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