Loss Of Confinement Due To Reduction Of The Edge Pedestal In JET

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Effect of nitrogen seeding on the energy losses and on the

for the high shape plasmas. The degraded confinement is mainly driven by a lower pedestal pressure due to a pedestal temperature approximately 20-30% lower than in JET-C. The pedestal density is instead comparable among JET-C and JET-ILW. To date, a JET-ILW pedestal pressure comparable to the baseline JET-C has been only in high achieved

Overview of JT-60U Results Toward the Resolution of Key

because fast-ion loss due to TF ripple induces counter rotation (Input torque is positive and similar in JT-60U and JET). On the other hand, no clear dependence was found for the edge pressure as shown in Fig 2(b). Electron pressure at the pedestal is almost unchanged at about 2.8 kPa when the pedestal density was scanned at 1-2.5 ×1019 m 3

OV/1-4 Overview of the JET results in support to ITER

configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H=1 at N ~1.8 and n/n GW ~0.6) have

Divertor Requirements and Performance

Energy loss during Type I ELMs is correlated with high pedestal pressure, which is required for good energy confinement, and consequently, the heat load could be severe. It is therefore of primary importance to predict the energy loss during ELMs in ITER by predictive models or scalings based on the ELM database.

Effect of ELMs on Rotation and Momentum Confinement in H-mode

pedestal region, R τ,edge =1.80±0.37. The significant reduction in the tj,edge is consistent with the large reduction in w near the pedestal top which, combined with the large elliptical volume

Confinement and edge studies towards low * and * at JET

A critical issue for ITER is the access to H-mode with good confinement, H 98(y,2)=1. At JET, good H-mode confinement in low triangularity plasmas is normally achieved for P IN>1.7 to 2P L-H [5]. The power above the predicted P L-H [10] is shown in figure 8 as a function of plasma current for these experiments. With the power available the

Divertor detachment studies - BOUT++

confinement to recycling/fueling Example from NSTX: lithium reduces divertor recycling, increases core confinement Major changes to pedestal profiles Not necessarily linked to detachment studies as yet, but indicative of need to understand better how edge influences core Becomes even more important for ITER, where recycling and

The Effect of a Metal Wall on Co nfinement in JET and ASDEX

Although the reduction in edge pedestal pressure in JET-ILW H- mode plasmas appears to be quite general, a comp ensating improvement in core confinement has been observed in the, so-called, hybrid scenario at N >2.5 through increased core temperature peaking.

High confinement/high radiated power H-mode experiments in

≥ 1 for edge power flows only marginally exceeding the scaled power for access to H-mode confinement in these conditions. For lower Z impurity seeding (N. 2, Ne), plasmas with high energy confinement are obtained with a radiative power fraction of 85% or larger and a reduction of the peak heat flux at the divertor by more than a

Sensitivity of the ITER Operating Window to Variation of

Fig. 2 - Te profiles for JET with enhancement factor 2 (blue) and 1 (red) that, in the absence of toroidal rotation resulting from toroidal momentum input, the pedestal may be less high and that the confinement may be reduced by ~10%. For the JET simulation, such a reduction of confinement is obtained if the enhancement factor on c is reduced from

Active Control of Type-I Edge Localized Modes with n = 1 and

of sight, one close to the magnetic axis (upper trace) and the other near the pedestal top (lower trace) (the integration lengths of core and edge probing beams are ~3 2 m and ~1 5 m, respectively), (e) electron temperature in the core and near the pedestal top, ( f ) the Dα signal measured at the inner divertor.

Effect of ELM mitigation on confinement and divertor heat

reduction of ELM size and the impact of each control method on plasma confinement and divertor heat loads. We find that the reduction in ELM size (up to a factor of 3), independently of the method used, is always accompanied by a reduction in pedestal pressure (mainly due to a loss in density) with only a moderate (10-15%)

Mikhail Tokar IEF - Plasmaphysik, Theory and Modeling

Edge Transport Barrier (ETB): diamagnetic electron rotation is of most importance Kinetic description of RMP penetration in plasma of low collisionality M.F.Heyn et al, Nucl. Fusion 48 (2008) 024005. Screening effect in collisional plasma edge (TEXTOR) D.Reiser et al, PoP 16 (2009) 042317 Vacuum RMP Screened RMP


The ELM AW for JET and DIII-D are plotted versus the edge pedestal energy in Fig. 1. We find the ELM AW is -36% of the pedestal electron energy in DIII-D and -26% in JET. The data is too sparse with too much scatter, however, to determine if the ELM fractional pedestal energy loss decreases with machine size or is constant.

