Performance Improvement of a Magnetized Coaxial Plasma Gun by Adopting Iron-core Bias Coil and New Pre-Ionization System

Introduction
n The C-2W machine is the world’s premier Advanced Beam-Driven FRC
n Monitoring the complete magnetic evolution of the plasma is essential for
understanding the system’s dynamics
n Over 1000 B-field signals are monitored to provide both post-shot analysis data and data for an advanced active feedback system under development
n Each Diagnostic Magnetic Probe (DMP) system is treated separately in order to keep track of the vast quantity of data; key signals are quickly analyzed and displayed after each shot to provide quick initial feedback to experimenters.
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610 DMP14 – Internal Flux Loop / B - Dot
DMP17 – Internal Rogowski Coils
Flux in Formation Sections (This shot only North)
Machine Overview
Abstract
AAA
Calibration data is used to calculate on and off diagonal probe effective areas and diagonalization matrix A
Sample data of 1 ring of 8 probes at single axial location FRC passes ring 3 times in this case
Copper TapeFluFx Lluooxp aLndoBo-dpot Probe
Commissioning and early operations are underway on C-2W, Tri Alpha Energy’s new FRC experiment. The increased complexity level of this machine requires an equally enhanced diagnostic capability. A fundamental component of any magnetically confined fusion experiment is a firm understanding of the magnetic field itself. C-2W is outfitted with over 700 magnetic field probes, ~550 internal and ~150 external. Innovative in-vacuum annular flux loop / B-dot combination probes will provide information about plasma shape, size, pressure, energy, total temperature, and trapped flux when coupled with establish theoretical interpretations. The massive Mirnov array, consisting of eight rings of eight 3D probes, will provide detailed information about plasma motion, stability, and MHD modal content with the aid of singular value decomposition (SVD) analysis. Internal Rogowski probes will detect the presence of axial currents flowing in the plasma jet in multiple axial locations. Initial data from this array of diagnostics will be presented along with some interpretation and discussion of the analysis techniques used.
n Plasma translates through CV n Slows down and expands after
n r = rl 1 p Bzv
n Velocity calculated by identifying peaks of DMP15 linear array signals
n Thisshottranslatedat~379km/s! n Initial energy 2x C-2U
Eight rings of Eight Mirnov probes along axis measure B (Bz displayed)
Mirnov rings detect translating plasma (2 passes this shot)
Prototype measures current as well as non- vacuum compatible commercial product
n n
Magnetic probes primarily in Confinement Chamber However, probes in all regions as described below
Mirnov Probe
Location
Formation Section
Outer Divertors
Code Name
DMP15b DMP15a
- DMP17 DMP14 DMP20 DMP14 DMP17 DMP16
DMP19 DMP17 DMP17
C – 2W
Linear Array (22 Bz) Mirnov Array
64 probes B, δB External Array (108 Bz)
In-Vacuum Rogowski (2)
In-Vacuum B-dot / Flux Loop (22)
External Flux Loops (48)
In-Vacuum B-dot / Flux Loop (6)
In-Vacuum Rogowski (2) Mirnov Array
16 probes B, δB Flux Loops (34) In-Vacuum Rogowski (2) In-Vacuum Rogowski (2)
Measurement
Excluded Flux
Plasma Motion / Plasma Fluctuations
Eddy Current Loss
Plasma Current
Excluded Flux
External Flux
Excluded Flux Plasma Translation
Plasma Current
Plasma Translation
FRC formation FRC translation
Plasma Current Plasma Current
Status
Active Active
Active (22 recorded) Active
Active Installed Active Installation Pending In Procurement
Active
Maybe
Ready for installation
2 chips per field component:
- Fast high field frequency chip (>1MHz)
to be digitized as δB/ δt
- Slow low field frequency chip (<1MHz)
to be integrated and digitized as B
n Total flux measured at ID of Equilibrium magnets
n Several loops installed on OD of vessel as well
n Signals will constrain solutions for real-time field and current reconstructions
Initial Results from C-2W Plasmas
C-2W Magnetic Measurement Suite
T. Roche, M.C. Thompson, M. Griswold, K. Knapp, B. Koop, A. Ottaviano, M. Tobin, and The TAE Team
Point and azimuthally averaged measurements of Bz along axis
DMP15 – Mirnov Arrays
DMP19 and 20 – External Flux Loops
n n
n n n
Mirnov Probes arranged in linear and azimuthal arrays in CV
n 88 probes in total, 8 rings of 8 and one linear array of 22
Direct measurements of plasma motion and mode structure
Vital plasma parameters inferred from these signals
Calibrations determine probe: Orthogonality, Effective Areas, Frequency Response
Helmholtz coil used to produce known field in r, θ, z directions and all cross terms are measured to calculate deconvolution matrix:
n Each saddle coil has a flux loop inside
n 17 Flux loops per formation section
DMP19 - Flux Loop
voltage divider
17 per formation section
Formation Section
0 3 6 9 12 15
θ chips r chips
z chips
Saddle Coil Flux Loop
CV probe locations
Constructed by ARi Industries Inc.
Example of signal from single probe observing translating plasma and DC field ramp up/down
Probe measures:
Bz average and Φ with 3 wires perpendicular to bend axis.
Spacing between wires is consistent
Linear frequency response to ~50 kHz
Images of Sectioned Cable Constructed by ARi Industries Inc.
rr r✓ rz
A =A✓r A✓✓ A✓z
Azr Az✓ Azz
n Where: 1~ ~˙ AV=B
n Plasma parameters such as RΔφ calculated using these signals
n Plasma current monitor n Multiple axial locations
n Electrode biasing effectiveness n Determine plasma current paths
n Changes in current may be important for plasma stability
Inner Confinement Divertors Vessel
Data from several Magnetic Probe systems
DMP16 – Inner Divertor Mirnov Arrays n Mirnov Array
n
Translating FRC observed by DMP14 and DMP15
n Connectedtofast switching magnet in ID
n 8probesinring n MeasureBr,t,z
n Plasma in/out flow diagnostic
n Probes will detect anisotropies in the Inner Divertors for
n TranslatingCTs n Jet perturbations
Same physical device as DMP15
reflectionoffSMirror
s
Bz pv
Plasma Current Measurements
North side: South side:
N0 N1 S0 S1
... ...
N15 N16 S15 S16
Flux Loop and Segmented B-dot Probe
C.V.