Implications of uncertainties on European DEMO design

Abstract

During the pre-conceptual design phase of fusion devices such as the European demonstration fusion power plant (DEMO), systems codes provide a fast evaluation of optimal design points and highlight high impact areas. However, determining or evaluating a design point at such an early stage comes with uncertainties in many of the design parameters. These uncertainties are both associated with the physics as well as the engineering basis of the European DEMO design. The work applies an uncertainty quantification analysis to the 2017 pulsed European DEMO design using the PROCESS systems code. It assumes that DEMO will be built as suggested by the baseline and explores what implications the currently known physics and engineering uncertainties have on the expected performance parameters (net electric output and pulse length), while optimising the fusion gain Q. A more detailed single parameter analysis is clearly identifying high impact parameters. This is confirming previous investigations as well as revealing new areas that warrant deeper investigation in particular in the technology area.

Toward DEMO Power Plant Concept Selection Under Epistemic Uncertainty

“…On the other hand, the thermal He-4 fraction shows a linear increase in feasibility. These results may indicate that the plasma elongation should be at least 1.83 to fulfill the net electric power output constraint of 400 MW, and greater concentrations of thermal He-4 in the plasma are favorable to achieve the pulselength constraint of 2 h. In fact, it has been shown that greater fusion power is associated with larger elongations [6], and He-4 contributes to increase the energy confinement time when it does not exceed the dilution upper limit [25]. To visualize the combination effects on the feasibility space, the scatterplots of the plasma elongation against the thermal He-4 fraction are displayed on the top right and bottom left figures of Fig.…”

“…The parameters chosen were related to the physics in PROCESS rather than technological (such as efficiencies), as the next step attempts to understand how these uncertainties impact on the different plasma scenarios. To maintain similarity with previous studies, these parameters are present in [6] and are given as follows.…”

“…Elongation is the dominant plasma parameter and has been reported as having the largest impact on the net electric power of the machine [6]. In conventional tokamaks, an elongation of over 2 is not expected to be controllable, and an elongation smaller than 1.70 could yield poor performances [16].…”

“…This application is particularly useful to quantitatively assess concept choices early in the design process and identify areas with high impact on the performance of the concept of choice that needs further development to meet the requirements or could pose a risk for finding a successful concept. Some previous work has been carried out in uncertainty quantification with PROCESS; on the European DEMOnstration power plant (DEMO) as in [4]- [6], on the China Fusion Engineering Test Reactor (CFETR) design [7], or the HELIcal Advanced Stellarator (HELIAS) 5-B stellarator [8]. This work adopts the technique of interval analysis (see [9], [10]) to describe the uncertainties associated with some parameters of the European H-mode DEMO baseline, allowing a wider exploration of their impact on the uncertainty of its major radius and feasibility.…”

Towards a fusion power plant: integration of physics and technology

“…One approach to handle uncertainties is to use scaling relations (empirical or theoretical) and then vary the input parameters, such as plasma density, hypothetical confinement multipliers (e.g. H-factor), elongation etc and propagate through a systems code optimiser to see the impact on the design [87,88]. However, as mentioned earlier, caution is needed on the use of large multisource databases for choosing an optimum design of a particular device, and of course use of multipliers on scalings beyond the statistical spread has weak rigour.…”