TY - JOUR
T1 - Performance and control of optimized shear discharges in JET
AU - Bécoulet, A.
AU - Eriksson, L.-G.
AU - Baranov, Y.F.
AU - Borba, D.N.
AU - Challis, C.D.
AU - Conway, G.D.
AU - Fuchs, V.
AU - Gormezano, C.
AU - Gowers, C.W.
AU - Hawkes, N.C.
AU - Hender, T.C.
AU - Huysmans, G.T.A.
AU - Joffrin, E.
AU - Litaudon, X.
AU - Lomas, P.J.
AU - Maas, A.
AU - Mayoral, M.L.
AU - Parail, V.V.
AU - Rimini, F.G.
AU - Rochard, F.
AU - Sarazin, Y.
AU - Sips, A.C.C.
AU - Söldner, F. X.
AU - Zastrow, K.-D.
AU - Zwingman, W.P.
PY - 2000/6/1
Y1 - 2000/6/1
N2 - High performance discharges are routinely obtained on JET with low or
reversed magnetic shear (s = (r/q)dq/dr), and the potential for steady
state operation of such discharges is under investigation. With the use
of the proper heating and fuelling, these `optimized shear' (OS)
discharges exhibit an internal transport barrier (ITB), resulting in a
strong peaking of the pressure profile, and thus in high fusion
performance. These regimes have been extensively studied during the last
(DD and DT) JET campaigns in order to promote this type of scenario as
the basis for `advanced tokamak' operation. A review is given of the
highest performance achieved on JET OS discharges during the last
experimental campaigns, in both DD (up to 5.6 ×
1016neutrons/s) and DT operation (fusion power up to 8.2 MW,
ni0Ti0τE up to 1021
m-3 keV s). The role of the plasma edge is pointed out, as
the power required to trigger an ITB is often higher than the H mode
power threshold, leading to double barrier regimes. The presence of an H
mode pedestal both modifies the ITB and induces edge bootstrap and ELM
activity, which should be controlled to prolong such discharges. The
operational procedure of optimization is then discussed, addressing the
problems of ITB formation (power threshold, timing of the main heating
phase, i.e. optimization of the target q profile, influence of the
heating scheme, electron versus ion ITBs), ITB evolution (expansion of
the ITB footpoint, H mode formation) and ITB termination (disruptive
and/or `soft' MHD limits). Finally, the crucial problem of the route to
steady state for such OS discharges is addressed, both in terms of ITB
sustainment and control within the stability domain and in terms of edge
pedestal control by means of impurity injection. The impurity behaviour
is found, and examples of high performance discharges sustained for
several energy confinement times are given (βN = 1.95,
H89 = 2.3, Pfusioneq~10 MW,
QDTeq~0.4 sustained for ~3 s). Extrapolation
towards fully non-inductive current drive is discussed.
AB - High performance discharges are routinely obtained on JET with low or
reversed magnetic shear (s = (r/q)dq/dr), and the potential for steady
state operation of such discharges is under investigation. With the use
of the proper heating and fuelling, these `optimized shear' (OS)
discharges exhibit an internal transport barrier (ITB), resulting in a
strong peaking of the pressure profile, and thus in high fusion
performance. These regimes have been extensively studied during the last
(DD and DT) JET campaigns in order to promote this type of scenario as
the basis for `advanced tokamak' operation. A review is given of the
highest performance achieved on JET OS discharges during the last
experimental campaigns, in both DD (up to 5.6 ×
1016neutrons/s) and DT operation (fusion power up to 8.2 MW,
ni0Ti0τE up to 1021
m-3 keV s). The role of the plasma edge is pointed out, as
the power required to trigger an ITB is often higher than the H mode
power threshold, leading to double barrier regimes. The presence of an H
mode pedestal both modifies the ITB and induces edge bootstrap and ELM
activity, which should be controlled to prolong such discharges. The
operational procedure of optimization is then discussed, addressing the
problems of ITB formation (power threshold, timing of the main heating
phase, i.e. optimization of the target q profile, influence of the
heating scheme, electron versus ion ITBs), ITB evolution (expansion of
the ITB footpoint, H mode formation) and ITB termination (disruptive
and/or `soft' MHD limits). Finally, the crucial problem of the route to
steady state for such OS discharges is addressed, both in terms of ITB
sustainment and control within the stability domain and in terms of edge
pedestal control by means of impurity injection. The impurity behaviour
is found, and examples of high performance discharges sustained for
several energy confinement times are given (βN = 1.95,
H89 = 2.3, Pfusioneq~10 MW,
QDTeq~0.4 sustained for ~3 s). Extrapolation
towards fully non-inductive current drive is discussed.
U2 - 10.1088/0029-5515/40/6/309
DO - 10.1088/0029-5515/40/6/309
M3 - Article
SN - 0029-5515
VL - 40
SP - 1113
EP - 1123
JO - Nuclear Fusion
JF - Nuclear Fusion
IS - 6
ER -