Fusion plasma engineers have made remarkable progress in designing a tokamak type of experimental reactor, as evidenced by the International Thermonuclear Experimental Reactor (ITER), which produces fusion energy of 1.5 GW(thermal) for 1000 s at least. However, the ITER design is more expensive and requires more advanced technology than earlier machines. With these concerns in mind, extending design options by using a high-temperature superconductor (HTSC) to improve plasma positional instability by placing HTSC ring coils inside the vacuum vessel would be desirable. Here, improving the plasma instability with HTSC coils is discussed, and a possible design of a smaller machine using the coils based on supporting experiments with HTSC tapes is given.