Member of the Helmholtz Association Fuel retention in carbon materials Arkadi Kreter et al

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June CFC in ITER ITER divertor cassette mock-up Carbon Fibre Composite (CFC) foreseen for strike plates – regions of highest heat loads Tungsten CFC NB41 by Snecma is successor of NB31 as ITER grade CFC with better thermo-mechanical properties [A.T.Peacock et al, Phys. Scr. T128 (2007) 23] Investigation of fuel retention in NB41 for ITER- relevant conditions is necessary ITER-relevant divertor conditions High D flux (up to D ~10 24 m -2 s -1 ) High D fluence ( >10 26 m -2 for 1 ITER pulse at SP) Low incident energy (E i ~10 eV) Range of wall temperatures (T s = 500 K K) Impurities Beryllium from the main wall He from D-T reactions Ar for divertor cooling Influence of impurities on retention in CFC needs to be tested

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Extensive database on retention in CFC/FGG Analysed materials: CFC NB41 (new EU ITER grade) [1] CFC NB31 (former ITER grade) [2] CFC DMS780 (JET) [2] CFC DMS701 (ASDEX Upgrade) [3] CFC N11 (Tore Supra) [4] fine-grain graphite (FGG) EK98 (i.e. TEXTOR) [2] FGG IG-430U (ALT-II TEXTOR) FGG ATJ (DIII-D) [1] Exposures in: PISCES-A/B [1,3,4], TEXTOR test limiter [2], TEXTOR ALT-II main limiter [1] A. Kreter et al., PFMC-12, Jülich 2009 [2] A. Kreter et al., J. Phys.: Conf. Series 100 (2008) [3] R. Pugno et al., J. Nucl. Mater. 375 (2008) 168 [4] J. Roth et al., J. Nucl. Mater. 363–365 (2007) 822

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Exposures in PISCES-A/-B linear plasma devices Eroded Material PISCES (-A, -B) schematic view Steady-state plasma n e = (2-3)·10 18 m -3 ; T e = 7-15 eV = (3-6)·10 22 D/m 2 s Variations of: E i = eV = 1· ·10 26 D/m 2 (~1 ITER pulse at strike point) T s = 370 K ('cold' ITER wall) K (ITER strike point) Controlled Be, He and Ar seeding All experiments in erosion-dominated conditions PISCES-A plasma and target Ex-situ analysis of samples for retention Thermal desorption spectrometry (TDS) Nuclear reaction analysis (NRA) with 3 He beam B

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Exposures on test limiter in TEXTOR tokamak Test limiter with CFC/FGG stripes 32 reproducible Ohmic discharges in 80% D 177 s total duration Limiter tip at LCFS (0.46 m) n e LCFS 1·10 19 m -3 ; T e LCFS 45 eV; T i T e LCFS 2.9·10 25 D/m 2 ; SOL ( ) 12 mm T lim 500 K Ex-situ analysis of samples for retention Thermal desorption spectrometry (TDS) Nuclear reaction analysis (NRA) with 3 He beam High-resolution NRA with m-size 3 He beam ( -NRA)

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Retention in NB41: Fluence dependence M=4 (D 2 ) desorption spectra (T s = 470 K, E i = 120 eV) =50e25 D/m 2 10e25 3e25 1e K Retention [D/m 2 ] Ion fluence [D/m 2 ] NB41 PISCES-A [1] N11 PISCES-A [2] NB31 TEXTOR [3] DMS780 TEXTOR [3] EK98 TEXTOR [3] Total D retention for exposures at T s = 470 K, E i = 120 eV No saturation up to = D/m 2 ATJ PISCES-A [1] [2] A. Kreter et al., J. Phys.: Conf. Series 100 (2008) [1] J. Roth et al., J. Nucl. Mater. 363–365 (2007) 822 Similar behaviour for different CFCs and fine-grain graphites 0.5 K/s [1] A. Kreter et al., PFMC-12, Jülich 2009

