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Stellarator-Mirror Based Fusion Driven Fission Reactor

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Stellarator-Mirror Based Fusion Driven Fission Reactor Research on controlled fusion at the Institute of Plasma Physics in Kharkiv Presented by V.E. Moiseenko on behalf of IPP-Kharkiv research team NATIONAL SCIENCE CENTER "KHARKOV INSTITUTE OF PHYSICS AND TECHNOLOGY" INSTITUTE OF PLASMA PHYSICS The Main Directions of Plasma research at IPP NSC KIPT 1. Fusion Investigations (theory and experiment) 1.1. Magnetic confinement of plasma in stellarators and electro- magnetic traps. 1.2. High frequency methods of plasma heating. 1.3. Diagnostic methods of high temperature plasma. 2. Powerful pulsed and quasi-steady-state plasma accelerators and their applications. 3. Problems of fusion reactor ITER 3.1. Problems of divertor and its materials. 3.2. First mirrors of diagnostic systems. 4. Plasma technologies. 5. Fundamental problems of plasma physics. All experimental devices related to fusion at Ukraine are located in IPP NSC KIPT. Significant part of fusion theoretical research ia also carried on here. 2 Infrastructure • 3 buildings: 2 with office area (19,000 m2) and 3 experimental halls (2x1,200 m2 and 1,500 m2 ) and one for power supply; • 2 workshops; • Water supply and electricity (1 MWe); • Two experimental installations of stellarator type; • Two quasi-stationary plasma accelerators (QSPA); • Tens small plasma devices. Stellarator • Stellarator is a toroidal device for plasma confinement with magnetic field; • Stellarator has magnetic surfaces in vacuum that exist without plasma currents; • Cons: stellarator has worse plasma confinement and lower beta than tokamak; • Pros: stellarator can provide stationary operation and less subjected to uncontrolled MHD phenomena; • Stellarator remains a candidate as a fusion reactor machine. • Stellarators in EU: W-7X, TJ-II, Vega Uragan-3M Uragan-3M is a small size torsatron with l=3, m=9, R0=1 m major radius, a 0.12 m average plasma radius and toroidal magnetic field B0 1 T. The whole magnetic system is enclosed into a large 5 m diameter vacuum chamber. In experiments B0~0.7 T Uragan-2M device It has both helical and toroidal field coils Major radius R=1.7 m Minor plasma radius – a 0.24m Toroidal magnetic field - B0 2.4 Т For K =0.31 (0)=0.34, (a)=0.47 Pumping rate 2x400 dm3/s Plasma production and heating in K is a ratio of the toroidal magnetic U-2M is performed by the RF field induced by the helical winding to power. the total toroidal field Initial goal of the device is studying of the magnetic confinement. After accidentalInitial aim ofinjection the device of is studyingthe vacuum oil from the pumping system to the vacuum chamber the studies become restricted to RF wall conditioning and support of the fusion-fission hybrid development. Studies on divertor flows in Uragan-3M CHARACTERISTICS OF THE HELICAL DIVERTOR OF THE URAGAN-3M TORSATRON A strong up-down asymmetry of plasma flows has been observed for the first time in the helical divertor of the Heliotron E heliotron/torsatron under ECRH and NBI conditions. А similar effect has been also revealed and studied in the U- 3M torsatron with an open natural helical divertor and a plasma RF-produced and -heated in the ω≲ωci range of frequencies. To detect divertor plasma flows (DPF) arrays of plane electric probes are used. Main characteristics of the asymmetry: - the larger ambipolar DPF on the ion ∇B drift side (“ion side”); - floating potential Vf and plasma current (current to the earthed probe) in DPF are positive on the ion side and negative on the electron side. Conclusion: the asymmetry is caused by the direct (non-diffusional) particle loss. Confirmed by: (1) measurements of ion energy in the DPF on the ion and electron sides, (2) a rising dependence of asymmetry degree on the fast ion content, and (3) numerical modeling of direct losses. V.V. Chechkin et al 2002 Nucl. Fusion 42 192 Runaway electrons at Uragan-3M Magnetic field evolution and signals of ECE, Rogovski coil, and x-ray detector for antenna voltages: +100V (left) , +20V (center) and -100V (right). Introduction of small negative electrostatic field to the confinement volume stops runaway electron avalanche V.E. Moiseenko et al Technical Physics Letters, 40 (2014) pp.669-672 Alfven resonance heating • We suggest to use compact antennas for AR heating that makes is competitive to ICRH; • The advantage of AR heating is that it is applicable both for small and big devices; • At big scale, the heating frequency is low and highly efficient RF generators could be used; • AR heating delivers energy to bulk plasma electrons and does not cause the instabilities of TAE and other modes. This is very advantageous for alpha-particles confinement. Alfvén resonance heating scheme KAW SQEW v Te v A v Te v A