Determining of Radial Profile of Hydrogen Isotope Composition of TCV plasmas

1. Determining of Radial Profile of Hydrogen Isotope Composition of TCV plasmas • A.Karpushov, B.P.Duval, Ch.Schlatter, H.Weisen • with contribution from Laboratory of Atomic Collision Physics, Ioffe PTI • for 32nd EPS Conference on Plasma Physics, • 27 June - 1 July 2005, Tarragona, Spain Centre de Recherches en Physique des Plasmas Association Euratom – Confėdėration Suisse, Lausanne, Switzerland RS TCV, Friday, June 3, 2005

2. Introduction.Direct measurement of plasma hydrogen isotope neutral particle emission has been used to study particle transport in TCV. A Compact NPA (CNPA), with mass and energy separation has, been used to obtain information on accumulation, propagation and relaxation of hydrogen particles in a deuterium background plasma using programmed H-gas puffs. A series of thermal hydrogen gas injections into a deuterium background plasma, with a simultaneous switch-off of the main deuterium gas injection, leads to partial replacement of deuterium ions by hydrogen. A recovery algorithm has been designed to get information on the temporal behaviour of the radial hydrogen density profile. Algorithm uses the measured electron temperature and density profiles (TS), ion temperature profiles (CXRS), information on Zeff profiles and numerical modelling of neutral density profiles and energy spectrums of neutrals escaping plasma with DOUBLE and KN1D codes. 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

3. M414 M 410: “Effects of plasma shape on tokamak operational space and performance” Jaunt 414: “Ion transport” p 414-1: “H-gas puff experiments on TCV” Method: • Modulated hydrogen gas injection in deuterium plasma. • Measurement of temporal variations of energy spectra of neutral hydrogen isotope fluxes: JcxH,D(E,t). • Reconstruction of temporal behavior of hydrogen isotope radial profiles: nH,D(). • Calculation of transport parameters (DH,D,VH,D,tH,D) and • Analysis of their dependences on plasma parameters (ne,Te, shape) - tbd. 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

4. hardware Compact NPA.Designed and manufactured in A.F.Ioffe Phisico-Technical Institute (St. Petersburg, Russia) Installed on TCV in 2004 Operating principles: magneto-electric separation, E||B scheme stripping in 100 Å diamond-like carbon foil 10 kG NdFeB permanent magnet electrostatic acceleration of ions ion focusing at the detector area Basic parameters: two CEM arrays for detection of H and D (or D and He) H:0.64-50keV (11 channels), D:0.56-33.6keV (17 ch.) E/E:0.6(for 0.6keV) – 0.1(for E>3keV) Operating regime: counting with pulse amplitude discrimination Acquisition time resolution 0.5-4 ms Max. count rate 800 pulse/ms (1) acceleration/stripping unit; (2) carbon stripping foil; (3) analysing magnet; (4) Hall probe; (5) analysing electrostatic condenser; (6) detector array; (A0) atomic flux emitted by plasma; (A+) secondary ions see http://www.ioffe.rssi.ru/ACPL/npd/npa05.htm 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

5. experimental scenario The CNPA views the TCV plasma along horizontal view-line thought plasma axis for Zo=0 Plasma current, 150 kA TS nemax: 4x1019m-3 FIR nl: 1.4x1019m-2 TS Temax: 900eV CNPA Tieff: 400eV Safety factor Gas injection, mbarl/sec Hydrogen Deuterium 5 CNPA countrates deuterium, counts/2.5ms A series of thermal hydrogen injection (duration of 10-100ms and period of 150-500ms) in background plasma with simultaneous switch-off main deuterium gas injection leads to partial replacement of deuterium ions by hydrogen CNPA countrates hydrogen, counts/2.5ms 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

6. N ch.1 N ch.2 N ch.3 NPA countrate (N) energy spectrum of atomic flux (J(E)) detection efficiency attenuation plasma parameters energy spectrum of atomic flux (J(E)) CNPA measurement Fitting of CNPA hydrogen countrates (N): Q – “source”, proportional to hydrogen injection rate;  – “confinement” (12-80 msec); t – “delay” (<<, 2-6 msec); NPA data analysis “CX spectrum”: Following H-gas puff, count-rates in the CNPA hydrogen channels (ch.1-5: 0.6-4keV) increase by a factor of 3-4 and counting rates in deuterium channels(ch.12-20: 0.5-6keV) decrease by ~1/2. “CX spectrums” for Ho and Do in TCV deuterium discharge emissivity (E,z) 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

7. DOUBLE-TCV code DOUBLE-TCV: Simulation of CX fluxes emitted by tokamak plasma (Maxim Mironov, A.F.Ioffe PTI, March 2005) The code uses the same Monte-Carlo technique to calculate neutrals distribution in plasma Assumes that plasma is surrounded by homogenous atomic gas Neutral beam injection (NBI) included • INPUT: • Plasma geometry ― poloidal flux map ((R,Z)); • Boundary conditions ― edge (=1) atomic neutral density and energy (H,D,(T,He)); • Electron and ion density and temperature profiles (up to 3x2 ion species, mass x temperature); • Impurity Zeff and Timp profiles, atomic mass and charge (one component ― carbon). • OUTPUT: • 2D distribution of total (wall+beam) neutral density of each mass species in poloidal plane; • Neutral densities along NPA view lines; • Emissivity distribution for each ion component along NPA view lines; • CX spectrums for each ion component for each view line. 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

