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1. Surface and sub-surface modifications of copper electrodes exposed to high-field conditioning at cryogenic temperatures

Author

Jacewicz, Marek, Profatilova, Iaroslava, Szaniawski, Piotr, Popov, Inna, Ashkenazy, Yinon, Calatroni, Sergio, and Wuensch, Walter

Subjects
Physics - Accelerator Physics, Condensed Matter - Materials Science, Physics - Plasma Physics
Abstract

In order to investigate the dependence of conditioning and field-holding on temperature, three pairs of copper electrodes underwent high voltage conditioning with direct current (DC) pulses while kept at a single temperature, unique for each set (300~K, 30~K and 10~K), until saturation field for each set was found. The sets conditioned at cold showed a significant increase in the field holding capability, reaching fields up to 147 MV/m after tens of millions of pulses and very few breakdowns (BDs). We interpret this as an indication of the conditioning effect being due to high field pulsing rather than exposure to BDs. The effect of the warm and cold conditioning was investigated with high-resolution microscopy, characterizing the BD spots on the anode and cathode according to their morphology and with scanning transmission electron microscopy (STEM) analyzing the changes in the sub-surface regions. Atypical BD spot features were found on the cryogenically conditioned cathode surfaces, with very shallow craters of a star-like shape. The number of atypical spots increased with decreased temperatures, reaching 26 and 53 percent of the total number of spots at 30~K and 10~K, respectively. A hypothesis explaining the formation of these features is also presented. The very different morphology of the anode and cathode BD spots is presented in detail that suggesting an unknown shielding mechanism that prevents the center of the anode spot from melting. These results provide important experimental input for the development of quantitative theories and models for BD initiation and inter-electrode plasma formation.

Published
2024

2. Mechanical tuning of a rectangular axion haloscope operating around 8.4 GHz

Author

Golm, Jessica, García-Barceló, Jose María, Calatroni, Sergio, Wuensch, Walter, and Döbrich, Babette

Subjects
Physics - Instrumentation and Detectors, High Energy Physics - Experiment
Abstract

The axion haloscope is the currently most sensitive method to probe the vanishingly small coupling of this prominent Dark Matter candidate to photons. To scan a sizeable axion Dark Matter parameter space, the cavities that make up the haloscope need to be tuned efficiently. In this article, we describe a novel technique to tune axion haloscopes around $8.4$ GHz in a purely mechanical manner without the use of dielectrics. We achieve tuning by introducing a gap along the cavity geometry. Losses are added due to the leaking of the field out of the structure only if the gap becomes too large concerning the total width. A tuning range of around $600$ MHz is achieved, depending on the environmental conditions. We present the results of a corresponding prototype and outline prospects to further develop this technique.

Published
2023

3. Local power coupling as a predictor of high-gradient breakdown performance

Author

Paszkiewicz, Jan, Grudiev, Alexej, and Wuensch, Walter

Subjects
Physics - Accelerator Physics
Abstract

A novel quantity for predicting the high-gradient performance of radio frequency accelerating structures is presented. The quantity is motivated, derived and compared with earlier high-gradient limits and experiments. This new method models a nascent RF breakdown as a current-carrying antenna and calculates the coupling of the antenna to an RF power source. With the help of an electron emission model to describe a nascent breakdown, the antenna model describes how a breakdown modifies the local surface electric field before it fully develops in any given structure geometry. For the structure geometries that this method was applied to, it was found that the calculated breakdown-loaded electric field was well-correlated with observed spatial breakdown distributions, and gave consistent values for the maximum breakdown-limited accelerating gradient between different geometries., Comment: 16 pages, 22 figures. Submitted to Physical Review Accelerators and Beams

Published
2022

4. Comparative study of H accumulation in differently oriented grains of Cu

Author

Lopez-Cazalilla, A., Serafim, Catarina, Djurabekova, F., Perez-Fontenla, Ana Teresa, Calatroni, Sergio, and Wuensch, Walter

Subjects
Condensed Matter - Materials Science
Abstract

When metal surfaces are exposed to hydrogen ion irradiation, the light ions are expected to penetrate deep into the material and dissolve in the matrix. However, these atoms are seen to cause significant modification of surfaces, indicating that they accumulate in vicinity of the surface. The process known as blistering may reduces the vacuum dielectric strength above the metal surface, which shows a dense population of surface blisters. In this paper, we investigate how a bubble can grow under the pressure exerted by hydrogen atoms on the walls of the bubble and how this affect to the surface of Cu, whether an external electric field is applied or not.

Published
2022

5. Explainable Machine Learning for Breakdown Prediction in High Gradient RF Cavities

Author

Obermair, Christoph, Cartier-Michaud, Thomas, Apollonio, Andrea, Millar, William, Felsberger, Lukas, Fischl, Lorenz, Bovbjerg, Holger Severin, Wollmann, Daniel, Wuensch, Walter, Catalan-Lasheras, Nuria, Boronat, Marçà, Pernkopf, Franz, and Burt, Graeme

Subjects
Physics - Accelerator Physics, Computer Science - Machine Learning
Abstract

The occurrence of vacuum arcs or radio frequency (rf) breakdowns is one of the most prevalent factors limiting the high-gradient performance of normal conducting rf cavities in particle accelerators. In this paper, we search for the existence of previously unrecognized features related to the incidence of rf breakdowns by applying a machine learning strategy to high-gradient cavity data from CERN's test stand for the Compact Linear Collider (CLIC). By interpreting the parameters of the learned models with explainable artificial intelligence (AI), we reverse-engineer physical properties for deriving fast, reliable, and simple rule-based models. Based on 6 months of historical data and dedicated experiments, our models show fractions of data with a high influence on the occurrence of breakdowns. Specifically, it is shown that the field emitted current following an initial breakdown is closely related to the probability of another breakdown occurring shortly thereafter. Results also indicate that the cavity pressure should be monitored with increased temporal resolution in future experiments, to further explore the vacuum activity associated with breakdowns.

Published
2022
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6. Hot electron enhanced photoemission from laser fabricated plasmonic photocathodes

Author

Martinez-Calderon Miguel, Groussin Baptiste, Bjelland Victoria, Chevallay Eric, Fedosseev Valentin N., Himmerlich Marcel, Lorenz Pierre, Manjavacas Alejandro, Marsh Bruce A., Neupert Holger, Rossel Ralf E., Wuensch Walter, and Granados Eduardo

Subjects
hot electrons, plasmonics, photoemission, accelerators, Physics, QC1-999
Abstract

Photocathodes are key elements in high-brightness electron sources and ubiquitous in the operation of large-scale accelerators, although their operation is often limited by their quantum efficiency and lifetime. Here, we propose to overcome these limitations by utilizing direct-laser nanostructuring techniques on copper substrates, improving their efficiency and robustness for next-generation electron photoinjectors. When the surface of a metal is nanoengineered with patterns and particles much smaller than the optical wavelength, it can lead to the excitation of localized surface plasmons that produce hot electrons, ultimately contributing to the overall charge produced. In order to quantify the performance of laser-produced plasmonic photocathodes, we measured their quantum efficiency in a typical electron gun setup. Our experimental results suggest that plasmon-induced hot electrons lead to a significant increase in quantum efficiency, showing an overall charge enhancement factor of at least 4.5 and up to 25. A further increase in their efficiency was observed when combined with semiconductor thin-films deposited over the laser processed surfaces, pointing at potential pathways for further optimization. We demonstrate that simple laser-produced plasmonic photocathodes outperform standard metallic photocathodes, and can be directly produced in-situ at the electron gun level in vacuum environments and without any disruptive intervention. This approach could lead to unprecedented efficient and continuous operation of electron sources, and is useful in many applications across scientific disciplines requiring high average and peak current electron beams.

