19 May, 1998

- In accordance with Article 10 of the ITER EDA Agreement,

- with reference to the SWG Charter decided by the ITER Council at its thirteenth meeting, Attachment 1, taking account, in particular, of the ITER Council charges regarding its two tasks, i.e.,

1) the SWG would propose technical guidelines for possible changes to the current detailed technical objectives and overall technical margins with a view to establishing option(s) of minimum cost still satisfying the overall programmatic objective of the ITER EDA Agreement,

2) pursuant to Art. 2(e), the SWG would also provide information on broader concepts as basis for its rationale for proposed guidelines, and articulate likely impacts on the development path towards fusion energy,

- recognizing that it is of crucial importance to the Parties' fusion programmes to pursue the joint activities during an expected three year extension of the EDA with a general intent to enable an efficient start of possible, future ITER construction at the end of this period, and in this regard recognizing the importance of pursuing joint preparatory efforts in all relevant domains,

- recognizing that in case the Parties would eventually be unable, for financial reasons to proceed to the construction of the presently foreseen device, it is prudent to plan now to have available, at the time of decisions on construction option(s) of ITER whose cost for the partners would be reduced. This should be accomplished by reducing the detailed technical objectives and possibly decreasing physics margins while insuring that the engineering margins remain such that safety and performance of the device are not impaired and retaining the overall programmatic objective of ITER.

Within Task #1, the SWG considered options which maintain the strategy to take one step between now and DEMO, while maintaining the overall programmatic objective of ITER, namely to demonstrate the scientific and technological feasibility of fusion power for peaceful purposes.

The Special Working Group has agreed to the following as its answer to Task #1.

1. Background

An ITER design which fulfills the overall programmatic objective of the EDA agreement and the detailed technical objectives adopted by the four Parties in 1992 has successfully been developed together with the supporting technology R&D and is documented in the Final Design Report. It is the view of the ITER Council that this design should form the basis against which ail other reduced cost options should be considered.

During the EDA a broad operating range has been identified on the basis of the database established by the Parties contributions to the Physics R&D programme which provides protection against unforeseen technical shortfalls and should allow an optimal choice of parameters for DEMO.

At its first meeting, the SWG provided initial guidance to have the Director and the JCT, supported by the Home Teams, assess opportunities for significantly reducing the direct capital cost of ITER. The guidance indicated that the direct capital cost should have a target of approximately 50% of the direct capital cost of the present design. The cost savings should be achieved primarily through reductions in the detailed technical objectives under the performance assumptions used for the present design. The SWG notes that for these cost reduction considerations any even limited reductions in the engineering margins and changes in technology choices should be implemented only after careful consideration to assure safe and reliable operation.

At its second meeting, the Director provided preliminary information from the initial cost reduction studies, which indicated that major reductions in the direct capital cost of the present design require a decrease in plasma performance. The Director further reported that, assuming the present physics design rules documented and agreed upon by the ITER Physics Expert Groups, and for a DT burning plasma in a device with a ratio of fusion power to auxiliary heating power of at least 10, significant reduction in the direct capital cost appears possible. He presented information from a preliminary survey which indicated that the lowest direct capital cost appears to be obtained by a substantially reduced-size machine (from the present 8.1 m to about 6.0-6.5 m) with substantially reduced fusion power (reduced to between one-third and one-half of the present nominal 1500 MW).

In light of this input from the Director, and of the discussions held at its two meetings, the SWG proposes the following technical guidelines for possible changes to the present detailed technical objectives and overall technical margins, with a view to establishing option(s) of minimum direct capital cost still satisfying the overall programmatic objective of the ITER EDA Agreement.

2. Performance and Testing Requirements

Plasma Performance

The device should:

• achieve extended burn in inductively driven plasmas with the ratio of fusion power to auxiliary heating power of at least 10 for a range of operating scenarios and with a duration sufficient to achieve stationary conditions on the time scales characteristic of plasma processes.
• aim at demonstrating steady-state operation using non-inductive current drive with the ratio of fusion power to input power for current drive of at least 5.