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June D 2 desorption flux [x10 19 D/m 2 s] Temperature [K] T s =470 K T s =370 K T s =820 K 470 K 370 K 820 K Higher retention for lower exposure temperatures due to additional trapping sites and higher population M=4 (D 2 ) desorption spectra (E i = 120 eV, = 2.4e26 D/m 2 ) Retention [D/m 2 ] Ion fluence [D/m 2 ] Total D retention for exposures at different temperatures in PISCES-A and -B Higher retention for lower T s Saturation for T s > ~800 K [1] R. Pugno et al., JNM 375 (2008) 168 Saturation NB41 Ts=370K NB41 Ts=470K NB41 Ts=820K DMS701 Ts=1070K [1] Retention in NB41: dependence on exposure temperature 0.5 K/s

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Retention in NB41: dependence on ion energy Higher retention for higher incident ion energy Total D retention vs E i ( = 1e26 D/m 2, T s = 470 K) M=4 (D 2 ) desorption spectra ( = 1e26 D/m 2, T s = 470 K) E i =20eV E i =50eV E i =120eV 0.5 K/s

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Retention in C: dependence on ion flux Data from PISCES and TEXTOR exposures compared to data from ion-beam facilities [J. Roth et al., JNM 363–365 (2007) 822] Ion beam data show higher retention than data from plasma devices Can be attributed to flux dependence (higher retention for lower fluxes) Typical ion fluxes Ion beam: m -2 s -1 PISCES, TEXTOR: ~ m -2 s -1

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June ALT-II main limiter in TEXTOR tokamak Inside view of TEXTOR History of analysed tile: Exposed Pulses: 8534; Plasma: s Area-averaged H+D fluence: 1.4e26 m -2 Temperature 400 K – 650 K Analysis for retention by laser desorption Laser desorption parameters: t = 1.5 ms A= 0.05 cm 2 P= 70 kW/cm 2 main toroidal limiter ALT-II a = 0.46 m

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June ALT-II main limiter in TEXTOR tokamak D retention in erosion zone: ~5e21 D/m 2, or ~1e22 D for total ALT-II D retention in deposition zone: ~1e23 D/m 2, or ~1e23 D for total ALT-II Retention in TEXTOR is dominated by co-deposition (~90%) Analysis for retention by laser desorption Retention [m -2 ] Poloidal position along tile surface [mm] deuterium hydrogen deposition zone erosion zone deposition close to bolts

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Long-term exposure vs dedicated experiments Retention [m -2 ] Ion fluence [m -2 ] NB41 PISCES-A N11 PISCES-A NB31 TEXTOR DMS780 TEXTOR EK98 TEXTOR ATJ PISCES-A Retention in long-term exposure in good agreement with dedicated experiments Retention in bulk of CFCs and FGGs H+D ALT-II TEXTOR (comparable T s, E i, )

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Retention in NB41: D penetrates deep in bulk NRA depth profile of NB41 ( = D/m 2, T s =470 K, E i =120 eV) 18 at% of D at surface saturated implantation layer Penetration in bulk -NRA 2D mapping of D in NB31 exposed in TEXTOR for = D/m 2 at T s = 500 K Inhomogeneous penetration of D in bulk over tens of m A. Kreter et al., J. Phys.: Conf. Series 100 (2008) P. Petersson et al., PFMC-12, Juelich MeV 3 He + beam

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Influence of Be on retention D2 TDS spectra for ATJ exposed w/o and with Be (T s =720K, E i =35 eV) Be carbide layer appears to prevent increase of retention with fluence Total Deuterium Retention With Be, =0.5e26 D/m 2 before Be, =2e26 D/m 2 total: 1.9e21 D/m 2 Pure D, =2e26 D/m 2 : 2.3e21 D/m 2 Pure D, =0.5e26 D/m 2 : 1.6e21 D/m pure D =0.5e26m -2 pure D =2e26m -2 Be containing plasma D 2 desorption flux [x10 19 D/m 2 s] Temperature [K] Scenario of Be experiment 1.Establishing background plasma ( =0.5e26 D/m 2 ) 2.Be injection from oven (total =2e26 D/m 2 ) 0.5 K/s

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Influence of Be+He on retention D2 TDS spectra for ATJ exposed to pure D, D+Be, D+Be+He (T s =720K, E i =35 eV, f He =16%) He appears to change the retention mechanism and reduce retention Sensitive to exposure parameters (not effective at high E i ) Similar effect of Argon Total Deuterium Retention D+Be, =0.5e26 D/m 2 before Be, =2e26 D/m 2 total: 1.8e21 D/m 2 Pure D, =0.5e26 D/m 2 : 1.6e21 D/m 2 D+Be+He, =0.4e26 D/m 2 before Be, =1.7e26 D/m 2 total: 0.5e21 D/m K/s

