Page 290 - Fundamentals of Magnetic Thermonuclear Reactor Design

Plasma Control System Chapter | 8 269

where U is external voltage evolution (usually is taken from TRANSMAK
ext
..
code), U = R (I − I ) is resistive voltage on plasma loop and L is plas-
R
p
P
pl
res
ma inductance.
l Plasma energy confinement model (τ ), which describes the transition from
E
losses along the magnetic field (τ ) to Bohm losses (τ Bohm ) and to L-mode
str
L
τ
scaling ( E ): τEL
 I p 
exp − 

1  I crit  1
-if > = +
q 11
τ E τ str τ Bohm
1 1− fq() fq()
-if 9 << = + ; fq) 5.5 0.5 × q; (8.48) -if q>11 1τE=exp−Ip-
=
−
q 11
(
E τ τ Bohm E τ L
-if < E τ = E τ L . Icritτstr+1τBohm-if 9<q<11 1τ
q 9
E=1−f(q)τBohm+f(q)τEL; f(q)=5.
Here, q is safety factor, I is the so-called critical current for closed 5−0.5×q;-if q<9 τE=τEL.
crit
magnetic surfaces formation (I ≈ 100 kA for ITER case).
crit
The SCENPLINT code is described in more detail in an educational
book [8], where numerous examples of code application to the analysis of
plasma initiation stage in tokamaks (for real experiments on Globus-M,
T-10, JT-60U, Tore Supra, KSTAR tokamaks and also for the ITER project)
are given.
The transport model used in the SCENPLINT code is a system of ordinary
differential equations for electron and ion temperatures (T and T , respective-
i
e
ly), neutral gas concentration (n ), plasma current (I ) and ‘runaway’ electron
e
Е
current (I ). The pre-breakdown fuel mixture pressure Е and ionisation γ are
R
0
used as initial conditions. These data are used to determine the initial concen-
20
−3
tration of the fuel mix n (10 m ) = 4.8 p (PЕ) and concentration of plasma
00
−3
−2
electrons n = γ n (γ ∼10 to 10 ). Electron and ion initial (T and T ,
i0
e0
0 00
e0
0
respectively) are usually (1–2) eV. Other parameters to be set up are the break-
down region geometry (R, a, k), the toroidal magnetic field (B ), the vortex
t0
electric field E in that region, the vacuum vessel volume (V ); stray magnetic
v
fields at the breakdown time (B ); the additional ECR heating (Q ECRH ), and
s
the parameters characterising the plasma confinement and the dynamics of
the plasma impurities.
The mentioned model underlies the SCENPLINT code that has been devel-
oped as part of the TRANSMAK code package for the simulation of plasma
initiation processes. For SCENPLINT simulations, it is necessary to specify
the discharge key characteristics, such as the time dependencies of loop voltage
U (t) or plasma current I (t), the breakdown region geometry and the plasma
Е
ext
intrinsic inductance. The SCENPLINT can also be used to pre-select the plasma
initial pressure and required auxiliary heating power. These parameters are em-
ployed by the TRANSMAK code as input data.