CCFE is the fusion research arm of the United Kingdom Atomic Energy Authority ITB formation and evolution with co- and counter NBI A. R. Field, R. J. Akers, M. De Bock, C. Michael, R. Scannell, M. Wisse and the MAST and NBI teams CCFE/EURATOM Association

Motivation  High resolution kinetic and q-profile diagnostics facilitate study of ITB formation and evolution  Strong driven toroidal rotation dominates ExB flow shear  Other factors known to be involved, e.g. magnetic shear  Comparison of co- and counter-NBI cases elucidates underlying physics, e.g. changing NBI power/torque ratio  Provides discharges in which flow shear effects dominate for comparison with simulations, e.g. with GYRO or GS2

Kinetic and q-profile measurements Kinetic profile diagnostics (CX & TS) with  R ~ 1 cm ~  i  NdYAG TS: 130 channels  R ~ 1 cm, 8 x 30 Hz lasers,  t ~ 4 ms  CXRS: 64 tangential channels (each beam),  R ~ 1 cm,  t ~ 5 ms MSE: q-profile evolution: 32 ch,  R ~ 2.5 cm,  t ~ 0.5 ms MSE polarisation angleT i (CXRS) and T e (TS)V i  (CXRS)

Integrated analysis (MC 3 )  Integrated analysis chain prepares TRANSP input data  Re-runs EFIT, including pressure and MSE constraints  Profile fitting, including rotation asymmetry  Z eff analysis from visible bremsstrahlung EFIT including MSE constraint TS fitting CX fitting Z eff

ITB Scenario  Early NBI heating at low-density during I p ramp favours reversed shear  Higher density with counter-NBI due to increased particle confinement  Absorbed power less than half with counter- compared to co-NBI but higher torque (prompt losses)  Similar stored energy and toroidal rotation with co- and counter-NBI  Later in discharge, confinement degraded by MHD activity Plasma current NBI power Stored energy Fast-ion energy Energy confinement time Toroidal rotation frequency Line-average density Central temperatures T i T e Co-NBICounter-NBI

Co-NBI: Profiles and transport coefficients  T i exceeds T e in plasma core r/a < 0.4, where  i ~  i NC  Foot of ITBs in ion and momentum channels near q min  ExB flow shear  SE peaks at foot of ITB

Co-NBI: ITB evolution  Negative magnetic shear maintained in plasma core  ITBs in ion and momentum channels form near q min  Momentum ITB forms at smaller radius than ion ITB  ITB terminated by MHD activity at 0.27 s 

Ctr-NBI: Profiles and transport coefficients  T i,e much lower than with co-NBI but rotation rate similar  T i ~ T e with  i ~  i NC over most of plasma radius  Much broader profile of  SE than with co-NBI

ITB evolution with ctr-NBI   Similar degree of shear reversal to co-NBI case  ITBs in ion and momentum channels broader than with co-NBI  Location of ITBs further outside q min surface than with co-NBI  Later in discharge MHD (n=2) weakens ITBs

Summary and conclusions Co-NBI:  ITBs in ion and momentum channels form in vicinity of q min  Momentum ITB forms at smaller radius than ion ITB  ExB shear peaks at location of ITB Counter-NBI:  ITBs in ion and momentum channels form outside q min  Broad ITBs with  i ~  i NC over most of plasma radius  Similar level of ExB flow shear in spite of lower absorbed power due to broad profile of prompt loss torque