1. The H-1NF Heliac and Engineering Subsystems Tolerance Band DC-DC Convertor PWM inherently voltage source -V out =  Vin Tolerance band –fast responding current source-high performance even in open loop, also removes 1 pole from FB loop –inherently variable frequencyconflicts with desire for phase interleaving in multiphase systems –inherent GTO protection (I<3kA) Upper limit Lower limit GTO Current Feedback Control Constant-power power converter  negative resistance I in =P/V in   I/  V ~ -1/V 2  input LC instability (45Hz) Output filter capacitor and magnet  second resonance (20Hz) 400ms time constant Feedback control is like PID, but voltage  derivative (proportional/integral/derivative) Implementation with real time 68000  P, 600  s per cycle programmed in “Hawk” C Mean value filters for quick response (top hat) 12MW Pulsed Power Supply for the H-1NF Magnet 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 Specifications H-1 was the first large scale “heliac”, a particular type of helical axis stellarator which was conceived in 1969 in mathematical form as a plasma configuration with strong inherent magnetic well for stability at high plasma pressure. A realizable form was invented at Princeton in 1982, and the first experimental device, “SHEILA” was built and operated at the ANU in 1985. The helical axis, strong plasma twist, “bean shaped” plasma and simple circular coils are features of this configuration. H-1 was constructed entirely (apart from the vacuum shell) by the Plasma Research Laboratory and RSPhysSE workshop staff, to extremely high accuracy (~1mm), in spite of the complicated interlinking shape and the large forces on the conductors (~ 5 Tonnes per coil). H-1 employs one small helical winding, which greatly increases the range of plasma shapes (“flexible heliac”). Other heliacs have been built in Japan and Spain, and a next generation machine, a large superconducting “helias” is under construction in Germany, which although quite different, has the familiar bean shape in some cross sections. 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 H-1 is controlled by a PLC system (Programmable Logic Controller). Each of 4 PLCs is a small, real-time computer executing 20-40 complete monitoring cycles every second. H-1 Control System Main Control Screen (Overview) Subsystems are summarised in each box, red and green indicating faults and normal operation. Each sub system has a deatiled screen such as that below. Cooling Sub system The magnetic field coils dissipate up to 12MW of power, which must be removed as heat. The high purity H-1 cooling water transfers this heat through a heat exchanger to an evaporative cooling tower. Each coil’s temperature is monitored closely (lower left) RF Heating Systems Microwave Source: (Kyoto-NIFS-ANU collab.) u 28 GHz gyrotron u 230 kW ~ 40ms H-1 may be heated at both the electron cyclotron resonance (ECH) (microwave ~28GHz)and lower radio frequencies near the ion cyclotron resonance(6-26MHz, helicon and ICH). Several hundred kW are available. Ion Range RF source (ex Radio Australia) 6-26 MHz, 250 kW Refurbished by British Aerospace New coax from NIFS Use for helicon, ICRF heating 6x30kW AWA transmitters for plasma production, and phased excitation “fish-eye” view of corrugated waveguide to H-1 on left. (H.Punzmann) by Ding-fa Zhou Photos: Tim Wetherill