Eddy current and gap voltage at electrical contacts of ITER diagnostic first walls and shield modules during plasma disruptions

ITER diagnostic port plugs perform many functions including structural support of diagnostic systems under high electromagnetic loads while allowing for diagnostic access to the plasma. During plasma disruptions, a large amount of induced current flows locally at electrical contacts between diagnostic first walls (DFWs) and the diagnostic shield modules (DSMs). Even a small gap voltage (10-30V) between DFWs, DSMs and supporting rails may trigger local arcing and cause arc damage to the conducting structure. This is particularly true when we consider the ionized gas environment and halo current effect. We perform global electromagnetic analysis with contact details for DFWs and DSMs to quantify the gap voltage and local current transfer effect during plasma disruptions. Electrical contacts between the DFWs and DSMs may also have significant impact on disruption load and thus affect design of the DFW attachment scheme. Large current transfer (>100 kA) between DFWs and DSMs through the attachment keys and tabs during disruption implies local heating and potential welding. This paper reviews the contact current and electrical potential difference between the DFWs, DSMs and the port plug structure. We also assess the impact on the system design itself due to electrical contact among various components.