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LNF:Estudios del confinamiento mejorado y de impurezas en los Stellarators TJ-II y W7-X mediante inyección de pastillas criogénicas (Pellets) y encapsulados de impurezas (TESPEL): Difference between revisions
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LNF:Estudios del confinamiento mejorado y de impurezas en los Stellarators TJ-II y W7-X mediante inyección de pastillas criogénicas (Pellets) y encapsulados de impurezas (TESPEL) (view source)
Revision as of 12:49, 18 September 2025
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1. The first aim is to investigate aspects of pellet injection that are still not fully understood as well as to understand better how pellets affect plasma magnetic activity, plasma turbulence and plasma performance. For this, the medium-sized heliac TJ-II will be used. It is equipped with a cryogenic pellet injector (PI) for producing solid hydrogen pellets that can be injected at high velocity into the plasma. During previous projects it was found that pellet injection into TJ-II results in enhanced plasma performance (simultaneously higher electron density and ion temperature, larger stored diamagnetic energy, longer particle confinement, higher plasma beta) <ref>1</ref> <ref>2</ref>. It was also seen how the injection of additional fuel pellets further increases and maintains this enhanced plasma performance. It is now necessary to understand the underlying physics of these experimental observations. This will be done using available codes to evaluate neoclassical and turbulent contributions. | 1. The first aim is to investigate aspects of pellet injection that are still not fully understood as well as to understand better how pellets affect plasma magnetic activity, plasma turbulence and plasma performance. For this, the medium-sized heliac TJ-II will be used. It is equipped with a cryogenic pellet injector (PI) for producing solid hydrogen pellets that can be injected at high velocity into the plasma. During previous projects it was found that pellet injection into TJ-II results in enhanced plasma performance (simultaneously higher electron density and ion temperature, larger stored diamagnetic energy, longer particle confinement, higher plasma beta) <ref>1</ref> <ref>2</ref>. It was also seen how the injection of additional fuel pellets further increases and maintains this enhanced plasma performance. It is now necessary to understand the underlying physics of these experimental observations. This will be done using available codes to evaluate neoclassical and turbulent contributions. | ||
2. The second aim is to continue to support and expand impurity transport studies in TJ-II, W7-X and LHD. Under the umbrella of a trilateral collaboration (2020-2029) with the National Institute for Fusion Science (Japan) and IPP-Max-Planck (Greifswald, Germany), the Tracer-Encapsulated Solid Pellet (TESPEL) method is now employed on TJ-II, W7-X and LHD. TESPELs are polystyrene spheres (diameter <1 mm) loaded with small quantities of selected impurities (atomic elements other than fuel). Thus, TESPEL allows delivering a precise quantify of tracer to a preselected location in the plasma core, after which its transport can be evaluated. An important aspect of previous projects was the establishment of a laboratory to fabricate TESPELs at Ciemat. Since then several hundred TESPELs prepared at Ciemat have been injected successfully into plasmas created in these devices. Thus, key goals of this current project are to continue TESPEL fabrication at this laboratory, thereby allowing Ciemat to maintain its fruitful collaborations with W7-X and LHD, and to expand TESPEL based impurity control studies. For instance, during recent experiments with TESPEL at LHD, project members determined that mid-/high- Z atomic ions can be flushed out of a high-density plasma if Li-granules are dropped continuously into the plasma edge. When results were compared with results from reference plasmas, confinement times of high-Z ions were reduced by a factor 4 or more. It is extend to explore further this new operational scenario for stellarators. | 2. The second aim is to continue to support and expand impurity transport studies in TJ-II, W7-X and LHD. Under the umbrella of a trilateral collaboration (2020-2029) with the National Institute for Fusion Science (Japan) and IPP-Max-Planck (Greifswald, Germany), the Tracer-Encapsulated Solid Pellet (TESPEL) method is now employed on TJ-II, W7-X and LHD. TESPELs are polystyrene spheres (diameter <1 mm) loaded with small quantities of selected impurities (atomic elements other than fuel). Thus, TESPEL allows delivering a precise quantify of tracer to a preselected location in the plasma core, after which its transport can be evaluated. An important aspect of previous projects was the establishment of a laboratory to fabricate TESPELs at Ciemat. Since then several hundred TESPELs prepared at Ciemat have been injected successfully into plasmas created in these devices. Thus, key goals of this current project are to continue TESPEL fabrication at this laboratory, thereby allowing Ciemat to maintain its fruitful collaborations with W7-X and LHD, and to expand TESPEL based impurity control studies. For instance, during recent experiments with TESPEL at LHD, project members determined that mid-/high- Z atomic ions can be flushed out of a high-density plasma if Li-granules are dropped continuously into the plasma edge <ref>3</ref>. When results were compared with results from reference plasmas, confinement times of high-Z ions were reduced by a factor 4 or more. It is extend to explore further this new operational scenario for stellarators. | ||
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