New linear plasma devices in the trilateral euregio cluster for an integrated approach to plasma surface interactions in fusion reactors

New linear plasma devices are currently being constructed or planned in the Trilateral Euregio Cluster (TEC) to meet the challenges with respect to plasma surface interactions in DEMO and ITER: i) MAGNUMPSI (FOM), a high particle and power flux device with super-conducting magnetic field coils which will reach ITER-like divertor conditions at high magnetic field, ii) the newly proposed linear plasma device JULE-PSI (FZJ), which will allow to expose toxic and neutron activated target samples to ITER-like fluences and ion energies including in vacuo analysis of neutron activated samples, and iii) the plasmatron VISION I, a compact plasma device which will be operated inside the tritium lab at SCK-CEN Mol, capable to investigate tritium plasmas and moderately activated wall materials. This contribution shows the capabilities of the new devices and their forerunner experiments (Pilot-PSI at FOM and PSI-2 Ju¨lich at FZJ) in view of the main objectives of the new TEC program on plasma surface interactions

Power exhaust in the snowflake divertor forL- and H-mode TCV tokamak plasmas

The snowflake (SF) divertor is a plasma configuration that may enable tokamak operation at high performance and lower peak heat loads on the plasma-facing components than a standard single-null divertor. This paper reports on the results of experiments performed on the TCV tokamak in both the low- and high-confinement regimes, wherein the divertor configuration was continuously varied between a standard single-null and a ‘SF-plus’, which features auxiliary strike points (SPs) in the private flux region of the primary separatrix. The measured edge properties show that, in L-mode, the fraction of the exhaust power reaching the additional SPs is small. During edge-localized modes, up to ~20% of the exhausted energy is redistributed to the additional SPs even at an x-point separation of 0.6 times the plasma minor radius, thereby reducing the peak heat flux to the inner primary SP by a factor of 2–3. The observed behaviour is qualitatively consistent with a proposed model for enhanced cross-field transport through the SF’s relatively large region of low poloidal field by instability-driven convection

Experimental evidence of enhanced recombination of a hydrogen plasma induced by nitrogen seeding in linear device Magnum-PSI

\u3cp\u3e In this work we investigate the effects induced by the presence of nitrogen in a detached-like hydrogen plasmas in linear plasma machine Magnum-PSI. Detachment has been achieved by increasing the background neutral pressure in the target chamber by means of H \u3csub\u3e2\u3c/sub\u3e /N \u3csub\u3e2\u3c/sub\u3e puffing and two cases of study have been set up, i.e. at 2 and 4 Pa. Achieved n \u3csub\u3ee\u3c/sub\u3e are ITER-relevant i.e. above 10 \u3csup\u3e20\u3c/sup\u3e m \u3csup\u3e−3\u3c/sup\u3e and electron temperatures are in the range 0.8–2 eV. A scan among five different N \u3csub\u3e2\u3c/sub\u3e /H \u3csub\u3e2\u3c/sub\u3e +N \u3csub\u3e2\u3c/sub\u3e flux ratios seeded have been carried out, at values of 0, 5, 10, 15 and 20%. A n \u3csub\u3ee\u3c/sub\u3e decrease while increasing the fraction of N \u3csub\u3e2\u3c/sub\u3e has been observed for both background pressures, resulting in a plasma pressure drop of ̴ 30%. T \u3csub\u3ee\u3c/sub\u3e remains constant among all scans. The peak intensity of NH*(A \u3csup\u3e3\u3c/sup\u3e ∏->X \u3csup\u3e3\u3c/sup\u3e ∑ \u3csup\u3e−\u3c/sup\u3e , ∆v = 0) at 336 nm measured with optical emission spectroscopy increases linearly with the N \u3csub\u3e2\u3c/sub\u3e content, together with the NH \u3csub\u3e3\u3c/sub\u3e signal in the RGA. A further dedicated experiment has been carried out by puffing separately H \u3csub\u3e2\u3c/sub\u3e /N \u3csub\u3e2\u3c/sub\u3e and H \u3csub\u3e2\u3c/sub\u3e /He mixtures, being helium a poorly-reactive atomic species, hence excluding a priori nitrogen-induced molecular assisted recombination. Interestingly, plasma pressure and heat loads to the surface are enhanced when increasing the content of He in the injected gas mixture. In the case of N \u3csub\u3e2\u3c/sub\u3e , we observe an opposite behavior, indicating that N–H species actively contribute to convert ions to neutrals. Recombination is enhanced by the presence of nitrogen. Numerical simulations with two different codes, a global plasma-chemical model and a spatially-resolved Monte Carlo code, address the role of NH \u3csub\u3ex\u3c/sub\u3e species behaving as electron donor in the ion conversion with H \u3csup\u3e+\u3c/sup\u3e by means of what we define here to be N-MAR i.e. NH \u3csub\u3ex\u3c/sub\u3e + H \u3csup\u3e+\u3c/sup\u3e → NH \u3csub\u3ex\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e + H, followed by NH \u3csub\u3ex\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e + e \u3csup\u3e−\u3c/sup\u3e → NH \u3csub\u3ex-\u3c/sub\u3e \u3csub\u3e1\u3c/sub\u3e + H. Considering the experimental findings and the qualitative results obtained by modelling, N-MAR process is considered to be a possible plasma-chemical mechanism responsible for the observed plasma pressure drop and heat flux reduction. Further studies with a coupled code B2.5-Eunomia are currently ongoing and may provide quantitative insights on the scenarios examined in this paper. \u3c/p\u3