Published
2023
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7. Effect of dc voltage pulsing on high-vacuum electrical breakdowns near Cu surfaces

Author

Saressalo, Anton, Profatilova, Iaroslava, Millar, William L., Kyritsakis, Andreas, Calatroni, Sergio, Wuensch, Walter, and Djurabekova, Flyura

Subjects
Physics - Instrumentation and Detectors, Condensed Matter - Materials Science, Physics - Accelerator Physics
Abstract

Vacuum electrical breakdowns, also known as vacuum arcs, are a limiting factor in many devices that are based on application of high electric fields near their component surfaces. Understanding of processes that lead to breakdown events may help mitigating their appearance and suggest ways for improving operational efficiency of power-consuming devices. Stability of surface performance at a given value of the electric field is affected by the conditioning state, i.e. how long the surface was exposed to this field. Hence, optimization of the surface conditioning procedure can significantly speed up the preparatory steps for high-voltage applications. In this article, we use pulsed dc systems to optimize the surface conditioning procedure of copper electrodes, focusing on the effects of voltage recovery after breakdowns, variable repetition rates as well as long waiting times between pulsing runs. Despite the differences in the experimental scales, ranging from $10^{-4}$ s between pulses, up to pulsing breaks of $10^5$ s, the experiments show that the longer the idle time between the pulses, the more probable it is that the next pulse produces a breakdown. We also notice that secondary breakdowns, i.e. those which correlate with the previous ones, take place mainly during the voltage recovery stage. We link these events with deposition of residual atoms from vacuum on the electrode surfaces. Minimizing the number of pauses during the voltage recovery stage reduces power losses due to secondary breakdown events improving efficiency of the surface conditioning., Comment: 14 pages, 11 figures. Submitted to Physical Review Accelerators and Beams

Published
2020
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8. Classification of vacuum arc breakdowns in a pulsed DC system

Author

Saressalo, Anton, Profatilova, Iaroslava, Kyritsakis, Andreas, Paszkiewicz, Jan, Calatroni, Sergio, Wuensch, Walter, and Djurabekova, Flyura

Subjects
Physics - Instrumentation and Detectors, Condensed Matter - Materials Science
Abstract

Understanding the microscopic phenomena behind vacuum arc ignition and generation is crucial for being able to control the breakdown rate, thus improving the effectiveness of many high-voltage applications where frequent breakdowns limit the operation. In this work, statistical properties of various aspects of breakdown, such as the number of pulses between breakdowns, breakdown locations and crater sizes are studied independently with almost identical Pulsed DC Systems at the University of Helsinki and in CERN. In high-gradient experiments, copper electrodes with parallel plate capacitor geometry, undergo thousands of breakdowns. The results support the classification of the events into primary and secondary breakdowns, based on the distance and number of pulses between two breakdowns. Primary events follow a power law on the log--log scale with the slope $\alpha \approx 1.33$, while the secondaries are highly dependent on the pulsing parameters., Comment: 11 pages, 13 figures

Published
2019
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9. Vacuum electrical breakdown conditioning study in a parallel plate electrode pulsed DC system

Author

Korsbäck, Anders, Morales, Laura Mercadé, Profatilova, Iaroslava, Djurabekova, Flyura, Castro, Enrique Rodriguez, Wuensch, Walter, Ahlgren, Tommy, and Calatroni, Sergio

Subjects
Physics - Applied Physics
Abstract

Conditioning of a metal structure in a high-voltage system is the progressive development of resistance to vacuum arcing over the operational life of the system. This is, for instance, seen during the initial operation of radio frequency (rf) cavities in particle accelerators. It is a relevant topic for any technology where breakdown limits performance, and where conditioning continues for a significant duration of system runtime. Projected future linear accelerators require structures with accelerating gradients of up to 100 MV/m. Currently, this performance level is only achievable after a multi-month conditioning period. In this work, a pulsed DC system applying voltage pulses over parallel disk electrodes was used to study the conditioning process, with the objective of obtaining insight into its underlying mechanics, and ultimately, to find ways to shorten the conditioning process. Two kinds of copper electrodes were tested: As-prepared machine-turned electrodes ("hard" copper), and electrodes that additionally had been subjected to high temperature treatments ("soft" copper). The conditioning behaviour of the soft electrodes was found to be similar to that of comparably treated accelerating structures, indicating a similar conditioning process. The hard electrodes reached the same ultimate performance as the soft electrodes much faster, with a difference of more than an order of magnitude in the number of applied voltage pulses. Two distinctly different distributions of breakdown locations were observed on the two types of electrodes. Considered together, our results support the crystal structure dislocation theory of breakdown, and suggest that the conditioning of copper in high field systems such as rf accelerating structures is dominated by material hardening.

Published
2019
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10. Axion Searches with Microwave Filters: the RADES project

Author

Melcón, Alejandro Álvarez, Cuendis, Sergio Arguedas, Cogollos, Cristian, Díaz-Morcillo, Alejandro, Döbrich, Babette, Gallego, Juan Daniel, Gimeno, Benito, Irastorza, Igor G., Lozano-Guerrero, Antonio José, Malbrunot, Chloé, Navarro, Pablo, Garay, Carlos Peña, Redondo, Javier, Vafeiadis, Theodoros, and Wuensch, Walter

Subjects
High Energy Physics - Experiment, High Energy Physics - Phenomenology
Abstract

We propose, design and construct a variant of the conventional axion haloscope concept that could be competitive in the search for dark matter axions of masses in the decade 10-100 $\mu$eV. Theses masses are located somewhat above the mass range in which existing experiments have reached sensitivity to benchmark QCD axion models. Our haloscope consists of an array of small microwave cavities connected by rectangular irises, in an arrangement commonly used in radio-frequency filters. The size of the unit cavity determines the main resonant frequency, while the possibility to connect a {large} number of cavities allows to reach large detection volumes. We develop the theoretical framework of the detection concept, and present design prescriptions to optimize detection capabilities. We describe the design and realization of a first small-scale prototype of this concept, called Relic Axion Detector Exploratory Setup (RADES). It consists of a copper-coated stainless steel five-cavities microwave filter with the detecting mode operating at around 8.4 GHz. This structure has been electromagnetically characterized at 2 K and 298 K, and it is now placed in ultra-high vacuum in one of the twin-bores of the 9 T CAST dipole magnet at CERN. We describe the data acquisition system developed for relic axion detection, and present preliminary results of the electromagnetic properties of the microwave filter, which show the potential of filters to reach QCD axion window sensitivity at X-band frequencies., Comment: approved for publication in JCAP, version after referee comments

