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Nucl. Fusion 59 (2019) 112009 H. Gota et al
Figure 3. Schematic of C-2W showing four distinct zones/regions of diagnostics interest such as Core, SOL/Jet, divertors, and formation with abridged list of instruments.
ramped up. Consequently, broad operating range and func- tionality for each diagnostic system is essential on C-2W. As shown in figure 3, plasma performance and parameters at dif- ferent zones/areas are investigated and provided by a com- prehensive suite of diagnostics that includes magnetic sensors [28], Langmuir probes [29], far-infrared interferometry/polar- imetry [30], Thomson scattering [31], VUV/visible/IR spectr- oscopy, bolometry, reflectometry [32], energy analyzers [33], neutral particle analyzers, fusion product detectors, secondary electron emission detectors [34], and multiple fast imaging cameras [35]. In addition, extensive ongoing work focuses on advanced methods of measuring separatrix shape and plasma current profile that will facilitate equilibrium reconstruction and active control of FRCs [36]. More detailed informa- tion of the C-2W diagnostic suite can be found elsewhere [37]. Signals and data from individual diagnostics are trans- ferred to a data-acquisition system that acquires about 2500 channels on every C-2W discharge currently and will increase as new diagnostics, measurements, and other subsystems come online. The acquired raw data is post-processed into plasma parameters and then stored on a physics database for further data analysis. Some raw data, such as magnetic probe signals, get processed continuously during a plasma discharge through the real time control system for use in active feedback control of the plasma. On typical C-2W discharges ~4 giga- bytes of data are currently generated after each shot, including analysis movies and computations; this data size will also increase as more signals with longer timescale get acquired and post processed for physics parameters.
3. C-2W experiments and results—operation phase 1
C-2W/Norman is a brand-new experimental device with substantially upgraded subsystems compared to C-2U, as
described in the previous sections. Early C-2W experimental program efforts have been mostly devoted to subsystem com- missioning/conditioning as well as to exploration of new operating parameters/settings, particularly in the formation pulsed-power systems and magnetic field profiles/waveforms in the CV and divertor areas. In order to gain early assurance of system functionality and develop robust FRC formation and translation schemes, C-2W experiments commenced with a single-sided configuration where half of the device was ini- tially constructed and operated while the other half was still being built. In C-2W operation phase 1, as listed in table 1, there are two major operating configurations/conditions: oper- ations phase 1.1 (OP1.1)—keeping strong guiding magnetic field at inner-divertor regions (in other words, without magn- etic field flaring) so that C-2W can operate in a ‘C-2/2U like’ machine configuration; operations phase 1.2 (OP1.2)—flaring magnetic field at inner-divertor regions with transferring edge biasing/control areas from outer to inner divertors. In a simple picture, this basically changes the operating machine configuration from figures 1(b) and (c). This section describes (i) key physics/engineering elements to produce an advanced beam-driven FRC plasma on C-2W, (ii) early experimental results using single-sided machine configuration to ensure and validate a robust FRC formation as well as its transla- tion through the inner divertor, and (iii) newly obtained experimental results with a full C-2W machine configuration in operation phase 1—with/without flaring magnetic field at inner-divertor regions but no field ramp-up or NB input power increase, as shown in table 1.
3.1. Advanced beam-driven FRCs
As previously identified and discussed in C-2/2U experi- ments[4,6,7],producingawellstabilizedinitialtargetFRC for effective NBI is the important key to achieve/obtain a
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