MAST ST developments towards

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Culham-Ioffe Symposium, 30.11.04
MAST ST developments towards high-?,
steady-state tokamak operation
Anthony Field for the MAST team
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Culham-Ioffe Symposium, 30.11.04

• Introduction
• MAST
• Overview
• Results
• Component test facility (CTF)
• Overview
• Current drive
• Proposed MAST Upgrades
• Overview
• NBI systems for current profile control
• Summary

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Culham-Ioffe Symposium, 30.11.04
EU ST programme Based at UKAEA Culham and
focussed on the MAST Spherical Tokamak
MAST Spherical Tokamak

• Goals of MAST
• Advance tokamak physics for ITER
• Explore the long-term potential of the ST

• On-going design studies at Culham
• ST Power Plant (STPP)
• Component Test Facility (CTF)

• Proposed upgrades to MAST facility
• Test physics basis of CTF
• Adaptable heating, Paux 10 MW
• Pumped divertor
• PF system enhancements

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Culham-Ioffe Symposium, 30.11.04
Plasma cross-section and current comparable to
ASDEX-U and DIII-D Adaptable fuelling systems -
inboard outboard gas puffing plus multi-pellet
injector Digital plasma control implemented June
2003 (PCS supplied by GA)
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Culham-Ioffe Symposium, 30.11.04
New centre column
New divertor

• Towards longer pulses
• Longer centre column (more Vs)
• New divertor to handle power
• New error field correction system
• Relocated P2 with reversing switch

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Culham-Ioffe Symposium, 30.11.04
Error field correction coils installed outside
vessel
Locked modes avoided at low density
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Culham-Ioffe Symposium, 30.11.04

• ?N gt 5, (?N gt 5li) achieved by avoiding NTMs
• Ideal no-wall beta limit approached - no
  obvious MHD limit to performance
• Main limit due to initial NBI system
  capabilities

PNBI 2.8 MW fBS 40 - 50 Wfast 15 - 20
Matthew Hole, Richard Buttery et al
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Culham-Ioffe Symposium, 30.11.04

• MAST data points expand the range of e by a
  factor 2.2 and bT by 2.5
• Replaces data from devices with
  non-conventional cross-sections
• Supports existing IPB(y,2) scaling, strengthens
  e dependence

Interplay of e and b dependencies Assuming
confinement independent of b gives negative e
dependence
Matthew Hole, Richard Buttery et al
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Current densities
Magnetic shear and q

• Hollow current profile produced with NBI
  heating during current ramp
• Weak magnetic shear s improves confinement of
  core plasma

A R Field, R J Akers et al
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Kinetic profiles
Transport Analysis

• Sawtooth-free, hybrid-like plasmas have
  improved core transport
• Ion transport close to neo-classical over much
  of plasma radius

A R Field, R J Akers et al
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Culham-Ioffe Symposium, 30.11.04
CTF
MAST

• Toroidal rotation increases with applied torque
  from NBI (M? ? 1.2)
• Confinement increases with ?T and is highest
  with counter injection
• Approaches that required for CTF (HH 1.3) or
  STPP (1.6)

R J Akers et al
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Culham-Ioffe Symposium, 30.11.04

• Density peaks and temperature flattens with
  counter injection
• Particle balance dominated by NBI fuelling and
  Ware pinch (Deff?n 0)
• Small additional (lt10) pinch due to NBI
  torque ctr-in/co-out
• Ware pinch absent in steady-state (CTF) - Beam
  fuelling peak density

R J Akers et al
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Culham-Ioffe Symposium, 30.11.04

• Highest rotation achieved with counter-NBI, M?
  ? 1.2
• ExB flow shear far exceeds ITG growth rate with
  low magnetic shear
• Strong electron ITB indicates suppression of
  electron transport

A R Field, R J Akers et al
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Culham-Ioffe Symposium, 30.11.04

• MAST data supports using local, rather than
  flux-surface averaged
• values of B? in HFS pedestal width scalings,
  e.g. with banana width
• Subject of on-going NSTX/MAST/DIII-D joint
  identity experiment
• (aim to determine aspect ratio scaling at
  fixed pedestal r and n)

A R Field, R J Akers et al
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Culham-Ioffe Symposium, 30.11.04

• Two JET-type PINIs (2.5 MW, 75 keV) for
  high-power,
• long-pulse operation (5 MW, 5 s)
• Actively cooled calorimeters
• Residual ion dumps with hyper-vapotrons
• Operation SW April 05 (M5), SS late 05

Calorimeter
JET-type PINI for MAST
Residual Ion Dumps
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Culham-Ioffe Symposium, 30.11.04
Culham STPP
Howard Wilson, Garry Voss et al
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Culham-Ioffe Symposium, 30.11.04

