Fig. 1. The R and R′ indicate the resistance of the heaters and the total resistance of the other part of the assemblies, respectively. P = I²(R + R′), under the same heating power, the total resistance decreases and the total current augments, which increases the heat generated in R′ and decreases the heat generated in the heaters. So the method of double-layer heaters can slow down the rapid rise of the cavity temperature.

Fig. 2. The schematic diagrams of two assemblies. (a) The schematic diagram of the DHA. Two layers of heaters were insulated by an aluminum tube, and the two heaters were connected with two 0.2 mm Ta electrodes in the assembly. (b) The schematic diagram of the SHA. It is a normal 10/4 assembly which is used widely.

Fig. 3. The power–temperature diagrams of assemblies. (a)–(c) The relationships for the sample diameters of 2.5 mm, 2.3 mm, and 2 mm, respectively. (d) The relationships for type No. 3 and type No. 11.

Fig. 4. The SEM images of recovered sample. (a) The image of recovered sample of the DHA (type No. 3). (b) Enlarged image of red circle in (a), the dendritic texture indicates the melting of the sample.