Published
2018
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13. Laser-induced asymmetric faceting and growth of nano-protrusion on a tungsten tip

Author

Yanagisawa, Hirofumi, Zadin, Vahur, Kunze, Karsten, Hafner, Christian, Aabloo, Alvo, Kim, Dong Eon, Kling, Matthias F., Djurabekova, Flyura, Osterwalder, Jürg, and Wuensch, Walter

Subjects
Condensed Matter - Materials Science
Abstract

Irradiation of a sharp tungsten tip by a femtosecond laser and exposed to a strong DC electric field led to gradual and reproducible surface modifications. By a combination of field emission microscopy and scanning electron microscopy, we observed asymmetric surface faceting with sub-ten nanometer high steps. The presence of well pronounced faceted features mainly on the laser-exposed side implies that the surface modification was driven by a laser-induced transient temperature rise -- on a scale of a couple of picoseconds -- in the tungsten tip apex. Moreover, we identified the formation of a nano-tip a few nanometers high located at one of the corners of a faceted plateau. The results of simulations emulating the experimental conditions, are consistent with the experimental observations. The presented conditions can be used as a new method to fabricate nano-tips of few nm height, which can be used in coherent electron pulses generation. Besides the direct practical application, the results also provide insight into the microscopic mechanisms of light-matter interaction. The apparent growth mechanism of the features may also help to explain the origin of enhanced electron field emission, which leads to vacuum arcs, in high electric-field devices such as radio-frequency particle accelerators., Comment: 6 figures

Published
2016
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14. Hot electron enhanced photoemission from laser fabricated plasmonic photocathodes

Author

Fundación BBVA, Ministerio de Ciencia e Innovación (España), Martinez-Calderon, Miguel [0000-0002-8410-5496], #NODATA#, Granados, Eduardo [0000-0002-6549-9303], Martinez-Calderon, Miguel, Groussin, Baptiste, Bjelland, Victoria, Chevallay, Eric, Fedosseev, Valentin N., Himmerlich, Marcel, Lorenz, Pierre, Manjavacas, Alejandro, Marsh, Bruce A., Neupert, Holger, Rossel, Ralf E., Wuensch, Walter, Granados, Eduardo, Fundación BBVA, Ministerio de Ciencia e Innovación (España), Martinez-Calderon, Miguel [0000-0002-8410-5496], #NODATA#, Granados, Eduardo [0000-0002-6549-9303], Martinez-Calderon, Miguel, Groussin, Baptiste, Bjelland, Victoria, Chevallay, Eric, Fedosseev, Valentin N., Himmerlich, Marcel, Lorenz, Pierre, Manjavacas, Alejandro, Marsh, Bruce A., Neupert, Holger, Rossel, Ralf E., Wuensch, Walter, and Granados, Eduardo

Abstract

Photocathodes are key elements in high-brightness electron sources and ubiquitous in the operation of large-scale accelerators, although their operation is often limited by their quantum efficiency and lifetime. Here, we propose to overcome these limitations by utilizing direct-laser nanostructuring techniques on copper substrates, improving their efficiency and robustness for next-generation electron photoinjectors. When the surface of a metal is nanoengineered with patterns and particles much smaller than the optical wavelength, it can lead to the excitation of localized surface plasmons that produce hot electrons, ultimately contributing to the overall charge produced. In order to quantify the performance of laser-produced plasmonic photocathodes, we measured their quantum efficiency in a typical electron gun setup. Our experimental results suggest that plasmon-induced hot electrons lead to a significant increase in quantum efficiency, showing an overall charge enhancement factor of at least 4.5 and up to 25. A further increase in their efficiency was observed when combined with semiconductor thin-films deposited over the laser processed surfaces, pointing at potential pathways for further optimization. We demonstrate that simple laser-produced plasmonic photocathodes outperform standard metallic photocathodes, and can be directly produced in-situ at the electron gun level in vacuum environments and without any disruptive intervention. This approach could lead to unprecedented efficient and continuous operation of electron sources, and is useful in many applications across scientific disciplines requiring high average and peak current electron beams.

Published
2024

18. Measurement of the dynamic response of the CERN DC spark system and preliminary estimates of the breakdown turn-on time

Author

Shipman, Nicholas, Calatroni, Sergio, Jones, Roger M., and Wuensch, Walter

Subjects
Physics - Accelerator Physics
Abstract

The new High Repetition Rate (HRR) CERN DC Spark System has been used to investigate the current and voltage time structure of a breakdown. Simulations indicate that vacuum breakdowns develop on ns timescales or even less. An experimental benchmark for this timescale is critical for comparison to simulations. The fast rise time of breakdown may provide some explanation of the particularly high gradients achieved by low group velocity, and narrow bandwidth, accelerating structures such as the T18 and T24. Voltage and current measurements made with the previous system indicated that the transient responses measured were dominated by the inherent capacitances and inductances of the DC spark system itself. The bandwidth limitations of the HRR system are far less severe allowing rise times of approximately 12ns to be measured.

Published
2012

19. Hot electron enhanced photoemission from laser fabricated plasmonic photocathodes.

Author

Martinez-Calderon, Miguel, Groussin, Baptiste, Bjelland, Victoria, Chevallay, Eric, Fedosseev, Valentin N., Himmerlich, Marcel, Lorenz, Pierre, Manjavacas, Alejandro, Marsh, Bruce A., Neupert, Holger, Rossel, Ralf E., Wuensch, Walter, and Granados, Eduardo

Subjects
HOT carriers, PHOTOEMISSION, PLASMONICS, SURFACE plasmons, QUANTUM efficiency, ELECTRON beams, PHOTOCATHODES
Abstract

Photocathodes are key elements in high-brightness electron sources and ubiquitous in the operation of large-scale accelerators, although their operation is often limited by their quantum efficiency and lifetime. Here, we propose to overcome these limitations by utilizing direct-laser nanostructuring techniques on copper substrates, improving their efficiency and robustness for next-generation electron photoinjectors. When the surface of a metal is nanoengineered with patterns and particles much smaller than the optical wavelength, it can lead to the excitation of localized surface plasmons that produce hot electrons, ultimately contributing to the overall charge produced. In order to quantify the performance of laser-produced plasmonic photocathodes, we measured their quantum efficiency in a typical electron gun setup. Our experimental results suggest that plasmon-induced hot electrons lead to a significant increase in quantum efficiency, showing an overall charge enhancement factor of at least 4.5 and up to 25. A further increase in their efficiency was observed when combined with semiconductor thin-films deposited over the laser processed surfaces, pointing at potential pathways for further optimization. We demonstrate that simple laser-produced plasmonic photocathodes outperform standard metallic photocathodes, and can be directly produced in-situ at the electron gun level in vacuum environments and without any disruptive intervention. This approach could lead to unprecedented efficient and continuous operation of electron sources, and is useful in many applications across scientific disciplines requiring high average and peak current electron beams. [ABSTRACT FROM AUTHOR]

