Application of a Plasma Accelerator of the Dense Plasma Focus Type in Simulation of Radiation Damage and Testing of Materials for Nuclear Systems

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Octavia Carpenter
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1 Appliction of Plsm Accelertor of the Dense Plsm Focus Type in Simultion of Rdition Dmge nd Testing of Mterils for Nucler Systems E.V. Demin, A.V. Durovsky, V.A. Grikov,2, S.A. Mslyev, V.N. Pimenov, I.P. Ssinovsky, R. Miklszewski 2, M. Scholz 2 A.A. Bikov Institute of Metllurgy nd Mteril Sciences RAS (IMET), Moscow, Russi 2 Institute of Plsm Physics nd Lser Microfusion (IPPLM), KBN, Wrsw, Polnd Emil contct of min uthor: pimvl@mil.ru Keywords: plsm, rdition dmge Astrct. We present some results of our experiments with use of numer of plsm ccelertors of the Dense Plsm Focus type, nmely PF-5M (IMET, nk energy 5 kj), PF-6 (IPPLM, 7 kj), nd the lrgest in the world DPF fcility operting with deuterium s working gs PF-000 (IPPLM,.2 MJ). We use this set of devices for ppliction in the field of rdition mteril sciences, in prticulr for Simultion of Rdition Dmge nd Testing of Mterils intended for use in Thermonucler Rectors (TNR) of oth types with mgnetic plsm confinement (MPC) nd with inertil plsm confinement (IPC). These devices cn produce directed strems of the sme types of rdition nd hving the sme prmeters (density, temperture, spectrum, energy of fst prticles, etc.), which re expected on the wlls of the rectors chmers. It is independent on DPF nk energy (it is cler tht we cn ensure the ove prmeters on different res of smple). Power flux density of plsm nd fst ion/electron strems on the smple s surfce during the experiments, which simulte conditions on plsm-fcing components inside thermonucler fusion rectors, my rech on the trget s surfce (on the fce of specimen under test) s much s 0 0 W/cm 2. It is out those expected in the rectors with the inertil (IPC) plsm confinement nd much higher thn those with the mgnetic plsm confinement (MPC). We descrie results on the interction of powerful deuterium plsm nd fst ion/electron strems with specimens mde of tungsten nd cron-fier-composites, which re counted s cndidte mterils for use s plsm fcing nd construction components of TNR with MPC nd IPC. In our nlysis of the irrdition consequences we pply opticl, scnning electron nd tomic force microcopy, X-Ry elementl nd structure nlysis, etc. Tking into considertion tht the ove mterils re the min construction nd plsm fcing resources for ITER nd NIF fcilities, the results received re fruitful for estimtions of prospects of their use in these rectors s well s in the next genertion of fusion rectors. Some recommendtions on the use of these mterils will e presented.. Introduction The ehvior of different plsm fced mterils in thermonucler fusion rector under irrdition in extreme conditions is of gret interest in connection with reliztion of interntionl projects Iter [] nd NIF [2]. They re relted to powerful thermonucler fusion devices with mgnetic plsm confinement (MPC) nd inertil plsm confinement (IPC). Formerly [3, 4] we hve shown the dvntge of Plsm Focus devices (DPF) for simultion of het lods nd for investigtion of dmge of divertor s nd first wll mterils in thermonucler fusion rector with MPC t extreme conditions of the types of plsm disruption or ELMs effects. The work is imed to investigte the min fetures of dmge of tungsten nd composite mteril CFC (cron fier composites) produced y powerful pulsed high energy ion em nd dense plsm strem in DPF device. Smple mterils W nd composite mteril CFC re considered usully s the min mterils for divertor in the ITER project. Smples of W nd CFC were irrdited t conditions closed to extreme cses in ITER s well s t more hrd conditions closed to ones expected for thermonucler fusion rector with IPC.

