Is Carbon a Realistic Choice for ITER's Divertor?

Skinner, C. H.; Federici, G.

doi:10.2172/840424

Cited by 3 publications

(5 citation statements)

References 14 publications

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“…If carbon PFCs are used in ITER (this is currently envisaged-section 6), the high T-retention rates measured in present tokamaks (due to co-deposition as a result of C erosion and migration) extrapolate to 1-5 g T retained per pulse, although these estimates are still associated with substantial uncertainties. Assuming that carbon is used only in the divertor target area and, optimistically, that there will be no C migration to areas remote from the divertor, T-removal efficiencies in the range 90-98% will be required if premature replacement of the divertor before the erosion lifetime of 3000 full power DT pulses is to be avoided [4]. Such restrictions are imposed by nuclear licensing which, for safety reasons, limits the in-vessel T-inventory in ITER to ∼350 g [5].…”

Section: Introductionmentioning

confidence: 99%

Material erosion and migration in tokamaks

Pitts

Coad

Coster³

et al. 2005

Plasma Phys. Control. Fusion

116

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The issue of first wall and divertor target lifetime represents one of the greatest challenges facing the successful demonstration of integrated tokamak burning plasma operation, even in the case of the planned next step device, ITER, which will run at a relatively low duty cycle in comparison to future fusion power plants. Material erosion by continuous or transient plasma ion and neutral impact, the susbsequent transport of the released impurities through and by the plasma and their deposition and/or eventual re-erosion constitute the process of migration. Its importance is now recognized by a concerted research effort throughout the international tokamak community, comprising a wide variety of devices with differing plasma configurations, sizes and plasmafacing component material. No single device, however, operates with the first wall material mix currently envisaged for ITER, and all are far from the ITER energy throughput and divertor particle fluxes and fluences. This paper aims to review the basic components of material erosion and migration in tokamaks, illustrating each by way of examples from current research and attempting to place them in the context of the next step device. Plans for testing an ITER-like first wall material mix on the JET tokamak will also be briefly outlined.

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Section: Introductionmentioning

confidence: 99%

Material erosion and migration in tokamaks

Pitts

Coad

Coster³

et al. 2005

Plasma Phys. Control. Fusion

116

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“…Specimens with deposited a-C:W films were exposed to a D beam in the Garching high current ion source facility at temperatures between 300 K and 1300 K, at a fluence of 10 24 D/m 2 This leads to an implantation energy of 200 eV/D for the ions and of 1200 eV/D for the neutrals.…”

Section: Deuterium Beam Exposure and Analysis Of The Film Thickness Omentioning

confidence: 99%

“…In literature it was shown that metal-doping leads to a significant reduction of the total erosion yield [3,7], at fluences up to 10 24 D/m 2…”

Section: Estimation Of the Concentration Of Neutrals In The D Beammentioning

confidence: 99%

“…The use of carbon materials together with metallic plasma-facing materials (PFMs) in fusion devices -as planned for ITER with beryllium (Be), tungsten (W), and carbon (C) -will lead to deposition of mixed carbon-metal layers during sputtering/erosion cycles of PFMs by hydrogen [1]. Therefore, the chemical erosion behavior of such mixed layers needs to be investigated as well as their hydrogen retention behavior (tritium inventory) [2].…”

Section: Introductionmentioning

confidence: 99%

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Temperature dependence of the erosion behavior of deuterium beam exposed tungsten-doped carbon films (a-C:W)

Sauter

Balden

2011

Journal of Nuclear Materials

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Tungsten-doped amorphous carbon films (a-C:W) are used as model system to study the deuterium (D) retention behavior and the erosion behavior of metal containing co-deposited layers. In our recent studies, the implantation temperature was increased towards an ITER relevant range. Pure and 7.5 at% tungsten-doped carbon films have been exposed to a deuterium beam of 200 eV/D at different implantation temperatures up to 1300 K and at a fluence of 10 24 D/m 2. Rutherford backscattering spectrometry with a 1.5 MeV + H beam was performed to obtain the total erosion yield. For each implantation condition and for each structure of doped films, the total erosion yield is reduced significant, compared to pure films. The temperature dependence of the total erosion yield is less pronounced for doped films.

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“…where f c accounts for the finite size of the detector pixels. For Swift f c ∼0.7 [3], which explains why for a given burst the rate trigger significance is greater than the imaging significance [4]. The BAT uses a more complex rate trigger than shown above.…”

mentioning

confidence: 96%

Burst Detector Sensitivity: Past, Present & Future

Band¹

2006

AIP Conference Proceedings

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Abstract. I compare the burst detection sensitivity of CGRO's BATSE, Swift's BAT, the GLAST Burst Monitor (GBM) and EXIST as a function of a burst's spectrum and duration. A detector's overall burst sensitivity depends on its energy sensitivity and set of accumulations times ∆t; these two factors shape the detected burst population. For example, relative to BATSE, the BAT's softer energy band decreases the detection rate of short, hard bursts, while the BAT's longer accumulation times increase the detection rate of long, soft bursts. Consequently, Swift is detecting long, low fluence bursts (2-3× fainter than BATSE).What is the relative sensitivity of different detectors for detecting gamma-ray bursts, and how should this sensitivity be compared? How do these differences shape the observed burst populations, which must be taken into account in determining the underlying burst distribution? Here I compare BATSE's Large Area Detectors on CGRO (the past), the Burst Alert Telescope (BAT) [1] on Swift (the present), and the GLAST Burst Monitor (GBM) and EXIST (the future). BATSE and the GBM are/were sets of NaI(Tl) detectors while the BAT and EXIST are/will be CZT coded mask detectors. The energy range of NaI(Tl) detectors is ∼20-1000 keV while for CZT it is ∼10-150 keV. I apply a semi-analytic methodology using simplified models of the trigger systems of the different detectors.Most instruments detect bursts using either rate triggers or image triggers. A rate trigger determines whether the increase in the number of counts in a time bin ∆t and energy band ∆E over the expected number of background counts is statistically significant. An image trigger determines whether the image formed from the counts in the time bin ∆t and energy band ∆E contains a new point source. Usually an image trigger is preceded by a rate trigger that starts the imaging process[2]; the rate trigger is set to permit many false positives that are eliminated by the image trigger. If the number of burst counts is S and the number of non-burst counts is B, then the rate trigger significance σ r (for BATSE and the GBM) and the image trigger significance σ i for ∆t and ∆E are σ r = S √ B andwhere f c accounts for the finite size of the detector pixels. For Swift f c ∼0.7[3], which explains why for a given burst the rate trigger significance is greater than the imaging significance [4]. The BAT uses a more complex rate trigger than shown above. For directions other than the burst position the counts S from the burst contribute to the

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Is Carbon a Realistic Choice for ITER's Divertor?

Cited by 3 publications

References 14 publications

Material erosion and migration in tokamaks

Material erosion and migration in tokamaks

Temperature dependence of the erosion behavior of deuterium beam exposed tungsten-doped carbon films (a-C:W)

Burst Detector Sensitivity: Past, Present & Future

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