Published
2024
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20. A Proposal for a Low‐Frequency Axion Search in the 1–2 μ$\umu$ eV Range and Below with the BabyIAXO Magnet

Author

Ahyoune, Saiyd, primary, Álvarez Melcón, Alejandro, additional, Arguedas Cuendis, Sergio, additional, Calatroni, Sergio, additional, Cogollos, Cristian, additional, Devlin, Jack, additional, Díaz‐Morcillo, Alejandro, additional, Díez‐Ibáñez, David, additional, Döbrich, Babette, additional, Galindo, Javier, additional, Gallego, Juan Daniel, additional, García‐Barceló, Jose María, additional, Gimeno, Benito, additional, Golm, Jessica, additional, Gu, Yikun, additional, Herwig, Louis, additional, Garcia Irastorza, Igor, additional, Lozano‐Guerrero, Antonio Jose, additional, Malbrunot, Chloé, additional, Miralda‐Escudé, Jordi, additional, Monzó‐Cabrera, Juan, additional, Navarro, Pablo, additional, Navarro‐Madrid, Jose Ramón, additional, Redondo, Javier, additional, Reina‐Valero, José, additional, Schmieden, Kristof, additional, Schneemann, Tim, additional, Siodlaczek, Marc, additional, Ulmer, Stefan, additional, and Wuensch, Walter, additional

Published
2023
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21. Thin Film (High Temperature) Superconducting Radiofrequency Cavities for the Search of Axion Dark Matter

Author

European Commission, European Research Council, Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Ciencia e Innovación (España), European Organization for Nuclear Research, Golm, Jessica [0000-0001-9551-5848], Calatroni, Sergio [0000-0002-2769-8029], Döbrich, B. [0000-0002-6008-8601], Gallego, Juan Daniel [0000-0002-7148-5127], García Barceló, J. M. [0000-0003-3565-4189], Irastorza, Igor G. [0000-0003-1163-1687], Lamas, Neil [0000-0002-7092-2807], Malbrunot, C. [0000-0001-6193-6601], Millar, W. Lee [0000-0003-1536-2269], Rosaz, Guillaume J. [0000-0001-5987-128X], Siodlaczek, Marc [0000-0003-1410-2975], Siodlaczek, Marc [0000-0002-2620-7283], Wuensch, Walter [0000-0001-7378-5345], Golm, Jessica, Arguedas Cuendis, S., Calatroni, Sergio, Cogollos, C., Döbrich, B., Gallego, Juan Daniel, García Barceló, José María, Granados, Xavier, Gutierrez Royo, Joffre, Irastorza, Igor G., Koettig, T., Lamas, Neil, Liberadzka-Porret, J., Malbrunot, C., Millar, W. Lee, Navarro, P., Pereira Carlos, Carlota, Puig Molina, Teresa, Rosaz, Guillaume J., Siodlaczek, Marc, Telles, Guilherme, Wuensch, Walter, European Commission, European Research Council, Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Ciencia e Innovación (España), European Organization for Nuclear Research, Golm, Jessica [0000-0001-9551-5848], Calatroni, Sergio [0000-0002-2769-8029], Döbrich, B. [0000-0002-6008-8601], Gallego, Juan Daniel [0000-0002-7148-5127], García Barceló, J. M. [0000-0003-3565-4189], Irastorza, Igor G. [0000-0003-1163-1687], Lamas, Neil [0000-0002-7092-2807], Malbrunot, C. [0000-0001-6193-6601], Millar, W. Lee [0000-0003-1536-2269], Rosaz, Guillaume J. [0000-0001-5987-128X], Siodlaczek, Marc [0000-0003-1410-2975], Siodlaczek, Marc [0000-0002-2620-7283], Wuensch, Walter [0000-0001-7378-5345], Golm, Jessica, Arguedas Cuendis, S., Calatroni, Sergio, Cogollos, C., Döbrich, B., Gallego, Juan Daniel, García Barceló, José María, Granados, Xavier, Gutierrez Royo, Joffre, Irastorza, Igor G., Koettig, T., Lamas, Neil, Liberadzka-Porret, J., Malbrunot, C., Millar, W. Lee, Navarro, P., Pereira Carlos, Carlota, Puig Molina, Teresa, Rosaz, Guillaume J., Siodlaczek, Marc, Telles, Guilherme, and Wuensch, Walter

Abstract

The axion is a hypothetical particle which is a candidate for cold dark matter. Haloscope experiments directly search for these particles in strong magnetic fields with RF cavities as detectors. The Relic Axion Detector Exploratory Setup (RADES) at CERN in particular is searching for axion dark matter in a mass range above 30 $\mu$eV. The figure of merit of our detector depends linearly on the quality factor of the cavity and therefore we are researching the possibility of coating our cavities with different superconducting materials to increase the quality factor. Since the experiment operates in strong magnetic fields of 11 T and more, superconductors with high critical magnetic fields are necessary. Suitable materials for this application are for example REBa$_2$Cu$_3$O$_{7-x}$, Nb$_3$Sn or NbN. We designed a microwave cavity which resonates at around 9~GHz, with a geometry optimized to facilitate superconducting coating and designed to fit in the bore of available high-field accelerator magnets at CERN. Several prototypes of this cavity were coated with different superconducting materials, employing different coating techniques. These prototypes were characterized in strong magnetic fields at 4.2 K.

