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# «Association EURATOM / IPP.CR I N S T I T U T E O F P L A S M A P H Y S I C S, v.v. i. ACADEMY OF SCIENCES OF THE CZECH REPUBLIC ANNUAL REPORT ...»

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The I-V characteristics are plotted for different collector positions, when the collector is partially exposed to plasma (h0). The probe current is normalized to the ion saturation current. It is evident that the value of the ratio R and the floating potential Vfl depend on the collector position.

This is in a good agreement with the experiment and the theoretical predictions.

The relation between ln(R) and Vfl can be approximately described by the linear function as seen in Fig. 2. The value of the plasma potential is according to the Eq. 1 estimated as Φ = -24V, which is below the value of the plasma potential given in the PIC simulation (Φ = 0V).

Fig.1. I-V characteristics of the ball-pen probe for Fig.2. The dependence of the ball-pen probe potential several collector positions calculated by the PIC Vfl on the logarithm of the ratio R. for several position simulations (Te=Ti=20 eV, Φ=0). of the ball-pen collector.

The discrepancy can by explained by detailed analysis of the potential around the ball-pen probe head. The 2D profile of the potential around the probe is plotted in Fig. 3. The plasma is injected

–  –  –

from the left and right side of the simulated area. The probe collector is exposed 0.2 mm to plasma and negatively biased by U = -150 V. In spite of the fact, that plasma potential is equal to 0 V at the left and right boundary of the simulated area the potential inside area is below that value. It means that the plasma potential provided by the ball-pen probe (see Fig. 2) should be equal to the potential given by PIC modeling a few ion Larmor radii far from the probe head along y coordinate. The potential above the probe orifice at coordinates y = 3.0 mm (dash line in Fig. 3) is approximately equal to -5 V and it might be assumed as the unperturbed plasma potential.

Fig.3. The 2D profile of the potential around the ball-pen probe. The probe collector is exposed 0.2 mm in plasma and negatively biased by U = -150 V. The plasma is injected from left and right side of the simulated area. The magnetic field is parallel with x coordinate, Bx =1 and By = 0 T.

.

It can be summarized that the results of the PIC simulations of the ball-pen probe confirmed that the relation between the difference of the plasma and floating potential and ln(R) is linear as predicted the Langmuir probe theory (Eq. 1). However, the plasma potential provided by the ball-pen probe in Fig. 2 is approximately 1*Te (Ti=Te=20 eV) less than the plasma potential estimated by using 2D profile of the potential in Fig. 3. The discrepancy can point out that the basic idea of the direct measurements of the plasma potential based on the simple Langmuir probe theory above mentioned is not suitable for this kind of magnetized plasma. However, it can be also explained by the fact that the model results in zero electron density inside the shielding tube, which was not observed in the experimental observation [1,2].

References:

[1] J. Adamek et al., Czech. J. Phys., 54 (2004), C95.

[2] J. Adámek et al., Czech. J. Phys., 55 (2005), 235-242.

[3] J.P. Verboncoeur, A.B. Langdon and N.T. Gladd, "An Object-Oriented Electromagnetic PIC Code", Comp. Phys. Comm., 87, May11, 1995, pp. 199-211.

In collaboration with:

V. Basiuk, Y. Peysson, Association EURATOM-CEA Cadarache, France I. Voitsekhovitch, Association EURATOM-UKAEA Abingdon, United Kingdom..

Transport codes solve coupled diffusion equations for heat, matter, and magnetic field (current).

These partial differential equations are coupled to a magnetic field equilibrium code and modules for LH and NB injection. Such codes thus allow fully self-consistent calculations of tokamak operation, and are highly desirable for the study of COMPASS operation with the planned LH and NB systems.

Currently, the transport modeling of the tokamak COMPASS is performed using the ASTRA [1] and CRONOS [2] codes. The ASTRA code had been in use at IPP for some time and it has limited internal capabilities as far as external heating and current drive is concerned. It was therefore decided that a more advanced code, CRONOS, is necessary for the prediction and analysis of COMPASS operating scenarios. During the mobility stay of M. Stránský at CEA Cadarache in April 2007, the CRONOS transport code was acquired and adapted for the COMPASS tokamak, and installed in Prague by the CEA staff in November 2007. Currently both codes are capable of simulating ohmic heating schemes of various equilibrium settings.

During the visit of Irina Voitsekhovitch last September (2007) a robust transport model for COMPASS was developed for the ASTRA code, including the possibility of external heating.

Simulations with externally calculated (ACCOME, FAFNER) NBI heating and current drive were also successfully performed using both of these codes [3,4]. Even though such calculations are not automatically self-consistent, the transport models show reasonable behavior, and it can be foreseen that once the modules for NBI heating currently being developed at CEA for CRONOS are satisfactorily finished, self-consistent predictive simulations of NBI heating on COMPASS with CRONOS will be possible on a routine basis.

