| AVS 58th Annual International Symposium and Exhibition | |
| Vacuum Technology Division | Tuesday Sessions |
| Session VT-TuM |
| Session: | Accelerator and Large Vacuum System Design, Outgassing and Pumping |
| Presenter: | Stefan Hanke, Karlsruhe Institute of Technology (KIT), Germany |
| Authors: | S. Hanke, Karlsruhe Institute of Technology (KIT), Germany M. Scannapiego, Karlsruhe Institute of Technology (KIT), Germany X. Luo, Karlsruhe Institute of Technology (KIT), Germany C. Day, Karlsruhe Institute of Technology (KIT), Germany F. Fellin, Consorzio RFX, Italy P. Zaccaria, Consorzio RFX, Italy |
| Correspondent: | Click to Email |
The ITER Neutral Beam Injection system (NBI) is one of the heating systems to achieve the required plasma temperatures to start the fusion process. Thereby, the NBI system is basing on the principle of provision and acceleration of deuterium and protium ions and the re-neutralization of the high energy ions to be injected into the plasma through the confining magnetic fields. Each heating NBI is designed to insert 16 MW of heating power to the plasma and presents major technical and physical challenges.
In order to solve these and to demonstrate the achievement of the required parameters, a robust R&D program is under way. A central milestone for this development is the establishment of a full scale test facility, which will be built on site of Consorzio RFX, Padova. Part of this test facility is MITICA (Megavolt ITER Injector and Concept Advancement), the test bed for the entire neutral beam injection system. Karlsruhe Institute of Technology (KIT), which is the lead party in design and R&D of the ITER cryopumps since more than a decade, is supporting this project with the development of a customized cryopump design which ensures that the requested density profiles for optimum beam performance can be produced.
The main operational task which has to be provided by the cryogenic pump at a speed of ~5000 m3/s is to handle very high gas loads of protium and deuterium. As basic pumping concept, cryosorption was chosen and the cryopump is operated with supercritical helium at 4.5 K for the adsorbing and gaseous helium at 80 K for the shielding circuit. As demonstrated in other NBI applications, cryosorption provides a wide and robust operational window at acceptable cryogenic loads to the cryoplant. The design was driven by two competing requirements: The high thermal heat loads ask for a closed pump, whereas the need for a high pumping speed asks for an open structure. To reconcile both objectives in an optimized geometry, modeling simulations were performed using the Test Particle Monte Carlo code MOVAK3D. To properly describe the density distribution in the NBI vessel with large thermal and pressure gradients, the time-of-flight cell code ProVac3D was developed.
Additional to the design activities for an optimized cryopump, a considerable effort has been spent to investigate the thermal hydraulic properties of the cryopump during the different operational and failure modes.