If a laser- or particle beam-driven plasma wakefield accelerator operates in the linear or moderately nonlinear regime, injecting an externally produced particle bunch (witness) to be accelerated may encounter an alignment problem. Witness alignment tolerances can be relaxed by using a damper, an additional particle bunch produced by the same injector and propagating at a submillimeter distance ahead of the witness. If misaligned, the damper perturbs the wakefield in such a way that the witness shifts on-axis with no quality loss.
{"title":"Oscillation damper for misaligned witness in plasma wakefield accelerator","authors":"K. V. Lotov, I. Yu. Kargapolov, P. V. Tuev","doi":"arxiv-2409.12041","DOIUrl":"https://doi.org/arxiv-2409.12041","url":null,"abstract":"If a laser- or particle beam-driven plasma wakefield accelerator operates in\u0000the linear or moderately nonlinear regime, injecting an externally produced\u0000particle bunch (witness) to be accelerated may encounter an alignment problem.\u0000Witness alignment tolerances can be relaxed by using a damper, an additional\u0000particle bunch produced by the same injector and propagating at a submillimeter\u0000distance ahead of the witness. If misaligned, the damper perturbs the wakefield\u0000in such a way that the witness shifts on-axis with no quality loss.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257414","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ihda Chaerony Siffa, Robert Wagner, Laura Vilardell Scholten, Markus M. Becker
Digital research data management is increasingly integrated across universities and research institutions, addressing the handling of research data throughout its lifecycle according to the FAIR data principles (Findable, Accessible, Interoperable, Reusable). Recent emphasis on the semantic and interlinking aspects of research data, e.g., by using ontologies and knowledge graphs further enhances findability and reusability. This work presents a framework for creating and maintaining a knowledge graph specifically for low-temperature plasma (LTP) science and technology. The framework leverages a domain-specific ontology called Plasma-O, along with the VIVO software as a platform for semantic information management in LTP research. While some research fields are already prepared to use ontologies and knowledge graphs for information management, their application in LTP research is nascent. This work aims to bridge this gap by providing a framework that not only improves research data management but also fosters community participation in building the domain-specific ontology and knowledge graph based on the published materials. The results may also support other research fields in the practical use of knowledge graphs for semantic information management.
{"title":"Semantic Information Management in Low-Temperature Plasma Science and Technology with VIVO","authors":"Ihda Chaerony Siffa, Robert Wagner, Laura Vilardell Scholten, Markus M. Becker","doi":"arxiv-2409.11065","DOIUrl":"https://doi.org/arxiv-2409.11065","url":null,"abstract":"Digital research data management is increasingly integrated across\u0000universities and research institutions, addressing the handling of research\u0000data throughout its lifecycle according to the FAIR data principles (Findable,\u0000Accessible, Interoperable, Reusable). Recent emphasis on the semantic and\u0000interlinking aspects of research data, e.g., by using ontologies and knowledge\u0000graphs further enhances findability and reusability. This work presents a\u0000framework for creating and maintaining a knowledge graph specifically for\u0000low-temperature plasma (LTP) science and technology. The framework leverages a\u0000domain-specific ontology called Plasma-O, along with the VIVO software as a\u0000platform for semantic information management in LTP research. While some\u0000research fields are already prepared to use ontologies and knowledge graphs for\u0000information management, their application in LTP research is nascent. This work\u0000aims to bridge this gap by providing a framework that not only improves\u0000research data management but also fosters community participation in building\u0000the domain-specific ontology and knowledge graph based on the published\u0000materials. The results may also support other research fields in the practical\u0000use of knowledge graphs for semantic information management.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257454","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The external-kink stability of a toroidal plasma surrounded by a rigid resistive wall is investigated. The well-known analysis of Haney & Freidberg is rigorously extended to allow for a wall that is sufficiently thick that the thin-shell approximation does not necessarily hold. A generalized Haney-Freidberg formula for the growth-rate of the resistive wall mode is obtained. Thick-wall effects do not change the marginal stability point of the mode, but introduce an interesting asymmetry between growing and decaying modes. Growing modes have growth-rates that exceed those predicted by the original Haney-Freidberg formula. On the other hand, decaying modes have decay-rates that are less than those predicted by the original formula. The well-known Hu-Betti formula for the rotational stabilization of the resistive wall mode is also generalized to take thick-wall effects into account. Increasing wall thickness facilitates the rotational stabilization of the mode, because it decreases the critical toroidal electromagnetic torque that the wall must exert on the plasma. On the other hand, the real frequency of the mode at the marginal stability point increases with increasing wall thickness.
