Preloading of HL-2A Divertor Tokamak Vacuum Chamber

Pre-installation of Tokamak Vacuum Chamber for HL-2A Divertor Liu Dequan, Zhou Caipin, Cao Zeng, Sun Lin Bai Gangyi Yang Guoyi, Lu Ping (Southwest Institute of Physics, Nuclear Industry, Chengdu 610041, China) China Circulator No. 2A under construction The (HL-2A) Tokamak device will be China's first large-scale experimental device with an axisymmetric divertor used for controlled nuclear fusion research. The main feature of this device is that the divertor is symmetrical in the vacuum chamber. The HL-2A device is based on the original Axis Divertor Filter (ASDEX) device that has been retired from the German Institute of Plasma Research (IPP) and presented to our hospital. It is a cross-sectional schematic diagram of the HL-2A device. 1, 23 are multipole field coils, 4 is a vacuum chamber, 5 is a vertical field coil, 6 is an ohmic heating coil, and 7 is a plasma. The relevant parameters of the device are: large radius R = 1.64m, plasma radius r = 0.4 claws, vertical field where = 2.8 length ratio 夂 = 1.2 ~ 1.6, plasma current Ip = 0.5 ~ 1.0mA. The device uses "inside The poloidal field coil structure, ie, all poloidal field coils (including ohmic heating coils, ie, hollow transformer coils, vertical field coils, and divertor coils) are placed in a field-of-situ coil.

The vacuum chamber is a key component in the HL-2A Tokamak host.

1HL-2A vacuum chamber and its structural characteristics HL-2A vacuum chamber is partially modified and repaired using the original ASDEX vacuum chamber. The volume of the two semi-ring vacuum chambers on the pre-installed platform is large and there are a large number of internal components, and the technical problems involved are complex. Due to missing parts, damage problems and problems in the original ASDEX vacuum chamber multipole field coil, as well as the mastery of this vacuum chamber technology, it is hoped that the above steps will be solved by the pre-installation step of the vacuum chamber. The host's total vacuum chamber. This vacuum chamber is an internationally advanced D-shaped cross section, which is composed of two 'half-rings'. The joint is covered with a polyimide insulating gasket for electrical insulation and vacuum sealing. The divertor chamber is an important part of the vacuum chamber. Located on the upper and lower parts of the discharge chamber, there are diverter coils and cooling water pipes, etc. The baffle separates the divertor chamber from the discharge chamber. The “spar” of the fixed multipole field coil separates the divertor chamber into 16 sections. The vacuum chamber body material is SS-304LN, and the vacuum chamber is generally composed of a 20mm thick annular shell (inner cylinder) and the remaining 30mm thick shell welded together. For the purpose of vacuum pumping, auxiliary heating, diagnosis and installation, A total of 218 windows with diameters ranging from 妁5 to 蚝00 mm are distributed on a 30 mm thick vacuum chamber housing. There are 10 large windows with a size of 600 mm. These are for manholes and meet the needs of experimental projects. Other windows can meet vacuum requirements. The need for pumping, neutral beam injection, experimental diagnosis and internal component installation, etc. Small windows and interfaces were opened on many blind windows for vacuum cooling, cooling, water intake, inlet and measurement. The surface is equipped with a pipe which can heat the vacuum chamber body to 150 C, through which the vacuum chamber can be baked to remove the moisture, and the cooling chamber can be cooled when the pipe is connected with cooling water. Covered with a layer of foamed silicone rubber thermal insulation material.Table 1 lists the main engineering parameters of the HL-2A device vacuum chamber pre-installed on the platform two semi-ring vacuum chamber Table 1HL-2A device vacuum chamber main engineering parameters parameters parameter values Inner diameter Outside diameter Height of chamber Wall thickness Inner cavity volume Inner cavity area Mass (Structural weight) Mass (Running weight) Vacuum chamber body AISI304LN Material joints Electrical insulation Polyimide 10mm Thickness Thermal insulation foamed silicone rubber Thick 1525mm 2 Pre-assembly of the vacuum chamber components and the vacuum chamber as a whole requires the following items in the vacuum chamber: 16 multi-pole field coils and their fixing and support parts; 2128 multi-pole field coil shields and their hot and cold water pipes; 332 cover plates and Its hot and cold water pipes; 2 rings of copper rods, insulation mats and supports; 54 fixed-hole columns, 2 divertor suction systems and hot and cold water pipes; 619 titanium sublimators; 72 ion cyclotron heating ( IC RH) experimental assembly; 8 a large number of first-wall graphite tile and carbon fiber protection sheet and some experimental diagnostic devices, a large number of connectors, fasteners.

The cleanliness of the vacuum chamber will directly affect its vacuum performance.

