Title: Contact mode thermal sensors for ultrahigh-temperature region of 2000–3500 K

Abstract: In this article, we reviewed several existing techniques that were capable of detecting local temperatures in the range of 2000–3500 K in a contact manner. These techniques included several non-standard thermocouples, Seger cones and ultrasonic meters. In particular, ultrasonic meters made of tungsten (W) wires were proven to be working well in nuclear plant for detecting the central temperature of reaction zone. We also presented two alternative approaches. One of them was a kind of single-metal-based thermal sensor made from W, Mo and Ta wires, which utilized the size effect of Seebeck coefficient and theoretically applicable in contact mode measurement up to 3500 K. The other was a kind of detectors with micro-/nano-patterns, which utilized the size effect of surface melting point of bulky materials. This work should shed light on measurement approaches for ultrahigh temperatures in a variety of practical applications.