Cryostat Wall Research Articles

Structural analysis of Wendelstein 7-X magnet weight supports

The Wendelstein 7-X (W7-X) optimized stellarator is presently under construction at the Max-Planck-Institut für Plasmaphysik in Greifswald. The goal of W7-X is to verify that the advanced stellarator magnetic confinement concept is a viable option for a fusion reactor. The W7-X coil system consisting of 70 superconducting coils of seven different types is supported by a massive central support structure (CSS), and thermally protected by the cryostat. The magnet system's weight is borne by supports (cryo-legs) which are bolted to the cold CSS. They reach down through the cryostat wall to the warm machine base which means that a small thermal conductivity is important to keep thermal losses at an acceptable level. Therefore, the design of the cryo-legs incorporates glass-reinforced plastic (GRP) tubes which are shrink-fitted into stainless steel flanges at the ends. In order to ensure free thermal shrinkage of the magnet system and to reduce stresses in the cryo-legs, sliding and rotating bearings are used as interfaces to the machine base. Tie rods between the machine base and the warm ends of the cryo-legs prevent toroidal movements of the magnet system with respect to the torus axis. Nevertheless, significant deformation of the CSS during operation results in tilting of the cryo-legs in such a way that toroidal movements of the whole magnet system take place. The number of cryo-legs and their stiffness are chosen such that the toroidal movement is kept within an acceptable range. All these restrictions, as well as requirements concerning simplicity and ease of assembly, make the cryo-leg design and structural analysis quite a complex and challenging task. The paper presents an overview of structural analyses of the W7-X magnet system with cryo-legs, local analyses of a cryo-leg under design loads, and FE simulation of the cryo-leg mechanical test.

적외선 카메라 KAONICS의 열해석

KAONICS(KAO Near Infrared Camera System)와 같은 적외선 카메라는 열잡음제거가 매우 중요하다. 입사창을 통해 들어오는 외부의 열복사 이외에도 카메라의 외벽을 통해 유입되는 열복사가 배경복사로서 검출기에 입사하여 시스템의 성능을 저하 시키며 그 양은 무시할 수 없다. 따라서 배경복사와 검출기 자체의 열잡음을 줄이기 위해서 카메라 내부의 광학계 전체와 검출기를 냉각해야만 한다. 이에 본 연구에서는 J, H, Ks, L 파장 대를 관측하기 위한 내부 냉각온도를 정량적으로 결정하였으며 카메라 외부에서 유입되는 복사량을 추산하고 냉각에 필요한 냉각 열용량을 추정하여 냉각기를 선택하였다. 선택된 냉각기를 이용하여 냉각할 때 Cold-Box가 목표온도에 도달하는 시간과 최종 냉각 온도를 계산하여 시스템 제작에 반영하였다. It is very important to eliminate thermal background radiation for the near infrared camera system such as KAONICS (KAO Near Infrared Camera System). Thermal background radiations which come from window and cryostat wall influence IR detector and decrease IR system performance. Therefore the cold box which contains optics and detector housing must be cooled down to eliminate thermal background radiation. We carried out quantitative analysis to determine internal cooling temperature to reduce thermal noise in the J, H, Ks, and L bandpass. Additionally, we estimated the incoming heat load and then chose the cryocooler adequate to KAONICS's requirements. The cooling time and the final cooling temperature of the cold box were calculated. These results were also implemented to the system design.

Progress in ATLAS central solenoid magnet

The ATLAS central solenoid magnet is being developed to provide a magnetic field of 2 Tesla in the central tracking volume of the ATLAS detector under construction at the CERN/LHC project. The solenoid coil design features high-strength aluminum stabilized superconductor to make the coil thinnest while maintaining its stability and the pure-aluminum strip technique for quench protection and safety. The solenoid coil is installed in a common cryostat with the LAr calorimeter in order to minimize the cryostat wall. A transparency of 0.66 radiation length is achieved with these integrated efforts. The progress in the solenoid coil fabrication is reported.

