A. A. IvanovB. Budker
Institute, Novosibirsk
FUSION NEUTRON RESEARCH IN NOVOSIBIRSK INCLUDING EXPERIMENTS
“Piero Caldirola” International Centre for the Promotion of Scienceand International School of Plasma Physics
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Brief description of the approachGDT as a Neutron Source for materials testing and
Hybrid Experiments:
Electron temperature measurements with extended NBs
MHD and micro stability of high- plasma Observation of AIC instability axial confinement ambipolar plugs
Conclusions
LAYOUT OF THE TALK
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 2
3WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 3
Gas Dynamic trap – general layout
The Gas-Dynamic Trap is a version of a standard simple mirror whose characteristic features are – a very high mirror ratio, R , in the range of a few tens;– a relatively large length, L , exceeding an effective mean free path, ii lnR /R, with respect to scattering into the loss cone.
The warm target plasma is almost Maxwellian– behaves like an ideal gas in a container with a pinhole leak
MHD-stable even though system is fully axially symmetric– non-negligible amount of plasma in the regions beyond the mirror throats, where magnetic field has favorable curvature
– MHD ballooning/interchange modes limit stability at 40-60%
The electron neat flux to the end walls is suppressed by potential drop in expanders which develops if H mirror / H wall exceeds ~ 40
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Fusion neutron spectrumAbout 2MW/m2 neutron flux or higher for
accelerated testsSmall enough gradient of neutron flux densityContinuous operationMore than 70% availabilityReasonably small tritium consumption
REQUIREMENTS TO VNS FOR FUSION MATERIALS TESTING
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 4
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LAYOUT OF GDT-BASED NEUTRON SOURCE
Neutron flux density as a function of electrontemperature for injection energy 65 keV
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 5
Power consumption, MW 60
D/T beam energy (keV) 65/65
NB power/trapped (MW) 36.3/27.2
Mirror-to-mirror length (m) 11.4
Electron temperature (keV) 0.65
Plasma density (m-3) 2 x1020
Plasma radius at the center (m) 0.08
Mirror ratio 10
Central field (T) 1.3
Injection angle (deg.) 30
Max. neutron flux (MW/m2) 1.8
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NEUTRON SHIELD & TESTING ZONE ARRANGEMENT
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 6
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Conceptual design is completed for a version of GDT-NS with 1.8MW/m2 neutron flux, 60MW power consumption (BINP, Efremov, Snejinsk)
Plasma physical model based on Monte-Carlo approach is developed (BINP, FZR)
Feasibility of neutron shield is proven by numerical calculation (FZR, ENEA, Snejinsk)
26T, 90mm bore mirror coil design is developed (Efremov)
Small specimen test technology is proposed (KFK, BINP)
Application of GDT-NS for MA burner is considered (FZR, BINP)
STATUS OF GDT-NS DEVELOPMENT
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 7
Conceptual parameters for GDT-based applications
Concept GDT PMI-HP-NS GDT-NS Hybrid
Length, m 8 10 10 30
Fusion power, MW - - 2 200
Radius, m 0.2 0.2 0.2 1
Magnetic field, T 0.3 1.0 1.3 2.5
Beam energy, keV 20 40 65 80
Beam power, MW 4 10 40 100
9WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 9
EXPERIMENTAL MODEL OF GDT
View before and afterupgrade of neutralbeams
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VORTEX PLASMA CONFINEMENT IN GDT
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011
Plasma flow linesfor m=1 mode with vortex.
Limiter biasing produces radial electric field and plasma rotation at periphery
U ~ Te
Steep potential gradient at periphery causes differential plasma rotation
The limiter biasing considerably improved plasma confinement
M=1 mode nonlinearly saturates
a
b
Potential profile Plasma decay a) with vortex, b) no vortex
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No gas puff Gas puff with 5mc, 3.5 MW beams
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011
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STEADY STATE IS ACHIEVED WITH PLASMA REFUELING
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AXIAL RE-DESTRIBUTION OF HIGH- PLASMA PRESSURE
Loop data Plasma diamagnetism WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 12
NB attenuation data –spontaneous excitation of m=2 mode in high- plasma
Oscillations
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Issues addressedFactors controlling electron
temperatureEquilibrium and stability of
anisotropic fast ions Steady state operation Ballooning instability
thresholdEffect of ambipolar fields on
confinementEffect of plasma
rotation/vortex barrier formation
Non-paraxial effects due to high β
Some important results Te is determined by balance
between fast ion drag power and collisional end losses
Fast ion relaxation is classical Skew NBI provide fast ion
density peaks at turning points High-β (>0.5) MHD – stable
plasma in axisymmetric field Suppression of axial electron
heat conduction to the end wall by decreasing magnetic field
Plasma is sustained during several characteristic times with extended neutral beams
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 14
FINDINGS IN GDT EXPERIMENTS
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Injected (Pinj) and trapped (Ptr) NBI power
Fast ion energy content
Linear DD yield near fast ion the mirror
point.
