Feasibility of creating an island divertor in the Uragan-2M torsatron. In stellarators, where the toroidal magnetic field plays a decisive role in the formation of closed magnetic surfaces, it is every so often difficult to create a helical magnetic divertor structure. The present work has reduced to finding (both experimentally and numerically) out of a vast number of possible regimes those several regimes with the islands at the edge, which would decide the issues of island divertor creation. The experimental magnetic field structure studies by the scanning luminescent rod technique as well as the computational investigations demonstrated an existence in the Uragan-2M torsatron of ten modes of configurations with the islands of resonances at the rotational transform angles i/2π=1/3, 3/7, 2/5, 1/2, 4/5, which lie outside the last closed magnetic surfaces. These modes are: (1) kφ=0.285, <B⊥/B0>=1.45% (islands i/2π≈1/3); (2) kφ=0.295, <B⊥/B0>=1.8% (islands i/2π=1/3); (3) kφ=0.295, <B⊥/B0>=3.21% (islands i/2π=2/5); (4) kφ=0.31, <B⊥/B0>=1.5% (islands i/2π=2/5); (5 and 6) kφ=0.31, <B⊥/B0>=1.14% and <B⊥/B0>=1.85% (islands i/2π≈1/3); (7 and 8) kφ=0.32, <B⊥/B0>=1.34% and <B⊥/B0>=1.58% (islands i/2π≈1/3); (9) kφ=0.33, <B⊥/B0>=1.92% (islands i/2π=2/5 and i/2π=3/7); (10) kφ=0.36, <B⊥/B0>=2.03% (islands i/2π=1/2). The combination of the low-density plasma discharge with the scanning luminescent rod procedure to measure the magnetic surface has first visually demonstrated the operation of the island divertor in U-2M fusion device. It has also been shown that by varying the value of vertical magnetic field in the configuration it is possible to provide the following capabilities for controlling the island divertor operation: i) to cut off the islands by the vacuum chamber wall; ii) to use the remains of the islands already broken down by the existing perturbations; iii) to reduce and suppress the islands. In another variant of the island divertor realization, when the islands are positioned inside but close to the last closed magnetic surfaces, a movable local limiter can be used. (G.G. Lesnyakov and others)
