S. Lazerson
A5048461676- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Fusion materials and technologies
- Superconducting Materials and Applications
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Solar and Space Plasma Dynamics
- Plasma Diagnostics and Applications
- Laser-induced spectroscopy and plasma
- Astronomical Observations and Instrumentation
- Atomic and Molecular Physics
- Stellar, planetary, and galactic studies
- Geomagnetism and Paleomagnetism Studies
- Nuclear reactor physics and engineering
- Gas Dynamics and Kinetic Theory
- Astro and Planetary Science
- Astronomy and Astrophysical Research
- Physics of Superconductivity and Magnetism
- Atomic and Subatomic Physics Research
- Particle Detector Development and Performance
- Dust and Plasma Wave Phenomena
- Astrophysics and Star Formation Studies
- Quantum chaos and dynamical systems
- Adaptive optics and wavefront sensing
- Electric Power Systems and Control
Max Planck Institute for Plasma Physics - Greifswald
2016-2025
Max Planck Institute for Plasma Physics
2014-2022
Princeton Plasma Physics Laboratory
2013-2022
Max Planck Society
2014-2021
HUN-REN Centre for Energy Research
2021
Princeton University
2013-2019
Princeton Public Schools
2019
National Institute for Fusion Science
2016-2018
Auburn University
2017-2018
The Graduate University for Advanced Studies, SOKENDAI
2018
After completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning device, first plasma operation started at end 2015. Integral start-up using electron cyclotron resonance heating (ECRH) an extensive set diagnostics have been completed, allowing initial physics studies during operational campaign. Both in helium hydrogen, breakdown was easily achieved. Gaining experience with vessel conditioning, discharge lengths could be extended gradually. Eventually,...
The optimized, superconducting stellarator Wendelstein 7-X went into operation and delivered first measurement data after 15 years of construction one year commissioning. Errors in the magnet assembly were confirmend to be small. Plasma was started with 5 MW electron cyclotron resonance heating (ECRH) power five inboard limiters. Core plasma values keV, keV at line-integrated densities achieved, exceeding original expectations by about a factor two. Indications for core-electron-root found....
Abstract Fusion energy research has in the past 40 years focused primarily on tokamak concept, but recent advances plasma theory and computational power have led to renewed interest stellarators. The largest most sophisticated stellarator world, Wendelstein 7-X (W7-X), just started operation, with aim show that earlier weaknesses of this concept been addressed successfully, intrinsic advantages persist, also at parameters approaching those a future fusion plant. Here we first physics...
Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future power plant. Plasma operation started in 2015 using limiter configuration. After installing an uncooled magnetic island divertor, extending energy limit from 4 80 MJ, continued 2017. For this phase, electron cyclotron resonance heating (ECRH) capability was extended 7 MW, and hydrogen pellet injection implemented. The enhancements resulted highest triple...
A significant improvement of plasma parameters in the optimized stellarator W7-X is found after injections frozen hydrogen pellets. The ion temperature post-pellet phase exceeds 3 keV with 5 MW electron heating and global energy confinement time surpasses empirical ISS04-scaling. realized such experiments are significantly above those comparable gas-fuelled discharges. In this paper, we present details these pellet discuss main properties during enhanced phases. Local power balance applied...
We describe the construction of stepped-pressure equilibria as extrema a multi-region, relaxed magnetohydrodynamic (MHD) energy functional that combines elements ideal MHD and Taylor relaxation, which we call MRXMHD. The model is compatible with Hamiltonian chaos theory allows three-dimensional equilibrium problem to be formulated in well-posed manner suitable for computation. energy-functional discretized using mixed finite-element, Fourier representation magnetic vector potential geometry;...
With the installation of non-axisymmetric coil systems on major tokamaks for purpose studying prospects ELM-free operation, understanding plasma response to applied fields is a crucial issue. Application different models, using standard tools, DIII-D discharges with from internal coils, shown yield qualitatively results. The can be treated as an initial value problem, following system dynamically unperturbed state, or nearby perturbed equilibrium approach, and both linear nonlinear models...