Published
2022

22. In-situ plasma treatment of Cu surfaces for reducing the generation of vacuum arc breakdowns.

Author

Saressalo, Anton, Kilpeläinen, Aarre, Mizohata, Kenichiro, Profatilova, Iaroslava, Nolvi, Anton, Kassamakov, Ivan, Tikkanen, Pertti, Calatroni, Sergio, Wuensch, Walter, and Djurabekova, Flyura

Subjects
VACUUM arcs, PARTICLES (Nuclear physics), PARTICLE accelerators, ELECTRIC fields, VACUUM circuit breakers, ELECTRIC arc, VACUUM
Abstract

High electric fields are present in a rapidly growing number of applications, which include elementary particle accelerators, vacuum interrupters, miniature x-ray sources, and satellites. Many of these applications are limited by the breakdown strength of the materials exposed to electric fields. Different methods have been developed to improve the quality of metal electrode surfaces, aiming to increase their breakdown strength. Not many systematical studies have been performed to provide a proper understanding of what contributes to the correlation between the breakdown strength and the quality of the surface. In this work, we apply a novel method for reducing vacuum arc breakdowns by cleaning the electrode surfaces with O and Ar plasma. The method can be used to alter the surfaces of the Cu electrodes in situ, i.e., without exposing them to air between the measurements. This plasma cleaning treatment is shown to reduce the number of surface impurities and to speed up the conditioning process of the samples under high-voltage pulses. Specifically, the first breakdown field was observed to increase by more than 90% after the plasma cleaning. [ABSTRACT FROM AUTHOR]

Published
2021
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23. A Proposal for a Low-Frequency Axion Search in the 1–2 micro-eV Range and Below with the BabyIAXO Magnet

Author

Ministerio de Ciencia e Innovación, Agencia Estatal de Investigación (España), Consejo Europeo de Investigación (ERC), Gobierno de Aragón, Fondo Europeo de Desarrollo Regional‏, Royal Society, Melcón Álvarez, Alejandro, Arguedas Cuendis, Sergio, Díaz Morcillo, Alejandro Benedicto, Lozano Guerrero, Antonio José, Monzó Cabrera, Juan, Navarro, Pablo, Navarro Madrid, José Ramón, García Barceló, José María, Redondo, Javier, Reina-Valero, José, Ahyoune, Saiyd, Calatroni, Sergio, Cogollos, Cristian, Devlin, Jack, Díez-Ibáñez, David, Döbrich, Babette, Galindo, Javier, Gallego, Juan Daniel, Gimeno, Benito, Golm, Jessica, Gu, Yikun, Herwig, Louis, Garcia Irastorza, Igor, Malbrunot, Chloé, Miralda-Escudé, Jordi, Schmieden, Kristof, Schneemann, Tim, Siodlaczek, Marc, Ulmer, Stefan, Wuensch, Walter, Ministerio de Ciencia e Innovación, Agencia Estatal de Investigación (España), Consejo Europeo de Investigación (ERC), Gobierno de Aragón, Fondo Europeo de Desarrollo Regional‏, Royal Society, Melcón Álvarez, Alejandro, Arguedas Cuendis, Sergio, Díaz Morcillo, Alejandro Benedicto, Lozano Guerrero, Antonio José, Monzó Cabrera, Juan, Navarro, Pablo, Navarro Madrid, José Ramón, García Barceló, José María, Redondo, Javier, Reina-Valero, José, Ahyoune, Saiyd, Calatroni, Sergio, Cogollos, Cristian, Devlin, Jack, Díez-Ibáñez, David, Döbrich, Babette, Galindo, Javier, Gallego, Juan Daniel, Gimeno, Benito, Golm, Jessica, Gu, Yikun, Herwig, Louis, Garcia Irastorza, Igor, Malbrunot, Chloé, Miralda-Escudé, Jordi, Schmieden, Kristof, Schneemann, Tim, Siodlaczek, Marc, Ulmer, Stefan, and Wuensch, Walter

Abstract

In the near future BabyIAXO will be the most powerful axion helioscope, relying on a custom-made magnet of two bores of 70 cm diameter and 10 m long, with a total available magnetic volume of more than 7 m3. In this document, it proposes and describe the implementation of low-frequency axion haloscope setups suitable for operation inside the BabyIAXO magnet. The RADES proposal has a potential sensitivity to the axion-photon coupling down to values corresponding to the KSVZ model, in the (currently unexplored) mass range between 1 and 2 eV, after a total effective exposure of 440 days. This mass range is covered by the use of four differently dimensioned 5-meter-long cavities, equipped with a tuning mechanism based on inner turning plates. A setup like the one proposed will also allow an exploration of the same mass range for hidden photons coupled to photons. An additional complementary apparatus is proposed using LC circuits and exploring the low energy range ( eV). The setup includes a cryostat and cooling system to cool down the BabyIAXO bore down to about 5 K, as well as an appropriate low-noise signal amplification and detection chain.

Published
2023

24. On the development of new tuning and inter-coupling techniques using ferroelectric materials in the detection of dark matter axions

Author

Agencia Estatal de Investigación (España), Ministerio de Ciencia e Innovación, Fondo Europeo de Desarrollo Regional‏, García Barceló, José María, Melcón Álvarez, Alejandro, Arguedas Cuendis, Sergio, Díaz Morcillo, Alejandro Benedicto, Gimeno, Benito, Kanareykin, A, Lozano Guerrero, Antonio José, Navarro, Pablo, Wuensch, Walter, Agencia Estatal de Investigación (España), Ministerio de Ciencia e Innovación, Fondo Europeo de Desarrollo Regional‏, García Barceló, José María, Melcón Álvarez, Alejandro, Arguedas Cuendis, Sergio, Díaz Morcillo, Alejandro Benedicto, Gimeno, Benito, Kanareykin, A, Lozano Guerrero, Antonio José, Navarro, Pablo, and Wuensch, Walter

Abstract

Tuning is an essential requirement for the search of dark matter axions employing haloscopes since its mass is not known yet to the scientific community. At the present day, most haloscope tuning systems are based on mechanical devices which can lead to failures due to the complexity of the environment in which they are used. However, the electronic tuning making use of ferroelectric materials can provide a path that is less vulnerable to mechanical failures and thus complements and expands current tuning systems. In this work, we present and design a novel technique for using the ferroelectric Potassium Tantalate (KTaO3 or KTO) material as a tuning element in haloscopes based on coupled microwave cavities. In this line, the structures used in the Relic Axion Detector Exploratory Setup (RADES) group are based on several cavities that are connected by metallic irises, which act as interresonator coupling elements. In this article, we also show how to use these KTaO3 films as interresonator couplings between cavities, instead of inductive or capacitive metallic windows used in the past. These two techniques represent a crucial upgrade over the current systems employed in the dark matter axions community, achieving a tuning range of 2.23% which represents a major improvement as compared to previousworks (<0.1%) for the same class of tuning systems. The theoretical and simulated results shown in this work demonstrate the interest of the novel techniques proposed for the incorporation of this kind of ferroelectric media in multicavity resonant haloscopes in the search for dark matter axions.