{"title":"An Extended Variational Method for the Resistive Wall Mode in Toroidal Plasma Confinement Devices","authors":"R. Fitzpatrick","doi":"arxiv-2409.11298","DOIUrl":"https://doi.org/arxiv-2409.11298","url":null,"abstract":"The external-kink stability of a toroidal plasma surrounded by a rigid\u0000resistive wall is investigated. The well-known analysis of Haney & Freidberg is\u0000rigorously extended to allow for a wall that is sufficiently thick that the\u0000thin-shell approximation does not necessarily hold. A generalized\u0000Haney-Freidberg formula for the growth-rate of the resistive wall mode is\u0000obtained. Thick-wall effects do not change the marginal stability point of the\u0000mode, but introduce an interesting asymmetry between growing and decaying\u0000modes. Growing modes have growth-rates that exceed those predicted by the\u0000original Haney-Freidberg formula. On the other hand, decaying modes have\u0000decay-rates that are less than those predicted by the original formula. The well-known Hu-Betti formula for the rotational stabilization of the\u0000resistive wall mode is also generalized to take thick-wall effects into\u0000account. Increasing wall thickness facilitates the rotational stabilization of\u0000the mode, because it decreases the critical toroidal electromagnetic torque\u0000that the wall must exert on the plasma. On the other hand, the real frequency\u0000of the mode at the marginal stability point increases with increasing wall\u0000thickness.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We develop a new algorithm to estimate the temperature of a nonneutral plasma in a Penning-Malmberg trap. The algorithm analyzes data obtained by slowly lowering a voltage that confines one end of the plasma and collecting escaping charges, and is a maximum likelihood estimator based on a physically-motivated model of the escape protocol presented in Beck [1990]. Significantly, our algorithm may be used on single-count data, allowing for improved fits with low numbers of escaping electrons. This is important for low-temperature plasmas such as those used in antihydrogen trapping. We perform a Monte Carlo simulation of our algorithm, and assess its robustness to intrinsic shot noise and external noise. Approximately 100 particle counts are needed for an accuracy of +/-10% -- this provides a lower bound for measurable plasma temperatures of approximately 3 K for plasmas of length 1 cm.
