Towards the construction of a model to describe the inter-ELM evolution of the pedestal on MAST

TY - JOUR

T1 - Towards the construction of a model to describe the inter-ELM evolution of the pedestal on MAST

AU - Dickinson, D.

AU - Saarelma, S.

AU - Scannell, R.

AU - Kirk, A.

AU - Roach, C. M.

AU - Wilson, H. R.

PY - 2011/11

Y1 - 2011/11

N2 - Pedestal profiles that span the ELM cycle have been obtained and used to test the idea that the pedestal pressure gradient in MAST is limited by the onset of kinetic ballooning modes (KBMs). During the inter-ELM period of a regularly type I ELM-ing discharge on MAST, the pressure pedestal height and width increase together while the pressure gradient increases by only 15% during the ELM cycle. Stability analyses show that the pedestal region over which infinite-n ballooning modes are unstable also broadens during the ELM cycle. To test the relationship between the width of the region that is unstable to n = infinity ideal magnetohydrodynamic ballooning modes and KBMs the gyrokinetic code, GS2, has been used for microstability analysis of the edge plasma region in MAST. The gyrokinetic simulations find that KBM modes with twisting parity are the dominant microinstabilities in the steep pedestal region, with a transition to tearing parity modes in the shallower pressure gradient core region immediately inside the pedestal top. The region over which KBMs are unstable increases during the ELM cycle, and a good correlation is found between the region where KBMs dominate and the region that is unstable to infinite-n ideal ballooning modes.

AB - Pedestal profiles that span the ELM cycle have been obtained and used to test the idea that the pedestal pressure gradient in MAST is limited by the onset of kinetic ballooning modes (KBMs). During the inter-ELM period of a regularly type I ELM-ing discharge on MAST, the pressure pedestal height and width increase together while the pressure gradient increases by only 15% during the ELM cycle. Stability analyses show that the pedestal region over which infinite-n ballooning modes are unstable also broadens during the ELM cycle. To test the relationship between the width of the region that is unstable to n = infinity ideal magnetohydrodynamic ballooning modes and KBMs the gyrokinetic code, GS2, has been used for microstability analysis of the edge plasma region in MAST. The gyrokinetic simulations find that KBM modes with twisting parity are the dominant microinstabilities in the steep pedestal region, with a transition to tearing parity modes in the shallower pressure gradient core region immediately inside the pedestal top. The region over which KBMs are unstable increases during the ELM cycle, and a good correlation is found between the region where KBMs dominate and the region that is unstable to infinite-n ideal ballooning modes.

UR - http://www.scopus.com/inward/record.url?scp=80054947566&partnerID=8YFLogxK

U2 - 10.1088/0741-3335/53/11/115010

DO - 10.1088/0741-3335/53/11/115010

M3 - Article

SN - 0741-3335

VL - 53

SP - 1

EP - 14

JO - Plasma Physics and Controlled Fusion

JF - Plasma Physics and Controlled Fusion

IS - 11

M1 - 115010

ER -