Published
2023

25. High-Power Test of Two Prototype X-band Accelerating Structures Based on SwissFEL Fabrication Technology

Author

Millar, William L., Grudiev, Alexej, Wuensch, Walter, Lasheras, Nuria Catalan, McMonagle, Gerard, Zennaro, Riccardo, Craievich, Paolo, Bopp, Markus, Lucas, Thomas G., Volpi, Matteo, Paszkiewicz, Jan, Edwards, Amelia, Wegner, Rolf, Bursali, Hikmet, Woolley, Benjamin, Magazinik, Anastasiya, Syratchev, Igor, Vnuchenko, Anna, Pitman, Samantha, Romano, Veronica del Pozo, Caballero, David Banon, Burt, Graeme, Millar, William L., Grudiev, Alexej, Wuensch, Walter, Lasheras, Nuria Catalan, McMonagle, Gerard, Zennaro, Riccardo, Craievich, Paolo, Bopp, Markus, Lucas, Thomas G., Volpi, Matteo, Paszkiewicz, Jan, Edwards, Amelia, Wegner, Rolf, Bursali, Hikmet, Woolley, Benjamin, Magazinik, Anastasiya, Syratchev, Igor, Vnuchenko, Anna, Pitman, Samantha, Romano, Veronica del Pozo, Caballero, David Banon, and Burt, Graeme

Abstract

This article presents the design, construction, and high-power test of two $X$-band radio frequency (RF) accelerating structures built as part of a collaboration between CERN and the Paul Scherrer Institute (PSI) for the compact linear collider (CLIC) study. The structures are a modified 'tuning-free' variant of an existing CERN design and were assembled using Swiss free electron laser (SwissFEL) production methods. The purpose of the study is two-fold. The first objective is to validate the RF properties and high-power performance of the tuning-free, vacuum brazed PSI technology. The second objective is to study the structures' high-gradient behavior to provide insight into the breakdown and conditioning phenomena as they apply to high-field devices in general. Low-power RF measurements showed that the structure field profiles were close to the design values, and both structures were conditioned to accelerating gradients in excess of 100 MV/m in CERN's high-gradient test facility. Measurements performed during the second structure test suggest that the breakdown rate (BDR) scales strongly with the accelerating gradient, with the best fit being a power law relation with an exponent of 31.14. In both cases, the test results indicate that stable, high-gradient operation is possible with tuning-free, vacuum brazed structures of this kind.

Published
2023

26. On the development of new tuning and Inter-coupling techniques using ferroelectric materials in the detection of dark matter axions

Author

Ministerio de Ciencia, Innovación y Universidades (España), Agencia Estatal de Investigación (España), European Commission, European Research Council, García Barceló, José María, Álvarez Melcón, Alejandro, Arguedas Cuendis, Sergio, Díaz-Morcillo, Alejandro, Gimeno, Benito, Kanareykin, A., Lozano-Guerrero, Antonio José, Navarro, Pablo, Wuensch, Walter, Ministerio de Ciencia, Innovación y Universidades (España), Agencia Estatal de Investigación (España), European Commission, European Research Council, García Barceló, José María, Álvarez Melcón, Alejandro, Arguedas Cuendis, Sergio, Díaz-Morcillo, Alejandro, Gimeno, Benito, Kanareykin, A., Lozano-Guerrero, Antonio José, Navarro, Pablo, and Wuensch, Walter

Abstract

Tuning is an essential requirement for the search of dark matter axions employing haloscopes since its mass is not known yet to the scientific community. At the present day, most haloscope tuning systems are based on mechanical devices which can lead to failures due to the complexity of the environment in which they are used. However, the electronic tuning making use of ferroelectric materials can provide a path that is less vulnerable to mechanical failures and thus complements and expands current tuning systems. In this work, we present and design a novel technique for using the ferroelectric Potassium Tantalate ( KTaO3 or KTO) material as a tuning element in haloscopes based on coupled microwave cavities. In this line, the structures used in the Relic Axion Detector Exploratory Setup (RADES) group are based on several cavities that are connected by metallic irises, which act as interresonator coupling elements. In this article, we also show how to use these KTaO3 films as interresonator couplings between cavities, instead of inductive or capacitive metallic windows used in the past. These two techniques represent a crucial upgrade over the current systems employed in the dark matter axions community, achieving a tuning range of 2.23% which represents a major improvement as compared to previous works ( <0.1% ) for the same class of tuning systems. The theoretical and simulated results shown in this work demonstrate the interest of the novel techniques proposed for the incorporation of this kind of ferroelectric media in multicavity resonant haloscopes in the search for dark matter axions.

Published
2023

27. High-Power Test of Two Prototype X-Band Accelerating Structures Based on SwissFEL Fabrication Technology

Author

Millar, William L., primary, Grudiev, Alexej, additional, Wuensch, Walter, additional, Lasheras, Nuria Catalan, additional, McMonagle, Gerard, additional, Zennaro, Riccardo, additional, Craievich, Paolo, additional, Bopp, Markus, additional, Lucas, Thomas G., additional, Volpi, Matteo, additional, Paszkiewicz, Jan, additional, Edwards, Amelia, additional, Wegner, Rolf, additional, Bursali, Hikmet, additional, Woolley, Benjamin, additional, Magazinik, Anastasiya, additional, Syratchev, Igor, additional, Vnuchenko, Anna, additional, Pitman, Samantha, additional, Romano, Veronica del Pozo, additional, Caballero, David Ba non, additional, and Burt, Graeme, additional

Published
2023
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29. Explainable machine learning for breakdown prediction in high gradient rf cavities

Author

Obermair, Christoph, primary, Cartier-Michaud, Thomas, additional, Apollonio, Andrea, additional, Millar, William, additional, Felsberger, Lukas, additional, Fischl, Lorenz, additional, Bovbjerg, Holger Severin, additional, Wollmann, Daniel, additional, Wuensch, Walter, additional, Catalan-Lasheras, Nuria, additional, Boronat, Marçà, additional, Pernkopf, Franz, additional, and Burt, Graeme, additional

Published
2022
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30. A Compact Inverse Compton Scattering Source Based on X-Band Technology and Cavity-Enhanced High Average Power Ultrafast Lasers

Author

Latina, Andrea, Cormier, Eric, Corsini, Roberto, Dyks, Luke, Granados, Eduardo, Grudiev, Alexej, Musat, Vlad, Santarelli, Giorgio, Stapnes, Steinar, Wuensch, Walter, Centre d'Etudes Lasers Intenses et Applications (CELIA), Université de Bordeaux (UB)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), and École polytechnique (X)

Subjects
electron, inverse, photon electron, [PHYS.PHYS.PHYS-ACC-PH]Physics [physics]/Physics [physics]/Accelerator Physics [physics.acc-ph], photon, nucleus, cavity, linear accelerator, Accelerators and Storage Rings, Accelerator Physics, laser, X-ray, flux, Electron Accelerators and Applications, linac, Compton scattering, burst, enhancement, performance, energy
Abstract

A high-pulse-current injector followed by a short high-gradient X-band linac is considered as a driver for a compact Inverse Compton Scattering source. We show that using a high-power ultrashort pulse laser operating in burst mode and a Fabry-Pérot enhancement cavity, X-rays with flux values over 10¹³ ph/s and photon energies up to MeV are achievable. The resulting high-intensity and high-energy X-rays allow for various applications, including cancer therapy, tomography, and nuclear waste management. A preliminary conceptual design of such a compact ICS source is presented, together with simulations of the expected performance., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Published
2022

31. Design of New Resonant Haloscopes in the Search for the Dark Matter Axion: A Review of the First Steps in the RADES Collaboration