During the entire process of disassembling, packaging, transporting, and storing the original vacuum chamber, the interior of the vacuum chamber cannot completely meet the most basic requirements for the cleanliness of the vacuum chamber. All the components inside the vacuum chamber are exposed to the atmosphere for too long and the pollution is serious. They must be removed for strict cleaning, baking and degassing.

The wall of the vacuum chamber must also be cleaned strictly and even properly polished to remove surface deposits to ensure ultra-high vacuum performance and to meet plasma and vacuum parameters. Select acceptable ultra-high vacuum materials and their ultra-high vacuum processing specifications to control impurities, gassing rate, and leak rate. The vacuum chamber pre-assembly shall be carried out on a pre-installed platform specially designed and processed. In addition to considering the dimensions, strength, and accuracy of the platform, the design of the platform shall be guided, limited, stabilized, and driven by the vacuum chamber on the platform. There are also reasonable and reliable methods to ensure the parallelism of the joint surface and the accurate alignment of the joints of the multipole field coil when the vacuum chamber is engaged. The pre-assembly process of the vacuum chamber must solve the sealing of the joint surface, the water connection and the electrical connection of the multipole field coil joint, the multi-pole field coil joint housing welding and the leak detection of the housing, the sealing of the vacuum chamber window and the overall vacuum chamber Problems such as time-outs and leak detection.

3 Vacuum chamber pre-installed technical problems Vacuum chamber seal, multi-pole field coil shell welding, multi-pole field coil shell leak detection, window sealing, vacuum chamber leak detection is the key technology to solve the vacuum chamber pre-installation problem.

3.1 The sealing problem of the vacuum chamber body There are 218 windows of different sizes on the vacuum chamber body. The sealing of most windows is the “edge” oxygen-free copper gasket seal, and the oxygen-free copper material is TU1M. The vacuum chamber is the surface of the vehicle. Fluorine rubber ring seal, according to the structural dimensions and sealing form of the seal groove on the vehicle surface, two types of seal ring are needed to achieve double seal in the car, and vacuum and leak detection will be performed between the seal rings. After the vehicle is inspected, the seal of the vehicle surface is checked to ensure that the seal is reliable. Since there is an electrically insulative seal plate sandwiched between the motorized surfaces, four seals per specification are required. Through calculations, the dimensions of the two types of seal rings are: a cross-sectional diameter of 纟 7.40.15 mm, a theoretical unfolding length L of the oligous body on the blunt tip of the unloading piece, and a good protection of the touched edge of Wish on the seal. Window Blinds Goto Miwa mw.cki.netbookmark5 Section diameter is 忉. 90. 15mm, the theoretical development length L = 6269mm, the actual processing length of 6269 persons mm. Due to the larger diameter of the rubber products, it is proposed to use multi-joint vulcanization method, non-uniform section diameter should be within the tolerance range, no obvious joint marks . The entire ring requires a smooth surface that does not allow any defects such as blow holes, cracks, and impurities to affect the ultra-high vacuum seal. The vacuum chamber body material is SS-304LN. The blind plates and flanges of all vacuum chambers also use SS-304LN. The required magnetic permeability under the condition of 16000 A/m 3 The pre-installation problem of the first wall component and the multi-pole field coil. The first wall system is the main part of the vacuum chamber and includes upper and lower sets of diverter coils, plasma facing graphite, carbon fiber protective sheets, divertor neutralization plates, and multipole field coil shielding assemblies. The original ASDEX carbon fiber protection sheet is replaced with a new one, and the graphite block will continue to be used. After this graphite block is removed, fine grinding, ultrasonic cleaning, vacuum oven baking, vacuum encapsulation, or gas-filled encapsulation are required. The quality of the first wall directly affects the discharge quality of the plasma.

The two groups of multi-pole field coils in the vacuum chamber are respectively arranged in the upper and lower divertor chambers of the discharge chamber, and there are 3 coils in each divertor chamber.

The multi-electrode field coils in the discharge operation of the main unit generate a "differential filter field" in the two divertor chambers and form a "striking off magnetic surface" between the plasma and the vacuum chamber to prevent impurity particles from the walls from entering the plasma. One of the three coils contains 8 turns of copper, and the other two coils each contain 4 turns of copper, and the coil cooling holes are centered in each turn of copper. Each coil is surrounded by a shell welded by a corrugated tube and hard segments. The inside of the housing is connected to the atmosphere through the coil feed connector, and the appearance of the coil is directly exposed to the vacuum chamber.Because of the original ASDEX device, the multi-pole field coil feed sleeve and the housing of the vacuum chamber have leaks. The focus will be on multi-pole field coil housing problems and electrical insulation testing.

Pre-installation will be carried out by lifting and placing the two semi-ring vacuum chambers, disassembling the inner parts, grinding and cleaning the vacuum chamber walls, sealing leakage detection of the car surface, leak detection of the multi-pole field coil housing, and overall evacuation of the entire vacuum chamber. Leak detection and other steps are performed. During the entire pre-assembly process of the vacuum chamber, all multi-pole field coil connectors and shell bellows should be protected to protect the sealed parts of the water connector.

