internal transport barrier investigations in mast
DESCRIPTION
ITPA CDBM: ITB and Transport, St Petersburg, 2003. Internal transport barrier investigations in MAST. Presented by Martin Valovic for:-. A R Field, C Challis, P G Carolan, N J Conway, G Cunningham, H Meyer, M J Walsh and the MAST team. EURATOM/UKAEA Fusion Association, Culham Science Centre - PowerPoint PPT PresentationTRANSCRIPT
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
Internal transport barrier investigations in MASTA R Field, C Challis, P G Carolan, N J Conway, G Cunningham, H Meyer, M J Walsh and the MAST team
• Introduction
• Discharge scenario
• Evidence for ITB
• Transport simulations
• Summary
Presented by Martin Valovic for:-
EURATOM/UKAEA Fusion Association, Culham Science CentreAbingdon, Oxon, OX14 3DB, UK
This work is funded jointly by the UK Department of Trade and Industry and EURATOM
ITPA CDBM: ITB and Transport, St Petersburg, 2003ITPA CDBM: ITB and Transport, St Petersburg, 2003
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
ITB Discharge ScenarioITB Discharge Scenario
Aim for weak/reversed magnetic shear and high toroidal flow shear:
• 4MA/s Ip ramp from initial 100 kA MC plasma
• Early NBI heating, 2 MW
• Low density, 1-21019 m-3
• Broad initial j(r) indicated by low Li ~ 0.6
• Significant NBI heating after 0.1 s due to poor initial fast ion confinement
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
Ti and V profiles, from CXR C6+, showing large thermal gradient at high velocity shear.
Electron and ion pressure profiles, showing steepgradients at position of high velocity shear.
ITB:- ITB:- TTii, , vvii (C(C6+6+) ) and and ppi,ei,e Profiles Profiles
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
Measured Measured TTii and Vand Vii profile evolution in ITB discharge profile evolution in ITB discharge
CXRS measurements of TTi i and Vand Vii on C on C6+6+ ions show s ions show steep Ti gradient coincides with high shear flow region.
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
TRANSP modelling indicates reversed magnetic shearTRANSP modelling indicates reversed magnetic shear
Inputs to TRANSP
• Te(r,t), ne(r,t) from Thomson scattering
• TC6+(r,t), VC6+(r,t) from CXRS of C 6+
• EFIT determined boundary shape
• Assumed Zeff profiles
Outputs
• Ti (r,t), Vi (r,t) of fuel ions (deuterium)
• neutron flux (compared with measurements)
• Vloop , li , etc.
• q(r,t) and j(r,t)
Some indications that ITB formation is associated with weak or reversed magnetic shear (e.g. in #7051, TRANSP suggests q 0 for extreme limits of Zeff ~ 1.5 to 3.0) but wider “causality” investigations and more detailed measurements are required; e.g. 200Hz TS and 200 chord Zeff now available)
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
Criterion for presence of ITBCriterion for presence of ITB
• Velocity shear rate exceeding the turbulent growth rate:-
• or, equivalently, (CEA criterion for presence of ITB):-
014.0/ ** ITBTsT L
linE 0
ITBITB
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
A simple 1D ad hoc time dependent code which uses:-
• Neo-classical thermal diffusivity:
• Momentum diffusivity smaller by 3/2:
gives:-
• Reasonable agreement with measured central C6+ temperature
and velocity (from CXRS)
• Close coupling of D+ and C6+ toroidal flow
2/3
22
68.0
iiinci
q
nci
nci 2/3
Preliminary Transport SimulationsPreliminary Transport Simulations
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
ConclusionsConclusions
• Initial attempts at ITB formation on MAST have been successful.
• Strongly sheared toroidal flow are accompanied by increases in pressure gradients.
• More experiments are underway (e.g. density scans, co- and counter-NBI) with improved diagnostics (e.g. 200 Hz TS and 200 chord Zeff).
• More in-depth tranport analyses are progressing (e.g. TRANSP).
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
q-profile TRANSP predictions: sensitivity to Zq-profile TRANSP predictions: sensitivity to Zeffeff
r/a
q
M Valovic. ITPA CDBM: ITB and Transport, St Petersburg, 2003
Preliminary Transport Simulations using an Preliminary Transport Simulations using an ad hocad hoc 1D code 1D code