The In-Vessel Protection Components for ITER First Plasma Operation

Abstract

ITER plasma operations begin with “first plasma,” with the main purpose of concluding integrated tokamak commissioning. This first plasma is targeted to last at least 100 ms with a 100-kA minimum plasma current. As in other tokamaks, the first plasma occurs prior to full installation of the baseline in-vessel components. For example, the blanket and divertor are installed only after the first plasma experiments are completed. Thus, several temporary components are installed to protect the vacuum vessel (VV) and other already-installed high-value components (in-vessel coils and cable looms) from the potentially adverse effects of startup plasma interaction. This protection is in part provided by temporary limiters (TLs) and divertor replacement structures (DRSs), which together create poloidal and toroidal guides to shelter the VV from the plasma and possible fast particle beams. The 72 TL segments are positioned at the first wall contour in four poloidal loops of 18 segments each. For engineering safety, the system is capable of maintaining plasma pulses of up to 3 s, tolerating up to 30 MJ of thermal energy and 1 MA of plasma current. DRSs complete the bottom periphery of the poloidal loop to interrupt any potential downward plasma movement. The vessel also requires protection from the electron cyclotron resonance heating (ECRH) beam, which injects 6.7 MW of microwave energy across the plasma null region to help energize and assist the breakdown of first plasma. To protect the VV, an inboard mounted mirror reflects the ECRH beam energy from its upper port origin into an outboard equatorial port, where a second component (a beam dump) absorbs the radiation.