Page 5 - Demo

Nucl. Fusion 59 (2019) 112009
H. Gota et al
Table 1. C-2W machine setting and functionality in various operating phases.
Setting/parameter
NB energy/power ramp
Edge biasing from outer divertor Edge biasing from inner divertor Magnetic field flaring at inner divertor
Equilibrium magnetic field ramp
Equilibrium mirror magnetic field ramp
Active feedback plasma control Particle refueling
OP1.1
Operations phase 1 OP1.2
Operations phase 2 OP2
Yes (ramp up to
40 keV/~21 MW during a shot) Yes
Yes
Yes
Yes (ramp up from ~0.1 T to ~0.3 T during a shot)
Yes (ramp up from ~0.3 T to ~1.0 T during a shot)
Yes Yes
No
(stay at 15 keV/~13 MW) Yes
No
No
No No
No No
No
(stay at 15 keV/~13 MW) Yes
Yes
Yes
No
Yes (optionally available)
Yes (optionally available) Yes (optionally available)
Figure 2. A layout of C-2W axisymmetric magnet systems, where non-axisymmetric Saddle coils are illustrated in cyan color. Pulsed- power formation coils/straps inside DC formation coils are not shown for simplicity.
previously used on C-2U, were repurposed on C-2W to gen- erate a quasi-static axial magnetic field, Bz, in the formation and outer divertor regions. All other coils specified above with associated power supplies, including formation pulsed-power systems, were newly designed and developed for C-2W. Magnets and power supplies are designed to satisfy goals for the two major operating phases in the C-2W experimental program. Equilibrium magnetic fields stay constant in opera- tions phase 1 and are ramped up during a shot in phase 2, as listed in table 1; the typical magnetic fields in those phases are Bz ~ 0.1 T increasing to ~0.3 T, respectively, while the mirror ratio of the magnetic fields in the confinement section is main- tained at about 3.0–3.5 even during the field ramp and at the flat-top. Current waveforms of each equilibrium and mirror coils are independently controlled, which allows for an ade- quate and flexible control of the external magnetic field profile as well as plasma shape and position. Trim coils are placed beneath each of the equilibrium coils, as shown in figure 2,
that can operate independently to correct error fields as well as to perform active feedback control. Non-axisymmetric saddle coils are deployed around the CV that can be operated either passively with a shorted-coil configuration or actively with power supplies for plasma position control. There are a set of in-vacuum fast-switching coils inside the inner divertors in order to provide adequate guide magnetic fields during FRC translation and then to quickly flare the fields (by reversing coil current within a few milliseconds), as depicted in fig- ures 1(b) and (c). Magnetic mirror plugs are placed in between the formation and outer divertor sections at each side of the device that can produce a strong magnetic field up to ~1 T. The mirror-plug coils as well as confinement mirror coils play an important role in contributing to the open-field-line plasma confinement as previously reported [8, 10] and also studied in mirror devices such as GDT [21, 22].
Initial FRC plasma is generated by newly upgraded pulsed- power systems in the formation section that is basically the
5