V.V.Prikhodko1,3, P.A.Bagryansky1,3, E.D.Gospodchikov1,2,,4, A.A.Lizunov1,Z.E.Konshin1,3, O.A.Korobeynikova1,3, Yu.V.Kovalenko1, V.V.Maximov1,3, S.V.Murakhtin1, E.I.Pinzhenin1,

V.Ya.Savkin1, A.G.Shalashov1,2,4, E.I.Soldatkina1,3, A.L.Solomakhin1,3, D.V.Yakovlev1

1 Budker Institute of Nuclear Physics, Novosibirsk, Russian Federation2 Institute of Applied Physics, Nizhny Novgorod, Russian Federation3 Novosibirsk State University, Novosibirsk,Russian Federation4 Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russian Federation

Stability and Confinement Studies inthe Gas Dynamic Trap

Interest to magnetic mirrors went missing in the 1980's because of three key problems: Interest to magnetic mirrors went missing in the 1980's because of three key problems: magnets' complexity, micro-instabilities, and low temperature of plasma. However, magnets' complexity, micro-instabilities, and low temperature of plasma. However, researches on the Gas Dynamic Trap (GDT) device at the Budker Institute of Nuclear researches on the Gas Dynamic Trap (GDT) device at the Budker Institute of Nuclear Physics demonstrated the possibility to overcome these difficulties. Confinement of Physics demonstrated the possibility to overcome these difficulties. Confinement of plasma with high energy density has been performed on GDT device with simple plasma with high energy density has been performed on GDT device with simple circular coils. “Vortex confinement” has been implemented to suppress the radial losses circular coils. “Vortex confinement” has been implemented to suppress the radial losses induced by flute-like MHD instability inherent for axially symmetric devices. This induced by flute-like MHD instability inherent for axially symmetric devices. This technique allowed reaching local plasma beta close to 0.6. The auxiliary microwave technique allowed reaching local plasma beta close to 0.6. The auxiliary microwave heating on electron cyclotron resonance (ECR) frequencies raised the electron heating on electron cyclotron resonance (ECR) frequencies raised the electron temperature up to 0.9 keV near the device axis. Alfven ion-cyclotron (AIC) instability temperature up to 0.9 keV near the device axis. Alfven ion-cyclotron (AIC) instability has been observed, but not affect to the plasma power balance. The proposed report is has been observed, but not affect to the plasma power balance. The proposed report is dedicated to three following topics. The first is optimization of the “vortex dedicated to three following topics. The first is optimization of the “vortex confinement” in presence of ECR heating. Introducing the additional “vortex” layer confinement” in presence of ECR heating. Introducing the additional “vortex” layer inside the existing one allows extending high-temperature phase behind the atomic inside the existing one allows extending high-temperature phase behind the atomic beams turn off time. The second is definition of critical parameters for the divertor. It beams turn off time. The second is definition of critical parameters for the divertor. It was shown, that the critical wall position corresponds to expansion ratio of magnetic was shown, that the critical wall position corresponds to expansion ratio of magnetic field field KKcritcrit~40. This value is in a reasonable agreement with a simple theoretical model ~40. This value is in a reasonable agreement with a simple theoretical model

and remains constant in the range of electron temperature up to 700 eV. The neutral gas and remains constant in the range of electron temperature up to 700 eV. The neutral gas in the divertor does not affect the discharge until its density exceeds an order of in the divertor does not affect the discharge until its density exceeds an order of magnitude the plasma density. The third is study of unstable modes. In addition to AIC, magnitude the plasma density. The third is study of unstable modes. In addition to AIC, the new type of oscillations was observed at the range of tens of ion-cyclotron the new type of oscillations was observed at the range of tens of ion-cyclotron frequencies. It was preliminary identified as Drift-Cyclotron Loss-Cone instability.frequencies. It was preliminary identified as Drift-Cyclotron Loss-Cone instability.