Parameter dependence of ELM loss reduction by magnetic

Jun 05, 2019 energy loss normalized to the energy stored in the plasma pedestal from about 30% to less than 5%, i.e. by a factor of six, below an electron pedestal collisionality ofn* e,PED=0.4. At this level of ELM mitigation a significant reduction of the pedestal pressure and, therefore, global plasma confinement occurs.

Role of Neutral in ELMy H-Mode Plasmas: Transport Simulation with

proposed as to the edge transport barrier. Then an increase of ELM frequency and degradation of confinement are demonstrated. Finally, in section 4., the present work will be summarized brieflv. 2. Simulation with COCONUT COCONUT is a two dimensional transport code developed at JET joint undertaking, during past l0 years.

Theory of Non-Diffusive and Non-Axisymmetric Transport in the

Theory of Non-Diffusive and Non-Axisymmetric Transport in the Edge Pedestal of Tokamaks W. M. Stacey, Georgia Tech, Atlanta, GA 30332, USA This paper will review the work of the author and colleagues over the past decade on plasma edge theory, in particular on i) edge pedestal structure. [1]; ii) non-diffusive transport arising from

Asia-Pacific Conference on Plasma Physics, 26-P1OctI 2020

Operation in high-confinement mode (H-mode) for tokamak devices is preferable due to improving particle confinement time and increasing density and temperature. HoweverI quasi-periodic occurrence of edge localized modes (ELF in H-mode plasmas leads to a strong power leakage of the plasma stored energy into the scrape-off layer (SOLF.

Pedestal confinement and stability in JET-ILW ELMy H-modes

Apr 04, 2020 JET-C as the reduction in pedestal confinement was compen-sated by increased core profile peaking [ 3]. When assessing the edge stability of JET ELMy H-mode plasmas, JET-C pedestals are typically found to be close to the peeling ballooning (P B) limit before a type I ELM crash, while the 2011/12 JET-ILW

First results on n=1 and n=2 ELM control on DIII-D & progress

Weak edge ergodisation Plasma braking Seeding of locked modes n=2: Good edge ergodisation Small influence on core plasma JET RMP fields I Coil ≤3 kA x 16 turns Size ~ 6 m x 6 m ~3 m from mag. axis [Liang, EPS 2007, PPCF 2007, Koslowski EPS 2007]


number density fluctuations and thus improved confinement due to the reduction of edge pressure gradient as well as of edge bootstrap current. 4-4. Edge Pedestal Edge pedestal structure affects both core confinement and divertor performance. The edge pedestal pressure could determine the confinement performance as H ∝ (p e PED)2/3 in DIII-D

Non -linear MHD modelling of ELMs and their interaction with

loss on pedestal pressure gradient No sharp transition from stable to unstable This dependence (and imposed pellet frequency) determines the maximum sustainable pedestal gradient and possible performance penalty due to pellet pacing. JET #82885 ballooning unstable

CCFE-PR(15)09 C.D. Challis, J. Garcia, M. Beurskens, P

confinement, which was also seen with the C-wall experiments at low triangularity, is due to both increased edge pedestal pressure and core pressure peaking at high power. By contrast, the high triangularity C-wall plasmas exhibited elevated H 98 over a wide power range with strong, IPB98(y,2)-like, power degradation. This

Overview of results from MAST - The FIRE Place

Normalised confinement across range of L-mode, H-mode and ITB discharges increases with v v driven by torque from the neutral beam. Highest torque in counter-NBI discharges due to asymmetric (co-counter) fast ion losses v driven by NBI torque

Research Article A Simulation of H-mode Plasma in DIII- D

The High Confinement mode (H-mode) is an important regime for burning plasma experiments using the magnetic confinement fusion concept because it provides high temperature and excellent energy confinement time. Many experiments, such as Doublet III-Device (DIII-D), Joint European Torus (JET), and Tokamak Fusion


2. CONFINEMENT IN DEUTERIUM PLASMAS WITH A HELIUM MINORITY 2.1. Helium seeding experiments at JET The e ect of He as a minority impurity in deuterium plasmas was investigated in baseline H-mode scenario plas-mas at JET (B t=2.1T, I p=2MA, D-fuelling of unseeded pulse 1:6 1022 e /s, N˘1:5, q 95˘3:1). Helium pu s were

M. Porkolab, P. C. Ennever, S. G. Baek, E. M. Edlund, J

1 Reduction of Turbulence and Transport in the Alcator C-Mod Tokamak by Dilution of Deuterium Ions with Nitrogen and Neon Injection M. Porkolab, P. C. Ennever, S. G. Baek, E. M. Edlund, J. Hughes, J. E.