Wendelstein 7-X (W7-X) is currently under commissioning in preparation for its initial plasma operation phase, phase 1.1 (OP1.1). This first serves primarily to provide an integral of all major systems needed operation, as well systems, such diagnostics, that need verify their foreseen functions. In OP1.1, W7-X will have a reduced set in-vessel components. particular, five graphite limiter stripes replace the later divertor. paper describes expected machine capabilities selection physics...
The neoclassical transport optimization of the Wendelstein 7-X stellarator has not resulted in predicted high energy confinement gas fueled electron-cyclotron-resonance-heated (ECRH) plasmas as modelled (Turkin et al 2011 Phys. Plasmas 18 022505) due to levels turbulent heat observed experiments. electron-turbulent-heat appears non-stiff and is electron temperature gradient (ETG)/ion (ITG) type (Weir 2021 Nucl. Fusion 61 056001). As a result, Te can be varied freely from 1 keV–10 keV within...
Abstract Wendelstein 7-X (W7-X), the largest advanced stellarator, is built to demonstrate high power, performance quasi-continuous operation. Therefore, in recent campaign, experiments were performed prepare for long pulse operation, addressing three critical issues: development of stable detachment, control heat and particle exhaust, impact leading edges on plasma performance. The exhaust W7-X realized with help an island divertor, which utilizes large magnetic islands at boundary. This...
The results from the investigation of neoclassical core transport and role radial electric field profile (Er) in first operational phase Wendelstein 7-X (W7-X) stellarator are presented. In plasmas, details Er expected to have a strong effect on both particle heat fluxes. Investigation is important understanding validation calculations. closely related perpendicular plasma flow (u⊥) through force balance equation. This allows be inferred measurements velocity, which can measured using x-ray...
Abstract Classical particle drifts are known to have substantial impacts on fluxes of particles and heat through the edge plasmas in both tokamaks stellarators. Here we present results from first dedicated investigation drift effects W7-X stellarator. By comparing similar plasma discharges conducted with a forward- reverse-directed magnetic field, could be isolated observation up-down asymmetries flux profiles divertor targets. In low-density plasmas, radial locations strike lines (i.e....
The Charge Exchange Recombination Spectroscopy (CXRS) diagnostic has become a routine on almost all major high temperature fusion experimental devices. For the optimized stellarator Wendelstein 7-X (W7-X), highly flexible and extensive CXRS been built to provide high-resolution local measurements of several important plasma parameters using recently commissioned neutral beam heating. This paper outlines design specifics W7-X system gives examples initial results obtained, including typical...
Pulsed injections of boron carbide granules into Wendelstein 7-X stellarator (W7-X) plasmas transiently increase the plasma stored energy and core ion temperatures above reference W7-X experimental programs by up to 30%. In a series 4 MW electron cyclotron resonance heating experiments, PPPL Probe Mounted Powder Injector provided 50 ms bursts 100 μm every 350 at estimated quantities ranging from approximately 1 mg/pulse over 30 mg/pulse. For each injection, was observed initially drop...
Wendelstein 7-X, a superconducting optimized stellarator built in Greifswald/Germany, started its first plasmas with the last closed flux surface (LCFS) defined by 5 uncooled graphite limiters December 2015. At end of 10 weeks long experimental campaign (OP1.1) more than 20 independent diagnostic systems were operation, allowing detailed studies many interesting plasma phenomena. For example, fast neutral gas manometers supported video cameras (including one fast-frame camera frame rates...
We consider the linear and nonlinear ideal plasma response to a boundary perturbation in screw pinch. demonstrate that three-dimensional, ideal-MHD equilibria with continuously nested flux-surfaces discontinuous rotational-transform across resonant rational-surfaces are well defined can be computed both perturbatively using fully equilibrium calculations. This rescues possibility of constructing MHD current sheets continuous, smooth pressure profiles. The results predict that, even if acts...