Plasma density Plasma Fast wave field antenna FAW , v A / k || Radius 2 2 Alfvén resonance condition , where k = щ/ c k|| = k0 е 0 2 2 2 2 2 1pB /( ) FAW cut-off condition k|| = k0 (е + g) k|| =(n+m/ q)/ R V.E. MOISEENKO et al, Plasma Physics Reports 35 (2009) 828. Alfvén heating strategies Alfvén heating: no propagating wave excitation => small antenna loading, big antenna Q Position of Alfvén resonance depends on k|| value => periphery heating possible • Two strategies for Alfvén heating: No periphery heating • Strict: remove all Periodic antenna occupies large small k|| from the space antenna spectrum Sensitivity to plasma density • Loose: concentrate antenna spectrum around selected k|| Periphery heating Relatively compact antenna No sensitive dependences on plasma parameters Compact antennas for Alfven resonance heating Uragan-3M antennas inside the vacuum vessel: THT antenna (left) and frame antenna (right). THT antenna is fed by K2 generator with frequency 8.8 MHz. Frame antenna is connected to K1 generator with frequency 8.6 MHz. The discharge is initiated by the frame antenna. Evolution of plasma parameters PROS: •Plasma with density 2x1012- 13 -3 280 2x10 cm is created and 7 P , kW 260 U heated by the THT antenna; 240 2 P , kW 6 U •Plasma is fully ionized and 220 1 , kW 2 12 -3 have a temperature ~50 eV. U 200 n , 10 cm e P 5 180 n T , a.u. (soft X-ray) e e , 10 , CONS: 160 4 , kW 1 140 12 •The energy confinement time U cm P 120 3 given by ratio of the plasma 100 -3 energy content to the heating , a.u. 80 2 e T 60 power gives low values (0.1-0.2 40 1 ms) 20 •The estimate for particle 0 0 0 10 20 30 40 50 60 70 80 90 100 confinement time as ratio of t, ms particle content to the influx of neutral gas is also low (0.5-1.5 ms) Time evolutions of average plasma density, average •There is a discrepancy in the electron temperature and RF power launched to plasma. electron temperature values Neutral gas pressure is 8x10-6 Torr. given by SXR and ECE diagnostics Spectral lines: H The central region <r> < 3 cm has minimal luminosity. This indicates low recycling rate there. Frame THT H-gamma chord The presence of hydrogen there is evidenced by the recombination peak. H-gamma radial Low threshold line emissions: CIII and OV High level emission of such impurities is normally observed in CIII radial Frame THT low temperature plasma (Te<100 eV), and this takes place at outer part of the plasma column <r> >3 cm. Presence of carbon and oxygen in the central region <r> < 3 cm is revealed by the recombination peaks. OV radial CV line emission and radiation temperature by ECE CV line emission is located at the central region of the plasma column. The temperature localization is even stronger. After power Frame THT CV radial switch-off, the longest decay time is at the 500 eV magnetic axis 0 Radiation temperature Uragan-3M magnetic configurations z, cm z, cm R, cm R, cm The regular magnetic configuration of Uragan-3M (left figure) has <r> = 12 cm. But the region of nested magnetic surfaces is restricted to <r> < 3 cm. There is better magnetic configuration (right) achieved with higher vertical field. Discussion • Spectroscopy and ECE data indicate that there are two regions in Uragan- 3M with different plasma energy confinement: the central region <r> < 3cm where the confinement is better, and surrounding it outer region with worse confinement. • The energy balance is possibly governed by the region with worse confinement since its volume is biggest. • Since the particle and energy confinements are connected each to other, worse particle confinement is expected in that region, and this is confirmed by enhanced hydrogen recycling there. • The magnetic field calculations indicate that the magnetic configuration looks different at r<.3 cm and r>3 cm. • Better magnetic configurations are possible in Uragan-3M. Their implementation may increase plasma parameters, decrease RF power and decrease the neutral gas pressure necessary to maintain the plasma. Uragan-2M RF antennas Frame antenna 4-strap antenna Small frame antenna New central strap of crankshaft antenna Crankshaft antenna U-2M RF discharge The discharge parameters are B0=0.37 T, -3 pH2=10 Pa. A small-power frame antenna pulse (f=3.9 MHz) goes first (t=10-16 ms) and makes the target plasma. The crankshaft antenna pulse (f=4.2 MHz) goes second (t=16-24 ms). PRF 150 kW. The light impurity radiation barrier is Time dependence of electron passed at the beginning of the discharge. temperature evaluated from SXR After few ms the discharge fades owing to measurements and optical emission contamination by impurities. (a.u.). Vertical magenta dotted lines indicate start and stop of the crankshaft antenna RF pulse U-2M short RF discharge This discharge is as previous, but the crankshaft antenna pulse terminates earlier (t=19 ms).
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