Relevant spatial and time scale in tokamaks. F. Bombarda ENEA-Frascati, FSN-FUSPHY-SAD

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1 Relevant spatial and time scale in tokamaks F. Bombarda ENEA-Frascati, FSN-FUSPHY-SAD PolFusion - one day discussion Meeting, 23rd of July 2015 Ferrara

2 Ignitor News MoU of April 2010 concerned the construction of the Ignitor Load Assembly in Italy and installation at Triniti NRC Kurchatov Institute + Rosatom and INFN have produced a CDR for evaluation by respective Research Ministries (June 2015) Intergovernmental agreement to be signed soon TDR to follow: engineering and physics activities, working groups.

3 MC Fusion with polarized atoms (an idea of the fab 80) 1 In theory, polarized D-T, D-D, or D- 3 He plasmas should have higher fusion yields by a factor Furthermore, fusion products, in particular neutrons, would be emitted in preferential directions If polarized atoms are injected in a fusion device, all the depolarization mechanisms (collisions, ionization, field gradients, etc.) were estimated to have a time scale longer than the ion life-time. BUT. 1 Kulsrud, Furth, et al., PPPL Report 1912 (1982)

4 BUT Coppi et al. 2,3 objected that magnetic field fluctuations in the plasma would quickly de-polarized the ions. Given also the technical difficulty of producing highly polarized beams, the idea was dismissed. 2 B. Coppi, F. Pegoraro, J. Ramos, Proceed. 11 th EPS Conf. Controll. Fusion and Plasma Phys. paper D47, p 241, B. Coppi, S. Cowley, R. Kulsrud, P. Detragiache, F. Pegoraro, Phys. Fluids 29, 4060 (1986) Review of de-polarization effects in magnetic fusion plasmas by R. Gatto, this meeting

5 Today. New polarization techniques and otherwise slow advances in fusion have revamped the idea, but mostly with Inertial Fusion in mind and for frozen pellets On our side, we are trying to understand if the powerful RF sources in use for tokamak plasma heating could polarize and/or prevent de-polarization, or be used for diagnostic purposes of a tokamak plasma. Together with the RF theory group at ENEA we have started to evaluate the possibility of including spin-wave interaction effects into propagation codes.

6 Magnetic Fields in Tokamaks I M B + X B T Y Fuel gas is first injected as molecules, then ionized. The toroidal field is applied before the plasma current is induced

7 Magnetic Fields in Tokamaks B pol B tor R B pol I p Y J tor J tor B tor B tor 1/R

8 From: Basic studies on polarized D-D- fusion, Naoaki Horikawa, College of Engineering, Chubu University International Symposium on Polarized Target and its Application Tsukioka-Hotel, Kaminoyama-Onsen, Yamagata (2008)

9 B// B

10 Nuclear Reactions of Relevance for Fusion 0 - D+T 4 He(3.5 MeV) + n(14.1 MeV) 1 - D+ 3 He 4 He(3.6 MeV) + p (14.7 MeV) 2 - D+D T(1.01 MeV) + p(3.02 MeV) 3-3 He(0.82 MeV) + n(2.45 MeV) 4 - T+T 4 He + 2n MeV H D T 3 He I f ci MHz/T μ 0 MHz/T ΔΕ m 10-7 ev/t μ 0 /f ci Additional reactions: D + p 3 He MeV H + H + n MeV T + p 3 He + n 0.76 MeV D* + D MeV 3 He + 3 He 4 He + 2p MeV

11 Fusion reaction rates for H and He isotopes Ideal Ignition Temperature Neutron production: 3.3x10 19 n/s in Ignitor DT 5.5x10 18 n/s in JET DT ~3x10 12 n/s in FTU DD ~5x10 13 n/s in C-Mod DD

12 Life expectancy for ions D-D (tot) D- 3 He D-T n i =2x10 14 cm -3 le 1 n i σv

13 Slowing down time of fusion charged products at birth 1 n i =2x10 14 cm -3 Solid line= D-T plasma Dashed line= D- 3 He plasma H 3.02 MeV H 14.7 T He He P. Batistoni and C.W. Barnes, Plasma Phys. Controll. Fusion 33, 1735 (1991)

14 Time scales The slowing-down time of charged fusion products are short relative to their life expectancy at birth: Important for stability; sd 100 msec Fusion products have small probabilities of undergoing further fusion reactions. For all relevant reactions : le 1/(n t fus v ) sec This is a long time! (sec) T pulse E sd le ITER p 5 E IGNITOR

15 Fuelling requirements The particle diffusion coefficient is generally similar in shape to the thermal energy diffusivity, and the global particle confinement time is usually higher than the energy confinement time (~5x). In Ignitor, the net particle flow at the plasma boundary should be ~ part/(sec m 2 ), for a central density n 0 ~ m -3. In Alcator C-Mod L-mode, is ~10 20 part/(sec m 2 ), but p in H-mode; in FTU high density plasmas is about part/(sec m 2 ) In good confinement regimes, particles in the plasma core take a long time to reach the edge: the problem is in the initial phase of the discharge Injection of polarized pellets could be an option to consider

16 Larmor radius of fusion charged products at birth ΔB/B 2% for ITER ρ L (th) 0.5 cm a=300 cm H 3.02 MeV H 14.7 T He He 3.5 ΔB/B 3% for Ignitor ρ L (th) 0.12 cm a=0.46 cm

17 x θ k z ICRH Heating Θ=π/2 : perpendicular propagation Slow wave E // B Fast wave E B y B 0 static magnetic field Alcator C-Mod 4-strap antenna (J-port) 4 MW, 80 MHz Courtesy of D. Hartmann

18 10 8 Wave polarization for D and T Cold plasma approximation polarizzazioni ignitor 65.4 MHz a n =5 f=65.4 MHz 8 6 polarizzazion of the ICRH electromagnetic field for ignitor plasma parameters f= MHz (Tritium) A. Cardinali a n z =5 E /E y x E /E z x f= MHz 6 4 alfay npa=5 alfaz npa=5 alfa+- npa=5 by/bx npa=5 bz/bx npa=5 4 2 E + /E - B y /B x B z /B x Most of the wave oscillating field is // to the external B field n // =5 n // =5-6 x k r/a 1 y θ z B 0 static magnetic field

19 Final remarks It s not clear (at least to me) if fuel polarization can be of any practical use, but there is enough fuzziness in preceding theoretical work to warrant more analysis using up-to-date plasma conditions. D-T and D-D reactions are the relevant reactions. Increase of reactivity and directionality of fusion products (especially neutrons) are the main points of interest, but plasma diagnostics could also included Good computational codes are available to study em wave propagations and could be adapted to include nuclear spin interactions : interesting by itself The experimental work on polarized D fusion cross section could possibly be complemented by experiments on existing tokamaks, for example looking at negative effects (i.e.,rf induced de-polarization or reduction of neutron production). The production of polarized pellet to inject in already formed plasmas may be considered.

20 ORNL Ballast/Target Chamber ENEA Target Diagnostics (4 each) ORNL Pellet Diagnostics (Light Gates, Photography, and Mass) ORNL Pellet Formation System ORNL Single-Stage Gas Drivers (4 each) ENEA Two-Stage Gas Drivers (4 each) ENEA Two-Stage Gas Acceleration Plant ORNL Controls and Data Acquisition Center ENEA Controls and Data Acquisition Center