Experimental results with the Cooled Lithium Limiter (CLL) on FTU

Transcription

1 Experimental results with the Cooled Lithium Limiter (CLL) on FTU Giuseppe Mazzitelli ENEA Technological Fusion Division The First IAEA Technical Mee<ng on Divertor Concepts Wien 29 Sep 2 Oct Many thanks to: M.L Apicella, M.Iafra;, G. Apruzzese, G. Calabrò, G. Ramogida, I. Lyublinski, A. Vertkov and the FTU TEAM

2 Outline Introduc;on CLL Experimental results A simple radia;ve model Future Plan IAEA Wien 2

3 Introduc<on Since 2006 experiments with a liquid lithium limiter (LLL) are carried out on FTU with very interes;ng and promising experiemnts. Even if the liquid limiter was always in the shadow of the main toroidal limiter between one and two cen;meters away from the last closed magne;c surface and its toroidal and poloidal extensions is very limited, few discharges were sufficient to get very clean plasma also in presence of addi;onal hea;ng power. But many other posi;ve effects have been observed as impurity reduc;on, increase of the energy confinement ;me, suppression of MHD ac;vity etc. Now, most of work is focused on heat loads and a comparison of low Z (Li) and high Z (Sn) liquid metals IAEA Wien 3

4 Cooled Lithium Limiter CPS W structure Mo tube IAEA Wien 4

5 Cooled Lithium Limiter Plasma interacting area ~ 100 cm 2 Li amount up to 70 cm 3 / 35 g CLL initial temperature > 200 o C CLL Melting point C Boiling point 1342 C IAEA Wien 5

6 CLL Main Characteris<cs Parameter Ini;al lithium surface temperature Lithium surface temperature during plasma interac;on Power of heat removal Value 200 o C o C up to 100 kw Plasma interac;ng area ~ 100 cm 2 Lithium amount (volume/weight) up to 70 cm 3 / 35 g Element dimensions (L H W) ~330 ~205 ~32 mm IAEA Wien 6

7 Experiments with CLL I p [10 5 A] n e [10 18 m - 3 ] Hor. Pos.[m] Vert. Pos[m] We focused our analysis on heat load on a specific shot #37789 IAEA Wien 7

8 Experiments with CLL Visible Spectroscopy Li Δ =+0.5 cm Δ =+1.0 cm Δ = +1.5 cm D α Δ = distance of CLL from LCMS IAEA Wien 8

9 Experiments with CLL Visible Spectroscopy IAEA Wien 9

10 Experiments with CLL Heat loads Surface CLL T ;me evolu;on ANSYS Simula;on The CLL surface temperature were monitored by a IR fast camera. CLL Input heat load Max 2.3MW/m2 for 1.5 s In the simula;on we takes into the account the shape of the plasma as reconstructed by the equilibrium code, the power to the SOL ( P ohm - P rad ) and λ q =1cm. Data cooling water: T in =190 C T out = C P = 2. 9 M P a Flow=0.06Kg/s (v=0.44 m/s) No droplets by visible camera during discharges or surface damages were observed aker shots IAEA Wien 10

11 Experiments with CLL Hot spots on the surface are automa;cally recognized by using a nonlinear image filtering approach, building up a CNN (Cellular Nonlinear Network) based algorithm developed in MATLAB environment, giving the capability to localize them in the limiter geometry. Using this tool it has been shown a posi;on matching between the hot spots and the intermediate space between strips on the limiter surface IAEA Wien 11

12 New improvements A new curvature radius IAEA Wien 12

13 New Improvements Long Pulse Sta;onary high heat flux controlled by plasma posi;on (up to 10MW/m 2 for 5s - 4.5s achieved) IAEA Wien 13

14 New Improvements D shaped plasma We have made some preliminary shots to verify the possibility to have a D- shaped plasma with the X- point near the CLL. In these discharges we plan to inject 0.5 MW of ECRH that using the usual scaling should permit to get H- mode IAEA Wien 14

15 The old Liquid Lithium Limiter Langmuir probes Thermocouples Heater electrical cables IAEA Wien 15

16 Radia<ve Model #33206 IAEA Wien 16

17 Radia<ve Model IR Temperature Bolometric measurements Time (s) IAEA Wien 17

18 Radia<ve Model What is the reason for the temperature decrease on the module surface? We start analyzing the heat equa;on in the approxima;on of semi- infinite module Where: Q in is the heat load on the limiter Q loss is the sum of three contribu;on: radia;ve losses, evapora;on and the replenishment liquid lithium. We are neglec;ng redeposi;on and spuwering!!! IAEA Wien 18

19 Radia<ve Model Q in is deduced by the well known formula for a semi- infinite module Where: K thermal conduc/vity α thermal diffusivity IAEA Wien 19

20 Radia<ve Model By solving the eq. in the previous slide is possible to deduce the heat load on the limiter IAEA Wien 20

21 Radia<ve Model First of all we have es;mated the contribu;on of the three different terms assuming constant values for the electron density and temperature consistent with the measurements In the following we neglect Q sost, i.e. the heat loss due to the refilling/subs;tu;on of the evaporated surface IAEA Wien 21

22 Radia<ve Model The evapora;ve lithium flux φ has been evaluated by the following formula In which T s is the surface temperature K B is Boltzmann s constant Δ H is latent evapora;on heat p 0 is a costant IAEA Wien 22

23 Radia<ve Model Solving the equa;on the fit is sa;sfactory T Time (s) The vapour shield is a very important effect IAEA Wien 23

24 Different Liquid Metal in FTU Cooled Liquid Li Limiter (2013/14/16) Water hea;ng/cooling Cooled Liquid Sn Limiter (2016) Electrical hea;ng Water cooling Ø New Experiments 2016 IAEA Wien 24

25 TLL in-vessel element Water Gas inlet pipes Atomizer W CPS + Sn Heater Mo pipe Cooling channel Outlet pipe Power flux Cooling media water spray in Ar or air. Spray generator gas assisted atomizer. Cooling process water evaporation Evaporation heat J/kg Courtesy by A. Vertkov Spray + vapor flow to calorimeter TLL structure scheme W CPS+Sn Mo pipe Cu pipe Spray flow from atomizer Heater

26 PLAN 2016 Experimental campaign at B t =2.5-4T up to 4-5 s Most of the work will be focused on heat loads. Experiments with 0.5 MW of ECRH will be performed Experimental activity on elongated discharges Experiments with the TLL and comparison with CLL Sn plasma compatibility IAEA Wien 26

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