DIII-D experiments using new detailed magnetic diagnostics show that linear, ideal magnetohydrodynamics (MHD) theory quantitatively describes the structure (as measured externally) of three-dimensional (3D) equilibria resulting from applied fields with toroidal mode number n = 1, while a nonlinear solution to MHD force balance, VMEC code, requires inclusion ≥ 1 achieve similar agreement. These tests are carried out near ITER baseline parameters, providing validated basis on which exploit 3D...
The role of error fields in stellarators is explored this work through simulations of, and experiments performed on, the Wendelstein 7-X (W7-X) stellarator. Previous experimental results, based on limiter plasmas W7-X, suggest that are small experiment plasmas. In work, we document results from first divertor campaign W7-X with a focus resonant edge island structure. Measurements obtained using thermocouples corroborate earlier correctable, requiring only 5% total rated current trim coil...
The three-dimensional plasma boundary displacements induced by applied non-axisymmetric magnetic perturbations have been measured in ASDEX Upgrade, DIII-D, JET, MAST and NSTX. arising from resonant (RMPs) are up to ±5% of the minor radius present-day machines. Good agreement can be found between different experimental measurements a range models—be it vacuum field line tracing, ideal MHD equilibrium modelling, or nonlinear amplification. various with predictions these models is presented,...
In stellarators, increasing the density is beneficial for energy confinement. While there no single reason this observation, it still very robust across different devices and reflected in empirical confinement time scaling ISS04. order to study whether also true Wendelstein 7-X, of analyzed compared ISS04 first divertor experiments. When increased beyond a critical density, however, radiative collapses are frequently observed. Existing analytical models revisited assess they can predict...
Abstract We compute reconstructions of 4D and 5D fast-ion phase-space distribution functions in fusion plasmas from synthetic projections these functions. The originating neutral beam injection (NBI) at TCV Wendelstein 7-X (W7-X) full, half, one-third energies can be distinguished particle densities each component inferred based on 20 spectra projected velocities 680 W7-X. Further, we demonstrate that an expansion into a basis slowing-down is equivalent to regularization using physics as...
Abstract By employing Bayesian inference techniques, the full electron density profile from plasma core to edge of Wendelstein 7-X (W7-X) is inferred solely neutral hydrogen beam and halo Balmer- α (H ) emission data. The a cloud neutrals forming in vicinity injected due multiple charge exchange reactions. W7-X equipped with several heating sources an H spectroscopy system that views these different angles penetration depths plasma. As form complex spectra for each spatial point are...
Abstract The impact of the SOL (Scrape-Off Layer) plasma on deposition, confinement and losses NBI fast ions was investigated in W7-X plasma. effect width, density, temperature profiles, radial electric field, charge-exchange reactions (CX) explored. Ionization slowing down partly counterbalance each other, as cold compensates for ionization effects radially decaying model profiles. However, more vulnerable steel components is mitigating over wide range
of different profiles those...
Abstract This research investigates the temporal evolution of toroidal plasma current in Wendelstein 7-X (W7-X) stellarator under different heating, fueling, and drive scenarios. The THRIFT code has been modernized its predictions have compared against experimentally measured currents W7-X. Good agreement is found with respect to characteristic timescale between simulated currents. total bootstrap under-predicted owing applicability BOOTSJ model for collisionalities question. Edge...
The first measurements made with a prototype Faraday cup fast ion loss detector (FC-FILD) on the Wendelstein 7-X (W7-X) device are presented and shown to be consistent lost neutral beam ions. FC-FILD is small form factor, energy resolving designed mounted inside wall armor tiles of W7-X. Such mounting will allow for future array installed, which has been critical demonstrating improved confinement plasma beta (β = 2μ0p/B2). diagnostic composed movable armature water cooled head, mimicking...