High power heating of magnetic reconnection in merging tokamak experimentsa)

Recent progress of magnetic reconnection research in the MAST spherical tokamak

“…1,2 This process is known as an effective way of converting magnetic energy into plasma energy in proportion to the square of the reconnecting field / B 2 rec . 3 Recent satellite observations of solar flares also revealed several important signatures of reconnection heating. In the solar flares, hard X-ray spots appear at loop-tops of coronas together with another two foot-point spots on the photosphere.…”

“…[20][21][22] In the recent TS-3 experiment, 2D ion and electron heating characteristics were revealed 23,24 as bulk heating of ions downstream and localized electron heating around the X-point. The energy inventory has been investigated in both push merging 3,25 and pull reconnection. 26,27 However, the electron temperature tends to be as low as 15 eV for most of the laboratory experiments due to a radiation barrier by low-Z impurities, the presence of invasive probe diagnostics inside the vessel, and convective loss under low guide field conditions.…”

“…Tokyo collaboration addressed this issue by the temporary repurposing of an existing collecting lens to provide a 32 chord tomographic ion Doppler spectroscopy capability on the midplane with a radial range spanning the diffusion region. 3,23,39 Here, this paper addresses the recent major progress of detailed profile measurement of both electron and heating using those fine diagnostics during a high field reconnection experiment in MAST. Figure 1 illustrates the geometric setting of the merging/ reconnection experiment in the MAST spherical tokamak (ST).…”

“…33,[41][42][43][44] The reconnected field forms a thick layer of the closed flux surface downstream, and the field line topology of two plasma rings is changed to a single spherical tokamak configuration after merging. 3,20,24 The toroidal field is $0:3-0:8 T the around diffusion region, and the reconnecting field is roughly B rec $ 0: 45 based on equilibrium fitting/reconstruction (EFIT) 46 of the radial component of poloidal B r field after magnetic reconnection at t ¼ 30 ms), ion skin depth c=x pi $ 0:1 m, ion Larmor radius q i < 0:01 m, and ion cyclotron frequency x ci > 10 Mrad/s. P1 is center solenoid, 47 P2 generates double null divertor configuration after merging, 48 P4 and P5 control radial equilibrium, 32,49 and P6 coils control the vertical position.…”

Compact fusion energy based on the spherical tokamak

“…Full details of its predicted performance, and of the expected evolution of electron and ion temperature profiles are provided in [12], based on extensive studies on both MAST and Japanese STs in collaboration with Y Ono and his team [13]. The ST40 device is currently under construction and is expected to begin operation in 2017.…”