This paper describes the realization of magnetic detection of the finite β free boundary plasma shin for a toroidal helical plasma. Recent experimental results, the normalized displacement Δb/ap as a function of volume average beta <β>, are discussed. The measured typical plasma boundary shift, Δb/ap, in the standard Heliotron E configuration (Rp=2.20m, ap=0.21m, Ԏ/2ᴨ(0)~0.53, Ԏ/2ᴨ(ap)~2.8) is (5–12)x10–3, when the volume averaged beta is 0.50%. The measured normalized plasma boundary shift is nearly proportional to the diamagnetic volume-averaged beta, for values of beta up to 0.95%. The magnetically determined plasma boundary shift Δb is less than 3 mm. The measured shift is in the range in-between the expected upper limit (Δb/ap = β(0)/2βeq) and the lower limit (Δb/ap = <β>/2βeq), where βeq = (Ԏ/2ᴨ(ap))2(ap/Rp)~0.77 for the standard configuration of Heliotron E.

We find that the measured free boundary plasma shift strongly depends on the initial vacuum magnetic configuration parameters such as the horizontal position of magnetic axis and the rotational transform. When the vacuum magnetic axis is shifted inward toward the major axis, we observed a significant decrease of the normalized plasma shift (Δb/ap) and the plasma induced vertical field, which we interpret as being due to a reduction of Pfirsch-Schlüter current.