Magnetic diagnostic suite of the C-2W field-reversed configuration experiment

REVIEW OF SCIENTIFIC INSTRUMENTS 89, 10J107 (2018) Magnetic diagnostic suite of the C-2W field-reversed
configuration experiment
T. Roche,a) M. C. Thompson, M. Griswold, K. Knapp, B. Koop, A. Ottaviano, M. Tobin, R. Magee, T. Matsumoto, and TAE Teamb)
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, California 92610, USA
(Presented 17 April 2018; received 20 April 2018; accepted 1 June 2018; published online 20 July 2018)
A fundamental component of any magnetically confined fusion experiment is a firm understanding of the magnetic field. The increased complexity of the C-2W machine warrants an equally enhanced diagnostic capability. C-2W is outfitted with over 700 magnetic field probes of various types. They are both internal and external to the vacuum vessel. Inside, a linear array of innovative in-vacuum annular flux loop/B-dot combination probes provide information about plasma shape, size, pressure, energy, temperature, and trapped flux when coupled with established theoretical interpretations. A linear array of B-dot probes complement the azimuthally averaged measurements. A Mirnov array of 64 3D probes, with both low and high frequency resolution, detail plasma motion and MHD modal content via singular value decomposition analysis. Internal Rogowski probes measure axial currents flowing in the plasma jet. Outside, every feed-through for an internal probe has an external axial field probe. There are many external loops that measure the plasma formation dynamics and the total external magnetic flux. The external measurements are primarily used to characterize eddy currents in the vessel during a plasma shot. Details of these probes and the data derived from their signals are described. Published by AIP Publishing. https://doi.org/10.1063/1.5037079
I. INTRODUCTION
The C-2W1 advanced beam-driven field-reversed config- uration (FRC) plasma experiment is the world’s most advanced device of its kind. In its first phase of operation, it has ∼13 MW of beam power as well as ∼10 MW of edge biasing power. Almost all of the machine’s 92 magnets has an independently controllable power supply that can be manipulated in real time using active feedback from magnetic, as well as other, diagnostics.2
In accordance with the increased level of complexity involved in C-2W over C-2/2U, the complexity of the mag- netic probe array has also increased by more than an order of magnitude.1,3,4 Although all of the magnetic diagnos- tics operate simply using Faraday’s law of induction, the design of the diagnostics and details of their sensing cir- cuits are optimized for measurement of various parameters: total magnetic flux, local magnetic field, average magnetic field, enclosed current, and change in the local magnetic field.
In this paper, we describe the various flavors of magnetic probes implemented on C-2W in Sec. II, the flow of data from diagnostic to acquisition in Sec. III, and some analysis method- ology and interesting results in Sec. IV, and finally summarize in Sec. V.
Note: Paper published as part of the Proceedings of the 22nd Topical Confer- ence on High-Temperature Plasma Diagnostics, San Diego, California, April 2018.
a) troche@tae.com
b)TAE Team members are listed in Nucl. Fusion 57, 116021 (2017). 0034-6748/2018/89(10)/10J107/5/$30.00
II. DIAGNOSTIC CATALOG
In this section, we detail all of the magnetic probe vari- eties. An overview of each diagnostic and their installation locations is provided in Fig. 1 and Table I.
A. Point B-field
Point measurements of the magnetic field are taken throughout the C-2W confinement vessel (CV). Each probe is capable of measuring all three components (Br , Bθ , Bz ) of the field. There are two separate measurements of each field com- ponent: one optimized for low ( f < 2 MHz) and the other for high ( f < 10 MHz) frequency fluctuations. The probes them- selves are actually surface mount chip inductors5 designed by CoilCraft CPS. They are designed for use in space or other ultra-high vacuum environments. The slow and fast chip part numbers are AE450RAA333GSZ and AE450RAA103JSZ, respectively. Each of the chips is calibrated with a Helmholtz coil including all cross terms so that a low error represen- tation of the total magnetic field is known at the point of measurement. The slow signals are routed through active inte- grators, Eagle Harbor Technologies, Inc., part number ISP-16, and digitized. The fast signals are digitized as dB/dt to pre- serve high-frequency fidelity. The fully assembled probes are detailed in Fig. 2.
Several of these probes are arranged in azimuthal Mirnov
arrays in order to measure and identify MHD mode struc-
tures in the plasma. Each array consists of 8 probes spaced
◦
∼45 apart. There are 8 such arrays spaced symmetrically
about the mid-plane or center of the CV for a total of
89, 10J107-1 Published by AIP Publishing.