Impact of nitrogen seeding on confinement and power load

on an integrated scenario. At JET, Ne and Ar also radiate in the pedestal and main plasma (respectively) adding an additional degree of difficulty in achieving stationary conditions due to their ability to reduce the power entering the edge region and as a result reduce the pedestal confinement [6][7]. This paper investigates the potential of N 2

Improved Confinement in JET High

of confinement, which was also seen with the C-wall experiments at low triangularity, is associated with both increased edge pedestal pressure and core pressure peaking at high power. By contrast, the high triangularity C-wall plasmas exhibited elevated H 98 over a wide power range with strong, IPB98(y,2)-like, power degradation.

Towards Baseline Operation Integrating ITER-Relevant Core and

~2.3 (Pulse No: 76687) and ELM energy losses about 70kJ or 1% of the stored pedestal energy. In JET-ILW, the unseeded high- d HT plasmas have reduced energy confinement in comparison to JET-C but with N injection, the energy confinement is partially recovered, see Fig.2, and the ELM

Reduction of Ion Transport and Turbulence via Dilution with

- Neon is preferred for reactor (ITER) applications due to tritium inventory control (no ammonia formation as with nitrogen) - How to mitigate edge pedestal pressure reduction needs further investigation (c/f JET) - Seeding induced change in intrinsic rotation was seemingly unrelated to a change in

Fusion Reactor Technology I

-Due to the pressure pedestal, the bootstrap current which is proportional to the pressure and temperature gradients starts to grow. Eventually, the bootstrap current destabilizes an effect known as ideal peeling which leads to an ELM crash (3) and the loss of the edge pressure pedestal (4). -The cycle then restarts from the beginning.

Toroidal field ripple effects on H-modes in JET and

loss mechanism in ITER will be ripple banana orbit diffusion, and that the magnitude of these losses is expected to be in the 1% region, therefore negligible in terms of c-particle confinement. Recent experimental results from JT60-U [5] and H-mode dimensionless H-mode experiments in JET and

Prof. Dr. Yong-Su Na (32-206, Tel. 880-7204)

- Due to the pressure pedestal, the bootstrap current which is proportional to the pressure and temperature gradients starts to grow. Eventually, the bootstrap current destabilizes an effect known as ideal peeling which leads to an ELM crash (3) and the loss of the edge pressure pedestal (4). - The cycle then restarts from the

Control of Transport Barriers

Control of edge transport barriers: Requirements Loss power due to ELMs: fELM x ∆WELM, However erosion, strong dependence on ∆WELM (control ∆WELM !) ELMs have non-uniform ∆WELM distribution: So ∆WELM, average. ~ 3-4 MJ 3000 pulses N u m b e r o f E L M s N u m b e r o f p u l s e s s W no melt losses. 0.5 ms acceptable lifetime

In Partial Fulfillment of the Requirements for the Degree

neutrals in the edge. The end result of this drop would be a decrease in heat flux through the edge, due to increased radiation, which caused the layer just outside the separatrix to become unstable [7-10]. Researchers at Alcator C had similar experiences [11]. However, the Alcator group observed a larger degree of heat flux loss,

The effect of helium on plasma performance at ASDEX Upgrade

5%, with an even stronger reduction of the measured neutrons Dilution due to helium explains only a small part of this reduction and the loss in confinement cannot be connected to a reduced pedestal top pressure, as this remains roughly constant ( with increasing d ensity and decreasing temperature).

The Effect of a Metal Wall on Confinement in JET and ASDEX

observation has been made for AUG in [7]. The good normalised confinement in the JET-C plasmas is maintained through a widening of the edge pedestal as the fuelling level is increased [8], where a steep pedestal pressure gradient could be maintained over a wider region, resulting in an increase of the pedestal-top pressure. However, at low plasma

EX/P6-14 Evolution and control of tungsten transport in the

edge transport barrier. In addition, even when the concentration of W at the pedestal is kept at low levels, unfavourable core W transport can lead to its uncontrolled accumulation and to loss of the H-mode due increased radiation. Strategies have been developed in present

Impact of large type I ELMs on plasma radiation in JET

To prevent unacceptable divertor target erosion due to ELMs, the loss in plasma stored energy at the single ELM should be restricted to ∆W ELM ~ 1 MJ [2] corresponding to the energy density at