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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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ANNUAL REPORT 2007 ASSOCIATION EURATOM/IPP.CR 8. MODELLING This part of the monitoring report summarizes briefly main results achieved in modeling during the last year. The first part deals with plasma performance with additional heating (NBI+LH), the second one on progress in modeling of resonant magnetic perturbation technique, which is envisaged to be applied on COMPASS for ELM mitigation.

8.1 Modeling of plasma performance Currently, transport modeling of the tokamak COMPASS is performed using the ASTRA and CRONOS codes. The CRONOS transport code was acquired last year from CEA Cadarache and adapted for the COMPASS tokamak. Currently both codes are capable of simulating ohmic heating schemes of various equilibrium settings. During I.Voitsekhovitch’s visit 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. Even though such calculation isn't 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. The following figures show 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 co-NBI and counter-NBI each at 300 kW:

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Fig. 8.1.1 The absorbed power in the co-NBI scheme is 190 kW while in the counter-NBI scheme it is 120 kW for the given equilibrium.

Our group has also recently acquired a LHCD simulations package from CEA Cadarche consisting of the ray-tracing code C3PO, and the 3-D relativistic bounce-averaged drift kinetic code LUKE.

With the help of Y.Peysson, the code was adapted to the COMPASS LH configuration with a

1.3 GHz lower hybrid RF power source. Preliminary simulations were performed for the SND equilibrium and a launched n|| ranging from 1.95 to 3. The results were satisfactory giving full power absorption of 210 kW and a driven current of 67 kA for n||=1.95; the deposition being mostly at normalized toroidal ρ of 0.25 and 0.5; while for larger n|| the absorption place moves outwards.

Compatible LHCD results were obtained with ACCOME. Currently we are in the process of learning and fine-tuning the code for the COMPASS tokamak, in view of eventually making selfconsistent predictive transport simulations including both LHCD and NBI sources.

Appendix – Tokamak COMPASS reinstallation in IPP Prague

8.2 Modelling of resonant magnetic perturbations and edge ergodization The COMPASS tokamak is equipped with a unique set of saddle coils for producing resonant magnetic perturbations (RMPs). During the operation of COMPASS at Culham these coils were used, for example, to investigate neoclassical tearing modes, mode penetration, and control of Type-III ELMs. It was then discovered on the DIII-D tokamak that RMPs can lead to complete suppression of Type-I ELMs [T. Evans et al.: Journal of Nuclear Materials, 337-339, (2005) 691].

As there is a possibility that the newly installed COMPASS will exhibit Type-I ELMs thanks to the planned NBI system, the availability of a flexible set of RMP coils opens a way to test this ELM mitigation technique.

As part of preparation for COMPASS operation in Prague, we performed calculations of spectra of RMPs caused by saddle coils. The emphasis was on edge ergodization, which is believed to be a key element of the ELM suppression mechanism. The calculations follow the same principle which was used for the calculations of RMP spectra for the ELM suppression experiments on DIII-D, JET and MAST and for the design work of RMP coils for ITER. The ERGOS codes, developed at CEA Cadarache, have been already used for those cases [E. Nardon et al.: J. Nucl. Mat. 363-365, (2007) 1071] and only required some modifications for the coil system of COMPASS, which is significantly more complicated than in other machines.

Fig. 8.2.1 Poincaré plot of field line tracing, showing the pedestal region. The x-axis is θ*– the straight field line poloidal angle, the y-axis is the radial position s=ψ1/2, with ψ being the normalized poloidal flux. Every dot represents an intersection of a field line with the poloidal plane.

Spectra of the perturbations are calculated by computing the vacuum field of the coils and the field components are then projected on a mesh of intrinsic coordinates created as part of the equilibrium calculation by the MHD equilibrium code HELENA [G. Huysmans et al.: Proc. CP90 Europhysics Conf. on Comput. Phys., (1991) 371]. The perturbation spectra are thus coupled to a specific

equilibrium. For our calculations we use equilibria predicted by the ACCOME code [K. Tani et al.:

J. Comput. Phys. 39, (1992) 332]. The perturbation field creates magnetic islands whose sizes are determined by Fourier harmonics of the radial perturbation. The leading toroidal mode of the perturbation has n=2 due to the symmetry of coils. Ergodization is then estimated by applying the criterion of island overlap and verified by field line tracing.





Results show that for the chosen configuration of RMP coils an ergodic layer appears in the pedestal region (Fig. 8.2.1). This is similar to the results for the ELM suppression experiment at DIII-D, thus a comparable effect on ELMs can be expected.

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Fig. 9.1 Schematics of the NBI system connection to the tokamak and CODAC systems Appendix – Tokamak COMPASS reinstallation in IPP Prague Third, following key decisions on design principles of the COMPASS control system and interlocks, final specifications of the NBIs control and safety could be released, see the Fig. 9.1. The NBIs will have their own control nodes, each of them running a state machine, whose parameters can be set from the central COMPASS control system. The systems will have an own XML description, which will allow their set-up from the central system. The interlocks will use a serial link of relays.

