Thermal analysis of the RFX-mod2 operating conditions for the design of the temperature measurement system
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Thermal analysis of the RFX‑mod2 operating conditions for the design of the temperature measurement system Mauro Dalla Palma1,2 · Roberto Cavazzana1 · Andrea Erculiani1 · Giulio Gambetta1 · Simone Peruzzo1 Received: 10 January 2020 / Accepted: 6 October 2020 / Published online: 3 November 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract High heat fluxes are exchanged in fusion machines (up to 50 MW m−2), thus producing elevated temperature and requiring thermal monitoring and control. The design of a temperature measurement system for the RFX experiment is developed through three-dimensional nonlinear transient finite element simulations of the torus assembly under upgrade from “mod” to “mod2” with enhanced magnetic front-end, vacuum confinement barrier, and first wall. Analyses show how heat fluxes applied at the plasma-facing materials are transmitted, attenuated and delayed, through the machine parts. Results identify the passive stabilising shell as the instrumentable component closest to the plasma boundary able to follow the thermal behaviour by the detection of temperature variations at least of 10 °C during plasma pulses with a response time of about 200 s. Allowable temperature limits of materials are verified simulating a full experimental day with 24 plasma pulses, in particular at the shell supporting rings made of polyamide-imide and at the vessel spacers made of polyether-ether ketone-coated stainless steel. Simulations of the pulse discharge cleaning demonstrated the capability of the system to provide the required power for first wall conditioning (25 kW) and the need to realise a duty cycle (1-h on/3-h off) limiting the average heat flux and the maximum temperature (55 °C) at the vacuum vessel sealing elements in order to minimise differential thermal deformations. Proposed layouts of temperature sensors are able to detect the maximum temperatures expected during operation. Keywords Plasma-facing components · Temperature monitoring and control · First wall conditioning · Locked mode pulse · Thermocouples · Finite element simulation
Introduction Magnetic confinement machines are developed and studied to demonstrate the scientific feasibility of fusion as a source of energy [1]. A conservative pulsed operating scenario is foreseen during the first integration phases to produce electrical power [2]. A concern towards the achievement of this goal is represented by large-scale plasma instabilities named fast terminations or disruptions [1] often initiated by a nonrotating, so called locked mode, magnetic island [3]. During disruptions, rapid loss of magnetic confinement and decay of the plasma current occur in a few milliseconds: energy and particles accumulated in the plasma volume are lost and
* Mauro Dalla Palma [email protected] 1
Consorzio RFX, 4 Corso Stati Uniti, Padova, Italy
CNR - Istituto per la Fisica e Tecnologia dei Plasmi, 4 Corso Stati Uniti, Padova, Italy
2
released on the plasma-facing materials [4]; high currents, up to a few MA, flowing in the plasma for
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