First plasma experiment on spherical tokamak device UTST

Ryota Imazawa, Makoto Nakagawa, Shuji Kamio, Ryuma Hihara, Takuma Yamada, Michiaki Inomoto, Yuichi Takase, Yasushi Ono

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


The UTST (University of Tokyo Spherical Tokamak) device was constructed for the purpose of exploring the formation of ultrahigh-beta ST (spherical tokamak) plasma using the double null plasma merging method. When two plasmas merge together to form a single plasma, magnetic field lines reconnect, and magnetic field energy is converted to plasma kinetic energy, increasing the plasma beta. Merging start-up has been demonstrated in the TS-3/4, START, and MAST devices using coils inside the vacuum vessel, and the TS-3 plasma obtained a 50% beta. In order to demonstrate start-up in a more reactor-relevant situation, UTST has all poloidal field (PF) coils outside the vacuum vessel. The first plasma experiment on the UTST was begun in December 2007. In the results, the plasma obtained 10 kA by using only the outer PF coils and a single ST was generated in the lower area (z = -0.3 to -1.0 m) close to a washer gun. This result suggests that another washer gun on the top of the UTST can allow the generation of ST in the upper area and merging start-up by using outer PF coils.

Original languageEnglish
Pages (from-to)20-26
Number of pages7
JournalElectrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi)
Issue number2
Publication statusPublished - Apr 30 2012
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Energy Engineering and Power Technology
  • Electrical and Electronic Engineering


Dive into the research topics of 'First plasma experiment on spherical tokamak device UTST'. Together they form a unique fingerprint.

Cite this