Anna Salmi

Core momentum and particle transport studies in the ASDEX Upgrade tokamak

Core momentum and particle transport in ASDEX Upgrade (AUG) have been examined in a wide variety of plasma discharges and via several different methods. Experiments were performed in which ECRH power was added to NBI heated H-modes causing the electron and impurity ion density profiles to peak and the core toroidal rotation to flatten. Turbulence calculations of these plasmas show a change in the dominant regime from ITG to TEM due to the ECRH induced changes in the electron and ion temperature profiles. The impurity and electron density behavior can be fully explained by the changes in the turbulent particle transport. Momentum transport analyses demonstrate that in the TEM regime there is a core localized, counter-current directed, residual stress momentum flux of the same order of magnitude as the applied NBI torque. The initial results from momentum modulation experiments performed on AUG confirm that the Prandtl number in AUG NBI heated H-modes is close to 1 and that there exists a significant inward momentum pinch. Lastly, an intrinsic toroidal rotation database has been developed at AUG which can be used to test theoretically predicted dependences of residual stress momentum fluxes. Initial results show a linear correlation between the gradient of the toroidal rotation and both the electron density gradient scale length and the frequency of the dominant turbulent mode.

Momentum transport studies from multi-machine comparisons

A database of toroidal momentum transport on five tokamaks, Alcator C-Mod, DIII-D, JET, NSTX and JT-60U, has been constructed under a wide range of conditions in order to understand the characteristics of toroidal momentum transport coefficients, namely the toroidal momentum diffusivity (??) and the pinch velocity (Vpinch). Through an inter-machine comparison, the similarities and differences in the properties of ?? and Vpinch among the machines have been clarified. Parametric dependences of these momentum transport coefficients have been investigated over a wide range of plasma parameters taking advantage of the different operation regimes in machines. The approach offers insights into the parametric dependences as follows. The toroidal momentum diffusivity (??) generally increases with increasing heat diffusivity (?i). The correlation is observed over a wide range of ??, covering roughly two orders of magnitude, and within each of the machines over the whole radius. Through the inter-machine comparison, it is found that ?? becomes larger in the outer region of the plasma. Also observed is a general trend for Vpinch in tokamaks; the inward pinch velocity (?Vpinch) increases with increasing ??. The results that are commonly observed in machines will support a toroidal rotation prediction in future devices. On the other hand, differences among machines have been observed. The toroidal momentum diffusivity, ??, is larger than or equal to ?i in JET and JT-60U; on the other hand, ?? is smaller than or equal to ?i in NSTX, DIII-D and Alcator C-Mod. In DIII-D, the ratio ?RVpinch/?? at r/a?=?0.5?0.6 is about 2, which is small compared with that in other tokamaks (?RVpinch/?????5). Based on these different observations, parametric dependences of ??/?i, RVpinch/?? and ?? have been investigated in H-mode plasmas. Across the dataset from all machines, the ratio ??/?i tends to be larger in low at fixed Te/Ti and . An increase in ?? is observed with decreasing ne and/or increasing Te. The pinch number (?RVpinch/??) is observed to increase with increasing at both q95?=?5.5?7.2 and q95?=?3.7?4.5. Here , , Te, Ti, and q95 are, respectively, the normalized effective electron collision frequency, the normalized ion poloidal Larmor radius, the electron and ion temperatures, the inverse ratio of density scale length, , to the major radius, R, and the safety factor at the 95% flux surface.

Predicting rotation for ITER via studies of intrinsic torque and momentum transport in DIII-D

Experiments at the DIII-D tokamak have used dimensionless parameter scans to investigate the dependencies of intrinsic torque and momentum transport in order to inform a prediction of the rotation profile in ITER. Measurements of intrinsic torque profiles and momentum confinement time in dimensionless parameter scans of normalized gyroradius and collisionality are used to predict the amount of intrinsic rotation in the pedestal of ITER. Additional scans of Te/Ti and safety factor are used to determine the accuracy of momentum flux predictions of the quasi-linear gyrokinetic code TGLF. In these scans, applications of modulated torque are used to measure the incremental momentum diffusivity, and results are consistent with the E×B shear suppression of turbulent transport. These incremental transport measurements are also compared with the TGLF results. In order to form a prediction of the rotation profile for ITER, the pedestal prediction is used as a boundary condition to a simulation that uses TGLF to det...

Co-designing (with) organizations: human-centeredness, participation and embodiment in organizational development

In this paper we study a design approach as a method for conducting organizational development in innovation process management. We have utilized personas, metaphorical design, scenarios and paper prototyping as ways of going beyond mere problem-solving. These methods have been used to create solutions that allow the organization to reflect on their activities from a wider perspective. We analyse the methods from the point of view of three important aspects of design work: human-centeredness, participation and embodiment. The research is based in an industry context in which a globally operating company is in the process of renewing their innovation processes. Building on these methods the participants in the three co-design workshops were able to generate a shared understanding of the motivations of their employees, plan new innovation practices and create future scenarios of digital tools and features that support the work in the R&D units. Based on our analysis we give recommendations for design methods in organizational development and suggestions for further research.

Supporting Empathetic Boundary Spanning in Participatory Workshops with Scenarios and Personas

This paper examines the employment of design methods in combination with SimLabâ„¢ process simulation method in the context of developing IT-based support and processes for the fuzzy-front end innovation in a real-world organizational setting. The authors bring together theories and concepts from the fields of design studies and knowledge management across boundaries. They use these theories, rooted in the practice-based perspective, as analytical lenses in the case study. Acting at the interface of different knowledge domains, the authors look into the role of empathy-laden boundary objects as potential enablers of boundary spanning. The authors present empirically grounded findings from an ongoing research project with an emphasis on the methods and techniques employed. Their empirical data consists of recorded and transcribed group discussions from a participatory workshop, and individual thematic interviews have been used as raw material for constructing the process map, personas and scenarios (the boundary objects). The data was analyzed applying qualitative content analysis with an interpretative approach. Their findings are explored more closely in the article.

