The lithium beam emission spectroscopy (Li-BES) is a powerful diagnostic to resolve the plasma edge density with high temporal and spatial resolution. The recent upgrades of the Li-BES at ASDEX Upgrade and the resulting gain in photon flux allow the plasma edge density to be determined with an advanced level of accuracy. Furthermore, electron density fluctuations are measured using Li-BES. The Li-BES capabilities and limitations to measure electron density profiles as well as density fluctuations are presented. It is well suited to characterize electron density turbulence in the scrape off layer (SOL) with decreasing sensitivity towards the plasma core. This is demonstrated by simulations as well as by comparisons with other diagnostics. The Li-BES is an appropriate tool to study transport phenomena in the SOL over a wide range of plasma parameters due to its robustness and routine usage.

/pdf/characterization-of-the-li-bes-at-asdex-upgrade-p75xbh0lfu.pdf

Characterization of the Li-BES at ASDEX Upgrade

Interpretation of radiative divertor studies with impurity seeding in type-I ELMy H-mode plasmas in JET-ILW using EDGE2D–EIRENE

Target particle and heat loads in low-triangularity L-mode plasmas in JET with carbon and beryllium/tungsten walls

This work describes the behaviour of the global energy and particle confinement on JET observed in a massive database of H-mode plasmas covering almost whole lifetime of JET operations, both with carbon and metal wall. The analysis is focused on type I ELMy H-modes in stationary phases. It is shown that plasma density in that regime is determined mainly by the plasma current, edge safety factor, triangularity of the last closed flux surface and the hydrogenic isotope mass. That behaviour is consistent for the whole database regardless of divertor configuration or the plasma facing materials. On average, thermal energy confinement time in JET with carbon wall (JET-C) is accurately predicted by the IPB98y,2 scaling. For JET with the ITER-like wall the energy confinement is found to be lower than expected from the scaling. The difference is found to be much stronger in divertor configuration with outer strike point at vertical target and pumping throat at the private flux. Observed lower confinement in JET-ILW can partially be attributed to the additional operational constraints of the metal wall machine, i.e. the avoidance of heavy impurity accumulation via additional gas dosing, but not in full. The isotope effect on the energy confinement in M=1-2 range is found to be the same in JET-C and JET-ILW, thus independent of the wall material, if correlation with plasma density is accounted for. The effect of toroidal magnetic field on the confinement is between zero and slightly negative. Triangularity has generally favourable effect on the energy confinement, but the magnitude changes across the database. Effect of triangularity on plasma density although is always much stronger than on energy confinement, therefore plasmas with high triangularity are in general more dense and colder than at the lower triangularity. The work described in this paper is done under the EUROfusion global confinement database project, and the data shown here will be available to the EUROfusion collaborators shortly. It is also either already a part of the international H-mode confinement database or will be in the future updated version.

https://iopscience.iop.org/article/10.1088/1741-4326/ab6482/pdf

Energy and particle confinement in JET H-mode plasma

Development of atomic beam probe for tokamaks

Introduction Diagnostic alkali beams are standard diagnostics in many fusion devices as they are capable of measuring plasma electron density profile in the edge and SOL plasma [1]. In these experiments the Doppler shifted emission of the collisionally excited beam particles is measured. Since the beam is weakened by the plasma, the light emission is not local function of the density. To reconstruct the density profile the populations of the different atomic states has to be followed along the beam using a collisional-radiative model [2]. With a fast detection system the high frequency density turbulence can also be characterized from the SOL to the outer part of the core plasma [3], which is the primary goal of the recent studies. The beam width is about 2 cm, which defines the poloidal localization. The radial resolution is determined by the finite lifetime of the excited 2p-2s atomic state. In the case of the TEXTOR 35 kV Li beam the smearing is about 2 cm. The ITG turbulence, thought to be responsible for the anomalous transport at the plasma edge, has similar spatial scale, therefore the major aim of this diagnostic is to characterize density fluctuation in TEXTOR. The precision of the reconstructed density profile is influenced by the background light level. As a solution the beam can be chopped to measure the actual background. The frequency of the chopping system can be adapted as needed in a wide range (10Hz 200kHz). The TEXTOR Li-beam diagnostic was upgraded with the following main components: newly designed high throughput optics with in-vessel elements, two parallel observation systems containing a scientific CCD camera and a 16 channel Avalanche Photodiode (APD) fast camera unit, fast deflection system, data acquisition system and control unit of the diagnostic. This paper describes the upgrades of the TEXTOR Li-beam diagnostics and demonstrates the capabilities through the first measurements.

First Measurements with the re-installed accelerated Lithium beam diagnostics on TEXTOR

A 60 kV neutral lithium diagnostic beam probes the edge plasma of JET for the measurement of electron density profiles. This paper describes recent enhancements of the diagnostic setup, new procedures for calibration and protection measures for the lithium ion gun during massive gas puffs for disruption mitigation. New light splitting optics allow in parallel beam emission measurements with a new double entrance slit CCD spectrometer (spectrally resolved) and a new interference filter avalanche photodiode camera (fast density and fluctuation studies).

Recent improvements of the JET lithium beam diagnostic.

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First Measurements with the re-installed accelerated Lithium beam diagnostics on TEXTOR

Recent improvements of the JET lithium beam diagnostic.