2 2 2. Mterils nd rdition conditions Specimens (0x0x2) mm of sintered W with impurities (Fe, C, C, N, H, O up to 0.05%) were prepred t A.A.Bikov Institute of Metllurgy nd Mteril Sciences (IMET), Russin Acdemy of Sciences. Specimens of the composition W/CFC 25x25x0 mm (CFC smple with shrunk-in W cylinder = 2 mm) were prepred in KFA, Julich (Germny). CFC mteril reinforced with SiC prticles up to 8 nd 40 vol. % (0x0x8) mm ws prepred in Royl Institute of Technology (Stockholm, Sweden). W nd W/CFC specimens irrdited were fixed on the steel rod with different distnces from node of DPF device PF-000 (Fig. ). СFC/SiC specimens were fixed t steel holder, which ws fixed on the end of the rod locted long the xis of DPF. Pulsed irrdition of specimens ws performed in the following regimes: power flux density q = W/cm 2, pulse durtion τ = μs, energy stored in the DPF nk ws ~ 600 kj. Deuterium ws used s working gs under initil pressure of 470 P. The specimens of W nd W/CFC were irrdited with N = 0 pulses in series wheres the specimens of CFC/SiC with N = 5. Some experiments with selected mterils were performed using DPF devices PF-5M (IMET), nk energy of 5 kj) nd PF-6 (Institute of Plsm Physics nd Lser Microfusion (IPPLM), 7 kj). 3. Results nd discussion 3. The surfce dmge of tungsten The nlysis hs shown tht pulsed irrdition ws resulted in melting nd evportion of tungsten surfce lyer with formtion of typicl wvelike surfce relief (see Fig. 2, 3). In Fig. 3 one cn see zones with nnoscle cellulr structure, which were oserved under q = 0 0 W/cm 2. There re lot of droplets nd highly long microcrcks on irrdited W surfce. With high power density q > 0 8 W/cm 2 not only intergrnulr ut lso trnsgrnulr microcrcks were oserved. The propgtion of microcrcks into ulk of mteril ws not s significnt s it ws long the surfce. It hd size of few microns. But in some prts of the surfce lyer the microcrcks penetrtion inside the mteril ws ~ 0 μm or more. It ws oserved in those res where grins were elongted normlly to the surfce (see Fig. 4). Under power flux density q > 0 8 W/cm 2 oth intergrnulr nd trnsgrnulr microcrck formtion were oserved. FIG.. Scheme of the experiments in the PF-000

3 FIG. 2. Microstructure of sintered W fter irrdition (0 pulses): - q = 8. 0 7 W/cm 2, - q = 2.

Typicl size of the ule ws of the order of μm.

3 3 FIG. 2. Microstructure of sintered W fter irrdition (0 pulses): - q = W/cm 2, - q = W/cm 2, c - q = 0 0 W/cm 2 ; opticl microscopy On some prts of irrdited W surfce the ggregte of ules ws oserved (see Fig. 5). Typicl size of the ule ws of the order of μm. We suggest tht gs phse in the ules contins implnted deuterium nd voltile compounds of deuterium with contmintion elements of initil mteril (C, N nd O). c 00 μm 00 μm 2 μm 0 μm FIG.3. Microstructure of W in W/CFC composition fter irrdition (0 pulses): - q = 0 0 W/cm 2, - q = W/cm 2 (scnning electron microscopy) [5, 6]

4 The nlysis hs shown, tht irrdition of mteril ws resulted in the erosion connected with mss loss nd reduction of the specimen thickness in comprison with the source stte.

4 4 The nlysis hs shown, tht irrdition of mteril ws resulted in the erosion connected with mss loss nd reduction of the specimen thickness in comprison with the source stte. For the specimens irrdited with power density q ~0 8 W/cm 2 the erosion depth d ws of hundredth prts of micron (see tle ). Under the highest power density q = 0 0 W/cm 2 erosion depth d ws pproximtely two order of mgnitude higher (2μm). The results otined re useful for preliminry express estimtion of mteril ehvior in extreme conditions of the type of plsm disruption or ELMs effects in Iter. Ion nd plsm em irrdition ws result in ion implnttion of working gs nd elements of mterils plced inside the DPF chmer within the surfce lyer of W. In the surfce lyer eside W we oserved such elements s Cu, O nd components of the steel. Ferrum nd Chromium were prts of structurl mterils plced in PF-000: cthode tues, steel holder for W specimens, et l. The copper node of PF-000 contins oxygen s contmintion. Cu, Fe, Cr nd O evported nd sputtered y electron (on the node), ion nd plsm ems were deposited on the surfce of W specimens. Under multifold pulsed irrdition the deposited elements were mixed in liquid phse nd penetrted inside the surfce lyer. It is importnt to hve in view the complex ction of working gs ions nd evported (sputtered) elements of structurl mterils of DPF device when tungsten is considered s mteril for divertor in Iter s well s lternte mteril for thermonucler fusion rector with inertil plsm confinement. 3.2 Dmge of CFC mteril in W/CFC composition Frgments of solidified W in form of droplets nd elongted ridges on the surfce of CFC mteril fter irrdition t q = W/cm 2 re presented in Fig. 6. These frgments were deposited on CFC surfce fter explosive ction of pulsed energy strem. Cron fiers of CFC mteril were evported more significntly when the fier ws norml to irrdited surfce (see Fig.7). 3.3 CFC/SiC mteril The microphotogrph of СFC-8SiC mteril in n initil stte nd fter n irrdition y pulses of energy is presented in Fig. 8. Dmge of the surfce lyer under deuterium ions nd plsm irrdition ws ttriuted to evportion nd sputtering. Structure of the mteril ws stedy under deuterium plsm irrdition in hrd conditions. It is significnt positive property of considered composite mteril for ppliction in divertor of Iter. FIG. 4. Cross-section microstructure of W specimen in W/CFC composition fter irrdition (0 pulses): q = W/cm 2, unetched surfce, etched surfce [5, 6]

