conn Configuration Studies The flexibility of the heliac configuration and the precision programmable power supplies provide an ideal environment for studies of magnetic configuration. The main parameter varied in this work is the helical core current ratio, kH which primarily varies the rotational transform iota. Magnetic well and shear also vary . Configuration Mapping: Electron Beam Wire Tomography A low energy (20eV, 100nA) electron beam traces out the magnetic geometry, and is intercepted by a rotating grid of 64 molybdenum wires, 0.15mm diameter. The data, similar to Xray CAT scan data can be inverted to obtain images of the electron transits, shown below in blue. The advantage of this technique is that the exact position of the electron transit can be determined to within <1mm, allowing the magnetic geometry of the H-1 heliac to be precisely checked. ECH plasma The figure shows an ECH produced plasma (200kW 28GHz gyrotron, 2CE at 0.5T). With a 10ms pulse, and rf preionization of ~11017m-3, a diamagnetic temperature of 100-200eV was observed provided gas feed was carefully controlled (p < 210-6 Torr). A highly localised ionization rate was observed in the emission from argon doping, and at higher gas fills, a peak density in excess of 31018 was obtained, with a lower temperature. Impurity levels, estimated by comparison of spectral line intensities, were lower than in the rf discharges. The H-1 heliac is a current-free stellarator with a helical magnetic axis which twists around the machine axis (a 1m circular ring conductor,) three times in one toroidal rotation. It is a “flexible” heliac composed almost entirely of circular coils with the exception of the helical control winding, which also wraps around the ring conductor, in phase with the magnetic axis of the plasma. Control of this current produces a range of rotational transform  from 1 to 1.5: (B0 =1T, r > 0.15-0.2 m), and 0.7 to 2.2 for B0 ~ 0.5 T, r> 0.1 m, allowing almost independent control of two of the three parameters: , magnetic well (–2% to +6%) and shear in rotational transform., which can be positive (stellarator-type) negative (tokamak-like), or near zero (<0.1). At 0.5 tesla, RF (20 ~150kW,  ~ cH) produces plasma in H:He and H:D mixtures at densities up to <ne> ~ 21018m-3, with temperatures initially limited to < 50eV by low-Z impurities. ECH ( = 2ce) produces considerably higher temperatures and centrally-peaked density profiles. • spectrum in excess of 100kHz • mode numbers not yet accurately resolved, but appear low: m ~ 1- 8, n > 0 • b/B ~ 2e-5 • both broad-band and coherent/harmonic nature • abrupt changes in spectrum for no apparent reason • some Alfvénic scaling with ne, iota Poloidal mode number measurements phase Expected for m =2 • Microwave Source: • (Kyoto-NIFS-ANU collab.) • 28 GHz gyrotron • 230 kW ~ 40ms Major/minor radius 1m/0.1-0.2m Vacuum chamber 33m2 good access Aspect ratio 5+ toroidal Magnetic Field 1 Tesla (0.2 DC) Heating Power 0.2MW 28 GHz ECH 0.3MW 6-25MHz ICH n3e18 T<200eV  0.2% Point by point comparison with computation magnitude RF configuration scans The density and time-evolution of RF produced plasma varies markedly with configuration as seen here, where kH is varied between 0 and 1. Below is the density at 50 ms for a similar range in kH. by Ding-fa Zhou Helical plasma (Argon) “bean-shaped” 20 coil Mirnov array Coil number 5 tonne support structure 14000Amp bus conductor and cooling • Phase vs poloidal angle is not simple • Magnetic coords • External to plasma • Propagation effects • Large amplitude variation Density (x1018m-3 ) “fish-eye” view of corrugated ECH waveguide to H-1 on left.(H.Punzmann) Time (seconds) 12MW Pulsed Magnet Power Supply DC-DC Convertor/Regulator: ABB Aust. /Technocon AG24 Pulse Rectifier: Cegelec AustraliaTransformers/Reactors: TMC AustraliaSwitchgear: Holec Australia and A-Force Switchboards, SydneyConsultant Engineers: Walshe & Associates, Sydney Points are matched one by one, allowing matching of rotational transform to better than 1 part in 104. Small deviations from the computation can by quantified in terms of small errors in construction ~1-2mm. Super computer modelling allows these errors to be tracked down. In this example, a better fit was obtained by more accurate modelling of the vertical field coil pair. mode numbers related to rationals Data Mining, Alfvénic Scaling: The figure to the left shows Fourier fluctuation data a), and b) after data mining by SVD analysis, grouping of SVDs by spectral content, and clustering the groups according to phase similarity. The cluster marked with the red lines in the lower figure exhibits scaling in rotational transform with the shear Alfvén eigenmode frequency (although a scale factor of 3 is unaccounted for). This is clarified by normalization to ne in c) and the cluster is enlarged below. Helical conductor control winding Photos: Tim Wetherell Pentagonal central support column Rotating 55 view Doppler tomography system Diamagnetic energy monitor Rotating 64 wire electron beam tomography system Sudden changes in density associated with resonance at zero shear