Author

Agencia Estatal de Investigación (España), Fondo Europeo de Desarrollo Regional‏, Consejo Europeo de Investigación (ERC), Díaz Morcillo, Alejandro Benedicto, García Barceló, José María, Lozano Guerrero, Antonio, Melcón Álvarez, Alejandro, Gimeno, Benito, Arguedas Cuendis, Sergio, Cogollos, Cristian, Calatroni, Sergio, Döbrich, Babette, Gallego, Juan Daniel, Golm, Jessica, Garcia Irastorza, Igor, Malbrunot, Chloé, Miralda Escudé, Jordi, Peña Garay, Carlos, Redondo, Javier, Wuensch, Walter, Navarro, Pablo, Agencia Estatal de Investigación (España), Fondo Europeo de Desarrollo Regional‏, Consejo Europeo de Investigación (ERC), Díaz Morcillo, Alejandro Benedicto, García Barceló, José María, Lozano Guerrero, Antonio, Melcón Álvarez, Alejandro, Gimeno, Benito, Arguedas Cuendis, Sergio, Cogollos, Cristian, Calatroni, Sergio, Döbrich, Babette, Gallego, Juan Daniel, Golm, Jessica, Garcia Irastorza, Igor, Malbrunot, Chloé, Miralda Escudé, Jordi, Peña Garay, Carlos, Redondo, Javier, Wuensch, Walter, and Navarro, Pablo

Abstract

With the increasing interest in dark matter axion detection through haloscopes, in which different international groups are currently involved, the RADES group was established in 2016 with the goal of developing very sensitive detection systems to be operated in dipole magnets. This review deals with the work developed by this collaboration during its first five years: from the first designs—based on the multi-cavity concept, aiming to increase the haloscope volume, and thereby improve sensitivity—to their evolution, data acquisition design, and finally, the first experimental run. Moreover, the envisaged work within RADES for both dipole and solenoid magnets in the short and medium term is also presented.

Published
2022

33. Pulsed DC High Field Measurements of Irradiated and Non-Irradiated Electrodes of Different Materials

Author

Peacock, Ruth, Bellodi, Giulia, Burt, Graeme, Calatroni, Sergio, Da Palma Serafim, Catarina, Grudiev, Alexej, Lombardi, Alessandra, Perez Fontenla, Ana Teresa, Ramberger, Suitbert, Sargsyan, Edgar, Sgobba, Stefano, and Wuensch, Walter

Subjects
Accelerators and Storage Rings, Proton and Ion Accelerators and Applications, Accelerator Physics
Abstract

Beam loss occurs in Radio Frequency Quadrupoles (RFQ), and has been observed in the H⁻ linear accelerator Linac4 (L4) at CERN. To determine if beam loss can induce breakdowns, and to compare the robustness of different materials, tests have been done using pulsed high-voltage DC systems. Electrical breakdown phenomena and conditioning processes have been studied using these systems. Cathodes of different materials were irradiated with 1.2x10¹⁹ H⁻ p/cm², the estimated beam loss of the L4 RFQ over 10 days. The irradiated electrodes were installed in a system to observe if the irradiated area coincided with the breakdown locations, with pulsing parameters similar to the RFQ. Tests of irradiated and non-irradiated electrodes of the same material were done for comparison. The main difference observed was an increase in the number of breakdowns during the initial conditioning that returned to non-irradiated sample values with further running. Visual observations after irradiation show the beam centre and a halo the same diameter of the beam pipe. Breakdown clusters occur in the centre and halo regions, suggesting irradiation is not the only factor determining the breakdown probability., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Published
2022
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34. Microscopy Investigation on Different Materials After Pulsed High Field Conditioning and Low Energy H$^{-}$ Irradiation

Author

Da Palma Serafim, Catarina, Bellodi, Giulia, Calatroni, Sergio, Djurabekova, Flyura, Grudiev, Alexej, Lombardi, Alessandra, Peacock, Ruth, Perez Fontenla, Ana Teresa, Ramberger, Suitbert, Sargsyan, Edgar, Sgobba, Stefano, and Wuensch, Walter

Subjects
Proton and Ion Accelerators and Applications, Accelerators and Storage Rings, Accelerator Physics
Abstract

During operation the LINAC4 RFQ (Radio-Frequency-Quadrupole) is exposed to high electric fields which can lead to vacuum breakdown. It is also subject to beam loss that can cause surface modification, including blistering, which can result in reduced electric field handling and an increased breakdown rate. An experimental study has been made to identify materials with high electric field capability and robustness to low-energy irradiation. In this paper we briefly discuss the selection criteria and we analyze these materials investigating their metallurgical properties using advanced microscopic techniques such as Scanning Electron Microscope, Electron Back Scattered Diffraction, Energy-dispersive X-ray Spectroscopy and conventional optical microscopy. These allow to observe and characterize the different materials on aμand a nano-scale, allowing us to compare results before and after irradiation and breakdown testing., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Published
2022

35. Device for providing a radiation treatment

Author

Bourhis, Jean Francois Marie, Germond, Jean-Francois, Moeckli, Raphael, Wuensch, Walter, and Gerbershagen, Alexander

Abstract

The present relates to a device for providing a radiation treatment to a patient comprising :- an electron source for providing a beam of electrons, and- a linear accelerator for accelerating said beam until a predetermined energy, and - a beam delivery module for delivering the accelerated beam from said linear accelerator toward the patient to treat a target volume with a radiation dose, The device further comprises intensity modulation means configured to modulate the distribution of the radiation dose in the target volume according to a predetermined pattern.The pattern is determined to match the dimensions of a target volume of at least about 50 cm3, and/or a target volume located at least about 5 cm deep in the tissue of the patient with said radiation dose,The radiation dose distributed is up to about 20 Gy delivered during an overall treatment time less than about 50 ms.

Published
2021

36. XLS - D2.3: Conceptual Design Report

Author

D'Auria, Gerardo (ed.), Thompson, Neil (ed.), Clarke, Jim (ed.), Ferrario, Massimo (ed.), Wuensch, Walter (ed.), Nguyen, Federico (ed.), Aksoy, Avni (ed.), Rochow, Regina (ed.), Chianchi, Alessandro (ed.), Latina, Andrea (ed.), and Aicheler, Markus (ed.)

Subjects
CompactLight, Free Electron Laser, X-band Technologies, C-band Technology, Compact Diagnostics, High Repetition Rate Linac, Compact Accelerators, Compact X-ray FELs, High Repetition Rate Injector, Compact Undulator
Abstract

The report presents, as the main result of the CompactLight project, the conceptual design of the CompactLight hard X-ray FEL. It is devided in the following chapters: 1. Executive Summary 2. Introduction 3. Science Goals and Photon Output Requirements 4. Systems Design and Performance 5. Accelerator 6. Light Production 7. Civil Engineering 8. Strategy and Implementation 9. Examples of CompactLight Facilities 10. Alternative Technology Solutions A. Appendices, On behalf of the CompactLight Partnership - see list of all authors in the document.