4 vacuum chamber pre-installed implementation process 1 vacuum chamber parts removal, grinding, cleaning first remove the first-wall graphite protective tiles, fixed hole bar and multi-pole field coil MP2 protection head graphite tiles and carbon fiber protection sheet, the removal of parts should pay attention Assortment packaging and protection, and proper placement and storage, must not be lost and damaged. In order to ensure the smooth assembly of internal components, appropriate records and markings should be made. Strictly protect the multi-pole field coil housing and strictly protect the components in the vacuum chamber.

The original ASDEX vacuum chamber was subjected to a series of surface treatments during its experimental operation. A complex surface layer had been deposited on the walls of the vacuum chamber. Its presence would seriously affect the plasma discharge, and therefore the vacuum chamber. The grinding of the wall will be an important part of the pre-installation process. Use sandpaper or fine grinding wheels to manually grind the parts that can be operated in the vacuum chamber. Important parts such as the main plasma inner wall, the divertor inner wall, and the diverter indoor can be completely polished. During the sanding operation, dust and dust are often blown by air compressors and vacuum cleaners, and relevant protective measures are taken to prevent damage to other non-demolition parts. After grinding, the inside walls and parts of the vacuum chamber are repeatedly scrubbed with wet cotton yarn, scrubbed with acetone and anhydrous alcohol, and dried by blowing. After the above-mentioned cleaning process, the surface is protected to prevent re-contamination.

When surface treatment is performed on the dismantled parts, the large-area surface is treated by grinding, and the complex-shaped parts can be sandblasted and pickled to remove the surface contamination layer. If pickling method is used, the picklings shall be etched in the pickling solution. The etching time may be determined according to the condition of the oxide film on the metal surface. After pickling, it is rinsed with ordinary water, rinsed with deionized water, and then dried. Dry, package, ready for installation. If sandblasting is used, attention should be paid to the protection of key parts. After sandblasting, sand grains in all gaps must be blown to clean and dry thoroughly.

2 Two-and-a-half vacuum chamber closure and leak detection of multi-pole field coil housing After all problems in the vacuum chamber components of the two-half ring are resolved, the two semi-ring vacuum chambers should be closed. The fluororubber seal ring is embedded in the seal groove of the end face of the vacuum chamber at the end face of the vacuum chamber, and a 10mm thick polyimide insulation baffle is placed on the end face of the vacuum chamber joint, and the connection bolt is connected to the vehicle surface to form a complete annular vacuum chamber. The evacuation and leak detection of the double seal of the vacuum chamber joint surface; the water joint at the multipolar field coil joint in the vacuum chamber is connected, and the water joint is pressure checked for leak detection. After the above two problems are ensured, the electric connector is connected to the bridge and the two connectors are welded with the outer shell of the joint end to form the complete housing of the multi-pole field coil. The inside of the housing is connected to the atmosphere. The field coil conductor and the vacuum chamber are separated by the housing. The six multi-pole field coil housings in the upper and lower parts of the vacuum chamber vacuum chamber have experienced some air leakage problems during the original ASDEX experiment. Now we can see from the appearance of the coil. There are some indentations on the corrugated pipe section, which may cause air leakage. In order to ensure the absolute reliability of the sealing performance of the coil housing, it is necessary to determine the integrity of the multi-pole field coil housing bellows when pre-installed. After the multi-pole field coil connector shell is welded well, a special interface cover is designed at the multi-pole field coil feeding lead port, and the leak detection system is connected to the leak detection system for leak detection. The multi-pole field coil vacuum sleeve leak detection schematic.

Multi-pole field coil vacuum sleeve leak detection 3 overall vacuum chamber vacuum pre-installed leak detection vacuum chamber pre-installed another main purpose is to test the sealing performance of the entire vacuum chamber, check the car surface deformation, only through pre-installed pumping time And leak detection to complete. When the vacuum chamber is in formal operation, there are actually two kinds of pumping systems, ie, 8 turbomolecular pumps (each pumping speed is 3500L/s) to form an external pumping system and titanium is deposited on the wall by sublimation using 19 titanium balls. Membrane-adsorbed internal suction system. The internal suction system is only activated when the HL-2A unit is in operation. In the pre-installation, four molecular pumps are used as the main pump plus the pumping system of the foreline pump. The diagram of the pumping unit is pre-installed for the vacuum chamber. 1 is the ZBS400 pneumatic valve and 2 is the F400 turbo molecular pump. The vacuum chamber pre-installed pumping system is designed as the main pump+Roots pump+mechanical pump's pre-stage lumped three-stage pumping unit, and 4 horizontal windows with 50 mm are selected as pre-installed pumping ports.

Pre-pumping system requirements are as follows: 1 Pumping system background pressure p0

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