PLASMA PARAMETERS IN GDT EXPERIMENT
DD reaction yield: axial profile radial profile
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PLASMA PARAMETERS IN GDT EXPERIMENT- ELECTRON TEMPERATURE
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On-axis magnetic field depression in turning point region vs energyaccumulated in fast ions
B/B variation across plasma at the turning point
55.022
B
B
B
B
Magnetic field depression and local diamagnetism vs time
PLASMA PARAMETERS IN GDT EXPERIMENT- PLASMA BETA
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011
2<i
i
18WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011
“Saw teeth” relaxations
Axial broadening of fast ion reflection region
“Saw teeth” relaxations
Spectrum of RF noise
EXPERIMENT WITH ADDITIONAL MIRROR CELL
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 19
Compactmirror cell
GDT central cell
Internal cell: Magnetic field: Background plasma:
L=30 cm, d =70 cm. B0=2.4 T, Bm=5.2 T hydrogen, n0 ≈ 1019 m-3,Te ≈ 70 eV, a =9 cm.
NBI: H0 or D0 , E0=20 keV, θ=90º, Pinj ≈ 1 MW, τinj=4 ms19
FAST ION DENSITY IN MIRROR CELL
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 2020
EXPERIMENTAL OBSERVATION OF AIC INSTABILITY IN MIRROR CELL
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HF oscillations threshold: n > 2.5·1019 m-3,A ≈ 35, β┴ = 0.02, сi/аp ≈ 0.23.
||
ciE
E=A,f
A<f
110 — anisotropy in velocity space
Br, arb. u.
Bφ, arb
. u.
PolarizationMain frequency f0 < fci
The magnetic field vector of the wave
rotates in the direction of ion gyration.
Azimuthal mode number m = 1-2
AIC instability
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011
AXIAL CONFINEMENT WITH AMBIPOLAR END PLUGS
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 22
AMBIPOLAR PLUGGING EXPERIMENT AT GDT.
Radial profile of the plasma potential.
with pluggingw/o pluggingdifference
Radial profile of the plasma density.
x 2 on axis
with pluggingw/o pluggingdifference
Linear plasma density time evolution
with pluggingone side plugging w/o plugging
Central cell
NBI
Plasma dump
Plug cellFas ions
Plasma source
Plasma dump
Expander
Magnetic coils
Limiter
OBSERVATION OF AIC INSTABILITYIN LOCAL CELL
WORKSHOP ON FUSION FOR NEUTRONS AND SUB-CRITICAL NUCLEAR FISSION Villa Monastero, Varenna, Italy, September 12 - 15, 2011 24
The probe measured potential fluctuations show the presence of waves having small azimuthal mode numbers m=1,2.
The oscillation frequency is below local ion-cyclotron frequency.
Magnetic fluctuation probes show that the mode is nearly left-circularly (direction of ion gyration) polarized.
These properties are all consistent with an Alfven-like wave generated by AIC instability.
The AIC instability threshold is observed
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Conclusions
Electron temperature achieved already at the GDT experiment corresponds to ~0.4MW/m2 neutron flux for GDT-NS
Below some limit in pressure plasma behavior is classical. No critical issues were found preventing from further improvement of plasma parameters
Reduction of axial losses with ambipolar plugs is demonstratedPlasma steady state conditions are planned to be achieved at
the next step device at higher electron temperatureConceptual design of GDT-NS for fusion materials and sub-
components development is completedPossible application of GDT-NS as a driver for fission/fusion
hybrids is under consideration
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