# Presentation: 213686

## MAST  ST developments towards

**high-********, steady-state tokamak operation**

**Anthony Field for the MAST team**

**Culham-Ioffe Symposium, 30.11.04**

## Culham-Ioffe Symposium, 30.11.04

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

**Culham-Ioffe Symposium, 30.11.04**

## Culham-Ioffe Symposium, 30.11.04

**EU ST programme**: Based at UKAEA Culham
- and focussed on the 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, *P**aux* ~ 10 MW
-   Pumped divertor
-   PF system enhancements

- MAST Spherical Tokamak

## 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)

## Culham-Ioffe Symposium, 30.11.04

**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

## Culham-Ioffe Symposium, 30.11.04

- Error field correction coils
- installed outside vessel

- Locked modes avoided at low density

## Culham-Ioffe Symposium, 30.11.04

-   N > 5, (N > 5*l**i*) 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

## Culham-Ioffe Symposium, 30.11.04

**Culham-Ioffe Symposium, 30.11.04**

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

- Matthew Hole, Richard Buttery et al

- Interplay of ** and ** dependencies:
-    Assuming confinement independent of **
-    gives *negative* ** dependence

##   Hollow current profile produced with NBI heating during current ramp

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

- Current densities

- Magnetic shear and q

- A R Field, R J Akers et al

##   Sawtooth-free, hybrid-like plasmas have improved core transport 

- 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

## Culham-Ioffe Symposium, 30.11.04

**Culham-Ioffe Symposium, 30.11.04**

- R J Akers et al

**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)

## Culham-Ioffe Symposium, 30.11.04

- R J Akers et al

-   Density peaks and temperature flattens with counter injection
-   Particle balance dominated by NBI fuelling and Ware pinch (Deffn ~ 0)
-   Small additional (<10%) pinch due to NBI torque: ctr-in/co-out
-   Ware pinch absent in steady-state (CTF) - Beam fuelling peak density

## 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

## Culham-Ioffe Symposium, 30.11.04

**Culham-Ioffe Symposium, 30.11.04**

- A R Field, R J Akers et al

-   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 * and *)

## Culham-Ioffe Symposium, 30.11.04

- Calorimeter

- Residual Ion Dumps

- JET-type PINI for MAST

-   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

## Culham-Ioffe Symposium, 30.11.04

- Howard Wilson, Garry Voss et al

- Culham STPP

## 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

## 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 n=1, 2 and 3 kink mode stable
-   NTMs: Stabilising Glasser term very strong, high q(0) avoids low order modes

- Howard Wilson et al

## Culham-Ioffe Symposium, 30.11.04

-   CTF is confinement, rather than stability limited as the STPP
-   Requires 60% external current drive (*f**BS* ~ 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

## Culham-Ioffe Symposium, 30.11.04

-  R J Akers, M O’Brien et al

## Culham-Ioffe Symposium, 30.11.04

- Howard Wilson et al

******-particles well confined: **
- Full-orbit calculations required
- Orbits large near axis
- ‘Pinched’ on outboard side
- < 1% losses

## 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

## 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

## 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**

- Additional PF coils

- Cryo-pump

- Baffle

##   Investigating bold options for NBI current profile control

- On-axis, counter-PINI

- Jackable on/off-axis co-PINI

- Double box: 2 co-PINIs
- on- and off-axis

-   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

##   TRANSP current profile simulations with 3 PINI operation

-   TRANSP current profile simulations with 3 PINI operation

- r/a

- q(r)

- Safety factor

- D L Keeling

##   Optimal 4-PINI configuration gives 1.05 MA NI-CD with q0 > 1.5 

-   Optimal 4-PINI configuration gives 1.05 MA NI-CD with q0 > 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
*I**p* = 1.2 MA, *B**t* = 0.64 T
*q**0* = 1.7,  = 2.5,  = 1.43
*T**i,e* (0) = 3 keV
- <*T**i,e*> = 1.35 keV

- Time [s]

- Beam driven current [A]

- D L Keeling

##   Compact, intense neutron source (line-integral flux same as JET, JT-60U)

-   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

##   MAST data contributes towards understanding of shape and

-   MAST data contributes towards understanding of shape and
-     aspect ratio dependence of high- 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