Radiative Measurements in C-2W

Interferometry technique to measure 2D FRC equilibria on TAE’s Norman device
Roger J Smith, Laura Galeotti, Sean Dettrick, Sangeeta Gupta, Marco Onofri, Jesus Romero and the TAE Team
Abstract
The mid-plane multi-chord FIR interferometer system on the Norman device is used in conjunction with the equilibrium (EQ) field coils and trim coil set to move the plasma axially and thereby determine the equilibrium density profiles in both r and z. Lifetimes for plasmas in Norman are routinely over 30 milliseconds. This allows sufficient time to displace the field reversed configuration (FRC) plasma meters on a millisecond time scale. The FRC is typically 2m long and the confinement vessel (CV) is 6m allowing generous capability to interrogate the plasma over its half- length. Translation can be initiated using waveform controlled EQ coils with feedback control and an spontaneous axial instability has been observed for magnetically compressed FRCs. Details of the FRC density distribution in r and z past the X point are discussed as well as implications of the coupling of NBI power to a displaced FRC. The measured 2D profiles are modeled using a Lamy Ridge – Monte Carlo code. The implications of the measured profiles as inputs and validation to numerical modeling with respect to heating and sustainment of the FRC by NBI will be presented and discussed.
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610 Programmed translation Shot: 119723
Spontaneous translation Shot: 116403
Formation Qtz tube
Radius [m]
Radius [m]
15.6 – 15.83 ms
Time of axial μ-Burst activity 16.7 – 22.4 ms translation
hollow initially
Plasma on-axis builds
119723 One sided and mirrored ne surface: (Abel inverted frames)
116403 One sided and mirrored ne surface: (Abel inverted frames)
Position: DZ trace
axial profile revealed
X-pt?
Position:DZ trace
Details of shots in the 1197xx series
Flat excluded flux radius , DFR, ~40cm Translation very rapid 40 km/s when DZ = 1m. FRC ne radial profile is hollow.
terminatio n
on wall
LID Profiles from
NB Injector (1 of 8)
• FRC. •
•
•
• .•
•
t = 15.7 ms
• •
Details of shots in the 1164xx series
Bz(wall) ramped significantly during these shots.
Excluded flux radius, DFR, is decreasing to 30 cm at the time of translation. Plasma is being magnetically compressed radially.
A spontaneous axial instability, not programmed.
Robust μBurst activity, indicative of fast ions pressure contributing substantially to pressure balance
t = 18.9ms
RDF/Ö2 and RDF
The ne distribution is hollow past the ends of the Peak ne radius lies inside of 40 cm.
outer divertor
central plasma
Inner divertor
Interferometer viewing ports in CV
Electrode biased plasma
Density depression, X-pt?
C-2W device: CV and NB injectors
Simulations of NBI sustained FRCs using a Monte Carlo + Lamy Ridge code
Key observations that suggest the magnetically compressed FRC is short
Laser Table
Beam Path
C-2W Vessel
Shot 116416
• On-axis ne profiles drop for z > 0.25m but closes and peak on-axis, z > 0.5 m.
Composition from shots: 116395-405
Distance from midplane
• Thomson scattering Te(r,t) profiles show lower Te for z > 0.25 m. Temperature recovers outside of X pt.
μ-Bursts activity stops
DZ =0.25m
• uBurst activity drops off for Z > 0.25m. Also
noticed in bolometer detector arrays.
#63483 L. Galeotti
#67082, L. Galeotti
#67082, L. Galeotti
• Peak ne radius was ~50 cm, > 40cm
• Now Peak ne radius < 40cm, which matches experiment.
• 2D profile matches shot 119723’s shape
7 vertical beams
7 beams tilted by 15°
xFIR
Conclusions/Summary
14 chord FIR core interferometer
For this study we found that the value of the neutral density background at the wall could be used as the knob to “simulate” in MC+LR the sink term needed..
The 2D ne profiles show that NBI heating of the plasma seems to be most effective in the axial region
Massive Support Structure
2D Te distribution
2D ne distribution
• •
• • •
Preliminary observations of 2D profiles, ne(r,z) suggests that the X pt may be located where there is a ~30% depression of on-axis ne, at Z ~ 0.5 m where a topological change in profile from hollow to occurs.
Shots, 1164xx series, show μ-Bursts activity, indicative of fast ion pressure on the order of thermal pressure, and are therefore of intrinsic interest. It may be that μ-Burst activity is indicative of a more closed equilibrium.
FRC plasma on-axis ne (at Z =0 m) rises during the shot but has never been seen to exceed the outlying peak ne. Code development now accurately captures mid-plane ne distributions with peak ne radius < 40cm.
Magnetically compressed FRCs with peaked ne profile outside of the X pt? have yet to be successfully modeled but work is ongoing.
Starting from an initial equilibrium with a lower separatrix radius we were able to find a midplane profile more similar to experimental results.
•
|Z| < 0.5m where the FRC has high on-axis density for shot 116403. This makes since as hollow ne profiles couple less efficiently to the neurtral beams.
T [eV]
Density [1019 m-3]
Density [1019 m-3]
3.06m