AbstractAbstract

Presented by : Vadim PrikhodkoPresented by : Vadim PrikhodkoE-mail: V.V.Prikhodko@inp.nsk.suE-mail: V.V.Prikhodko@inp.nsk.su

27th IAEA Fusion Energy Conference (FEC2018)27th IAEA Fusion Energy Conference (FEC2018)Gandhinagar (Ahmedabad) Gujarat, India, 22-27 October 2018Gandhinagar (Ahmedabad) Gujarat, India, 22-27 October 2018

GDT deviceGDT device

Western expander tank

Neutral beam injectors

Beam dumps

Arc generator of pre-plasma

Mirror

Eastern expander tank

Mirror-to-mirror distance 7 mMirror ratio 30-40Magnetic field at midplane 3.1-3.5 kGsPlasma density at midplane ~ 1013 cm-3

Electron temperature up to 0.9 keV

Mirror

ECR waveguide

Movable collector experiments (heat by NBI + ECR):Movable collector experiments (heat by NBI + ECR):The collector position is defined by The collector position is defined by KK = = BBmirrormirror / / BBwallwall..

Theoretical prediction isTheoretical prediction isExperimental value is Experimental value is KKcritcrit ≈ 30 at ≈ 30 at TTee ≤ 700 eV. ≤ 700 eV.

Test of vacuum conditions in the expander (heat by NBI only):Test of vacuum conditions in the expander (heat by NBI only):Estimation: gas flow with density 10Estimation: gas flow with density 101212 cm cm-3-3 and temperature of and temperature of 300 300 ooK will double the ion flux to the endplate.K will double the ion flux to the endplate.Experiment: gas produce no effect up to 10Experiment: gas produce no effect up to 101414 cm cm-3-3 (at higher (at higher densities vacuum conditions of central cell degrades).densities vacuum conditions of central cell degrades).Explanation: plasma heats the gas and rising pressure extrudes Explanation: plasma heats the gas and rising pressure extrudes gas away from plasma.gas away from plasma.

Expander physicsExpander physics

K crit≈√mi /me≈40 .

MirrorMirrorcoilcoil

Western expander tankWestern expander tank

EndplateEndplateMovableMovablecollectorcollector

Optimization of the confinement in high-temperature regimeOptimization of the confinement in high-temperature regime

One gyrotron was used to produce pre-plasma by microwave discharge, another one One gyrotron was used to produce pre-plasma by microwave discharge, another one heated the plasma. Central parts of segmented endplates were electrically biased to heated the plasma. Central parts of segmented endplates were electrically biased to suppress MHD activity at the near-axis region. Electron axial losses: <suppress MHD activity at the near-axis region. Electron axial losses: <EEee> = 4.6> = 4.6±0.4 ±0.4 TTee..

EX/P5-25

High-frequency oscillationsHigh-frequency oscillations

HF

amp

litude, arb

. u.

Oscillations at frequencies 20-70 MHz.Oscillations at frequencies 20-70 MHz.Distance between lines is 5.3-5.5 MHz, that is close Distance between lines is 5.3-5.5 MHz, that is close to ion-cyclotron frequency at fast ions turning point.to ion-cyclotron frequency at fast ions turning point.Preliminary identified as DCLC instability.Preliminary identified as DCLC instability.

AIC

NB injection

nwarm /nhot

ω/Ω

ci

Example calculations of the most unstable modes for different loss Example calculations of the most unstable modes for different loss cone size (cone size (RRGG=2 – empty and =2 – empty and RRGG=6 – filled markers) [I.A.Kotelnikov, =6 – filled markers) [I.A.Kotelnikov,

et. al. Phys. Plasmas 24, 122512 (2017)].et. al. Phys. Plasmas 24, 122512 (2017)].

DCLCDCLC

Bernstein modes Bernstein modes (suppressed by axial (suppressed by axial

inhomogeneity).inhomogeneity).

P.A.Bagryansky, A.G.Shalashov, E.D.Gospodchikov, et. P.A.Bagryansky, A.G.Shalashov, E.D.Gospodchikov, et. al., Phys. Rev. Lett. 114, 205001 (2015).al., Phys. Rev. Lett. 114, 205001 (2015).

D.V.D.V.Yakovlev, Yakovlev, A.G.A.G.Shalashov, Shalashov, E.D.E.D.Gospodchikov, et. Gospodchikov, et. al., Nucl. Fusion 58, 094001 (2018).al., Nucl. Fusion 58, 094001 (2018).

E.E.Soldatkina, Soldatkina, M.M.Anikeev, Anikeev, P.P.Bagryansky, et al., Phys. Bagryansky, et al., Phys. Plasmas 24, 022505 (2017).Plasmas 24, 022505 (2017).

ReferencesReferences