Fig. 1 shows an example calculation of the ion and electron temperature profiles calculated by the ASTRA code using the transport model developed with I.Voitsekhovitch for the SND equilibrium with Ip = 200 kA, BT = 1.2 T and central electron concentration of 3.5·1019 m-3 for coNBI and counter-NBI each delivering 300 kW. The NB power deposition profiles were calculated using the FAFNER code [5-7].

In December 2007, Yves Peysson of the CEA staff has also made available to us the “Starwars” suite of lower hybrid (LH) toroidal ray-tracing (C3PO) and 3-D Fokker-Planck (LUKE) codes [8], which can simulate LH heating and current drive in a stationary state. This LH current drive module takes as an input an externally provided equilibrium, provided presently by the ACCOME code [9]. One of the results of the “Starwars” calculation are the LH power deposition and driven current density profiles.

Results from the “Starwars” module were compared with ACCOME LH results, and several conclusions about the COMPASS LH heating scheme became evident. The particularly unfavorable lower hybrid slow wave accessibility conditions at the foreseen Phase I level operating conditions (Ip=170 kA, B0=1.2 T) indicate that rays travel around the plasma edge for a ANNUAL REPORT 2007 ASSOCIATION EURATOM/IPP.CR long time before penetrating into the central plasma region with significant absorption near the edge, and the rays also show very stochastic behavior in COMPASS.

Presently there is an ongoing effort to incorporate the non-inductive current drive modules into CRONOS for the COMPASS configuration with promised help from CEA staff.

–  –  –

Fig. 1. Ion and electron temperature profiles calculated by the ASTRA code for the SND equilibrium with Ip=200 kA, BT=1.2 T and central electron concentration of 3.5·1019 m-3 for the co-NBI and counter-NBI each at 300 kW.

References:

[1] G. V. Pereverzev and P. N. Yushmanov: ASTRA - Automated System for Transport Analysis, IPP Garching report IPP 5/98, February 2002.

[2] V. Basiuk, J. F. Artaud, F. Imbeaux et al.: Nucl. Fusion 43 (2003) 822.

[3] V. Fuchs, I. Voitsekhovitch, O. Bilyková et al.: 33rd EPS Conf. Proceedings, ECA, 30I (2006) 1.103.

[4] O. Bilyková, V. Fuchs, R. Pánek et al.: Czech. J. Phys. 56B (2006) B24-B30.

[5] G. G. Lister: A fully 3D neutral beam injection code using Monte Carlo methods, Max-Planck-Institut für Plasmaphysik Technical Report IPP 4/222, 1985.

[6] A. Teubel and F. P. Penningsfeld: Plasma Phys. Control. Fusion 36 (1994) 143.

[7] J. Urban, V. Fuchs, R. Pánek et al.: Czech. J. Phys. 56B (2006) B176-B181.

[8] J. Decker and Y. Peysson: On Self-consistent Simulation of Lower-Hybrid Current Drive, 33rd EPS Conference on Plasma Physics, Roma, Italy, June 19-23, 30I (2006).

[9] K. Tani and M. Azumi: J. Comput. Phys. 98 (1992) 312.

III TECHNOLOGY

In the Association EURATOM-IPP.CR, research for the technology tasks is focussed on properties of various diagnostic and structural elements and materials of future thermonuclear reactors, both before and under neutron irradiation. Two irradiation sites are available for this purpose: the light water experimental fission reactor LVR-15 (operated by NRI plc), and the isochronous cyclotron U-120M with the maximum proton energy of 37 MeV (operated by NPI ASCR). Both institutes are members of the Association EURATOM-IPP.CR and their facilities are located in Řež research site about 20 km north of Prague.

The technology research in the Association EURATOM/IPP.CR covered the following

areas in 2007:

• Tritium Breeding and Materials o Breeding Blanket o Materials Development

• Physics Integration o TPDC Diagnostics - Ceramics

• Vessel/In Vessel o Blanket All the technology tasks are listed below; followed by a more detailed report on the progress in individual deliverables.

UT7_IFMIF_IPPCR_NPI Measurement of activation cross sections at neutron energies below 35 MeV. Data for Nickel.

Field/Area: Tritium Breeding and Materials / Materials Development Principal Investigator: P. Bém, Nuclear Physics Institute Řež Co-authors: V. Burjan, M. Götz, M. Honusek, V. Kroha, J. Novák and E. Šimečková In collaboration with: U. Fischer and S.P. Simakov, Association FZK-Euratom, Forschungszentrum Karlsruhe, Germany Due date, 30.11.2007, status: completed UT7-WELD-IPPCR-IAM Development of new numerical macroelements method for distortion prediction of the big welded construction Principal Investigator: M. Slováček, IAM Brno Field: Vessel/In-Vessel Collaborative staff: L.Vlček, PhD.

