TJ-II has two fast reciprocating drives for Langmuir probes (with a displacement velocity of approximately 1 m/s).    Probe drive 1 is located at φ = 38.2°, R=134 cm (sector D4) and probe drive 2 at φ = 195° (sector B2).
Several different heads can be mounted on the reciprocating drives: e.g., staircase Langmuir probes, a rake probe (as of 2009), or a multi-pin Langmuir probe (2010). A biasing probe has also been used.
- M.A. Pedrosa et al, Fast movable remotely controlled Langmuir probe system, Rev. Sci. Instrum. 70 (1999) 415
- E. Calderón et al, On the Influence of Probe Presheath on the Measurement of Fluctuation and E × B Turbulent Transport by Langmuir Probes, Contributions to Plasma Physics 44, Issue 7-8 (2004) 700 - 704
- M.A. Pedrosa et al, Evidence of Long-Distance Correlation of Fluctuations during Edge Transitions to Improved-Confinement Regimes in the TJ-II Stellarator, Phys. Rev. Lett. 100 (2008) 215003