Refurbishment of the JET halo current diagnostics

Riccardo, V.; Lam, N.; Lawler, A.; Starkey, Derek

doi:10.1016/s0920-3796(03)00376-4

Cited by 11 publications

(11 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The JET halo current diagnostics have been refurbished [93] with measurements of the poloidal halo current now available in three locations, 90˚apart, at the top of the vessel. The old system had at most two locations 180˚apart available at the top of the vessel.…”

Section: Halo Currentsmentioning

confidence: 99%

Overview of JET results

2003

View full text Add to dashboard Cite

Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and their beta limits can be raised by destabilization (modification) of sawteeth by ion cyclotron radio frequency heating (ICRH). Alpha simulation experiments with ICRH accelerated injected 4He beam ions provide a new tool for fast particle and magnetohydrodynamic studies, with up to 80–90% of plasma heating by fast 4He ions. With or without impurity seeding, a quasi-steady-state high confinement (H98 = 1), high density (ne/nGW = 0.9–1) and high β (βN = 2) ELMy H-mode has been achieved by operating near the ITER triangularity (δ∼ 0.40–0.5) and safety factor (q95∼ 3), at Zeff∼ 1.5–2. In advanced tokamak (AT) scenarios, internal transport barriers (ITBs) are now characterized in real time with a new criterion, . Tailoring of the current profile with lower hybrid current drive provides reliable access to a variety of q profiles, lowering access power for barrier formation. Rational q surfaces appear to be associated with ITB formation. Alfvén cascades were observed in reversed shear plasmas, providing identification of q profile evolution. Plasmas with ‘current holes’ were observed and modelled. Transient high confinement AT regimes with H89 = 3.3, βN = 2.4 and ITER-relevant q < 5 were achieved with reversed magnetic shear. Quasi-stationary ITBs are developed with full non-inductive current drive, including ∼50% bootstrap current. A record duration of ITBs was achieved, up to 11 s, approaching the resistive time. For the first time, pressure and current profiles of AT regimes are controlled by a real-time feedback system, in separate experiments. Erosion and co-deposition studies with a quartz micro-balance show reduced co-deposition. Measured divertor thermal loads during disruptions in JET could modify ITER assumptions.

show abstract

Section: Halo Currentsmentioning

confidence: 99%

Overview of JET results

2003

View full text Add to dashboard Cite

show abstract

“…Measurements of halo currents have been made on a number of tokamaks for many years, traditionally using Rogowski coil sensors and/or resistive shunts [1][2][3][4][5][6]. The toroidal variation and rotation of the halo current distribution has been well-documented [3][4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

High-resolution disruption halo current measurements using Langmuir probes in Alcator C-Mod

et al. 2017

View full text Add to dashboard Cite

Halo currents generated during disruptions on Alcator C-Mod have been measured with Langmuir "rail" probes. These rail probes are embedded in a lower outboard divertor module in a closelyspaced vertical (poloidal) array. The dense array provides detailed resolution of the spatial dependence (~1 cm spacing) of the halo current distribution in the plasma scrape-off region with high time resolution (400 kHz digitization rate). As the plasma limits on the outboard divertor plate, the contact point is clearly discernible in the halo current data (as an inversion of current) and moves vertically down the divertor plate on many disruptions. These data are consistent with filament reconstructions of the plasma boundary, from which the edge safety factor of the disrupting plasma can be calculated. Additionally, the halo current "footprint" on the divertor plate is obtained and related to the halo flux width. The voltage driving halo current and the effective resistance of the plasma region through which the halo current flows to reach the probes are also investigated. Estimations of the sheath resistance and halo region resistivity and temperature are given. This information could prove useful for modeling halo current dynamics.

show abstract

“…It is the purpose of this paper, however, to study a fourth major disruption consequence: the phenomenon of 'halo currents' [2,3,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. The tokamak concept generally optimizes towards large elongation of the plasma cross-section, essentially due to the additional safety factor that such plasma boundary shaping provides [41][42][43][44].…”

Section: Introductionmentioning

confidence: 99%

“…Halo currents have been characterized in a large number of conventional tokamak devices, including ALCATOR C-Mod [28], ASDEX-Upgrade [30,37,38], COMPASS-D [29], DIII-D [4,22,23,26,36], JET [24,[31][32][33]35] and JT-60U [27]. These devices have generally shown large halo currents, with worst-case events having up to 50% of the pre-disruption plasma currents flowing into the vessel and plasma facing components [2].…”

Section: Introductionmentioning

confidence: 99%

Characterization of disruption halo currents in the National Spherical Torus Experiment

Gerhardt¹,

Ménard²,

Sabbagh³

et al. 2012

Nucl. Fusion

View full text Add to dashboard Cite

This paper describes the general characteristics of disruptions halo currents in the National Spherical Torus Experiment [M. Ono, et al. Nuclear Fusion 40, 557 (2000)].The commonly observed types of vertical motion and resulting halo current patterns are described, and it is shown that plasma discharges developing between components can facilitate halo current flow. The halo current fractions and toroidal peaking factors at various locations in the device are presented. The maximum product of these two metrics for localized halo current measurements is always significantly less than the worst-case expectations from conventional aspect ratio tokamaks (which are typically written in terms of the total halo current). The halo current fraction and impulse is often largest in cases with the fastest plasma current quenches and highest quench rates. The effective duration of the halo current pulse is comparable to or shorter than the plasma current quench time. The largest halo currents have tended to occur in lower β and lower elongation plasmas. The sign of the poloidal halo current is reversed when the toroidal field direction is reversed. PACS: 52.55. Ez, 52.55.Tn

show abstract

Refurbishment of the JET halo current diagnostics

Cited by 11 publications

References 2 publications

Overview of JET results

Overview of JET results

High-resolution disruption halo current measurements using Langmuir probes in Alcator C-Mod

Characterization of disruption halo currents in the National Spherical Torus Experiment

Contact Info

Product

Resources

About