{"title":"Limitations from charge quantization on the parallel temperature diagnostic of nonneutral plasmas","authors":"Adrianne Zhong, Joel Fajans, Jonathan S. Wurtele","doi":"arxiv-2409.11610","DOIUrl":"https://doi.org/arxiv-2409.11610","url":null,"abstract":"We develop a new algorithm to estimate the temperature of a nonneutral plasma\u0000in a Penning-Malmberg trap. The algorithm analyzes data obtained by slowly\u0000lowering a voltage that confines one end of the plasma and collecting escaping\u0000charges, and is a maximum likelihood estimator based on a physically-motivated\u0000model of the escape protocol presented in Beck [1990]. Significantly, our\u0000algorithm may be used on single-count data, allowing for improved fits with low\u0000numbers of escaping electrons. This is important for low-temperature plasmas\u0000such as those used in antihydrogen trapping. We perform a Monte Carlo\u0000simulation of our algorithm, and assess its robustness to intrinsic shot noise\u0000and external noise. Approximately 100 particle counts are needed for an\u0000accuracy of +/-10% -- this provides a lower bound for measurable plasma\u0000temperatures of approximately 3 K for plasmas of length 1 cm.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257416","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thanks to advances in plasma science and enabling technology, mirror machines are being reconsidered for fusion power plants and as possible fusion volumetric neutron sources. However cross-field transport and turbulence in mirrors remains relatively understudied compared to toroidal devices. Turbulence and transport in mirror configurations were studied utilizing the flexible magnetic geometry of the Large Plasma Device (LAPD). Multiple mirror ratios from $ M = 1 $ to $ M = 2.68 $ and three mirror-cell lengths from $L = 3.51 $m to $ L = 10.86 $m were examined. Langmuir and magnetic probes were used to measure profiles of density, temperature, potential, and magnetic field. The fluctuation-driven $ tilde{ E } times B $ particle flux was calculated from these quantities. Two probe correlation techniques were used to infer wavenumbers and two-dimensional structure. Cross-field particle flux and density fluctuation power decreased with increased mirror ratio. Core density and temperatures remain similar with mirror ratio, but radial line-integrated density increased. The physical expansion of the plasma in the mirror cell by using a higher field in the source region may have led to reduced density fluctuation power through the increased gradient scale length. This increased scale length reduced the growth rate and saturation level of rotational interchange and drift-like instabilities. Despite the introduction of magnetic curvature, no evidence of mirror driven instabilities -- interchange, velocity space, or otherwise -- were observed. For curvature-induced interchange, many possible stabilization mechanisms were present, suppressing the visibility of the instability.
由于等离子体科学和使能技术的进步，人们正在重新考虑将镜像设备用于核聚变发电厂，并将其作为可能的核聚变体积中子源。利用大型等离子体装置（LAPD）的灵活磁性几何结构，研究了镜像配置中的湍流和传输问题。研究了从 $ M = 1 $ 到 $ M = 2.68 $ 的多个镜像比和从 $L = 3.51 $m 到 $L = 10.86 $m 的三个镜像单元长度。使用朗缪尔探针和磁探针测量了密度、温度、电势和磁场曲线。波动驱动的 $ tilde{ E } times B $ 粒子通量times B $粒子通量是根据这些数据计算出来的。两种探针相关技术被用来推断波数和二维结构。跨场粒子通量和密度波动功率随着镜像比的增加而减小。核心密度和温度与镜像比保持相似，但径向线积分密度有所增加。通过在源区使用更高的磁场，镜室中的等离子体发生了物理膨胀，这可能导致密度波动功率因梯度尺度长度的增加而降低。尺度长度的增加降低了旋转交换和漂移类不稳定性的增长速度和饱和水平。尽管引入了磁曲率，但没有观察到镜像驱动的不稳定性--交换、速度空间或其他。对于曲率引起的互换，存在许多可能的稳定机制，抑制了不稳定性的可见性。
{"title":"Turbulence and transport in mirror geometries in the Large Plasma Device","authors":"Phil Travis, Troy Carter","doi":"arxiv-2409.11557","DOIUrl":"https://doi.org/arxiv-2409.11557","url":null,"abstract":"Thanks to advances in plasma science and enabling technology, mirror machines\u0000are being reconsidered for fusion power plants and as possible fusion\u0000volumetric neutron sources. However cross-field transport and turbulence in\u0000mirrors remains relatively understudied compared to toroidal devices.