Verification of Gyrokinetic codes: theoretical background and applications

In fusion plasmas the strong magnetic field allows the fast gyro-motion to be systematically removed from the description of the dynamics, resulting in a considerable model simplification and gain of computational time. Nowadays, the gyrokinetic (GK) codes play a major role in the understanding of the development and the saturation of turbulence and in the prediction of the subsequent transport. Naturally, these codes require thorough verification and validation. Here we present a new and generic theoretical framework and specific numerical applications to test the faithfulness of the implemented models to theory and to verify the domain of applicability of existing GK codes. For a sound verification process, the underlying theoretical GK model and the numerical scheme must be considered at the same time, which has rarely been done and therefore makes this approach pioneering. At the analytical level, the main novelty consists in using advanced mathematical tools such as variational formulation of dynamics for systematization of basic GK code's equations to access the limits of their applicability. The verification of numerical scheme is proposed via the benchmark effort. In this work, specific examples of code verification are presented for two GK codes: the multi-species electromagnetic ORB5 (PIC) and the radially global version of GENE (Eulerian). The proposed methodology can be applied to any existing GK code. We establish a hierarchy of reduced GK Vlasov-Maxwell equations implemented in the ORB5 and GENE codes using the Lagrangian variational formulation. At the computational level, detailed verifications of global electromagnetic test cases developed from the CYCLONE Base Case are considered, including a parametric $\beta$-scan covering the transition from ITG to KBM and the spectral properties at the nominal $\beta$ value.Comment: 16 pages, 2 Figures, APS DPP 2016 invited pape

Long-term outcome after pulmonary retransplantation

ObjectiveBronchiolitis obliterans syndrome has become the most limiting factor for long-term outcome after lung transplantation. Redo lung transplantation was performed for end-stage bronchiolitis obliterans syndrome. Long-term outcome was compared with that after primary lung transplantation as well as with other indications for retransplantation.MethodsOf 614 lung transplantation procedures performed at our institution, 54 (8.5%) were redo transplants. These were stratified into different groups according to the indication for redo transplantation, including chronic graft failure/bronchiolitis obliterans syndrome, acute graft failure, and posttransplantation airway complications. Long-term survival was compared with that of the primary lung transplantation cohort, thereby respecting the need for pretransplant mechanical ventilatory support in a subanalysis. In addition, recurrence of bronchiolitis obliterans syndrome after redo lung transplantation was compared with the occurrence of bronchiolitis obliterans after primary transplantation.ResultsA 1-year survival of 50% was achieved after redo lung transplantation for acute graft failure and airway complications as well as after primary lung transplantation in patients with pretransplant ventilatory support. Retransplantation for bronchiolitis obliterans syndrome revealed superior 1- (78%) and 5-year (62%) survivals, which were not different from those of first-time lung transplant recipients. In addition, we found a similar incidence of bronchiolitis syndrome after retransplantation for BOS compared with its occurrence after primary lung transplantation.ConclusionRedo lung transplantation for end-stage bronchiolitis obliterans syndrome leads to acceptable long-term outcome in selected patients. Future analyses of redo lung transplantation data should generally stratify bronchiolitis obliterans syndrome from other indications with higher mortality

Development of a Global Version of the Gyrokinetic Microturbulence Code GENE

In order to address non-local effects in turbulent transport of magnetic-fusion devices, the gyrokinetic code GENE has been extended from a flux tube to a more global geometry. This global version of GENE includes radial variations of temperature and density profiles, as well as of magnetic equilibrium quantities. Non-periodic radial boundary conditions allow for profile evolution. Thanks to an interface with the MHD equilibrium code CHEASE, as well as the implementation of various types of source and sink terms, the global GENE version will provide a realistic model for carrying out gyrokinetic, quasi-stationary, microturbulence simulations over a major fraction of the core plasma. Validation of the code has in particular been ensured thanks to detailed comparisons with the global PIC codes GYGLES and ORB5

Development and Benchmarking of the Global Gyrokinetic Code GENE

Development and Benchmarking of the Global Gyrokinetic Code GEN