Tritium-Concentration Requirements in the Fueling Lines for High-Q Operation in ITER
V. Graber and E. Schuster
European Physical Society (EPS) Conference on Plasma Physics (CPP)
Milan, Italy, July 8-12, 2019
Abstract
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One of the most fundamental control problems arising in ITER and future
burning-plasma tokamaks is the regulation of the plasma temperature and
density to produce a determined amount of fusion power while avoiding
undesired transients. ITER is designed to achieve a ratio of fusion power
to auxiliary power, Q, of 10. The reactor’s high plasma density (> 1×10^20 m^−3)
and low burn fraction (∼ 1%) will require high deuterium (D) and tritium (T)
fueling rates. Gas puffing will have a low fueling efficiency (< 1%)
due to poor neutral penetration [1]. Therefore, the initial phase of
ITER will rely on two pellet injectors located on its magnetic
high-field-side (HFS) for deep core fueling. The D pellet injector
(with pellets of 100% D nominal concen- tration) and the D-T pellet
injector (with pellets of 10%D-90%T nominal concentration) are planned
to have maximum throughputs of 120 Pa m^3/s and 111 Pa m^3/s, respectively [2].
However, limitations in the tritium plant subsystems could result in a
lower T concentration. Even if the nominal concentration could be initially
achieved, it might not be possible to sustain it for the total duration
of long pulses. This not only imposes burn-control challenges [3] but
also raises serious concerns over having sufficient concentration of T
in the fueling lines to sustain long-pulse high-Q operation. In this work,
a volume-averaged model of ITER’s burning plasma is used to assess the
feasibility of accessing Q = 10 operation for different levels of T
concentration. Operation points characterized by Q = 10 are sought within
ITER’s limits for fueling rates and auxiliary heating powers. The results
are presented in the form of Plasma Operation CONtour (POPCON) plots that
span the density-temperature space. The minimum tritium concentration that
can maintain the plasma at Q = 10 is determined for different
\particle-recycling assumptions. Although this work is concerned with
the design parameters of ITER, the analysis can be extended to other
future burning-plasma reactors such as DEMO.
[1] S. K. Combs, L. R. Baylor and others, “Overview of recent developments in pellet injection for ITER,” Fusion Engineering and Design, vol. 87, pp. 634-640, 2012.
[2] J.A. Snipes, D. Beltran and others, “Actuator and diagnostic requirements of the ITER Plasma Control Sys- tem,” Fusion Engineering and Design, vol. 87, no. 12, pp. 1900-1906, 2012.
[3] A. Pajares and E. Schuster, “Robust Burn Control in ITER Under Deuterium-Tritium Concentration Varia- tions in the Fueling Lines,” 27th IAEA Fusion Energy Conference, Gandhinagar, India, October 22-27, 2018.