\u0000Turbulence and transport in mirror configurations were studied utilizing the\u0000flexible magnetic geometry of the Large Plasma Device (LAPD). Multiple mirror\u0000ratios from $ M = 1 $ to $ M = 2.68 $ and three mirror-cell lengths from $L =\u00003.51 $m to $ L = 10.86 $m were examined. Langmuir and magnetic probes were used\u0000to measure profiles of density, temperature, potential, and magnetic field. The\u0000fluctuation-driven $ tilde{ E } times B $ particle flux was calculated from\u0000these quantities. Two probe correlation techniques were used to infer\u0000wavenumbers and two-dimensional structure. Cross-field particle flux and\u0000density fluctuation power decreased with increased mirror ratio. Core density\u0000and temperatures remain similar with mirror ratio, but radial line-integrated\u0000density increased. The physical expansion of the plasma in the mirror cell by\u0000using a higher field in the source region may have led to reduced density\u0000fluctuation power through the increased gradient scale length. This increased\u0000scale length reduced the growth rate and saturation level of rotational\u0000interchange and drift-like instabilities. Despite the introduction of magnetic\u0000curvature, no evidence of mirror driven instabilities -- interchange, velocity\u0000space, or otherwise -- were observed. For curvature-induced interchange, many\u0000possible stabilization mechanisms were present, suppressing the visibility of\u0000the instability.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. K. Warrens, N. P. Inman, G. M. Gorman, B. T. Husick, S. J. Bradshaw, T. C. Killian
We present observations of wave steepening and signatures of shock formation during expansion of ultracold neutral plasmas formed with an initial density distribution that is centrally peaked and decays exponentially with distance. The plasma acceleration and velocity decrease at large distance from the plasma center, leading to central ions overtaking ions in the outer regions and the development of a steepening front that is narrow compared to the size of the plasma. The density and velocity change dramatically across the front, and significant heating of the ions is observed in the region of steepest gradients. For a reasonable estimate of electron temperature, the relative velocity of ions on either side of the front modestly exceeds the local sound speed (Mach number $M gtrsim 1$). This indicates that by sculpting steep density gradients, it is possible to create the conditions for shock formation, or very close to it, opening a new avenue of research for ultracold neutral plasmas.
{"title":"Wave Steepening and Shock Formation in Ultracold Neutral Plasmas","authors":"M. K. Warrens, N. P. Inman, G. M. Gorman, B. T. Husick, S. J. Bradshaw, T. C. Killian","doi":"arxiv-2409.11319","DOIUrl":"https://doi.org/arxiv-2409.11319","url":null,"abstract":"We present observations of wave steepening and signatures of shock formation\u0000during expansion of ultracold neutral plasmas formed with an initial density\u0000distribution that is centrally peaked and decays exponentially with distance.\u0000The plasma acceleration and velocity decrease at large distance from the plasma\u0000center, leading to central ions overtaking ions in the outer regions and the\u0000development of a steepening front that is narrow compared to the size of the\u0000plasma. The density and velocity change dramatically across the front, and\u0000significant heating of the ions is observed in the region of steepest\u0000gradients. For a reasonable estimate of electron temperature, the relative\u0000velocity of ions on either side of the front modestly exceeds the local sound\u0000speed (Mach number $M gtrsim 1$). This indicates that by sculpting steep\u0000density gradients, it is possible to create the conditions for shock formation,\u0000or very close to it, opening a new avenue of research for ultracold neutral\u0000plasmas.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"76 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Emanuele Sobacchi, Masanori Iwamoto, Lorenzo Sironi, Tsvi Piran
Fast radio bursts (FRBs) are bright extragalactic transients likely produced by magnetars. We study the propagation of FRBs in magnetar winds, assuming that the wind is strongly magnetized and composed of electron-positron pairs. We focus on the regime where the strength parameter of the radio wave, $a_0$, is larger than unity, and the wave frequency, $omega_0$, is larger than the Larmor frequency in the background magnetic field, $omega_{rm L}$. We show that strong radio waves with $a_0>1$ are able to propagate when $omega_0 > a_0omega_{rm L}$, as the plasma current is a linear function of the wave electric field. The dispersion relation is independent of the wave strength parameter when $omega_0 > a_0omega_{rm L}$. Instead, radio waves could be damped when $omega_0 < a_0omega_{rm L}$, as a significant fraction of the wave energy is used to compress the plasma and amplify the background magnetic field. Our results suggest that FRBs should be produced at large distances from the magnetar (i.e., $R>10^{12}{rm; cm}$, where the condition $omega_0 > a_0omega_{rm L}$ is satisfied). Alternatively, the structure of the magnetar wind should be strongly modified during a flare to allow the escape of FRBs produced at radii $R<10^{12}{rm; cm}$.
{"title":"Escape of fast radio bursts from magnetars","authors":"Emanuele Sobacchi, Masanori Iwamoto, Lorenzo Sironi, Tsvi Piran","doi":"arxiv-2409.10732","DOIUrl":"https://doi.org/arxiv-2409.10732","url":null,"abstract":"Fast radio bursts (FRBs) are bright extragalactic transients likely produced\u0000by magnetars. We study the propagation of FRBs in magnetar winds, assuming that\u0000the wind is strongly magnetized and composed of electron-positron pairs. We\u0000focus on the regime where the strength parameter of the radio wave, $a_0$, is\u0000larger than unity, and the wave frequency, $omega_0$, is larger than the\u0000Larmor frequency in the background magnetic field, $omega_{rm L}$. We show\u0000that strong radio waves with $a_0>1$ are able to propagate when $omega_0 >\u0000a_0omega_{rm L}$, as the plasma current is a linear function of the wave\u0000electric field. The dispersion relation is independent of the wave strength\u0000parameter when $omega_0 > a_0omega_{rm L}$. Instead, radio waves could be\u0000damped when $omega_0 < a_0omega_{rm L}$, as a significant fraction of the\u0000wave energy is used to compress the plasma and amplify the background magnetic\u0000field. Our results suggest that FRBs should be produced at large distances from\u0000the magnetar (i.e., $R>10^{12}{rm; cm}$, where the condition $omega_0 >\u0000a_0omega_{rm L}$ is satisfied). Alternatively, the structure of the magnetar\u0000wind should be strongly modified during a flare to allow the escape of FRBs\u0000produced at radii $R<10^{12}{rm; cm}$.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The entropy of strongly coupled Yukawa fluids is discussed from several perspectives. First, it is demonstrated that a vibrational paradigm of atomic dynamics in dense fluids can be used to obtain a simple and accurate estimate of the entropy without any adjustable parameters. Second, it is explained why a quasiuniversal value of the excess entropy of simple fluids at the freezing point should be expected, and it is demonstrated that a remaining very weak dependence of the freezing point entropy on the screening parameter in the Yukawa fluid can be described by a simple linear function. Third, a scaling of the excess entropy with the freezing temperature is examined, a modified form of the Rosenfeld-Tarazona scaling is put forward, and some consequences are briefly discussed. Fourth, the location of the Frenkel line on the phase diagram of Yukawa systems is discussed in terms of the excess entropy and compared with some predictions made in the literature. Fifth, the excess entropy scaling of the transport coefficients (self-diffusion, viscosity, and thermal conductivity) is reexamined using the contemporary datasets for the transport properties of Yukawa fluids. The results could be of particular interest in the context of complex (dusty) plasmas, colloidal suspensions, electrolytes, and other related systems with soft pairwise interactions.