–  –  –

UT 2007 PFW_IPPCR_NRI Establishing of a specialized laboratory for handling, manipulations and analysis of Beryllium specimens (e.g. Be coated PFW mock-ups) Principal Investigator: Vl. Masařík, NRI, Řež Field: Vessel /In Vessel, Area: Blanket, Materials Coordinated by NRI staff: Vl. Masařík, T Klabík, J. Hájek UT7_SURF_IPPCR_IPM1 Structure and phase composition of surfaces of materials modified by plasma treatment Field/Area: Tritium Breeding and Materials/ Materials Development Principal Investigator: Oldřich SCHNEEWEISS, Institute of Physics of Materials, Brno Co-authors: Jiří BURŠÍK, Jiří ČERMÁK, Petr KRÁL, Pavla ROUPCOVÁ Due date, status: 2007, completed IPP-CR_UT7_DEGR_IPM2 The Eurofer steel: microstructural degradation and embrittlement Field/Area: Tritium Breeding and Materials / Materials Development Principal Investigator: I. Dlouhý, Institute of Physics of Materials AS CR, Brno Co-authors: H. Hadraba, V. Kozák, P. Čupera, Z. Chlup Due date, status: 2007, completed TW6-TVV-SYSEG Assessment of PSM Welding Distortions and Field Welding Principal Investigator: M. Slováček, IAM Brno Field: Vessel/In-Vessel Collaborative staff: L.Vlček PhD.,V. Diviš, M. Slováček,PhD.

TW3-TVB-FWPAMT Mechanical Testing of PFW panel attachment system Contract: FU06-CT 2004 – 00061, EFDA/04-1137 Field/Area: Vessel / Mechanical Structures Principal Investigator: Vladislav Oliva, CTU in Prague - FNSPE Prague Co-authors: Aleš Materna (FNSPE Prague), Jaroslav Václavík (ŠKODA Výzkum Ltd., Pilsen) In collaboration with: P. Lorenzetto, A. Furmanek, EFDA- CSU, Garching Revised due date: 31. 12. 2007 Status: completed IPP-CR_ TW4-TVB-TFTEST2, 1 Thermal fatigue testing of PFW mock-ups at high heat flux conditions.

Principal Investigator: T. Klabík, NRI, Řež Field: TV – Vessel in Vessel, Area: TVB Blanket Collaborative staff: Vl. Masarik, P. Hájek, O. Zlámal In collaboration with: P.Lorenzetto, F4E, Barcelona, Spain IPP-CR_ TW6-TTMS-003, D5 Study of fatigue and crack propagation issues of EUROFER in liquid Pb-Li.

Development and testing cold traps, high temperature flanges and circulation pump for the liquid metal Pb-Li loop Principal Investigator: Vl. Masarik, NRI, Řež Part III - TECHNOLOGY Field: Tritium Breeding and Materials, Area: Breeding Blanket Collaborative staff:: L. Kosek, J. Berka, M. Ruzickova, M. Zmitko, K. Splichal IPP-CR_ TW6-TTMS-003, D5 Development of design of Pb-Li auxiliary system for HCLL TBM.

Evaluation Pb-Li compatibility of EUROFER samples coated by Al and Er2O3 layers under higher temperature conditions Principal Investigator: K. Šplíchal, NRI, Řež Field: Tritium Breeding and Materials, Area: Materials Development Collaborative staff: L. Kosek, J. Berka, M. Zmitko IPP-CR_ TW2-TTMS-003b, D4 Hydrogen compatibility and emrbittlement issues of EUROFER weldments.

EUROFER and Pb-Li melts testing under higher temperature irradiation conditions Principal Investigator: K. Šplíchal, NRI, Řež Field: Tritium Breeding and Materials, Area: Materials Development Collaborative staff: J. Berka, M. Zmitko, Vl. Masarik, Z. Lahodová, L. Viererbl IPP-CR_ TW2-TTMS-001, D3 Behaviour of EUROFER weldments in Pb-Li.

Static and dynamic fracture toughness of plates and weldments at the transition irradiated up to 2.5 dpa at 200°C – 250°C Principal Investigator:P. Novosad, NRI, Řež Field: Tritium Breeding and Materials, Area: Materials Development Collaborative staff:, M. Falcnik M. Kytka, K. Splichal TW7-8_TTMN_002B_D6 Development of activation foils dosimeters for determination of IFMIF-relevant flux spectra: validation experiments.

Experiments for the validation of Bi cross-sections up to 35 MeV in a quasi-monoenergetic neutron spectrum Field/Area: Tritium Breeding and Materials / Materials Development Principal Investigator: P. Bém, Nuclear Physics Institute Řež Co-authors: V. Burjan, M. Götz, M. Honusek, V. Kroha, J. Novák and E. Šimečková In collaboration with: U. Fischer and S.P. Simakov, Association FZK-Euratom, Forschungszentrum Karlsruhe, Germany Due date, 30.06.2008, status: in progress

–  –  –

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