0 8 W/cm 2, 0 pulses)[5,6] TABLE I: EROSION OF THE

Contct zone etween W nd CFC fter deuterium ion nd

6]. Cron fiers re prllel with surfce irrdited 200

5 5 25 μm μm FIG. 5. Formtion of ules on the irrdited W surfce (q = W/cm 2, 0 pulses)[5,6] TABLE I: EROSION OF THE TUNGSTEN Specimen # Power density q, 0 8 W/cm ions 0 plsm Erosion depth per one pulse d, 0-2 µm μm 20 μm 0 μm FIG. 6. Contct zone etween W nd CFC fter deuterium ion nd plsm em irrdition (q = 0 0 W/cm 2, 0 pulses) [5, 6]. Cron fiers re prllel with surfce irrdited 200 μm 00 μm FIG. 7. Contct zone etween W nd CFC fter deuterium ion nd plsm em irrdition (q = W/cm 2, 0 pulses) [5, 6]. Cron fiers re normlly to surfce irrdited

of evported lyer thickness d for considered composite under irrdition with deuterium ion nd plsm pulsed ems when cron fiers of CFC mteril were oriented in prllel to the em.

It is sufficiently higher vlue in comprison with sintered W nd ferritic steel type of Eurofer 97 [4].

6 µm FIG. 8. Composite mteril CFC-8SiC in initil stte () nd fter irrdition (): q = 0 9 W/cm 2, 5 pulses; fiers re in prllel with irrdited surfce, 2 fiers re normlly to irrdited surfce The tle 2 presents estimtion of evported lyer thickness d for considered composite under irrdition with deuterium ion nd plsm pulsed ems when cron fiers of CFC mteril were oriented in prllel to the em. The results show tht under power flux density q = 0 9 W/cm 2 the thickness of evported lyer d ws out two or more microns. It is sufficiently higher vlue in comprison with sintered W nd ferritic steel type of Eurofer 97 [4]. For these mterils the thickness of evported lyer d ws out 2 μm t power flux density one order of mgnitude higher. If the fiers of CFC mteril were in prllel with irrdited surfce then the erosion rte ws remrkle lower. The influence of the cron fiers orienttion upon erosion rte of CFC/SiC composite under high energy ems should e tken into considertion when it will e pplied s structurl or functionl mteril in devices of the type of plsm ccelertor nd thermonucler fusion rector. TABLE 2: Type of mteril CFC 8SiC Power flux density, q, W/cm 2 EROSION OF THE CFC/SiC MATERIAL Numer of shots, N Thickness of evported lyer (per one shot) d, μm ,6 CFC 40SiC 0 9 5,9 In initil stte SiC prticles re displced in CFC composite minly in zone etween fier undles (see Fig. 9). After ion-plsm ction the Fe, Cr, Si nd Cu were oserved on the irrdited surfce (Fig. 0). The presence of these elements is connected with evportion of steel holders (Fe nd Cr) nd node (Cu) nd with the following-up re-deposition of them on the trget surfce. Deposited toms under multifold shots were emedded into the surfce lyer. Disperse compounds of the type of crides nd intermetllides (Fe 2 C, Fe 5 C 2, Cu 4 Si, (Cr,Fe) 7 C 3 ) were presented in the surfce lyer with thickness of few µm. The ppernce of these compounds my result in lttice distortion, which will ffect the composite CFC/SiC diffusion permeility of deuterium in comintion with therml lttice distortion in the surfce lyer fter ction of high energy pulsed ems.

composites sed on CFC re proposed s the most perspective mteril for ppliction in divertor of Iter.

