Transport simulation of ITER (International Thermonuclear Engineering Reactor) startup Page: 1 of 3
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TRANSPORT SIMULATION OF ITER STARTUP*
S. E. Anenberger and W. A. Houlberg
Oak Ridge National Laboratory
Oak Ridge. TN 37831-8058
The present Internationa] Thermonuclear Engineering Reactor
(ITER) reference configuiationa are the Technology Phase,’ in
which the plasma current is maintained noninductively at a
subignition density, and the “Physics Phase," »teh u igmred but
requires inductive maintenance of the current The WHIST 1.5-D
transport code is used to evaluate the voh-secood requirements of
both configurations. A slow current ramp (60-30 s) is required for
fixed-radius rtirtup in ITER to avoid hollow currem density profiler.
To reach the operating point requires about 203 V i for the
Technology Phare (18 MA) and about 270 V-s for the Physics Phase
(22 MA).The resistive losses can be reduced with ertpanding-radius
The polcidal magnetic flux available to establish the plasma
toroidal current and to maintain it against resistive and disruptive
losses is limited by engineering constraints. At steady state, the
number of volt-ieopnds of magnetic flux stored in the poloidal
magnetic field is directly proportional to the inductively maintained
toroidal current, with the proportionality contaant being determined
by the plasma current profile- Since experimental evidence shows
that higher currents give better energy confinement, it is desirable to
minimize volt-second losses.
The primary volt-second loss mechanisms are resistive current
decay and direct volt-second dissipation via flux surface reconnection
during sawtooth disruptions.1 The resistive dissipation rate becomes
smaller as the plasma temperature increases; therefore, it is
particularly helpful to rentp the current quickly at low temperatures.
If sawteeth are present, the increased tamp rate also reduces the total
volt-seconds dissipated by sawteeth during startup. However, if the
current is ramped too quickly in a fixed-radius startup, the plasma is
likefy to form an unstable hollow currem density profile, resulting in
a major dinuption. An expanding-ndius sunup, in option not
dismissed in this paper, could relax this limit.2
The volt-second startup requirements lend to be reduced by
currem drive from neutral beam injection and other auxiliary soutres.
The magnitude of this effect is evaluated.
The flat-top currem in the Physics Pheaeof ITER3 ia fully
inductive since no auxiliary hearing is requited at ignition. However,
it would be possible to add a small amount of noninductive current
drive for profile-shaping purposes, provided it does nor cause beta to
exceed the critical value tor stability. It may be possible to use
noninductive current drive 10 tailor the current profile in order to
Research sponsored by the Office of Fusioa Energy, U.S.
Department of Energy, under contract DE-AC05-84OR21400 with
Martin Marie tlx Energy Systems. Inc.
reduce or avoid sawteeth. (Cenainly it is possible to increase
sawtooth activity by driving a narrow spike of current density at the
magnetic axis.) It may also be possible to directly influence the
energy confinement rime by tailoring the current profile, although the
physical relations involved are nor fully understood. The two HER
phases represent the end points of a range of potentially interesting
devices, non no auxiliary sources to full maintenance of plasma
currem by noninductive sources. Designing ITER to accommodate
those endpoints permits future considentionef immediate designs,
tailored to new physical models as they become available.
The present work focuses on a quantitative estimate of the volt-
seconds required for ataitup for both phases of the ITER device. The
WHIST 1J-D transput code is used to simulate the time-dependent
behavior of the plasma, including beam-driven and bootstrap
currents. No rf or lower hybrid current drive is assumed. Sawtooth
disruptions are the only magnetohydnxlynamic activity simulated,
although a simple condition for ballooning stability is monitored. At
each time step the profiles of toroidal current, electron and ion
temperature, and deuterium and tritium densities are computed. The
electron energy confinement is assumed to be governed by
anomalous Goldston scaling with Chang-Hinton neoclassical ion
conductivity. The flux surface equilibrium is updated periodically
and the beam deposition solved in a fully three-dimensional
geometry. A more extensive description of the models was
published previously. *■*
The following scenario for startup of the ITER Techology Phase
device (R = 5.5 m. a ■= 1.8 m, K - 1.88. B = 5.3 T. I = 18 MA) is
intended to reduce volt-second consumption by reaching the
operating point ax quickly as possible with a full-radius startup while
avoiding significant akin currents. The startup consists of a 50-s
inductive currem ramp followed by 10 s of combined inductive and
noninductive current ramp. The currem ramp rate is held at 0.2 MA/s
over the whole interval. Figure 1(a) shows the avenge and peak
electron and ion temperatures during the startup and the initial pan of
the bum. The avenge electron density [Fig. 1(b)] is ramped by gas
puffing slowly enough to avoid thermal collapse due to line radiation
but quickly enough to reduce the edge plasma tempenture and
increase the plasma resistivity, avoiding a buildup of skin current. At
501, the current reaches 14.5 of the required 18 MA, and there is no
longer much advantage in keeping the temperature low. At this
point. 90 MW of 1-MeV beams are turned on and the density lamp
rate is increased sharply for the next 10 s. At 60 s, the operating
point is reached, and the current is then maintained non inductively by
the beams for the duration of the simulation.
The poloidal flux required during the startup and initial bum is
shown in Fig. 1(c). The individual terms are derived from a
Faraday's law representation in which
1 I l
Tro ' *
i i i
100 150 200
100 150 200
100 150 200
Fig. I. Technology Phase startup evolution of (a) temperature, (b) average election density, and (c) volt-second requirements.
This report was prepared as an account of work sponsored by an agency ot the United States
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Attenberger, S.E. & Houlberg, W.A. Transport simulation of ITER (International Thermonuclear Engineering Reactor) startup, article, January 1, 1989; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1093721/m1/1/: accessed March 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.