Target Facilities 3/17
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Target Facilities 3/17 |
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In addition to the bolted backwall reference design, two new backwall attachment schemes were introduced at the 2nd Design Integration Meeting, May, 1996.
The first alternative option uses a "bayonet connection" method shown schematically in Figure 2.5.2-5a; more details are given in the Figures 2.5.2-5b and 2.5.2-5c. The replaceable backwall is inserted/removed by a simple loading machine operating either in the vertical or horizontal directions. The permanent structure is equipped with slide guides and hinges for secure insertion and locking. The seal is inserted inside a cavity machined in the internal part of the backwall. This scheme has the advantage of accommodating the backwall differential deformation due to thermal expansions. A particular advantage of the horizontal insertion is the possibility of insertion/removal of the backwall without removing the test assembly. In this case a different penetration from the test cell removable cover has to be provided.
The second alternative option uses bolts for mechanical attachment of the backwall and high average power YAG laser welding to provide a good seal. As shown in Figure 2.5.2-6, this laser system prevents lithium leakage by power-controlled fine lip-seal welding on the edge of the two thin-plate rims of the backwall and the target assembly. The pressing plate fixes the backwall onto the target assembly. By increasing the laser power, the system cuts the welded edge of the rims. For one pair of rectangular rims, more than five times of welding/cutting procedure are possible. The thin rims can be placed on the test assembly side for ease of backwall maintenance. Minimization of the amount of sputter during the cutting operation is one issue to limit radioactive spread around the target assembly.
This laser system is applicable to any part of the target assembly including inlet piping, nozzle, diffuser, and so on. The remotely-replacing flange with "lip-seal" structure is used to join piping, enabling the remote replacement of the whole target assembly without a seal ring. A distinct advantage of this system is the capability to maximize the laser output while keeping sufficient beam quality for coupling into the optical fiber cable. The silica-glass-made optical fibers with a core diameter of 1.0 mm enables transmission of 4.8 kW laser power with high transmission efficiency (> 90%) over a distance of more than 120 m. A major concern of this welding/cutting technique is material reweldibility because rewelding of material exposed to radiation damage (as low as 0.01 dpa) may not be feasible due to helium effects.
Figure 2.5.2-5a. The schematic of the bayonet concept.
Figure 2.5.2-5b. Cross section of the bayonet concept.
Figure 2.5.2-5c. Closeup view of backwall connection concept.
Figure 2.5.2-6. Replaceable backwall attachment scheme with weld-seal.
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Target Facilities 3/17 |
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