Studying the influence of nitrogen seeding in a detached-like hydrogen plasma by means of numerical simulations

\u3cp\u3eThe leading candidate for impurity seeding in ITER is currently nitrogen. To date, there have only been a few studies on the plasma chemistry driven by N\u3csub\u3e2\u3c/sub\u3e/H\u3csub\u3e2\u3c/sub\u3e seeding and its effect on the molecular-activated recombination of incoming atomic hydrogen ions in a detached-like scenario. Numerical simulations are needed to provide insights into such mechanisms. The numerous plasma chemical reactions that may occur in such an environment cannot be entirely included in a 2- or 3-dimensional code such as Eirene. A complete global plasma model, implemented with more than 100 plasma chemical equations and 20 species, has been set up on the basis of the Plasimo code. This study shows that two main nitrogen-including recombination reaction paths are dominant, i.e. the ion conversion of NH followed by dissociative recombination, and the proton transfer between and N\u3csub\u3e2\u3c/sub\u3e, producing N\u3csub\u3e2\u3c/sub\u3eH\u3csup\u3e+\u3c/sup\u3e. These two processes are referred to as N-MAR (nitrogen molecular-activated recombination) and have subsequently been implemented in Eunomia, which is a spatially resolved Monte Carlo code designed to simulate the neutral inventory in linear plasma machines such as Pilot-PSI and Magnum-PSI. To study the effect of N\u3csub\u3e2\u3c/sub\u3e on the overall recombination, three studies have been set up, and from a defined puffing location with a constant total seeding rate of H\u3csub\u3e2\u3c/sub\u3e + N\u3csub\u3e2\u3c/sub\u3e, three N\u3csub\u3e2\u3c/sub\u3e ratios were simulated, i.e. 0%, 5% and 10%. The parameter monitored is the density of atomic hydrogen, being the final hydrogenic product of any recombination mechanism in the scenario considered. The difference in H density between the 0% case and the 10% case is about a factor of three. The importance of NH as an electron donor is highlighted, and the N-MAR reaction routes are confirmed to enhance the conversion of ions to neutrals, making the heat loads to the divertor plate more tolerable. This work is a further step towards a full understanding of the role of N\u3csub\u3e2\u3c/sub\u3e-H\u3csub\u3e2\u3c/sub\u3e molecules in a detached divertor plasma.\u3c/p\u3

Rotation of a strongly magnetized hydrogen plasma column determined from an asymmetric Balmer-beta spectral line with two radiating distributions

A potential buildup in front of a magnetized cascaded arc hydrogen plasma source is explored via .vector.E * .vector.B rotation and plate potential measurements. Plasma rotation approaches thermal speeds with max. velocities of 10 km/s. The diagnostic for plasma rotation is optical emission spectroscopy on the Balmer-beta line. Asym. spectra are obsd. A detailed consideration is given on the interpretation of such spectra with a two distribution model. This consideration includes radial dependence of emission detd. by Abel inversion of the lateral intensity profile. Spectrum anal. is performed considering Doppler shift, Doppler broadening, Stark broadening, and Stark splitting. [on SciFinder (R)

Development of real-time plasma analysis and control algorithms for the TCV tokamak using Simulink

\u3cp\u3eOne of the key features of the new digital plasma control system installed on the TCV tokamak is the possibility to rapidly design, test and deploy real-time algorithms. With this flexibility the new control system has been used for a large number of new experiments which exploit TCV's powerful actuators consisting of 16 individually controllable poloidal field coils and 7 real-time steerable electron cyclotron (EC) launchers. The system has been used for various applications, ranging from event-based real-time MHD control to real-time current diffusion simulations. These advances have propelled real-time control to one of the cornerstones of the TCV experimental program. Use of the Simulink graphical programming language to directly program the control system has greatly facilitated algorithm development and allowed a multitude of different algorithms to be deployed in a short time. This paper will give an overview of the developed algorithms and their application in physics experiments.\u3c/p\u3

Extreme hydrogen plasma fluxes at Pilot-PSI enter the ITER divertor regime

\u3cp\u3ePilot-PSI produces hydrogen plasma with a cascaded arc. It is demonstrated that the output electron density reaches 4 × 10\u3csup\u3e21\u3c/sup\u3e m\u3csup\u3e-3\u3c/sup\u3e by pushing the input power to 45 kW. Increasing the diameter of the discharge channel (studied from 4 to 7 mm) does not affect the plasma output but reduces the power input by up to 25%. The plasma was post-heated by feeding the plasma column with a net current. This increased the electron temperature from ∼2 to 4 eV. Calorimetric and voltage measurements on the cascade plates showed that this also influenced the discharge characteristics inside the arc.\u3c/p\u3