Important modifications are under implementation in the RFX-mod fusion machine regarding the magnetic front-end, the vacuum confinement barrier, and the first wall [ 1]. The arrangement of the machine components changed by the removal of the former vacuum vessel, replaced by the larger toroidal support structure vacuum sealed, and by the containment in the vacuum environment of the shell for passive magnetic stabilisation of the plasma. The material of the first wall changed to high thermal conductivity polycrystalline graphite in order to reduce the surface temperature of tiles during plasma pulses; moreover, the first wall conditioning technique changed to pulse discharge cleaning with pulse frequency for heating within 0.2-0.5 Hz. The active control capabilities of the plasma improved by increasing the number of magnetic pick-up coils and electrostatic-magnetic field sensors [1]. All these modifications will allow to investigate new experimental scenarios in RFX-mod2 with different temperature field in the in-vacuum components to be monitored and controlled during plasma pulses and first wall conditioning. Tree-dimensional non-linear transient finite element analyses shown attenuation and delay of the heat flux through the machine parts, and identified the passive stabilising shell as the instrumentable component closest to the plasma boundary able to follow the thermal behaviour by the detection of a temperature variation of 10 °C during a plasma pulse with a response time of about 200 s. The simulation of a full experimental day with 24 plasma pulses produced the thermal profiles with local values of the maximum temperatures achieved by the components, so verifying the compatibility with allowable limits of materials, in particular at the shell supporting rings made of polyamide-imide and at the vacuum sealing elements made of fluoroelastomer and acrylic foam [2]. Simulations of the pulse discharge cleaning demonstrated the capability of the system to provide the required power for first wall conditioning (18 MW) and the need to realise a duty cycle (1 hour on /3 hours off) limiting the average heat flux and the maximum temperature (60 °C) at the vacuum vessel sealing elements in order to minimise differential thermal deformations. Some layouts with different spatial resolutions of the temperature sensors have been proposed and all of them are able to detect the maximum temperatures expected during operation; the final layout has been selected considering cabling technology and the design of the signal feedthroughs i.e. the number of available electrical contacts shared with mechanical and electrostatic-magnetic field sensors [3]. Cable routing and fixing technique of thermocouples have been tested on a mock-up of the modified machine so validating sensor realisation and installation.
Thermal analysis of the RFX-mod2 operating conditions for the design of the temperature measurement system
Dalla Palma Mauro;
2019
Abstract
Important modifications are under implementation in the RFX-mod fusion machine regarding the magnetic front-end, the vacuum confinement barrier, and the first wall [ 1]. The arrangement of the machine components changed by the removal of the former vacuum vessel, replaced by the larger toroidal support structure vacuum sealed, and by the containment in the vacuum environment of the shell for passive magnetic stabilisation of the plasma. The material of the first wall changed to high thermal conductivity polycrystalline graphite in order to reduce the surface temperature of tiles during plasma pulses; moreover, the first wall conditioning technique changed to pulse discharge cleaning with pulse frequency for heating within 0.2-0.5 Hz. The active control capabilities of the plasma improved by increasing the number of magnetic pick-up coils and electrostatic-magnetic field sensors [1]. All these modifications will allow to investigate new experimental scenarios in RFX-mod2 with different temperature field in the in-vacuum components to be monitored and controlled during plasma pulses and first wall conditioning. Tree-dimensional non-linear transient finite element analyses shown attenuation and delay of the heat flux through the machine parts, and identified the passive stabilising shell as the instrumentable component closest to the plasma boundary able to follow the thermal behaviour by the detection of a temperature variation of 10 °C during a plasma pulse with a response time of about 200 s. The simulation of a full experimental day with 24 plasma pulses produced the thermal profiles with local values of the maximum temperatures achieved by the components, so verifying the compatibility with allowable limits of materials, in particular at the shell supporting rings made of polyamide-imide and at the vacuum sealing elements made of fluoroelastomer and acrylic foam [2]. Simulations of the pulse discharge cleaning demonstrated the capability of the system to provide the required power for first wall conditioning (18 MW) and the need to realise a duty cycle (1 hour on /3 hours off) limiting the average heat flux and the maximum temperature (60 °C) at the vacuum vessel sealing elements in order to minimise differential thermal deformations. Some layouts with different spatial resolutions of the temperature sensors have been proposed and all of them are able to detect the maximum temperatures expected during operation; the final layout has been selected considering cabling technology and the design of the signal feedthroughs i.e. the number of available electrical contacts shared with mechanical and electrostatic-magnetic field sensors [3]. Cable routing and fixing technique of thermocouples have been tested on a mock-up of the modified machine so validating sensor realisation and installation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
