H-1NF: The National Plasma Fusion Research Facility Helical plasma (Argon) Helical conductor control winding 5 tonne support structure Rotating 55 view Doppler tomography system Rotating 64 wire electron beam tomography system Diamagnetic energy monitor Pentagonal central support column 14000Amp bus conductor and cooling by Ding-fa Zhou Photos: Tim Wetherell 11kV 3  switchgear 11kV :: 800V transformer 24 pulse rectifier ea. 1MW DC-DC convertor SVC switched power factor adjustment 1-4MVAr, 800V + H-1 800VDC 14,000A permanent harmonic filter (11kV, 2.5MVAr) 2kHz PWM 1 second critical accuracy time window 12MW Pulsed Magnet Power Supply DC-DC Convertor/Regulator: ABB Aust. /Technocon AG 24 Pulse Rectifier: Cegelec Australia Transformers/Reactors: TMC Australia Switchgear: Holec Australia and A-Force Switchboards, Sydney Consultant Engineers: Walshe & Associates, Sydney “fish-eye” view of corrugated ECH waveguide to H-1 on left. (H.Punzmann) 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  m -3, a diamagnetic temperature of eV was observed provided gas feed was carefully controlled (p < 2  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  was obtained, with a lower temperature. Impurity levels, estimated by comparison of spectral line intensities, were lower than in the rf discharges. Microwave Source: (Kyoto-NIFS-ANU collab.)  28 GHz gyrotron u 230 kW ~ 40ms 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: (B 0 =1T,  r  > m), and 0.7 to 2.2 for B 0 ~ 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 ~ 2  m -3, with temperatures initially limited to < 50eV by low-Z impurities. ECH (  = 2  ce ) produces considerably higher temperatures and centrally-peaked density profiles. 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. Point by point comparison with computation Points are matched one by one, allowing matching of rotational transform to better than 1 part in 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. RF configuration scans The density and time-evolution of RF produced plasma varies markedly with configuration as seen here, where k H is varied between 0 and 1. Below is the density at 50 ms for a similar range in k H. 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, k H which primarily varies the rotational transform iota. Magnetic well and shear also vary. Time (seconds) Density (x10 18 m -3 ) Sudden changes in density associated with resonance at zero shear Magnetic Fluctuations high temperature conditions: H, He, D; B ~ 0.5T; ne ~ 1e18; Te<50eV  i,e > conn 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 n e, iota Coil number Poloidal mode number measurements Phase vs poloidal angle is not simple –Magnetic coords –External to plasma Propagation effects Large amplitude variation Expected for m =2 phase magnitude Major/minor radius1m/ m Vacuum chamber33m 2 good access Aspect ratio5+ toroidal Magnetic Field  1 Tesla (0.2 DC) Heating Power0.2MW 28 GHz ECH 0.3MW 6-25MHz ICH n3e18 T<200eV  0.2% mode numbers related to rationals 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 4-5, 7-8 Mostly , 7-8 “bean-shaped” 20 coil Mirnov array 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  n e in c) and the cluster is enlarged below.