First Results From Neutral Beam Heating of Diverted Asdex Discharges

Wagner, F.; NI-Team,; ASDEX-Team,

doi:10.1016/b978-1-4832-8428-6.50009-6

Cited by 3 publications

(6 citation statements)

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“…The Ha LIM measurement shows that the intensity of particle recycling near the primary limiter for a divertor discharge is, by a factor of about 15, smaller than that for a limiter discharge. During beam injection, HQ; LIM for the divertor discharge shows many short bursts [2]. The details of the burst are not shown in the figure.…”

Section: Discharges With Good Energy Confinement In Divertor Equilibriamentioning

confidence: 99%

“…[ 1 ], rg of the limiter discharge was found to be proportional to \ / K a I p at I p <600kA, where K a is the vertical elongation of the outermost magnetic surface. Another approach is presented by the ASDEX experiment [2], where the divertor equilibrium improves the energy confinement time of beam-heated plasmas with I p = 300-450 kA up to 50-60 ms, which is comparable to INTOR scaling.…”

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confidence: 99%

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Energy confinement of beam-heated divertor and limiter discharges in Doublet III

Nagami¹,

Kasai²,

Kitsunezaki³

et al. 1984

Nucl. Fusion

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Observation of the intensity of the recycling particle flux at the main plasma edge for various limiter and divertor discharges indicates that the gross energy confinement of beam-heated discharges is closely related to the intensity of the edge particle flux. In limiter discharges, the global particle confinement time and the energy confinement time τE show many similarities: 1) linear Ip dependence at Ip < 600 kA, 2) no BT dependence, and 3) deterioration against injection power. Improvement of τE by increasing Ip, for example, is associated with high temperatures at the plasma edge region accompanied by reduced particle recycling. – Divertor discharges with low particle recycling around the main plasma show better energy confinement than limiter discharges at high plasma densities. The improvement of τE is primarily originated in the reduction of heat transport at the main plasma edge region, which is associated with the reduction of recycling particle flux at the main plasma edge. Under certain operation condition, for example, excessive cold-gas puffing, the discharge shows relatively high scrape-off plasma density and strong particle recycling between the main plasma and the limiter. The energy confinement time of these discharges degrades somewhat or reduces completely to that of the limiter discharge. – In low-recycling divertor discharges, the central electron and ion temperature is proportional to the injection power, and the plasma stored energy is proportional to n̄ePabs (scales as INTOR scaling). With ≈ 4 MW beam injection, high-temperature and high-density plasmas were obtained (stored energy up to 280 kJ, Te(0) ≈ Ti(0) ≈ 2.5–3.0 keV at n̄e ≈ (6–7) × 1013 cm−3, τE* ≈ 70 ms).

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Section: Discharges With Good Energy Confinement In Divertor Equilibriamentioning

confidence: 99%

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confidence: 99%

Energy confinement of beam-heated divertor and limiter discharges in Doublet III

Nagami¹,

Kasai²,

Kitsunezaki³

et al. 1984

Nucl. Fusion

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“…Only with ELMs a quasi-steady-state situation could be established. The H-mode and its characteristics as they could be identified with the limited diagnostic capabilities at the time were first presented to an international community at the 3rd Joint Grenoble-Varenna International Symposium, March 1982 [31] and then at the Baltimore IAEA conference in fall 1982 [32]. Outside the official agenda of this conference a special evening session was organised by Rutherford where the author of this paper was cross-questioned by an audience which fulfilled the ground rule of science -to be sceptical.…”

Section: The H-mode Of Asdex [23-25]mentioning

confidence: 99%

The history of research into improved confinement regimes

Wagner

2017

EPJ H

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Abstract. Increasing the pressure by additional heating of magnetically confined plasmas had the consequence that turbulent processes became more violent and plasma confinement degraded. Since this experience from the early 1980ies, fusion research was dominated by the search for confinement regimes with improved properties. It was a gratifying experience that toroidally confined plasmas are able to self-organise in such a way that turbulence diminishes, resulting in a confinement with good prospects to reach the objectives of fusion R&D. The understanding of improved confinement regimes revolutionized the understanding of turbulent transport in high-temperature plasmas. In this paper the story of research into improved confinement regimes will be narrated starting with 1980.

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“…The ASDEX finding that received the greatest attention was the discovery of the H-regime of neutralbeam-heated plasmas. In a study of single-null diverted discharges it was noted in February 1982 that beyond a minimum heating power two confinement regimes exist (with a bifurcation-type character) [15,16]: The regime with degraded confinement (L-mode) already known from limiter tokamaks and a high-confinement regime (H-mode) that could reproducibly be obtained over a wide range of plasma parameters (n e = (2-8) X 10 13 cm" 3 , q cy i > 2.4), provided the discharges were diverted.…”

Section: Plasma Confinement: Discovery Of the H-regimementioning

confidence: 99%

“…n e : line-averaged bulk plasma density, 0 a : flux of neutral atoms backscattered from collector plate, <f> x : hard-X-ray flux, j3 p + fij/2 and j3pi" beta poloidal from plasma equilibrium and from the diamagnetic loop, respectively. Neutral injection (P m £* 2 MW) starts at 1.11 s. Main characteristics of H-mode plasmas are broad temperature and density profiles [16,17]. A number of observations and experiments [18] support the conjecture of a high near-edge temperature (or a related quantity like plasma conductivity or collisionality) being a prerequisite of H-discharges:…”

Section: Fig 6 Characteristic Features Of H-discharge (Solid Curves) ...mentioning

confidence: 99%

The ASDEX divertor tokamak

Keilhacker

Team²

1985

Nucl. Fusion

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ASDEX is a large tokamak (R = 1.65 m, a = 0.4 m, I p < 500 kA) that started operation in 1980. Its distinctive features are a double-(or single-) null poloidal divertor, the capability for long-pulse operation (up to 10 s) and high.power neutral-beam (4.3 MW), ICRH (3 MW) and LH (2.4 MW) heating systems. Several highly significant experimental findings have been obtained, facilitated by the large flexibility of the machine. The high-recycling divertor regime is considered the most viable solution for handling the large power fluxes envisaged for the next generation of tokamak devices. Studies of impurity transport in the bulk plasma led to the postulation of an additional inward particle drift, while gas puffing experiments revealed the importance of thermoelectric forces along field lines for impurity retainment by the divertor. The highconfinement regime (H-mode) of neutral-beam-heated plasmas, discovered on ASDEX, is also intimately connected with the divertor configuration. The H-mode.confinement, in turn, enabled the investigation of /J-limits resulting in the experimental scaling / 3 ^^ 2.8 I p /(a Bj) [%; MA, m, T], in excellent agreement with theoretical predictions. The most important results from recent experiments with RF heating and current drive include the recharging of the OH transformer at constant plasma current, and the observed high heating efficiency obtained with combined second-harmonic ICRH and neutral-injection heating.

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First Results From Neutral Beam Heating of Diverted Asdex Discharges

Cited by 3 publications

References 0 publications

Energy confinement of beam-heated divertor and limiter discharges in Doublet III

Energy confinement of beam-heated divertor and limiter discharges in Doublet III

The history of research into improved confinement regimes

The ASDEX divertor tokamak

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