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The Compass-D Project

The Compass device is now in Prague. The last experimental campaign at Culham ended before the commissioning of MAST. The following information was prepared when Compass-D was still fully operational.

Role

Collaborative exchanges and attachments are an important feature of the work on Compass-D, as in all the UK Fusion Programme, serving to broaden the range of skills and experience in our research activity.

The programme of experimental work on Compass-D is divided into related topic areas:

  • Control of instabilities: this is vital to tokamak development, as instabilities reduce the confinement properties of the plasma and/or create disruptive plasma behaviour.
  • Impurity control: low impurity levels and control of plasma exhaust are critical prerequisites for efficient tokamak operation.
  • "H-mode" (i.e. High energy confinement mode) operation: the characterisation and control of Edge Localised Modes (ELMs), which are a feature of H-mode operation, are important for power exhaust and impurity control optimisation.

Facilities

Compass-D is a highly flexible, medium-sized tokamak that has been specifically designed to address the key physics issues associated with magnetic confinement fusion.

The extensive facilities on Compass-D include:

  • Magnetic perturbation coils for correcting internal instabilities and for modifying the plasma edge region.
  • 2MW 60GHz microwave system for precise, localised heating and current drive, for bulk heating and instability control.
  • 1.3GHz Lower Hybrid system for bulk current drive and current profile control.
  • Flexible plasma shaping and control systems and special diagnostics.
  • Real-time electronic neural network for feedback control of the plasma equilibrium position and shape.
  • The same magnetic geometry as JET (Joint European Torus) and the planned Next Step device, ITER (International Tokamak Experimental Reactor).
  • Compact and flexible design, readily modified.

Technical Specification

Vacuum Vessel

Major radius (R)				0.557 m
Minor semi-axis, horizontal (a)			0.232 m
Minor semi-axis, vertical			0.385 m
Aspect ratio, R/a				2.53
Material					Inconel 625
Baking temperature				150 deg C

Magnetic Perturbation Coils

Helical mode numbers (m,n)			4,1 3,1 2,1 1,1
						4,2 3,2 2,2 1,2

Toroidal Field

Maximum toroidal field on axis			2.1 T
Rise time					approx 1 s
Flat top duration at max field			1 s
Decay time					approx 1 s
Number of field coils				16
Field ripple on axis				< 0.006%

Magnetising Field System

Plasma current					< 400 kA
Plasma duration (without current drive)		approx 600 ms
		(with RF current drive)		approx 2 s
Plasma rise time				< 80 ms
Flux swing:	rise				0.52 Vsec
		flat top			0.30 Vsec

Vertical Field System

Maximum field on axis				200 mT

Microwave Heating Systems

Electron Cyclotron Resonance			2 MW at 60 GHz
Lower Hybrid Wave				600 kW at 1.3 GHz

Toroidal Field Power Supply

24-phase thyristor convertor			40 MVA

Main Poloidal Field Power Supplies

Capacitor banks (various functions)		3.6 MJ total
12-phase thyristor convertors:
		Magnetising field		9.7 MVA
		Main vertical field		4.2 MVA
		Shaping field			5.4 MVA

Auxiliary Supplies for Fast Positional Feedback Coils and Resonant Magnetic Perturbation Coils

Transistor amplifiers				4 x 275 kVA
6-phase thyristor convertor			0.8 MVA
Fast 3-rail chopper				16 MVA

Fast Positional Feedback

Maximum radial and vertical field on axis	< 10 mT
Feedback response time				< 100 microsec