H. Chikaraishi

National Institute for Fusion Science (NIFS-Repository)

A helical-type reactor is suited to steady-state op-eration and has the advantage that the electro-magneticforce acting on the helical coil is balanced. In particu-lar, the overturning forces on helical coil become zero inthe top and bottom positions, so a simple self-supportingstructure that can provide a large space for vertical portsis required. It is not a fusion plasma experimental device,and the magnetic ﬁeld conﬁguration will be optimizedfor steady-state plasma burning and the ﬂexibility of themagnetic ﬁeld control will be minimized. This report in-troduces a conceptual design for a dc power system toexcite the superconducting coils of the helical type reac-tor. In this design, the poloidal coils are divided into amain part, which generates a magnetic ﬁeld for steady-state burning, and a control part, which is used in theignition process to control the magnetic axis. The fea-sibility of this conﬁguration was studied using the LHDcoil parameters, and the coil voltages required to sweepthe magnetic axis were calculated.To control the magnetic axis, the following two-coilset system is considered.Main coil set This set is used to create the basic mag-netic ﬁeld for operation. The axis of the magneticﬁeld is optimized for steady-state plasma burning.Control coil set This coil set generates a vertical ﬁeldand is used to shift the magnetic axis while theplasma heating process proceeds toward ignition.A feasibility study of this system requires the de-tailed parameters of the coils, and we use the parame-ters of the LHD. Figure 1 shows the coil conﬁgurationand Figure 2 shows the power system for excitation. Toconnect the main coil sets in series, the turn number ofthe coil are adjusted as shown in Table I. The total in-ductance of coil sets are calcurated and the necessaryvolt-second to control the magnetic axis is calcurated asshown in Table II.For case 1 in this table, the magnetic ﬁeld is main-tained at 2.75 T at the magnetic axis. In this case, somevoltage is necessary for driving the main power supplywhen the magnetic axis is swept. It is approximately1/40 of the voltage supplied by the control power andcan be supplied by the main power. If the magneticﬁeld is decreased by approximately 0.1%, the main coilvoltage can be almost zero, as shown in case 2. In thissecond case, the main power does not charge the coilsystem even though it supplies current to the coils. Thisresult demonstrates that a small adjustment in magneticﬁeld or coil position can reduce the voltage required bythe main power supply if the required voltage is not suﬃ-ciently small when this conﬁguration is applied to FFHR.Helical CoilIV main coil(IVm)IV controlcoil  (IVc)OV controlcoil  (OVc)OV main coil(OVm)IS main coil(ISm)IS controlcoil  (ISc)H1 H2Fig. 1: Assumed coil arrangement of LHDIVmH1H2DC power supply for main excitation(Current: 10kA)OVm ISmImVmIVcDC power supply for magnet axis control(Current 260A)OVc IScIcVcFig. 2: Main and control coil excitation for LHDTable I: Coil parameters after turn number adjustment.H1, H2 OV IS IVMain coil setTurn num. 450 −233.9 −46.1 264.7Currentat R = 3.55m 9,861 A ← ← ←Currentat R = 3.60m 10,000 A ← ← ←Control coil setTurn num. - 144 −422.6 −918.8Currentat R = 3.60m - 255.6 A ← ←Table II: Terminal volt-second for the axis shift.Controlcoilcurrent Volt-sec of coilsMain ControlCase 1B=2.75 T 255.8 A 73 Vs 2,792 VsCase 2B=2.748 T 255.4 A −0.1 Vs 2,825 Vs258§26. Design Study of Dc Power Supply of Super-conducting Coils for Helical ReactorChikaraishi, H.

Design Study of Dc Power Supply of Super-conducting Coils for Helical Reactor

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