Ion energy measurements on MAST using a midplane RFEA

Allan, S.; Elmore, S.; Kirk, A.; Kočan, M.; Tamain, P.

doi:10.1016/j.jnucmat.2013.01.263

Cited by 9 publications

(10 citation statements)

References 18 publications

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“…1, a collection of T i /T e measurements from a number of tokamak SOL has been examined for measurements taken before 2010, showing values that range from the lower T i /T e $ 1 to the extreme T i /T e $ 10, with most of the data falling between 1 and 4. More recent measurements, in HL-2A, 3 in MAST, 2,4 in Alcator C-MOD, 7,8 and in ASDEX Upgrade 6 have confirmed these findings. The ion temperature is therefore usually higher than the electron one in the SOL.…”

Section: Introductionmentioning

confidence: 54%

Finite ion temperature effects on scrape-off layer turbulence

et al. 2015

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Ion temperature has been measured to be of the same order, or higher, than the electron temperature in the scrape-off layer (SOL) of tokamak machines, questioning its importance in determining the SOL turbulent dynamics. Here, we present a detailed analysis of finite ion temperature effects on the linear SOL instabilities, such as the resistive and inertial branches of drift waves and ballooning modes, and a discussion of the properties of the ion temperature gradient (ITG) instability in the SOL, identifying the g i ¼ L n =L T i threshold necessary to drive the mode unstable. The non-linear analysis of the SOL turbulent regimes by means of the gradient removal theory is performed, revealing that the ITG plays a negligible role in limited SOL discharges, since the ion temperature gradient is generally below the threshold for driving the mode unstable. It follows that the resistive ballooning mode is the prevailing turbulence regime for typical limited SOL parameters. The theoretical estimates are confirmed by non-linear flux-driven simulations of SOL plasma dynamics. [http://dx

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Section: Introductionmentioning

confidence: 54%

Finite ion temperature effects on scrape-off layer turbulence

et al. 2015

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“…Uncertainty in α LP , given in equation 2, arrises from uncertainty in T i /T e . Previous measurements on MAST have shown that 1 ≤ T i /T e ≤ 2.5 is reasonable for L-mode conditions [26][27][28] .This then gives α LP = 2.7 ± 0.1. Since α BP P cannot be measured directly in the system described in this paper the empirical value of α BP P = 0.6 ± 0.3 6,10,12,14 found across a number of experiments is adopted.…”

Section: Electron Temperature Measurementsmentioning

confidence: 78%

“…Figure 6 shows the profile of α LP obtained with this technique in each shot. In these calculations T i = 2T e was assumed, which is motivated by previous measurements on MAST [26][27][28] . Figure 6 shows that the secondary electron emission can have a major impact on the calculation of α LP .…”

Section: Electron Temperature Measurementsmentioning

confidence: 99%

Profile measurements in the plasma edge of mega amp spherical tokamak using a ball pen probe

Walkden

Adámek

Allan

et al. 2015

Review of Scientific Instruments

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The ball pen probe (BPP) technique is used successfully to make profile measurements of plasma potential, electron temperature, and radial electric field on the Mega Amp Spherical Tokamak. The potential profile measured by the BPP is shown to significantly differ from the floating potential both in polarity and profile shape. By combining the BPP potential and the floating potential, the electron temperature can be measured, which is compared with the Thomson scattering (TS) diagnostic. Excellent agreement between the two diagnostics is obtained when secondary electron emission is accounted for in the floating potential. From the BPP profile, an estimate of the radial electric field is extracted which is shown to be of the order ∼1 kV/m and increases with plasma current. Corrections to the BPP measurement, constrained by the TS comparison, introduce uncertainty into the ER measurements. The uncertainty is most significant in the electric field well inside the separatrix. The electric field is used to estimate toroidal and poloidal rotation velocities from E × B motion. This paper further demonstrates the ability of the ball pen probe to make valuable and important measurements in the boundary plasma of a tokamak.

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“…These measurement techniques, which have been used on MAST at the mid-plane [5] [6] and at the divertor [7], operate on timescales slower than the ELM event and therefore do not give any information on the evolution of the temperature during the ELM rise and fall as seen in both deuterium alpha (D α ) light at the mid-plane and current signals measured by electrical probes such as Langmuir probes (LP). A new measurement technique and associated analysis method has been employed on MAST using the divertor RFEA which allows measurements within the time during which ions from the ELM arrive at the target.…”

Section: Introductionmentioning

confidence: 99%

Scrape-off layer ion temperature measurements at the divertor target during type III ELMs in MAST measured by RFEA

Elmore

Allan

Fishpool

et al. 2015

Journal of Nuclear Materials

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In future nuclear fusion reactors high heat load events, such as edge-localised modes (ELMs), can potentially damage divertor materials and release impurities into the main plasma, limiting plasma performance. The most difficult to handle are type I ELMs since they carry the largest fraction of energy from the plasma and therefore deposit the largest heat flux at the target and on first wall materials. Knowing the temperature of the ions released from ELM events is important since it determines the potential sputtering they would cause from plasma facing materials. To make measurements of T i by retarding field energy analyser (RFEA) during type I ELMs a new operational technique has been used to allow faster measurements to be made; this is called the fast swept technique (FST). The FST method allows measurements to be made within the time of the ELM event which has previously not been possible with T i measurements. This new technique has been validated by comparing it with a slower average measurement previously used to make ion temperature measurements of ELMs. Presented here are the first T i measurements during Type I ELMs made at a tokamak divertor. Temperatures as high as 20 eV are measured more than 15 cm from the peak heat flux of an ELM, in a region where no inter-ELM current is measured by the RFEA; showing that ELM events cause hot ions to reach the divertor target far into the scrape off layer. Fast camera imaging has been used to investigate the type of ELM filaments that have been measured by the divertor RFEA. It is postulated that most of the ion temperatures measured in type I ELMs are from secondary ELM filaments which have not been previously identified in MAST plasmas.2

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Ion energy measurements on MAST using a midplane RFEA

Cited by 9 publications

References 18 publications

Finite ion temperature effects on scrape-off layer turbulence

Finite ion temperature effects on scrape-off layer turbulence

Profile measurements in the plasma edge of mega amp spherical tokamak using a ball pen probe

Scrape-off layer ion temperature measurements at the divertor target during type III ELMs in MAST measured by RFEA

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