• Neutron wall loading (3.5 MW m-2) determines
  the size R 3.4 m
• Cost of electricity limits toroidal field, Irod
  Ip
• MHD limits ?N 8.2
• High elongation required for 90
• pressure-driven current
• vertical instability
• ? ? 3.2 (fs 3.0)
• Required fusion power ( 3GW) ? Irod 30.2 MA
  (Ip 31 MA)
• Non-inductive current drive requires low
  density 1.1?1020 m-3
• (60 Greenwald)
• Confinement, ?E 1.6 ? IPB98(y,2) or 1.4 ?
  IPB98(y,1)

fBS ?Nh(?)Irod/Ip
Howard Wilson et al
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Culham-Ioffe Symposium, 30.11.04

• Ballooning modes 2nd stable solution exists
  with 90 pressure driven current
• High central safety factor
• Uniform magnetic shear across the plasma ?
  Hollow current profile
• BUT in an ST q(?) can remain monotonic
• Close fitting wall and high q(0) ensures n1, 2
  and 3 kink mode stable
• NTMs Stabilising Glasser term very strong,
  high q(0) avoids low order modes

Howard Wilson et al
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Culham-Ioffe Symposium, 30.11.04

• CTF is confinement, rather than stability
  limited as the STPP
• Requires 60 external current drive (fBS 40
  at modest ?N 3.5)
• Off-axis CD required to maintain hollow current
  profile for qa 5.2, q0 1.5)

Howard Wilson et al
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Culham-Ioffe Symposium, 30.11.04
R J Akers, M OBrien et al
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Culham-Ioffe Symposium, 30.11.04

• ?-particles well confined
• Full-orbit calculations required
• Orbits large near axis
• Pinched on outboard side
• lt 1 losses

Howard Wilson et al
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Culham-Ioffe Symposium, 30.11.04

• MAST ?N and ? close to CTF values
• Understanding ?? dependence
• important ??, MAST/?, CTF 90
• MAST data alone gives

M. Valovic et al
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Culham-Ioffe Symposium, 30.11.04

• Establish high-?, steady state physics basis for
  CTF (STPP)
• Control of current, flow and pressure profiles
  for optimised
• long-pulse performance
• Effective fuelling, exhaust and density control
  for
• steady-state operation
• Confinement scaling over extended parameter
  range,
• e.g. lower??
• Start-up without solenoid

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Culham-Ioffe Symposium, 30.11.04

• Heating upgrade (10 MW, long pulse)
• 3-4 ? JET PINIs for 7.5-10 MW, 5 s
• Off-axis NBCD capability
• EBW CD, 20 GHz, 2 MW
• New centre stack (higher Bt and Vs)
• Pre-chilled, cyanate ester resin
• Pumped divertor (density control)
• Closed configuration
• 2 ? 100,000 L/s cryo-pumps
• Modified poloidal field coils
• Vertical stability at high elongation
• Strike point control
• Improved diagnostics, e.g. turbulence, q(r)

Proposed Divertor Upgrade
Baffle
Additional PF coils
Cryo-pump
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• Investigating bold options for NBI current
  profile control
• Flexible system 3-4 PINIs, 7.5-10 MW (1
  counter- and 2 or 3 co-current)
• Off-axis NBDC optimised with 2 off-axis co- and
  2 on-axis co/counter PINIs

Double box 2? co-PINIs on- and off-axis
On-axis, counter-PINI
Jackable on/off-axis co-PINI
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• TRANSP current profile simulations with 3 PINI
  operation

Safety factor
q(r)
r/a
D L Keeling
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• Optimal 4-PINI configuration gives 1.05 MA
  NI-CD with q0 gt 1.5

Configuration off on ctr INI MA 1
2 2 - 1.2 2 1 2 1 0.8 3
2 1 1 1.05 4 1 3 -
1.0 Ip 1.2 MA, Bt 0.64 T q0 1.7, ? 2.5, ?
1.43 Ti,e (0) 3 keV ltTi,egt 1.35 keV
Beam driven current A
Time s
D L Keeling
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• Compact, intense neutron source (line-integral
  flux same as JET, JT-60U)
• Beam-target neutron distribution sensitive
  diagnostic of fast-ions
• Investigating possibilities for diagnostics,
  e.g. Stilbene detectors

R J Akers
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• MAST data contributes towards understanding of
  shape and
• aspect ratio dependence of high-b tokamak
  performance, e.g.
• Confinement and pedestal width scalings
• Transport barrier formation
• Role of plasma rotation
• Current and proposed upgrades to MAST facility
  will allow
• investigation of key issues for future
  tokamak devices, e.g.
• NBI current profile and shear flow control
• Scaling of confinement and transport
• Density control and power handling
• ST offers potential for a future steady-state
  burning plasma device,
• e.g. CTF or STPP