MageePosterV2

Abstract
Measurements of fusion products in the C-2U and C-2W1 FRCs reveal the dynamics of the highest energy fusile ions in the plasma. In the case of deuterium neutral beam injection (NBI) into deuterium plasmas, fast ions born from charge exchange of injected beam neutrals are studied. Measurements of 3 MeV DD protons and 2.45 MeV DD neutrons are used to discern their confinement, accumulation, and spatial distribution in the plasma. In the case of pure hydrogen NBI into deuterium plasma, measurements of fusion products reveal plasma ion acceleration by a beam-driven wave. A fast tail in the bulk ion population is drawn out on sub-collisional timescales. This wave has been identified as an Ion
Measuring fusion products Proton detectors
Emission from beam-injected fast ions
Emission from plasma-accelerated fast ions
Bernstein Wave though particle-in-cell simulation. [1] H. Gota et al, Nucl. Fusion 59, 112009 (2019)
[2] R. Magee et al, Nature Physics 15, 281-286 (2019)
Background
2
0.8
0.6
0.4
0.2 0.0
calculated
• The C-2W/Norman neutral beam injector system: Parameter
Number of fixed energy beams Number of tunable beams Beam energy (keV)
Ion current per beam (A) Pulse duration (ms)
Injected power/beam (MW) Total NB power (MW)
Horizontal divergence (mrad) Vertical divergence (mrad)
1 2
t (ms)
3
4
• Measurements of fusion products can be used to diagnose the dynamics of beam-injected fast ions and their effects on the plasma
• The deuterium-deuterium fusion reaction has 2 branches: D + D è T (1 MeV) + p (3 MeV)
• • • •
• • • •
•
•
•
Fast ion density profile is self-consistently calculated using experimentally measured plasma profiles and Monte Carlo simulation of fast ion (see poster by S. Gupta)
Beam-target neutron rate calculated from resulting profile (red diamonds) is consistent with measurement (black line) in plasmas without strong ion acceleration
In plasmas with strong ion acceleration, the measured flux exceeds the calculated flux
Measurements of fusion products in the beam-driven field reversed configuration
R. M. Magee, B. Fox, S. Korepanov, S. Nicks, T. Tajima, and the TAE Team
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
è He3 (0.8 MeV) + n (2.5 MeV)
10 12 14 16 18 20
• Depending on neutral beam fueling, beam-plasma or thermonuclear fusion can be the dominant process
4
103
102
101
100
0.0 0.2
105
10
Beam energy (keV)
Value
4
4
15 → 40 keV
130 30
1.7 → 3.5 MW 20
38
11
01234 t (ms)
0.4 0.6 0.8 T (keV)
1.0
•
•
•
•
•
•
Passivated Implanted Planar Silicon (PIPS) detector from Canberra Industries 3°, 6°, or 9° swappable collimators for profile measurements
Automated 2D aiming with two remote controlled linear feedthroughs
Operated in pulse counting mode
2 Active area = 5000 mm
X-rays and low energy particles blocked by 5 – 40 μm Al foil
•
•
•
•
Radial fast ion density profile (black line) is inferred from measured proton emission profile (blue diamonds)
Trial radial profile is line integrated (right) to produce trial line integrated profile (red diamonds)
Profile is qualitatively consistent
with classical Monte Carlo simulations
Fast ion lifetimes are inferred from the decay in the neutron signal after beam termination
1.5 1.0
0.5
0.0
-20 0 20 40 60 80 r (cm)
50 0 -50
-50 0 50 x (cm)
•
•
•
•
•
•
•
•
•
•
•
•
In deuterium plasmas with hydrogen NBI,
the dynamics of beam and plasma ions 10 are separated using an EM-NPA 5
Neutron detectors
1.2 1000 peaked 800
1.0 flat
0.8 400
0.6 200 1000
0.4 800 600
0.2 400 0.0 200
0.0 0.5 1.0 1.5 2.0 0 velocity (106 m/s)
peaked
• • •
•
Plastic scintillator + PMT High time resolution (10 μs) Limited spatial resolution
Good agreement between the two diagnostics
Fast ions in the FRC vs tokamak
NBI = principal sustainment component large, plasma-sized orbits, ρfi ~ a perpendicular injection, vperp >> vpar
No observed fast ion density limit
NBI = auxiliary heating/current drive small fast ion orbits, ρfi << a tangential injection, vfi,perp << vfi,par EPM and AEs limit fast ion density
flat
Comparison to 1d pressure balance calculation
Particle-in-cell simulation
Modeled as initial value problem with EPOCH particle-in-cell (PIC) code
Wave vector perpendicular to magnetic field
Dispersion relation in low beta case
(“SOL plasma”) reveals Ion Bernstein modes at many ion cyclotron harmonics (see
poster by S. Nicks)
Summary
Measurements of fusion neutrons and protons are complementary – neutrons are good for temporal dynamics, protons for spatial profile
In the C-2U and C-2W FRCs, classical confinement is confirmed by measurements of fast ion lifetime and fast ion spatial profile
In plasmas with large velocity space gradients, beam driven ion acceleration is observed.
0
15 deuterium
We observe a large tail of high energy 10 deuterium and supra-thermonuclear 5 neutron emission 0
Magnetic fluctuations at the deuterium Ωci appear coincident with acceleration
Two cases are compared:
• “peaked” - 5 beams at 14.4 kV
• ”flat” - 2 beams at 11.5 kV,
3 beams at 16 kV
Both fluctuation amplitude and high energy tail are reduced when beam energy distribution is flattened
Indicative of df/dv driven mode
012345 t (ms)
1.4 1.2 1.0 0.8 0.6 0.4
0.2 0.0
peaked
40 30
20
10 0 15
hydrogen
5 4
3
2
1
0 -1
54
32
10 -1
1.8
1.5
1.2
0.9
0.6
0.3 0.0
flat
1.0 measured
600
reaction rate (cm-3s-1)
neutron rate (a.u.)
f(v)
f (kHz)
f (kHz)
b2 (10-4 G2)
y (cm)
normalized profiles
neutrons (a.u.)
energy (keV)
energy (keV)
r∆φ (cm)
signal (a.u.)
signal (a.u.)