In GAMMA 10, divertor simulation study has been started as a new research plan. Finding of the reduction method of high heat-load to the divertor plates is an important key of an operation scenario of fusion reactors. So precise estimation of divertor heat flux is an important task to do it. The paper describes advanced concept of heat flux estimation and proposes the improvement of the sensor used in GAMMA 10. First experimental result of a new sensor is also shown.