7 7 FIG. 9. Second electron imge () nd distriution of chrcteristic X-ry rdition of Si () for initil stte of СFC-8SiC specimen SE Fe Cr Si Cu FIG. 0. Second electron imge nd distriution of chrcteristic X-ry rditions for Fe, Cr, Si nd Cu in СFC-8SiC specimen fter irrdition (q = 0 9 W/cm 2, 5 pulses) This result should e tken into ccount ecuse composites sed on CFC re proposed s the most perspective mteril for ppliction in divertor of Iter. The elements of impurities contined in fusion plsm cn e implnted into divertor mteril nd my form new chemicl compounds with the mteril components. It cn ffect diffusion moility of deuterium nd tritium in divertor mteril. 4. Conclusion It ws shown tht the min fctors for dmge of tungsten under high-energy pulses in DPF devices re het lods resulted in melting of the irrdited surfce lyers, erosion of mterils (mss loss y evportion nd thinning of smples), formtion of different types of surfce defects nd microcrcks. Wvelike relief of irrdited surfce hs

8 8 dvntge for more effective extrction of gses produced inside the mteril in thermonucler fusion rector under plsm irrdition. Dmge of composite mterils of the type of CFC due to erosion is enhnced if cron fiers displced normlly to irrdited surfce. Experiment results hve confirmed the dvntge of Dense Plsm Focus devices for preliminry estimtion nd test of mteril ehvior in extreme conditions in thermonucler fusion rector with inertil plsm confinement. 5. Acknowledgments This work ws prtilly supported y the Interntionl Atomic Energy Agency (Reserch Contrcts No 4540RO, No 4638RO, No 4526RO) nd the "PF-6, Trnsntionl Access Progrm, MJPF-000, Contrct No RITA References [] GAUSTER, W.B., SPEARS, W.R. nd ITER Joint Centrl Tem Requirements nd Election Criteri for Plsm-Fcing Mterils nd Components in the ITER EDA Design, Nucl. Fusion 5 Suppl (994) pp. 7 8 [2] LAWRENCE LIVERMORE NATIONAL LABORATORY (992) Inertil Confinement Fusion, In 99 ICF Annul Report, pp [3] PIMENOV, V.N., MASLYAEV, S.A., IVANOV L.I., PANIN O.V. et l. Interction of Pulsed Strems of Deuterium Plsm with Aluminum Alloy in Plsm Focus Device.. The New Methodology of the Experiment. Proceedings of the Tllinn University of Socil nd Eductionl Sciences. Tllinn (2003) B2 pp [4] PIMENOV, V.N., DEMINA, E.V., MASLYAEV, S.A., IVANOV L.I., GRIBKOV, V.A., DUBROVSKY, A.V., UGASTEE, Ü.E., LAAS, T., SCHOLZ, M., MIKLASZEWSKI, R., KOLMAN, B., TARTARI, A. Dmge nd Modifiction of Mterils Produced y Pulsed Ion nd Plsm Strems in Dense Plsm Focus Device, Nukleonik 53 No3 (2008) pp. 2 [5] PINTSUK, G., LINKE, J. Mcro nd Microscopic Anlysis of Irrdited W/CFC- Components, Report on the 2nd Expert Meeting Plsm strems interction with mterils, EURATOM/Institute of Plsm Physics nd Lser Microfusion nd IAEA, Wrsw, Polnd, Novemer (2006) (on CD) [6] PIMENOV, V.N., MASLYAEV, S.A., DEMINA, E.V., KOVTUN, A.V., SASINOVSKAYA, I.P., GRIBKOV, V.A., DUBROVSKY, A.V. Interction of powerful pulse strems of energy with surfce of tungsten in Plsm Focus Device, Physics nd Chemistry of Tretment of Mterils (2008) No3 pp. 5 4 (in Russin)

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