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This study examines the mechanisms underlying sawtooth suppression in the High Beta Tokamak-Extended Pulse (HBT-EP) device. It is observed that strong-intensity sawtooth activities correlate with reduced-amplitude magnetohydrodynamics (MHD) edge modes which are identified as $m/n = 3/1$ external kink modes, while sawtooth suppression correlates with larger and saturated edge mode amplitudes. To further investigate these correlations, the plasma–wall coupling was manipulated by adjusting the positions of the conducting walls in HBT-EP. It was found that strong sawtooth events occur when the normalized wall radius $b/a$ is within a critical value. This implies that the plasma–wall distance must be sufficiently small to ensure effective stabilization of the edge mode. Even slight differences in major radius result in significantly different discharge styles, categorized as ‘sawtoothing discharges’ and ‘sawtooth-suppressed discharges’ respectively. Through a series of mode structure analyses, we confirm the coexistence and coupling of the $m/n = 1/1$ helical core, $m/n = 2/1$ tearing mode, and $m/n = 3/1$ external kink mode during sawtooth-suppression, and that this coupling induces anomalous current broadening. Based on these findings, we conclude that sawtooth suppression in the HBT-EP tokamak is consistent with the process of magnetic flux pumping.

Evidence of a MHD dynamo brought about by intrinsic helical core structures in negative triangularity (NT) and ITER baseline scenario (IBS) plasmas demonstrates paths to operating tokamaks without seeds for deleterious global MHD modes. A stationary sawtooth- and edge localized mode-free state maintains high performance for long durations in a strong NT shape in the DIII-D tokamak. Disparity between minimum safety factor values predicted by magnetic flux diffusion theory and derived from experiment suggests anomalous flux diffusion by an MHD dynamo, driven by flows associated with quasi-interchange modes. Stability calculations with the GATO code find NT and IBS experimental equilibria unstable to quasi-interchange modes, in agreement with observed saturated activity. IBS discharges with similar magnetic winding structure occupy robust helical core states following a transition from sawtooth instabilities. These states agree with prior modeling of helical core bifurcation thresholds with the VMEC equilibrium code.

In this article, we discuss how flux pumping can be applied to multiple inductively coupled superconducting circuits and describe its importance to the operation of a novel planar magnetic field source for quantum technology applications. Specifically, we discuss how applying a transformer–rectifier flux pumping technique to several double-loop superconducting structures simultaneously allows for the effect of crosstalk—the inevitable coupling between neighboring superconducting loops—to be accounted for. Using both a theoretical model and an experimental verification, we introduce a method of calibrating a flux-pumped magnetic field source such that any desired magnetic field distribution within the critical current limits of the used materials can be obtained. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel kind of Josephson Energy Suppression Pump (JESP) controlled by a fully magnetic flux drive. The device presented here is composed of two superconducting loops interrupted at one side by superconducting nanowires which are joined together by a superconducting island. The phase difference developed at the edges of the nanowires by means of the magnetic flux threading the loops can collapse their Cooper condensates, leading to complete suppression of the Josephson energies. This mechanism allows to greatly reduce the leakage current when performing Cooper pair pumping by a pure magnetic pumping cycle without involving any gate modulation. The pumping capability of the JESP is studied through a master equation approach in the non-adiabatic case. [ABSTRACT FROM AUTHOR]

In high- β scenarios with on-axis co-current electron cyclotron current drive, which normally lowers q _0 below unity, the absence of sawteeth suggests the involvement of an additional current redistribution mechanism beyond neoclassical current diffusion. This is supported by imaging motional Stark effect diagnostic measurements, which indicate that q _0 remains consistently around 1. This phenomenon is observed in the presence of a 1/1 mode, indicating its potential role in the current redistribution. It is shown that the mode’s ability to modify the central current and suppress sawteeth increases with plasma pressure. These findings align with a recent theoretical model, which predicts a pressure threshold for sawtooth avoidance by a 1/1 quasi-interchange mode and where this threshold increases with the strength of inward current diffusion. Moreover, the advantages of the flux pumping scenario for future machines are highlighted.

We describe a novel use for superconducting flux pumping, namely a method for magnetizing a planar magnetic field source. The method is useful for many applications, but we illustrate it with the planar Penning trap with applications in quantum technology. A flux pumping mechanism and associated mathematical model are described. The method allows for complete control of the induced persistent current in a double-loop superconducting structure, whereby the final current is a known function of the applied flux and the loop geometry. We have tested our flux pumping technique and found excellent agreement with the theory. [ABSTRACT FROM AUTHOR]

High Temperature superconductors are able to carry very high current densities, and thereby sustain very high magnetic fields. There are many projects which use the first property and these have concentrated on power generation, transmission and utilization, however there are relatively few which are currently exploiting the ability to sustain high magnetic fields. There are two main reasons for this: high field wound magnets can and have been made from both BSCCO and YBCO but currently their cost is much higher than the alternative provided by low Tc materials such as Nb3Sn and NbTi. An alternative form of the material is the bulk form which can be magnetized to high fields and using flux pumping this can be done in situ. This paper explores some of the applications of bulk superconductors and describes methods of producing field patterns using the highly uniform magnetic fields required for MRI and accelerator magnets as the frame of reference. The patterns are not limited to uniform fields and it is entirely possible to produce a field varying sinusoidally in space such as would be required for a motor or a generator. The scheme described in this paper describes a dipole magnet such as is found in an accelerator magnet. The tunnel is 30\times 50\times 1000\ mm and we achieve a uniformity of better than 200 ppm over the 1000 mm length and better than 1 ppm over the central 500 mm region. The paper presents results for both the overall uniformity and the integrated uniformity which is 302 ppm over the 1000 mm length. [ABSTRACT FROM AUTHOR]

High temperature superconducting trapped field magnets (TFM) offer great potential as an alternative to second generation YBCO wire, both in cost and performance. The difficulty of activating this material is the primary problem hindering their incorporation into electromechanical devices. An alternate method called flux pumping is discussed in which the magnetic field trapped within a precooled TFM is increased, i.e., pumped up incrementally. A boundary element formulation is employed to illustrate what happens to the current density within the TFM during this pumping procedure. This is followed by a rigorous analytical formulation to simulate flux pumping within a 2-cm diameter TFM; the simulation is compared to an experiment using a NdFeB magnet as the pumping source. [ABSTRACT FROM PUBLISHER]

In circumstances where it is not possible to make perfectly persistent joints, it is not necessary to rework all the joints as a simple flux pump injector could be built with the magnet to stabilize the decay. This is particularly important in the case of NMR magnets where the magnetic field decay is of order 0.01 ppm/hr. This paper describes a flux pump which is used in the first instance to energize a coil to a very high current. In a second stage, the flux pump was used to periodically inject a small incremental current to the magnet and thus stabilize its decay. [ABSTRACT FROM AUTHOR]

We report here measurements of flux lensing behaviour which have been performed on Bi2Sr2CaCu2O8+δ single crystals placed on top of linear Hall probe arrays. In the crossing lattices regime we observe significant flux focussing as the in-plane field is swept up with a small constant density of pancake vortices. We also observe a sharp discontinous lock-in feature in local magnetic induction when the net field is close to the a–b plane. [Copyright &y& Elsevier]