C.S. Pitcher

Port-Based Plasma Diagnostic Infrastructure on ITER

Abstract The port-based plasma diagnostic infrastructure on ITER is described, including the port plugs, the interspace support structure and port cell structure. These systems are modular in nature with standardized dimensions. The design of the equatorial and upper port plugs and their modules is discussed, as well as the dominant loading mechanisms. The port infrastructure design has now matured to the point that port plugs are now being populated with multiple diagnostics supplied by a number of ITER partners - two port plug examples are given.

Dynamic Amplification Factor of the ITER Diagnostic Upper Port Plug

The diagnostic upper port plug in ITER is a long metal box cantilevered to the vacuum vessel port with 42 × M52 studs and nuts. The plug structure has a heavy payload at the front, such as the diagnostic first wall and the diagnostic shield module to protect the diagnostic components from plasma and neutron fluxes. This kind of structural configuration is susceptible to a resonance with the transient external load. For the upper port plug, the design-driving load is electromagnetic (EM) forces due to plasma disruptions. In this paper, the dynamic amplification factor (DAF) of the structure is calculated for such EM loads. The bolted joint at the back flange of the plug structure is also considered together with the port extension of the vacuum vessel and its influence on the dynamic behavior is investigated. The analysis results show that the bolted joint reduces the DAF as well as the natural frequency of the structure.

Progress in the Development of the ITER ECE Diagnostic

Abstract This paper explains the present status of the ITER electron cyclotron emission (ECE) diagnostic and gives an outlook on the upcoming technical and design activity. The open questions of calibration and stability of ECE systems, as well as proposals for the calibration, the design of the front end, and the transmission line are reviewed. The possible role of ECE in the neoclassical tearing mode detection and stabilization by electron cyclotron heating is also discussed. Because integration of the ITER ECE diagnostic within the tokamak requires proper definition of interfaces with many different components located both in-vessel and ex-vessel, a special attention is paid to address the associated issues.

ITER Diagnostic First Wall

Abstract The ITER Diagnostic Division is responsible for designing and procuring the First Wall Blankets that are mounted on the vacuum vessel port plugs at both the upper and equatorial levels. This paper will discuss the effects of the diagnostic aperture shape and configuration on the coolant circuit design. The Diagnostic First Wall (DFW) design is driven in large part by the need to conform the coolant arrangement to a wide variety of diagnostic apertures combined with the more severe heating conditions at the surface facing the plasma, the First Wall (FW). At the FW, a radiant heat flux of 35W/cm2 combines with approximate peak volumetric heating rates of 8W/cm3 (equatorial ports) and 5W/cm3 (upper ports). Here at the FW, a fast thermal response is desirable and leads to a thin element between the heat flux and coolant. This requirement conflicts with the desire to have a thicker FW element to accommodate surface erosion and other off-normal plasma events.

Preliminary Thermal and Hydraulic Analysis on the ITER Upper Diagnostic Port Plug During Normal Operation and Baking

A preliminary thermo-hydraulic analysis was performed on the ITER diagnostic upper port plug. Relevant thermal and hydraulic parameters, such as coolant pressure drop, maximum structure temperature and bake-out time, were calculated for normal operation and baking. The upper port plug considered is based on the preliminary generic structure design of Princeton Plasma Physics Laboratory and the Blanket Shield Module (BSM) developed in Europe. The diagnostic shield modules are modeled so that the Korean diagnostic procurement package, which includes Vacuum Ultra-Violet (VUV) spectrometer and neutron activation system, can be integrated. The analysis provides design inputs to optimize flow in the cooling channels of the plug. The conjugated heat transfer analysis for the port plug confirms that it is important to secure accurate nuclear heat and accurate electro-magnetic (EM) force for the design of the joining flange between the BSM and the main body. Thermal analysis shows that it will take ten hours for the port plug to reach the bake-out temperature (240°C), if the window plate is heated additionally from the rear side.

Integration of diagnostics on ITER

Diagnostics play a very important role in the modern Tokamak where optimum performance is essential. To achieve this, the device must be equipped with reliable and robust sensors and instrumentation that allow the operation envelope to be fully explored. Development of these diagnostics to maintain this reliability is necessary. Further to the development, the systems must be integrated in a way that maintains their performance while simultaneously satisfying the key requirements needed for safety and tokamak operation. ITER will have 50 diagnostics; almost all of which are utilized primarily for the real-time operation of the tokamak. While there is still much work to do, to date, significant progress has been made in the development of these systems. The work load for the developments is shared across all the ITER partners. This paper focuses on the challenges for the integration of the systems.

Dynamic response of the ITER diagnostic upper port plug during a plasma disruption

The diagnostic upper port plug in ITER is a long metal box cantilevered to the vacuum vessel port with 42 × M52 studs and nuts. The plug structure has a heavy payload at the front such as the Diagnostic First Wall (DFW) and the Diagnostic Shield Module (DSM) to protect the diagnostic components from plasma and neutron fluxes. This kind of structural configuration is susceptible to a resonance with the transient external load. For the upper port plug, the design-driving load is electromagnetic (EM) forces due to plasma disruptions. In this study the dynamic amplification factor (DAF) of the structure is calculated for such EM loads. The bolted joint at the back flange of the plug structure is also taken into account together with the port extension of the vacuum vessel and its influence on the dynamic behavior is investigated. The analysis results show that the bolted joint reduces the DAF as well as the natural frequency of the structure.

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.