 p 414-1: “H-gas puff experiments on TCV”

1. p 414-1: “H-gas puff experiments on TCV” Mission 410: “Effects of plasma shape on tokamak operational space and performance”, Jaunt 414: “Ion transport” Goal: • Study of mass dependence of ion transport (diffusion and pinch velocity) in different regimes (OH: Ip, ECH: PECH, L- and H-modes, etc.) for variety of plasma configurations (LIM, DIV, , ) Background and motivation: • A physical nature of cross field transport: diffusion, pinch, turbulent transport is still a question of tokamak physics. • Hydrogen isotopes and impurities composition profiles are important for fusion reactor. • An existing experimental database for mass dependences on ion transport is quite poor. Methods/Strategy: • Modulated or pulsed hydrogen or deuterium gas injection in deuterium or hydrogen plasma. • Measurement of temporal variations of energy spectrums of neutral fluxes for hydrogen isotopes: JcxH,D(E,t). • Reconstruction of temporal behaviour of hydrogen isotope composition radial profiles: nH,D(). • Calculation of transport parameters (DH,D,VH,D,tH,D) and analysis of their dependences on plasma parameters.

2. p 414-1: “H-gas puff experiments on TCV” Experimental sessions in June-September 2004 WWW page:http://crppwww.epfl.ch/~karpusho/Missions/M414/index.htm 16.06.2004:First observation of H-gas puff in p401-2, (CNPA commissioning) 3 shots (2 useful):The isotope replacement (from D to H) is clearly seen for H-mode discharges with H2 gas multi-puffing (#26859) 09.07.2004 Session 1 :H puffs & plasma vertical position (Zo) scan 14(8):Zo: -1,7,14,22,29,33cm, OH, LIM, Ip:150, NL:1.4, 95:1.41.3, 95:0.240.20, Qedge:6.55, TeSoftX: 800eV, TS: ne: 3.5±0.2, Te: 880±30eV • learning of H-puff optimisation (temporal characteristics and amplitude) • useful for pseudo-multichord NPA measurement: analysis to be presented by Ch. Schlatter 27.08.2004:Edge TS and CXRS measurement of deuterium target 4 (3): Ti,Te,ne() profiles measured for modelling of H-puff 16.09.2004 Session 2,3 :ECH power and Ip scan : model #27115 14 (7): PECH:360,540,1080,1500kW : Ti is very low (~300eV) poor CNPA counting statistics. Ip: 220,270,320kA: Ip  time constants for H propagation 17.09.2004 Session 4,5 :Ip and NL scan 10 (5): Ip: 350kA NL: 1.4,2.2,3.4,4.0x1019m-2 : CNPA measurement are sensitive to plasma density. negative  - 1 shot – required reoptimisation of H-puff Summary: 45 shots, 25 useful

3. p 414-1: “H-gas puff experiments on TCV” Results (1) Plasma current, 150 kA TS nemax: 3.5x1019m-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

4. Fitting of CNPA hydrogen countrates (N): Q – “source”, proportional to hydrogen injection rate;  – “confinement” (12-80 msec); t – “delay” (<<, 0.3-6 msec); p 414-1: “H-gas puff experiments on TCV” Results (2) hydrogen injection, mbarl/sec H, 0.64keV H, 1.10keV H, 1.64keV After each H-gas pulse a counting rates of hydrogen relaxes to a high level, this indicates an accumulation of hydrogen in machine. Some increase of initial level of hydrogen flux was also observed during full day (about 25 plasma discharges) from shot to shot, that corresponds to hydrogen accumulation in vacuum vessel (graphite tiles). Response time () of NPA counrates on H-puff increases with increase of plasma density

5. 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 p 414-1: “H-gas puff experiments on TCV” Results (3) “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%

6. LF side HF side p 414-1: “H-gas puff experiments on TCV” Results (4) Reconstruction of radial profile of hydrogen isotope composition energy spectrum of atomic flux (J(E)) -- Modelling: fi(E,) – Maxwellian, ne, Te() from TS, Ti() from CXRS (TiCVITiH) Zeff()=const na() from KN1D code (Kinetic Transport Algorithm) D H A spatial emissivity function (E,z) of deuterium and hydrogen atoms reaching NPA can be calculated for different atom energies from information about neutral, ion end electron density and temperature distributions along NPA view line.

7. energy spectrum of atomic flux (J(E)) -- p 414-1: “H-gas puff experiments on TCV” Results (4 cont.) Reconstruction of radial profile of hydrogen isotope composition – emissivity function A neutral particle flux in first CNPA hydrogen channel (0.65keV) is mainly contributed from =0.750.11, a flux in forth channel (2.61keV, well pronounce measurement) corresponds to =0.450.16. This allows to transform an energy variation of isotope “CX spectrum” ratio FdcH/FdcD(E) to radial variation of isotope ion density ratio Rn()

8. radial profiles of hydrogen isotope composition FdcH/(FdcD+FdcH) ratio p 414-1: “H-gas puff experiments on TCV” Results (4 cont.) Reconstruction of radial profile of hydrogen isotope composition Before H2-gas injection (T1 time slice) the isotope ratio (~11% of hydrogen) have homogeneous radial distribution in 0.45≤≤0.75. After opening of H2 gas valve during 15-20ms nH/(nH+nD) ratio evaluates from hollow radial profile to flat profile (T2 and T3 time slices). Later, profile becomes peaked; a hydrogen “accumulation” in internal regions is detectable.

9. radial profiles of hydrogen isotope composition 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 behavior of radial profile of hydrogen isotope ratio probably can be explained by dependence on mass pinch velocities and ion diffusion coefficients. p 414-1: “H-gas puff experiments on TCV” Results (4 cont.) 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)

10. p 414-1: “H-gas puff experiments on TCV” • 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 in the region 0.4≤≤0.8. A plasma centre can not be resoled due to low NPA counting rates at high energies (>2-3keV); high  is limited by a low energy limit of NPA (Ti(=1)~30eV) . • From given analysis we learn, that we need to optimise conditions of experiment for realizing an experimental program. • Plans • Repeat experiments with D-gas puff in hydrogen plasma (OH, L-mode, LIM) 1session • Installation of DOUBLE code (Ioffe PTI) and adaptation for TCV: Code calculates radial distribution of neutrals in plasma and simulates charge-exchange flux generated by thermal part of multi-component hydrogen plasma. • Development of procedure to get transport coefficients from recovered radial profile of hydrogen isotope composition. • Modification of CNPA: increase energy range  additional point(s) at <0.4