In addition, the possibility of controlled ignition should not be precluded.

Engineering Performance and Testing

The device should:

• demonstrate the availability and integration of technologies essential for a fusion reactor (such as superconducting magnets and remote maintenance);
• test components for a future reactor (such as systems to exhaust power and particles from the plasma)
• test tritium breeding module concepts that would lead in a future reactor to tritium self-sufficiency, the extraction of high grade heat, and electricity production.

3. Design Requirements

Engineering choices and design solutions should be adopted which implement the performance requirements set forth in Section 2 and make maximum appropriate use of the existing R&D database (technology and physics) developed for ITER. The choice of machine parameters should be consistent with margins that give confidence in achieving the required plasma and engineering performance in accordance with physics design rules documented and agreed upon by the ITER Physics Expert Groups. The design should be capable of supporting advanced modes of plasma operation under investigation in existing experiments, and should permit a wide operating parameter space to allow for optimizing plasma performance. The design should be confirmed by the scientific and technological database available by the end of the EDA.

In order to satisfy the plasma performance requirements of Sec. 2, an inductive pulse flat top capability during burn of about 300 s to 500 s, under nominal operating conditions, should be provided. In order to limit the fatigue of components, operation should be limited to a few 10s of thousands of pulses. In view of the goal of demonstrating steady-state operation using non-inductive current drive in reactorrelevant regimes, the machine design should be able to support equilibria with high bootstrap current fraction and plasma heating dominated by fusion alpha particles.

To carry out nuclear and high heat-flux component testing relevant to a future fusion reactor, the engineering requirements are:

Average neutron flux > 0.5 MW/m²
Average fluence > 0.3 MWa/m²

The option for later installation of a tritium breeding blanket on the outboard of the device should not be precluded.

The engineering design choices should be made with the objective of achieving the minimum cost device which meets the requirements described in Sec. 2 through Sec. 4.

4, Operation Requirements

The operation should address the Issues of burning plasmas, steady-state operation and improved modes of confinement, and testing of blanket modules,

- Burning plasma experiments will address confinement, stability, exhaust of helium ash, and impurity control in plasmas dominated by alpha-particle heating.

- Steady-state experiments will address issues of non-inductive current drive and other means for profile and burn control and for achieving improved modes of confinement and stability.

- Operating modes should be determined having sufficient reliability for nuclear testing. Provision should be made for low-fluence functional tests of blanket modules to be conducted early in the experimental programme. Higher fluence nuclear tests will be mainly dedicated to DEMO-relevant blanket modules in the flux and fluence conditions described in Sec. 3.

In order to execute this combined program, the device is anticipated to operate over an approximately 20 year period. Planning for operation must provide for an adequate tritium supply. It is assumed that there will be an adequate supply from external sources throughout the operational life.

5. Conclusions & Recommendations

The SWG notes that the preliminary studies conducted by the Director and the Parties suggest that the direct capital cost of ITER can be reduced significantly by targeting the less demanding performance objectives recommended in this report. In the view of the SWG, these less demanding performance objectives will satisfy the overall programmatic objectives of the ITER EDA Agreement even though these performance objectives are necessarily less than those that could be achieved with the present design.

The SWG recommends that the ITER Council ask the Director to continue these efforts with high priority keeping in mind the desire to make the most cost effective use of existing design solutions and their associated R8D. The SWG underlines the importance of completing the planned R&D efforts.

The SWG recommends that the ITER Council ask the Director to emphasize the following efforts until the end of 1998: propose a set of major parameters and describe the rationale including information on the performance margins, range of operation and cost drivers, identify engineering design solutions for key components including possibly the need for additional R&D, and describe the flexibility to study advanced tokamak modes. The SWG believes it may be useful, if requested by the Council, for the SWG to continue to interact with the Director as this work progresses.

The SWG also offers for consideration by the Council the following possible sequence of events: