# Optimization of DC Energy Storage in Tokamak Poloidal Coils
## 10 Conclusions  
This paper analyzed the design and optimization of a PS system for the PF coils of a tokamak. Even though the examples are focused on the last-generation tokamak DTT, the approach is generally applicable to all tokamaks and to other nuclear fusion plants. The problem was approached both by theoretical formulations and by circuital simulations. This was possible after introducing the right foundations. The main steps for it were developed for the first time in this paper:  
1. Defining a voltage and current reference scenario, including all the plasma phases. 2. Identifying analytical formulas and parameters to set and evaluate the optimization. 3. Designing a circuital model to include in its simulations all the tokamak phenomena. The developed models and algorithms, also implemented in the PLECS software, will be available for future studies that may incorporate more detailed component behaviors and transient analyses. In particular, they are going to be implemented in a hardware-in  
Figure 16: Instantaneous power drawn from the grid by the pair PF1–PF2. the-loop (HIL) setup [44] combining the SC and H-bridge models with a real control board operating on the desired scenario. The benefits of DC storage based on SC technology were extensively shown. Once these benefits were clarified, the design moved to the problem of identifying the best compromise between the size of SC banks and the power demand from the grid. The concept of complementary among the power and energy profiles of different PF coils was introduced for the first time and was crucial for the optimization. By leveraging the complementarity of shared DC storage, the peaks of power from the grid are limited both by temporal shifts (compensation of demand fluctuations over time) and by load balancing (distribution of energy storage requirements across multiple PSs). Such a rational use of available energy reduces the footprint of the DC storage, together with capital and operational costs, without affecting the required performance or the reliability and stability standards. A comprehensive simulation campaign revealed that sharing the DC storage bank for the coil pairs PF1-PF2 and PF5-PF6 offers substantial benefits. For PF1-PF2, the shared storage configuration could potentially halve the required storage bank size, while for PF5-PF6, the reduction could be as significant as two-thirds. At the same time, the analysis of the power demand from the grid demonstrated that increasing the peak power limit from 1 MW to 2 MW results in a more substantial reduction in the required energy for DC storage compared with the increase from 2 MW to 3 MW. This suggests that a peak power limit of 2 MW strikes the best balance between dimensions and efficiency. Considering the reference SC modules and cabinets, this corresponds to a saving of 18 cabinets for the PF system. The entire DC storage could consist of 80 or 64 cabinets occupying 58 m\({}^{2}\) or 46 m\({}^{2}\), respectively. Observing the trend and the roadmap of SC technology independently of nuclear fusion applications, it is reasonable to predict that the dimensions and the costs of storage will decrease in the future. A more rapid improvement is expected for batteries due to the massive investments and the gigafactories under construction. Superconducting magnetic energy storage (SMES) is another technology that may be particularly suitable in fusion applications [6], with optimization problems similar to SC banks. While the paper's results provide a clear direction for optimizing the DC storage and PS system, several practical considerations must be addressed for real-world implementation. Future works should focus on detailed implementation plans, including validation tests. In addition, they should assess alternative topologies (such as boost converters or hybrid storage joining SCs and batteries) that are able to overcome some intrinsic limitations noticed in this paper. A relevant issue consists of the layout of the DC link for its connections to different PSs.