The core issue for the implementation of NV center qubit technology is a sensitive readout of the NV spin state. We present here a detailed theoretical and experimental study of NV center photoionization processes, used as a basis for the design of a dual-beam photoelectric method for the detection of NV magnetic resonances (PDMR). This scheme, based on NV one-photon ionization, is significantly more efficient than the previously reported single-beam excitation scheme. We demonstrate this technique on small ensembles of ∼10 shallow NVs implanted in electronic grade diamond (a relevant material for quantum technology), on which we achieve a cw magnetic resonance contrast of 9%-three times enhanced compared to previous work. The dual-beam PDMR scheme allows independent control of the photoionization rate and spin magnetic resonance contrast. Under a similar excitation, we obtain a significantly higher photocurrent, and thus an improved signal-to-noise ratio, compared to single-beam PDMR. Finally, this scheme is predicted to enhance magnetic resonance contrast in the case of samples with a high proportion of substitutional nitrogen defects, and could therefore enable the photoelectric readout of single NV spins. The negatively charged nitrogen-vacancy (NV -) center in diamond has attracted particular attention as a room temperature solid-state qubit [1] that can be read out by optical detection of magnetic resonances (ODMR) [2]. Numerous applications in the field of solid-state quantum information processing [3] and sensing [4][5][6][7][8][9][10] are being studied.We have recently developed a method for the photoelectric detection of NV -electron spin magnetic resonances (PDMR) [11], performed directly on a diamond chip equipped with electric contacts and based on the electric detection of charge carriers promoted to the diamond conduction band (CB) by two-photon ionization of NV -under green illumination (single-beam PDMR, or s-PDMR) (Fig. 1) To explore the photophysics behind the PDMR scheme and optimize its performances, we performed ab initio calculations of N 0 s , NV -, and NV 0 ionization cross sections, and compared the results to experimental characterizations of the ionization bands. In this way we demonstrate that under blue illumination, the ionization of NV -can be achieved by a more effective one-photon process, leading to a higher photocurrent-and therefore a higher signal-to-noise (S/N) ratio-than green illumination of identical power. Based on this result, we designed a dual-beam PDMR (d-PDMR) scheme (Fig. 1), in which pulsed blue light directly ionizes NV -and converts the resultant NV 0 back to NV -by one-photon processes, while simultaneous cw green illumination independently controls the MR contrast. We validated this scheme on small ensembles of ∼10 shallow NV -centers implanted in electronic grade diamond, which represents a downscaling of the photoelectric detection by a factor ∼10 5 compared to a previous publication [11]. The d-PDMR scheme leads to enhanced MR contrast under low power illu...

Please cite this article in press as: M. Oberkofler, et al., Plasma-wall interactions with nitrogen seeding in all-metal fusion devices: Formation of nitrides and ammonia, Fusion Eng. Des. (2015), http://dx.h i g h l i g h t s• Nitrogen chemistry is a potential issue for the use of N 2 as seeding species to cool the edge of fusion plasmas.• Surface nitride formation on Be and W in laboratory experiments.• Reduced erosion rate of Be by injection of N in D plasma in PISCES-B.• Ammonia formation observed in AUG and JET. a b s t r a c tNitrogen is routinely used to control the power load to the divertor targets of tokamak fusion reactors. However, its chemical reactivity can have implications on design and operation of a fusion device. In this contribution experimental results from recent years on three topics are briefly presented. These are the formation of nitrides, the sputtering of beryllium in the presence of nitrogen and the production of ammonia. Laboratory experiments have shown that surface nitrides are formed both on beryllium and tungsten upon exposure to energetic nitrogen ions. Erosion rates of Be by energetic N ions are in good quantitative agreement with modeling. Erosion upon exposure of Be to a mixed N/D plasma is reduced with respect to a pure D plasma. Finally, the appearance of ammonia has been observed in mixed N/D plasmas as well as in the exhaust gas of AUG and JET. The production rate in AUG reached 5% of the injected N atoms in a series of three subsequent N 2 -seeded discharges.

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The secondary electron yields as a result of highly charged ions impinging on clean Au(111) and thin films of C 60 on Au have been measured. This has been done for film thicknesses of one to five monolayers and several charge states of Ar and Xe ions. For all ions an increase of 35% in the secondary electron yield is observed when going from Au(111) to multiple C 60 layers. The increase remains constant for a wide range (7-26) of charge states. Possible scenarios are given to explain the increase in electron yield.

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