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Influence of Be+Ar on retention D2 TDS spectra for ATJ exposed to pure D, D+Be, D+Be+Ar (T s =720K, E i =35 eV, f Ar =10%) Ar appears to change the retention mechanism and reduce retention Total Deuterium Retention D+Be, =0.5e26 D/m 2 before Be, =2e26 D/m 2 total: 1.8e21 D/m 2 Pure D, =0.5e26 D/m 2 : 1.6e21 D/m 2 D+Be+Ar, =0.1e26 D/m 2 before Be, =0.5e26 D/m 2 total: 0.8e21 D/m K/s

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Summary and discussion: pure D plasma (I) In-bulk retention is similar in different CFCs and fine-grain graphites CFCs and fine-grain graphites are porous In-bulk retention is higher for lower exposure temperatures Additional trapping sites at lower temperatures Higher population of available trapping sites at lower temperatures In-bulk retention scales as fluence with depending on temperature: <~0.5 for low T s (surface diffusion along pores) =0 for T s >~800K – saturation of retention for < D/m 2 (few sec of ITER pulse) 1.Incident deuterium ions saturate the implantation layer (~ nm) 2.The level of saturation is defined by the balance between adsorption and ion-induced desorption for a given number of available trapping sites 3.From the implantation layer, D 'diffuses' further in-bulk along surfaces of the pores

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Summary and discussion: pure D plasma (II) 1.Incident deuterium ions saturate the implantation layer (~ nm) 2.The level of saturation is defined by the balance between adsorption and ion-induced desorption for a given number of available trapping sites 3.From the implantation layer, D 'diffuses' further in-bulk along surfaces of the pores In-bulk retention is higher for higher incident ion energies Higher D concentration in implantation layer [Staudenmaier JNM79] leads to higher D amount in bulk In-bulk retention is higher for lower fluxes Amount of diffused deuterium t, longer time available for D to diffuse in for the same fluence

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Summary and discussion: influence of impurities 1.Incident deuterium ions saturate the implantation layer (~ nm) 2.The level of saturation is defined by the balance between adsorption and ion-induced desorption for a given number of available trapping sites 3.From the implantation layer, D 'diffuses' further in-bulk along surfaces of the pores With addition of Be no further increase of in-bulk retention Be carbide layer appears to suppress the in-bulk penetration of deuterium (Be 2 C layer thickness is a few 100 nm) He and Ar impurities decrease the in-bulk retention Presumably due to depletion (ion-induced detrapping) of the implantation layer, from where it otherwise moves deeper in the bulk Do impurities deplete co-deposited layers from D? To be tested experimentally

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Estimations of retention in ITER [Roth et al., PPCF 50 (2008) ] Estimated T inventory for initial wall material choice (C/W/Be) with CFC NB31 (CFC bulk retention scaled up from ion beam data) Estimated T inventory for different wall material choices NB41 has similar retention characteristics as other CFCs incl. NB31 Generally, estimations for retention in ITER done for NB31 still valid However, Roth et al overestimated retention in CFC significantly, because of neglecting the flux dependence and saturation at high temperatures Effects of impurities are also favourable, maybe even for co-deposition

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June Recent studies on retention in CFC MaterialProducerApplication Density [g/cm 3 ] Porosity Retention studied in Reference CFC NB41SnecmaITER> 1.94< 7%PISCESthis study Fine-grain ATJ UCARDIII-D % PISCESthis study CFC NB31Snecma former ITER 1.87 – 1.937% - 9%TEXTOR[Kreter08] CFC DMS780 DunlopJET1.75 – % - 15%TEXTOR[Kreter08] Fine-grain EK98 Ringsdorff TEXTOR, other % TEXTOR[Kreter08] CFC DMS701 Dunlop ASDEX Upgrade 1.75 – 1.910% - 15%PISCES[Pugno08] CFC N11 SEP /Snecma Tore Supra1.71 – % PISCES[Roth07] [Kreter08] A. Kreter et al., J. Phys.: Conf. Series 100 (2008) [Pugno08] R. Pugno et al., J. Nucl. Mater. 375 (2008) 168 [Roth07] J. Roth et al., J. Nucl. Mater. 363–365 (2007) 822