An overview of ITER diagnostics (invited)

The requirements for plasma measurements for operating and controlling the ITER device have now been determined. Initial criteria for the measurement quality have been set, and the diagnostics that might be expected to achieve these criteria have been chosen. The design of the first set of diagnostics to achieve these goals is now well under way. The design effort is concentrating on the components that interact most strongly with the other ITER systems, particularly the vacuum vessel, blankets, divertor modules, cryostat, and shield wall. The relevant details of the ITER device and facility design and specific examples of diagnostic design to provide the necessary measurements are described. These designs have to take account of the issues associated with very high 14 MeV neutron fluxes and fluences, nuclear heating, high heat loads, and high mechanical forces that can arise during disruptions. The design work is supported by an extensive research and development program, which to date has concentrated on the effects these levels of radiation might cause on diagnostic components. A brief outline of the organization of the diagnostic development program is given.

Biological shield around the neutral beam injector ducts in the ITER conceptual design

There are gaps between the toroidal field coils and neutral beam injector (NBI) duct wall for the thermal insulator in tokamak reactors such as ITER (International Thermonuclear Experimental Reactor). Neutrons stream through the duct, and some of them penetrate the wall and stream through the gaps. These neutrons activate the materials composing the duct wall, toroidal field coil (TFC) case and cryostat wall surfaces. The dose rate is enhanced just outside the cryostat around the ducts in the reactor room after reactor operation by activation. We investigated the gamma-ray dose rate just outside the cryostat after shutdown due to gamma-rays from activity induced by the neutrons streaming through the gaps. By evaluating the difference between the dose rate in models with and without gaps, we decided whether the thickness of the cryostat as biological shielding is sufficient or not. From these investigations, we recommend a cryostat design suitable for radiation shielding. Dose rates after shutdown at a point just outside the cryostat around the NBI ducts in the model with gaps are two orders larger than those without gaps. The value at this point is approximately 400 mrem h −1 (4 mSv h −1), which is two orders larger than the design value for workers to enter the reactor room. In order to reduce the dose rate after shutdown, a method of providing the shielding function of the cryostat is suggested.

Neutron transport studies for the Ignitor neutron diagnostics

As a preliminary step for the project of the neutron diagnostics in the Ignitor tokamak, the overall neutron field in the device has been calculated with the help of the MCNP code, which solves, with the Monte Carlo method, neutron and photon transport problems in arbitrary three-dimensional geometries. The poloidal distribution of the fluxes on the first wall and the related energy spectra have been calculated to estimate the backscattered contribution to signals at spectrometers and collimated detectors for measurements with spatial resolution in the plasma. The average fluxes on the top and the lateral cryostat surfaces and the local fluxes on the equatorial plane outside the cryostat wall are also calculated in order to determine the neutron counters characteristics and expected performances.

The design of stable race-track superconducting switch

The development of the concept of the race-track switch mounted between magnet flanges, parallel and close to winding surface is described. The concept is urgent in the case of severe limitation on space between the magnet and cryostat wall. The problems concerning the mechanical and electrical instabilities of such a switch construction and danger of thermal interaction with magnet winding as well as the role of mutual coupling of insulated high resistive matrix wires on instabilities in current redistribution within the strands of the switch have been taken into account and overcame. The way of improvement of adiabatic stability of switch winding and all the switch structure are described in detail. The reliability of the switch was tested and proved in connection with a laboratory 12T magnet.

Compact heat switch for persistent current loops

The development of the concept of the race-track switch mounted between magnet flanges, parallel and close to winding surface is described. The concept is urgent in the case of severe limitation on space between the magnet and cryostat wall. The problems concerning the mechanical and electrical instabilities of such a switch construction and danger of thermal interaction with magnet winding as well as the role of mutual coupling of insulated high resistive matrix wires on instabilities in current redistribution within the strands of the switch have been taken into account and overcame. The way of improvement of adiabatic stability of switch winding and all the switch structure are described in detail. The reliability of the switch was tested and proved in connection with a laboratory 12T magnet.

Research news

The paper reports the results of the latest experiments to support the development and validation of the numerical model for high-current arcs at the power cables (busbars) to the toroidal field (TF) coils. The busbar arcs have significant potential of danger in case of an accident due to the huge inductive energy of about 40 GJ stored permanently inside the TF coils. In a worst case these arcs may propagate to and penetrate the cryostat wall. The experiments were set up to understand the propagation and damage potential of such arcs. The present work investigates the influence of residual pressure on arcing.