The Call for Tender for the two Neutral beam injectors for the COMPASS tokamak will be released in early 2008. The successful contender will be notified in summer 2008, and the complete system of the two NBIs is expected to be installed in the COMPASS experimental hall in the second half of 2009.

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10. HUMAN RESOURCES FOR THE REINSTALLATION OF THE

COMPASS TOKAMAK (status as of January 2008) At the beginning of the year 2008, the total number of the IPP.CR staff involved in the reinstallation of the COMPASS tokamak is 48 employees. Not all of them are involved full time – the total manpower is 39.9 ppy. The manpower is slightly above the number promised in the Phase II

proposal (35+). This manpower is divided according categories as follows:

Persons ppy Senior scientists and postdocs: 21 19.2 PhD students 12 12 Engineers and technicians: 9 8.5 Undergraduate students 6 1.2 The support of the project from IPP (management of IPP, financial matters and mechanical workshop) is very important, but not specified. The list of IPP staff is shown in Table 1. The involvement in particular topics is indicated.

In addition, a strong collaboration on COMPASS re-installation has been established between IPP and Association EURATOM HAS and IST. Our colleagues from Portugal and Hungary are involved in design and implementation of the CODAC and development of particular diagnostics. The number of collaborators changes in time, the total manpower is estimated as not less than 2 ppy for HAS and 2 ppy for IST. More detailed information on collaborating staff is shown in Table 10.2.

The distribution of duties of the staff according to topics is as follows:

• Management: J.Stockel (project leader), R.Pánek (deputy project leader), M.Hron (administr.)

• Supervision of building construction: R. Pánek, J. Kladrubský

• Supervision of power supplies: R. Pánek, J. Kladrubský, J. Zajac

• Control and Data Acquisition: M. Hron, J. Písačka, J. Adámek, J. Sova + IST staff

• Installation of IT: J. Písačka, K. Rieger, P. Cahyna, F. Janky

• Feedback system and PS control: M. Hron, J. Horáček, O. Bilyková, M. Stránský, J. Vlček, K. Rieger, F. Janky, R. Beňo, J. Seidl + IST

• Vacuum and gas handling system: J. Stránský, F. Žáček, M. Šatava, J. Stockel

• Additional heating: J. Stockel, J. Mlynář, V. Piffl (NBI), F. Žáček, J. Zajac (LHCD)

• Diagnostics development: V. Weinzettl o Magnetics: I. Ďuran, O Bilyková, J Havlíček (EFIT), K Kovařík, J Stockel o Optical diagnostics: V Weinzettl, D Naydenkova, V Piffl, M Vácha, + HAS o Thomson scattering: P Bílková, J Brotánková, P Bohm, M Aftanas, Z Melich, D. Šesták o Edge plasma diagnostics: R. Dejarnac, J. Adámek, J. Horáček o Microwave diagnostics: J. Zajac, F. Žáček, J. Vlček, M. Vašulka, M. Kazda + IST o Beam diagnostics: HAS + V. Weinzettl, J. Stockel

• Theory and modeling: R. Pánek o LHCD+transport: V. Fuchs, V. Petržílka, P. Pavlo, M. Stránský o NBI: J. Urban, J. Preinhealter o RMP: P. Cahyna, L. Krlín o Edge pasma modeling: R. Dejarnac, E. Havlíčková, M. Komm

• General technical support: M. Šatava (drawings), F. Jiránek, K. Boušek, K. Rieger, V. Havlík Appendix – Tokamak COMPASS reinstallation in IPP Prague The composition of the groups may change according progress of individual topics and other duties, which may appear.

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Potential Risks Manpower foreseen and necessary for the success of the COMPASS project is currently fully available. However, a large part of it is represented by PhD students mostly funded by scholarships.

Though they are all competent and intend to continue their work into employment by IPP, this will soon imply an increasing demand on salaries which may be difficult to meet.

We have originally counted upon EURATOM contribution (baseline support) of the order of 20%.

However, the ceiling for baseline allocated to IPP.CR for 2008 (221.7 keuro) represents only 16% contribution, and that only due to the fact that COMPASS operational costs will start up growing gradually this year (depreciation, in particular); otherwise, it would be around 14% only. If the diagnostics (included in the original Phase 2 proposal as non-eligible for PS) were charged against the CoA under baseline support as investments in 2008, the EURATOM support would be even less (11% in 2008).

Lack of resources to provide adequate salaries to these young people upon their regular employment represents a potential risk of loosing them for the work on COMPASS, or even for the Community.

Encouraging people to increase their work under COMPASS-unrelated EFDA tasks, or seeking long-term secondments in other associations, CSUs etc. would have, at this moment, the same detrimental effect of reducing the manpower available.