8. LF side HF side DOUBLE-TCV code DO distribution in plasma, log(no, m-3) Neutral density profiles calculated by DOUBLE-TCV are in good agreement with KN1D simulation (slab geometry) for >0.6 DO , HO , D2Odistribution along NPA view line 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

9. DOUBLE-TCV code H and D CX-spectrums before H-puff nH/nD:[5.6-7.8]% CX-spectrums of H-ion population created by H-puff 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

10. Assume a hydrogen density distribution as a linear combination of density base functions and build base functions. with For each nibase calculates CX-spectrums (Fibase) Model CX spectrum is a linear combination of “base CX-spectrums” with same ki recovery algorithm nH/nD(=1)=0 nH/nD=const nH/nD(=0)=0 Density base functions Fond ki from minimisation of difference between “model” and “experimental” CX-spectrums CX-spectrum base functions 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

11. results CX-spectrum and density profile at 5-7 ms black – result, colours – ki “base functions” CX-spectrum and density profile at 10-15 ms black – result, colours – ki “base functions” 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

12. results CX-spectrum and density profile at 30-40 ms black – result, colours – ki “base functions” CX-spectrum and density profile at 100-125 ms black – result, colours – ki “base functions” 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

13. results During H2-puff, the nH/nD ratio evolves from a hollow radial profile (<20ms) to a flat profile (20-25ms). After puff switch off hydrogen accumulated in internal region. density profiles during H-puff CX-spectrums during H-puff 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

14. results With successive H-puffs, the hydrogen profile becomes peaked; hydrogen “accumulation” in internal regions takes place. “Confinement time” for low density, low current L-mode discharges was 15-25ms. density profiles after H-puff CX-spectrums after H-puff 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

15. results To explain H-puff results from TCV, a plasma pinch must be considered. An estimation of effective diffusion coefficient yields a value ~1m2/sec, pinch velocity is ~1m/s for dn/dt1020 m-3sec-1 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

16. NPA data analysis “CX spectrum”: – effective NPA ion temperature NPA countrate (N) energy spectrum of atomic flux (J(E)) plasma parameters energy spectrum of atomic flux (J(E)) H-puff results “CX spectrums” for Ho and Do in TCV deuterium discharge detection efficiency attenuation hydrogenand deuterium interpolated “background” and subtracted additional hydrogen population Subtraction of interpolated “background” from hydrogen “CX-spectrum” allows to get temporal behavior of NPA “CX-spectrum” and ion temperature of additional hydrogen population created due to H-gas injection. Energy spectra of additional hydrogen population relaxes to background Maxwellian CX-spectra in 10-30 ms. (Ion-Ion local thermal equilibration time < 1 ms) effective CNPA ion temperature for E[0.5 3.0keV], error bars ~15% 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

17. Fitting of CNPA hydrogen countrates (N): Q – “source”, proportional to hydrogen injection rate;  – “confinement” (12-80 msec); t – “delay” (<<, 0.3-6 msec); results hydrogen injection, mbarl/sec H, 0.64keV H, 1.10keV H, 1.64keV Response time () of NPA counrates on H-puff increases with increase of plasma density 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

18. discussion TCV result is contradictory to the observation of deuterium transport in hydrogen plasma observed on JET with short pulses of D2 gas injection (JET discharge #43446), where the nD/nH ratio was hollow during and after gas injection. Such behaviour of radial profile of hydrogen isotope ratio probably can be explained by dependence on mass pinch velocities and ion diffusion coefficients. V I Afanasyev, A Gondhalekar, and A I Kislyakov, “On the Possibility of Determining the Radial Profile of Hydrogen Isotope Composition of JET Plasmas, and of Deducing Radial Transport of the Isotope Ions”, JET report JET–R(00)04 (Oct. 2000) 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

19. limitations • Analysis of H propagation in TCV plasma with high current and high density is “difficult” due to effects of sawtooth activity. • In CNPA measurement a plasma centre can not be resoled due to low NPA counting rates at high energies (>3-4keV); high  is limited by a low energy limit of NPA (Ti(=1)~30eV) “GOOD” L-mode, OH Te > 400 eV, NL<3x1019m-2 “BAD” • sawtooth • ELMs + H-mode • X2 ECH non-Maxwellian F(E) • High density Ip:340kA, FIR nl: 3.2x1019m-2, TS ne:5.5x1019m-3, Te=1keV 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain

20. summary CNPA was successfully tested as tool to measure hydrogen isotope composition. A recovery algorithm of hydrogen isotope ratio radial profile from NPA measurement was developed and tested for TCV. A density profiles can be recovered for TCV L-mode, low density, low current discharges. Ion transport coefficients are in reasonable agreement with other observations on TCV (D~1m2/sec, V~-1m/s). 32nd EPS Conference on Plasma Physics, 27 June - 1 July 2005, Tarragona, Spain