A path to stable low-torque plasma operation in ITER with test blanket modules

New experiments in the low-torque ITER Q = 10 scenario on DIII-D demonstrate that n = 1 magnetic fields from a single row of ex-vessel control coils enable operation at ITER performance metrics in the presence of applied non-axisymmetric magnetic fields from a test blanket module (TBM) mock-up coil. With n = 1 compensation, operation below the ITER-equivalent injected torque is successful at three times the ITER equivalent toroidal magnetic field ripple for a pair of TBMs in one equatorial port, whereas the uncompensated TBM field leads to rotation collapse, loss of H-mode and plasma current disruption. In companion experiments at high plasma beta, where the n = 1 plasma response is enhanced, uncorrected TBM fields degrade energy confinement and the plasma angular momentum while increasing fast ion losses; however, disruptions are not routinely encountered owing to increased levels of injected neutral beam torque. In this regime, n = 1 field compensation leads to recovery of a dominant fraction of the TBM-induced plasma pressure and rotation degradation, and an 80% reduction in the heat load to the first wall. These results show that the n = 1 plasma response plays a dominant role in determining plasma stability, and that n = 1 field compensation alone not only recovers most of the impact on plasma performance of the TBM, but also protects the first wall from potentially damaging heat flux. Despite these benefits, plasma rotation braking from the TBM fields cannot be fully recovered using standard error field control. Given the uncertainty in extrapolation of these results to the ITER configuration, it is prudent to design the TBMs with as low a ferromagnetic mass as possible without jeopardizing the TBM mission.

Estimate of convection–diffusion coefficients from modulated perturbative experiments as an inverse problem

The estimate of coefficients of the Convection-Diffusion Equation (CDE) from experimental measurements belongs in the category of inverse problems, which are known to come with issues of ill-conditioning or singularity. Here we concentrate on a particular class that can be reduced to a linear algebraic problem, with explicit solution. Ill-conditioning of the problem corresponds to the vanishing of one eigenvalue of the matrix to be inverted. The comparison with algorithms based upon matching experimental data against numerical integration of the CDE sheds light on the accuracy of the parameter estimation procedures, and suggests a path for a more precise assessment of the profiles and of the related uncertainty. Several instances of the implementation of the algorithm to real data are presented.

Understanding of the fundamental differences in JET and JT-60U AT discharges

Plasma current density simulations of JET and JT-60U shots in reverse-q advanced scenarios based on the previous data analysis of the identity plasma experiments have been performed. The effects of the main differences between the shots (neutral beam current density (jnbi), electron density and geometry) have been studied. The reversed q-profile (which was the target in this identity experiment and is observed at the beginning of each shot) was sustained in JT-60U while it became flat in JET towards the end of the shot. In JET, jnbi is peaked on-axis whereas in JT-60U it is peaked off-axis (at ρ = 0.5) while the NBI fraction of the selected shots is the same (22–24%). A strong density ITB appeared (at ρ = 0.5) in JT-60U but not in JET. The plasma geometry was mainly set to match but it was not identical. In addition, the extrapolation to JET steady-state operation has been done by testing the sensitivity of q to different externally driven currents, electron density and geometry in predictive current diffusion simulations. Moreover, critical bootstrap current density has been analysed.The reasons for the different time evolution of q-profile have been studied with predictive current simulations with the 1.5D transport code JETTO. The current diffusion model was validated against reverse-q shots, and simulations were performed with experimental data profiles, jNBI given by ASCOT and neoclassical resistivity and bootstrap current calculated by NCLASS.Bootstrap current density was the most efficient way to sustain the beneficial reverse shape of q-profile. Replacing the JET ne profile with one from JT-60U leads to an increase of 0.2–0.3 MA in the bootstrap current (f bs increases from 15% to 30%). However, sustaining the stationary reverse q is not achieved in JET with bootstrap current induced by the density gradient of JT-60U. Even 10 times larger gradient than in JT-60U helps to sustain the shape of the q-profile longer than the experimentally observed density profile in JET but the minimum value of q moves closer to central plasma and the shape of q is not stationary in a 10 s simulation. The effect of different shape of NBI current density profile is negligible due to quite small fraction. Sustaining the reverse q requires 45% or larger added off-axis fraction. However, increasing the inverse aspect ratio increases bootstrap current and decreases the critical bootstrap current more effectively than increasing the density gradient: two times larger inverse aspect ratio produces almost three times larger bootstrap fraction but ten times larger density gradient only two times larger bootstrap fraction. The conclusions based on these simulations indicate that the need for bootstrap current is larger in JET and the same conditions cause smaller bootstrap fraction, which suggests that achieving steady-state operation in JET under these conditions is unlikely.

Supporting empathy in business process simulation with scenarios

This paper examines the employment of scenario-based design approach in combination with SimLab business process simulation method in the context of studying the fuzzy-front end innovation process in a real-world technology business setting. In this paper we aim to show how these divergent techniques of inquiry can be combined in order to produce knowledge on the one hand about peoples experiences, feelings and practices, and on the other hand, about the business process, its bottlenecks and improvement opportunities. Furthermore, our objective is to study how these different modes of knowledge can complement each other in creating an understanding about innovation-related activities as well as in facilitating the building of a shared vision among project participants. Our primary interest is in exploring if scenarios, combined with small-scale personas and business process simulation method have the potential to evoke empathy in a co-design setting. In this paper we present early insights from an ongoing research project with an emphasis on the methods and techniques employed.