29th Symposium on Fusion Technology (SOFT 2016)

P4.080 New piezoelectric valve for disruption mitigation studies at ASDEX Upgrade

8 Sep 2016, 14:20

1h 40m

Foyer 2A (2nd floor), 3A (3rd floor) (Prague Congress Centre)

Board: 80

Poster D. Diagnostics, Data Acquisition and Remote Participation P4 Poster session

Speaker

Mathias Dibon (Max-Planck-Institute for Plasmaphysics)

Description

A disruption is a major plasma instability that follows a sudden loss of plasma energy. During such an event, large electromagnetic forces and high heat loads occur, as well as electrons at relativistic speed. These effects can cause damage to the plasma facing components and thus have to be mitigated. For this purpose high speed gas valves are used to inject a strong pulse of noble gas onto the plasma, shortly before it disrupts. Most of the plasmas thermal energy is radiated, preventing highly localized heat loads. Electromagnetic forces are decreased due to a fast decaying plasma current. Relativistic electrons, if generated, can be dispersed before they lose confinement by injecting high-Z gas into the beam. A new valve for in-vessel high field side injection has been developed for ASDEX Upgrade. In the idle state, the gas reservoir (42 cm³) of the valve is sealed pressure-tight by the valve plate which is pressed into the Viton sealing by a steel bellow. The reservoir can now be filled with mitigation gas up to 50 bar. If the valve is triggered, a voltage of 200 V is applied to two piezoelectric stack actuators which expand immediately by a length of 0.07 mm. This stroke is amplified through a monolithic titanium frame by a factor of 30, while thereby reducing the force of the actuators and maintaining their linear behavior. Additionally, the frame serves as preload spring for the actuators. The valve stem and the valve plate are pulled back within 2 ms, opening the valve orifice, which has a diameter of 14 mm. This allows a maximal flow rate of 8*10⁴4 Pam³/s after 1.8 ms and an average flow rate of 2*10⁴4 Pam³/s over the total evacuation time of 10 ms. A detailed characterization will be presented at the conference.