htpd2018-troche_v3

Magnetic Diagnostic Suite of the C-2W Field-Reversed Configuration Experiment
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 500 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
DMP19 and 20 – External Flux Loops
T. Roche, M.C. Thompson, M. Griswold, K. Knapp, B. Koop, A. Ottaviano, M. Tobin, and The TAE Team
CV probe locations – 22
Constructed by ARi Industries Inc.
B-Dot
Flux Loop
a)
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
X B-Field
b)
Probe measures:
• Bz average and Φ with 3 wires
perpendicular to bend axis.
• Spacing between wires is consistent
• Linear frequency response to ~50 kHz
Formation Section
0 3 6 9 12 15
North side: South side:
N0 N1 S0 S1
... ...
N15 N16 S15 S16
Copper TapeFluxFLlouopxaLndoBo-dpot Probe
Flux Loop and Segmented B-dot Probe
Top View
C.V.
Side View
Images of Sectioned Cable
Constructed by ARi Industries Inc.
Inner Divertors
Confinement Vessel
Data from several Magnetic Probe systems
Machine Overview
Abstract
n Magnetic probes primarily in Confinement Chamber n However, probes in all regions as described below
n n
n
Plasma translates through CV
Slows down and expands after reflection off S Mirror
Translation velocities over 400 km/s achieved
s
n Plasmaradiusestimatedasexcludedflux n Linear arrays of probes provide detailed
information about plasma shape and evolution
n Coupled with pressure balance many plasma parameters can be determined
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 establish 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-thru 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.
Plasma Current Measurements
l
flux measurements
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
Flux Loops (34) In-Vacuum Rogowski (2) In-Vacuum Rogowski (2)
Measurement
Excluded Flux
Plasma Motion Plasma Fluctuations
Flux Leakage
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 Active Active Active Active Active Preparing for Install
Active Pending Active
Sample data of 1 ring of 8 probes at single axial location FRC passes ring 3 times in this case
n MirnovProbesarrangedinlinearandazimuthalarraysinCVandID
n 102 probes in total, 10 rings of 8 (8 in CV, 1 in each ID) and one linear array of 22 (in CV)
n Directmeasurementsofplasmamotionandmodestructure n Totalfieldandfluctuationoutput
n Vitalplasmaparametersinferredfromthesesignals
n External B probe at every vacuum interface
DMP16 Inner Divertor Arrays
n Detection of anisotropies
a) b)
c)
r=rls1p Bzv Bzp v
z
n 2sensorsperfieldcomponent
n n
Translating CTs Jet perturbations
n Fast – sensitive to high frequency oscillations (>1MHz) digitized as dB/dt n Slow – sensitive to low frequency oscillations (<2MHz) digitized as B
Bz
Br Bθ
n First translated FRC in C-2W observed by DMP14
This shot had strong n=1 Averaged out by DMP14 Visible in Point Measurement Helpful in determining RΔΦ
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
DMP15 and DMP16 – Mirnov Arrays
Selected Results from C-2W Plasmas
DMP17 – Internal Rogowski Coils
n Plasma current monitor n Multiple axial locations
n Electrode biasing effectiveness n Determine plasma current paths
n Current important for plasma stability Plasma current
1 p Bv Eth = ↵Bp2VF RC v Bp
signals due to edge biasing at indicated locations
FRCvol = ⇡ r2 (z) dz pol = 0.31⇡ Bp
r = rl
Z✓2 ◆ 1 ✓r,max ◆2
FRCl=z 3rmax max=12 rw l r3
n MHDmodecontentofthe64Mirnovprobesdetermined using SVD analysis
n n = 1 – 4 detectable, n = 1 example displayed above
n No imposed model, just matrix algebra n Incoherent fluctuations also detected
rw
n Many plasma parameters derived from excluded
Saddle Coil Flux Loop