{"title":"Excess entropy of strongly coupled Yukawa fluids","authors":"Sergey Khrapak","doi":"arxiv-2409.10645","DOIUrl":"https://doi.org/arxiv-2409.10645","url":null,"abstract":"The entropy of strongly coupled Yukawa fluids is discussed from several\u0000perspectives. First, it is demonstrated that a vibrational paradigm of atomic\u0000dynamics in dense fluids can be used to obtain a simple and accurate estimate\u0000of the entropy without any adjustable parameters. Second, it is explained why a\u0000quasiuniversal value of the excess entropy of simple fluids at the freezing\u0000point should be expected, and it is demonstrated that a remaining very weak\u0000dependence of the freezing point entropy on the screening parameter in the\u0000Yukawa fluid can be described by a simple linear function. Third, a scaling of\u0000the excess entropy with the freezing temperature is examined, a modified form\u0000of the Rosenfeld-Tarazona scaling is put forward, and some consequences are\u0000briefly discussed. Fourth, the location of the Frenkel line on the phase\u0000diagram of Yukawa systems is discussed in terms of the excess entropy and\u0000compared with some predictions made in the literature. Fifth, the excess\u0000entropy scaling of the transport coefficients (self-diffusion, viscosity, and\u0000thermal conductivity) is reexamined using the contemporary datasets for the\u0000transport properties of Yukawa fluids. The results could be of particular\u0000interest in the context of complex (dusty) plasmas, colloidal suspensions,\u0000electrolytes, and other related systems with soft pairwise interactions.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"75 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257455","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Niannian Wu, Zongyu Yang, Rongpeng Li, Ning Wei, Yihang Chen, Qianyun Dong, Jiyuan Li, Guohui Zheng, Xinwen Gong, Feng Gao, Bo Li, Min Xu, Zhifeng Zhao, Wulyu Zhong
The drive to control tokamaks, a prominent technology in nuclear fusion, is essential due to its potential to provide a virtually unlimited source of clean energy. Reinforcement learning (RL) promises improved flexibility to manage the intricate and non-linear dynamics of the plasma encapsulated in a tokamak. However, RL typically requires substantial interaction with a simulator capable of accurately evolving the high-dimensional plasma state. Compared to first-principle-based simulators, whose intense computations lead to sluggish RL training, we devise an effective method to acquire a fully data-driven simulator, by mitigating the arising compounding error issue due to the underlying autoregressive nature. With high accuracy and appealing extrapolation capability, this high-fidelity dynamics model subsequently enables the rapid training of a qualified RL agent to directly generate engineering-reasonable magnetic coil commands, aiming at the desired long-term targets of plasma current and last closed flux surface. Together with a surrogate magnetic equilibrium reconstruction model EFITNN, the RL agent successfully maintains a $100$-ms, $1$ kHz trajectory control with accurate waveform tracking on the HL-3 tokamak. Furthermore, it also demonstrates the feasibility of zero-shot adaptation to changed triangularity targets, confirming the robustness of the developed data-driven dynamics model. Our work underscores the advantage of fully data-driven dynamics models in yielding RL-based trajectory control policies at a sufficiently fast pace, an anticipated engineering requirement in daily discharge practices for the upcoming ITER device.
{"title":"High-Fidelity Data-Driven Dynamics Model for Reinforcement Learning-based Magnetic Control in HL-3 Tokamak","authors":"Niannian Wu, Zongyu Yang, Rongpeng Li, Ning Wei, Yihang Chen, Qianyun Dong, Jiyuan Li, Guohui Zheng, Xinwen Gong, Feng Gao, Bo Li, Min Xu, Zhifeng Zhao, Wulyu Zhong","doi":"arxiv-2409.09238","DOIUrl":"https://doi.org/arxiv-2409.09238","url":null,"abstract":"The drive to control tokamaks, a prominent technology in nuclear fusion, is\u0000essential due to its potential to provide a virtually unlimited source of clean\u0000energy. Reinforcement learning (RL) promises improved flexibility to manage the\u0000intricate and non-linear dynamics of the plasma encapsulated in a tokamak.