Appendix – Tokamak COMPASS reinstallation in IPP Prague

11. FINANCIAL REPORT The table 11.1 compares the current estimates for re-installation of COMPASS with numbers presented in the Phase II proposal.

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The first column is taken over from the Phase II proposal, where just a single flying-wheel generator was envisaged to operate the tokamak at 1.2 T. The original calculation of the cost increase for operation at maximum BT is presented in the second column.

The third column represents the current estimate of the final cost for 2.1 T. The last column shows the difference between the Phase II proposal (based on 2005 costs) and the current status of the budget.

Before discussing the differencies in individual items in detail, we have to note that:

• The estimates of the cost for the Phase II proposal were based on the 2005 costs in Czech crowns (CZK), using the exchange rate 29.70 CZK / EUR. Current estimates are based on the exchange rate 26.00 CZK / EUR, expected for 2008.

• Inflation rate was 2.5% in 2006 and 2.8% in 2007, 6% is expected in 2008.

• The increase of costs of raw materials (Cu, Fe, etc.) was disproportional and significantly above the inflation rate.

These factors are partially responsible for the increase of the current costs with respect to the Phase II proposal.

Let us discuss the individual items in more detail.

Transport from Culham Additional expenditures for transport (by 44 kEuro) have appeared after dismantling of the COMPASS tokamak in Culham. The main reasons for this were a/ the constructruction of a special transport frame for the facility and b/ the cost of the oversized transport.

Power supplies An increase of the power supplies cost is due to the decision to install both flying-wheel generators from the very beginning of the project. This arrangement will allow to operate the tokamak at maximum toroidal magnetic field up to B= 2.1 T and provide some redundancy.

This decision follows the recommendation of the AHG.. Furthermore, during the specification of the contract with the manufacturer it turned out that the overall cost of two generators manufactured simoulaneously is much lower than the total cost of step-by-step purchase. This solution also avoids the necessary shut-down for installation of the second generator at a later phase of the project.

The tendered price for the complete solution was higher by ~707 kEuro, namely due to the increase of the raw material costs, increase of technical requests, and more strict safety regulations.

ANNUAL REPORT 2007 ASSOCIATION EURATOM/IPP.CR CODAC Some increase of the budget appeared also in the CODAC. The status of the analogue feedback system for the plasma control has been found non-satisfactory after the dismantling (namely because some elements, like waveform generators were controlled by an old fashion and nonexisting software. Therefore, a completely new, fully digital control system was designed, which had some impact on the budget (an increase by 35 kEuro).

Diagnostics The cost of diagnostic systems has also increased by 41 kEuro with respect to the Phase II proposal.

This increase has appeared mainly after revision of the detail design of the key diagnostics – the high resolution Thomson scattering. A more precise estimate is now 700 kEuro, which is higher by 215 kEuro than the Phase II value. The increase is caused by an enhancement of the core detection, which is designed as multi-channel with spatial resolution (there was only a single central channel in the Phase II proposal). On the other hand, the estimates for re-installation of the magnetic diagnostics were overestimated by ~50 kEuro in the original proposal. After dismantling of the system in Culham and after the decision to exploit the digital control system it was found that only ~12 kEuro is required for refurbishment of the magnetic diagnostics. In addition, the planned expenditures for microwave reflectometry were also reduced significantly (by ~144 kEuro), because the full responsibility for this diagnostics was taken over by the Association IST. A more detail cost breakdown for plasma diagnostics is shown in the Table 11.2.

–  –  –

However, an enhancement of the diagnostic capabilities would be required in the later phase of the project. Installation of the neutral particle analyzer (after NBI), VUV & XUV spectrometers, reciprocating Langmuir probe and radiometry is envisaged. These equipments already exist, but their refurbishment will require additional costs, which are estimated as ~84 kEuro.

Refurbishment Furthermore, it was found during the dismantling of COMPASS in Culham and preliminary tests at IPP Prague that some key elements for re-installation of COMPASS require a refurbishment. In particular, new gauges for vacuum and gas handling systems are required for their computer control, new oil for turbo-molecular pumps, etc. There are also some construction elements (supports for diagnostic cables, galleries around the machine, …) that have to be replaced. These expenditures were not envisaged. Therefore, a new line is added to the Table 11.1 is added indicating the amount of 93 kEuro required for refurbishment of the above items.

Appendix – Tokamak COMPASS reinstallation in IPP Prague

Building construction The construction of the new tokamak building is not a subject of the preferential support. However, for information we note here that its cost has risen to 3 963 kEuro, which is significantly more than originally estimated in the year 2005, i.e. before starting the tendering process. In spite of the fact that the tenderer offered the lowest price, the tendered amount was much higher. Furthermore, during the realization of the project, the technology part of the building appeared to be more complex than expected (equipment for de-mineralized water, fire-protection systems, basement of the second fly-wheel generator, unexpected problems at excavation of the ground, …). The extra costs for the building construction were provided by the Government of the Czech Republic and by the Academy of Sciences of the Czech Republic.

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