Self Organization of high βp plasma equilibrium with negative triangularity
Tokamak plasma are subjected to a βp equilibrium limit, which forms an natural inboard
divertor (IPN). Previous experiment shows such configuration rarely observed under very high
heating power or transiently during current ramp up. We present high βp equilibrium with IPN
sustained in steady state near an equilibrium limit.
Ip [kA]
Vloop [V]
-15
-5
4
0
0
8.2 GHZ ECW ~ 100 kW
6
5
0.01
5
10
15
-0.01
6s
βp*=βp + li/2
IL
0.4
0.2
15 s
IPN
Rin [m]
0.3
10
time [s]
-0.5
0.5
0
IPN-0.5
Rlimiter=0.22m
5
0.5
0
IL
IPN
15
0.2
A simple analytic model shows
that βp can be raised by
suitably
shaping
plasma
boundary
for
negative
triangularity. This supports
our experimental result.
IPN -0.5
3
2
0.5
-0.15
Z [m]
-25
-0.2
Z [m]
1.75 s
triangularity 
-0.25
0.5
Z [m]
-35
Fullyno.
Non-Inductive
discharge
Shot
#19408
0.02
0.6
R [m]
1
High βp plasma discharge in realized fully non-inductive
(Vloop=0) current drive by EC. Equilibrium is sustained
close to equilibrium limit (βp1) with a natural
divertor. At high βp plasma self organized its shape to
enhance negative triangularity.
-0.4
-0.2
0
triangularity parameter in model D
Our experiment shows that spontaneous
formation of inboard divertor may not be just a
transient phenomenon, but might be sustained
as a stable equilibrium. With sufficiently high
heating power, such scenario may bring an
surprising issue in future fusion reactors.