Search results for "magnetic confinement fusion"
showing 10 items of 13 documents
Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating
2017
We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of 3He ions to high energies in dedicated hydrogen–deuterium mixtures.…
Overview of the JET results
2015
Since the installation of an ITER-like wall, the JET programme has focused on the consolidation of ITER design choices and the preparation for ITER operation, with a specific emphasis given to the bulk tungsten melt experiment, which has been crucial for the final decision on the material choice for the day-one tungsten divertor in ITER. Integrated scenarios have been progressed with the re-establishment of long-pulse, high-confinement H-modes by optimizing the magnetic configuration and the use of ICRH to avoid tungsten impurity accumulation. Stationary discharges with detached divertor conditions and small edge localized modes have been demonstrated by nitrogen seeding. The differences in…
Core (XUV/VUV) and boundary (UV/vis/IR) plasma spectroscopy in fusion devices
2021
This contribution describes the basic applications of passive optical emission spectroscopy in the visible and far-UV region of electromagnetic radiation to diagnostics of the magnetic confinement fusion plasma. To simplify and condense the broad topic it presents the most common ways of analyzing the spectra of atoms, ions and molecules in fusion plasma and disseminating results of those analysis to the non-spectroscopists. It provides the reasons for choosing some particular regions, elements and charge states to determine the impurity content and plasma-surface interactions in MCF (Magnetic Confinement Fusion) reactor. Examples used in the contribution are predominantly from measurements…
Efficiency investigation of a negative hydrogen ion beam production with the use of the gasdynamic ECR plasma source
2020
Abstract Negative hydrogen ion sources are of great demand in modern physics as injectors into accelerators and drivers for neutral beam injectors for fusion devices. It has been shown earlier that the use of the gasdynamic ECR discharge provides the opportunity to extract up to 80 mA/cm2 of negative ion current density. We studied experimentally the volumetric negative hydrogen ion production and vacuum ultraviolet emission in a gasdynamic ECR discharge. The high-density plasma was sustained by the pulsed 37 GHz / 100 kW gyrotron radiation in a magnetic configuration consisting of two consecutive simple mirror traps. The future prospects of the volumetric H− source based on the gasdynamic …
Major results from the first plasma campaign of the Wendelstein 7-X stellarator
2017
After completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning the device, first plasma operation started at the end of 2015. Integral commissioning of plasma start-up and operation using electron cyclotron resonance heating (ECRH) and an extensive set of plasma diagnostics have been completed, allowing initial physics studies during the first operational campaign. Both in helium and hydrogen, plasma breakdown was easily achieved. Gaining experience with plasma vessel conditioning, discharge lengths could be extended gradually. Eventually, discharges lasted up to 6 s, reaching an injected energy of 4 MJ, which is twice the limit originally agreed for t…
The power threshold of H-mode access in mixed hydrogen–tritium and pure tritium plasmas at JET with ITER-like wall
2022
The heating power to access the high confinement mode (H-mode), PLH, scales approximately inversely with the isotope mass of the main ion plasma species as found in (protonic) hydrogen, deuterium and tritium plasmas in many fusion facilities over the last decades. In first dedicated L–H transition experiments at the Joint European Torus (JET) tokamak facility with the ITER-like wall (ILW), the power threshold, PLH, was studied systematically in plasmas of pure tritium and hydrogen–tritium mixtures at a magnetic field of 1.8 T and a plasma current of 1.7 MA in order to assess whether this scaling still holds in a metallic wall device. The measured power thresholds, PLH, in Ohmically heated t…
Modeling Non-Confined Coronal Flares: Dynamics and X-Ray Diagnostics
2001
Long-lasting, intense, stellar X-ray flares may approach conditions of breaking magnetic confinement and evolving in open space. We explore this hypothesis with hydrodynamic simulations of flares occurring in a non-confined corona: model flares are triggered by a transient impulsive heating injected in a plane-parallel stratified corona. The plasma evolution is described by means of a numerical 2-D model in cylindrical geometry R,Z. We explore the space of fundamental parameters. As a reference model, we consider a flare triggered by a heating pulse that would cause a 20 MK flare if delivered in a 40000 km long closed loop. The modeled plasma evolution is described. The X-ray emission, spec…
X-ray emission from early-type stars in the Orion Nebula Cluster
2005
The X-ray properties of twenty ~1 Myr old O, B, and A stars of the Orion Trapezium are examined with data from the Chandra Orion Ultradeep Project (COUP). On the basis of simple theories for X-ray emission, we define two classes separated at spectral type B4: hotter stars have strong winds that may give rise to X-ray emission in small- or large-scale wind shocks, and cooler stars that should be X-ray dark due to their weaker winds and absence of outer convection zones where dynamos can generate magnetic fields. Only two of the massive stars show exclusively the constant soft-spectrum emission expected from the standard model for X-ray emission from hot stars involving many small shocks in a…
First observation of trapped high-field seeking ultracold neutron spin states
2011
Ultracold neutrons were stored in a volume, using a magnetic dipole field shutter. Radial confinement was provided by material walls. Low-field seeking neutrons were axially confined above the magnetic field. High-field seeking neutrons are trapped inside the magnetic field. They can systematically shift the measured neutron lifetime to lower values in experiments with magnetic confinement. ISSN:0370-2693 ISSN:0031-9163 ISSN:1873-2445
First results with the yin-yang type electron cyclotron resonance ion source
2007
Abstract Highly charged heavy-ion beams are often produced with Electron Cyclotron Resonance Ion Sources (ECRIS). The so-called conventional minimum-B ECRIS design includes two solenoid magnets and a multipole magnet (usually a hexapole). A minimum-B configuration can also be formed with “yin-yang” (“baseball”) type coils. Such a magnetic field configuration has been extensively tested in magnetic fusion experiments but not for the production of highly charged heavy ions. The application of the afore-mentioned coil structure to the production of multiply charged ion beams was studied. In this paper we present a design of a yin-yang type ion source known as the ARC-ECRIS and some preliminary…