\u0000However, RL typically requires substantial interaction with a simulator capable\u0000of accurately evolving the high-dimensional plasma state. Compared to\u0000first-principle-based simulators, whose intense computations lead to sluggish\u0000RL training, we devise an effective method to acquire a fully data-driven\u0000simulator, by mitigating the arising compounding error issue due to the\u0000underlying autoregressive nature. With high accuracy and appealing\u0000extrapolation capability, this high-fidelity dynamics model subsequently\u0000enables the rapid training of a qualified RL agent to directly generate\u0000engineering-reasonable magnetic coil commands, aiming at the desired long-term\u0000targets of plasma current and last closed flux surface. Together with a\u0000surrogate magnetic equilibrium reconstruction model EFITNN, the RL agent\u0000successfully maintains a $100$-ms, $1$ kHz trajectory control with accurate\u0000waveform tracking on the HL-3 tokamak. Furthermore, it also demonstrates the\u0000feasibility of zero-shot adaptation to changed triangularity targets,\u0000confirming the robustness of the developed data-driven dynamics model. Our work\u0000underscores the advantage of fully data-driven dynamics models in yielding\u0000RL-based trajectory control policies at a sufficiently fast pace, an\u0000anticipated engineering requirement in daily discharge practices for the\u0000upcoming ITER device.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"41 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. P. Kennedy, M. Coughlan, C. R. J. Fitzpatrick, H. M. Huddleston, J. Smyth, N. Breslin, H. Donnelly, C. Arthur, B. Villagomez, O. N. Rosmej, F. Currell, L. Stella, D. Riley, M. Zepf, M. Yeung, C. L. S. Lewis, B. Dromey
Ionising radiation interactions in matter can trigger a cascade of processes that underpin long-lived damage in the medium. To date, however, a lack of suitable methodologies has precluded our ability to understand the role that material nanostructure plays in this cascade. Here, we use transient photoabsorption to track the lifetime of free electrons (t_c) in bulk and nanostructured SiO2 (aerogel) irradiated by picosecond-scale (10^-12 s) bursts of X-rays and protons from a laser-driven accelerator. Optical streaking reveals a sharp increase in t_c from < 1 ps to > 50 ps over a narrow average density (p_av) range spanning the expected phonon-fracton crossover in aerogels. Numerical modelling suggests that this discontinuity can be understood by a quenching of rapid, phonon-assisted recovery in irradiated nanostructured SiO_2. This is shown to lead to an extended period of enhanced energy density in the excited electron population. Overall, these results open a direct route to tracking how low-level processes in complex systems can underpin macroscopically observed phenomena and, importantly, the conditions that permit them to emerge.
{"title":"Real-time observation of frustrated ultrafast recovery from ionisation in nanostructured SiO2 using laser driven accelerators","authors":"J. P. Kennedy, M. Coughlan, C. R. J. Fitzpatrick, H. M. Huddleston, J. Smyth, N. Breslin, H. Donnelly, C. Arthur, B. Villagomez, O. N. Rosmej, F. Currell, L. Stella, D. Riley, M. Zepf, M. Yeung, C. L. S. Lewis, B. Dromey","doi":"arxiv-2409.08689","DOIUrl":"https://doi.org/arxiv-2409.08689","url":null,"abstract":"Ionising radiation interactions in matter can trigger a cascade of processes\u0000that underpin long-lived damage in the medium. To date, however, a lack of\u0000suitable methodologies has precluded our ability to understand the role that\u0000material nanostructure plays in this cascade. Here, we use transient\u0000photoabsorption to track the lifetime of free electrons (t_c) in bulk and\u0000nanostructured SiO2 (aerogel) irradiated by picosecond-scale (10^-12 s) bursts\u0000of X-rays and protons from a laser-driven accelerator. Optical streaking\u0000reveals a sharp increase in t_c from < 1 ps to > 50 ps over a narrow average\u0000density (p_av) range spanning the expected phonon-fracton crossover in\u0000aerogels. Numerical modelling suggests that this discontinuity can be\u0000understood by a quenching of rapid, phonon-assisted recovery in irradiated\u0000nanostructured SiO_2. This is shown to lead to an extended period of enhanced\u0000energy density in the excited electron population. Overall, these results open\u0000a direct route to tracking how low-level processes in complex systems can\u0000underpin macroscopically observed phenomena and, importantly, the conditions\u0000that permit them to emerge.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"213 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142257462","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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