Published
2021
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37. Design of New Resonant Haloscopes in the Search for the Dark Matter Axion: A Review of the First Steps in the RADES Collaboration

Author

Díaz-Morcillo, Alejandro, primary, García Barceló, José María, additional, Lozano Guerrero, Antonio José, additional, Navarro, Pablo, additional, Gimeno, Benito, additional, Arguedas Cuendis, Sergio, additional, Álvarez Melcón, Alejandro, additional, Cogollos, Cristian, additional, Calatroni, Sergio, additional, Döbrich, Babette, additional, Gallego-Puyol, Juan Daniel, additional, Golm, Jessica, additional, Irastorza, Igor García, additional, Malbrunot, Chloe, additional, Miralda-Escudé, Jordi, additional, Peña Garay, Carlos, additional, Redondo, Javier, additional, and Wuensch, Walter, additional

Published
2021
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40. First results of the CAST-RADES haloscope search for axions at 34.67 μeV

Author

Álvarez Melcón, Alejandro, Arguedas Cuendis, Sergio, Baier, Justin, Barth, Klaus, Bräuninger, Heinrich, Calatroni, Sergio, Cantatore, Giovanni, Caspers, Fritz, Castel Pablo, Juan Francisco, Cetin, Serkant Ali, Cogollos Triviño, Cristian, Dafni, Theopisti, Davenport, Martyn, Dermenev, Alexander, Desch, Klaus, Díaz-Morcillo, Alejandro Benedicto, Döbrich, Babette, Fischer, Helene, Funk, Wolfgang, Gallego Puyol, Juan Daniel, García Barceló, José María, Gardikiotis, Antonios, Gracia Garza, Javier, Gimeno Martínez, Benito, Gninenko, Sergei, Golm, Jessica, Hasinoff, Michael D., Hoffmann, Dieter H.H., García Irastorza, Igor, Jakovčić, Krešimir, Kaminski, Jochen, Karuza, Marin, Lakic, Biljana, Laurent, Jean Michel, Lozano Guerrero, Antonio José, Luzón Marco, Gloria, Malbrunot, Chloé, Moroudas, Marios, Miralda Escudé, Jordi, Mirallas Sánchez, Héctor, Miceli, Lino, Navarro Lorente, Pedro Javier, Ozbey, Aydin, Özbozduman, Kaan, Peña Garay, Carlos, Pivovaroff, ‪Michael James, Redondo Martín, Javier, Ruz Armendáriz, Jaime, Ruiz Chóliz, Elisa, Schmidt, Sebastian, Schumann, Marc, Semertzidis, Yannis K., Solanki, Sami Khan, Stewart, L., Tsagris, Ioannis, Vafeiadis, Theodoros, Vogel, Julia Katharina, Wuensch, Walter, and Zioutas, Konstantin

Subjects
CERN Axion Solar Telescope (CAST), Teoría de la Señal y las Comunicaciones, Magnetic field, Relic Axion Dark-Matter Exploratory Setup (RADES), Axions, Dark Matter and Double Beta Decay (experiments), Dark matter, Sun, 21 Astronomía y Astrofísica
Abstract

We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is part of the CERN Axion Solar Telescope (CAST), searching for axion dark matter in the 34.67μeV mass range. A radio frequency cavity consisting of 5 sub-cavities coupled by inductive irises took physics data inside the CAST dipole magnet for the first time using this filter-like haloscope geometry. An exclusion limit with a 95% credibility level on the axion-photon coupling constant of gaγ & 4 × 10−13 GeV−1 over a mass range of 34.6738μeV < ma < 34.6771μeV is set. This constitutes a significant improvement over the current strongest limit set by CAST at this mass and is at the same time one of the most sensitive direct searches for an axion dark matter candidate above the mass of 25μeV. The results also demonstrate the feasibility of exploring a wider mass range around the value probed by CAST-RADES in this work using similar coherent resonant cavities We wish to thank our colleagues at CERN, in particular Marc Thiebert from the coating lab, as well as the whole team of the CERN Central Cryogenic Laboratory for their support and advice in speci c aspects of the project. We thank Arefe Abghari for her contributions as the project's summer student during 2018. This work has been funded by the Spanish Agencia Estatal de Investigacion (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under project FPA-2016-76978-C3-2-P and PID2019-108122GB-C33, and was supported by the CERN Doctoral Studentship programme. The research leading to these results has received funding from the European Research Council and BD, JG and SAC acknowledge support through the European Research Council under grant ERC-2018-StG-802836 (AxScale project). BD also acknowledges fruitful discussions at MIAPP supported by DFG under EXC-2094 { 390783311. IGI acknowledges also support from the European Research Council (ERC) under grant ERC-2017-AdG-788781 (IAXO+ project). JR has been supported by the Ramon y Cajal Fellowship 2012-10597, the grant PGC2018-095328-B-I00(FEDER/Agencia estatal de investigaci on) and FSE-GA2017-2019-E12/7R (Gobierno de Aragón/FEDER) (MINECO/FEDER), the EU through the ITN \Elusives" H2020-MSCA-ITN-2015/674896 and the Deutsche Forschungsgemeinschaft under grant SFB-1258 as a Mercator Fellow. CPG was supported by PROMETEO II/2014/050 of Generalitat Valenciana, FPA2014-57816-P of MINECO and by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreements 690575 and 674896. AM is supported by the European Research Council under Grant No. 742104. Part of this work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

Published
2021

41. XLS – D2.2: FEL design with accelerator and undulator requirements

Author

Di Mitri, Simone, Aksoy, Avni, Bernhard, Axel, Castañeda Cortés, Hector M., Clarke, Jim, D'Auria, Gerardo, Dunning, Dave, Ferrario, Massimo, Latina, Andrea, Marin, Edu, Nguyen, Federico, Schmidt, Thomas, Thompson, Neil, and Wuensch, Walter

Subjects
CompactLight, X-ray Free Electron Lasers, X-band technology, Compact accelerators, Undulators
Abstract

This report describes the salient conceptual features of the CompactLight photon source, describing the machine layout and its modus operandi. The main parameters of the facility, grouped into facility sub-systems, are summarized in tables, which identify the baseline facility configuration, the proposed upgrade phases, and the technological recommendations provided by the individual work packages for its implementation. As a result, this document anticipates the CompactLight design study, and paves the way to the production of a more detailed conceptual design report., On behalf of the CompactLight Collaboration

Published
2021
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44. Measurements of Field Emission Induced Optical Spectra

Author

Peacock, Ruth, Burt, Graeme, Calatroni, Sergio, and Wuensch, Walter

Subjects
MC7: Accelerator Technology, Accelerators and Storage Rings, Accelerator Physics
Abstract

Field emission induced optical spectra in a dc electrode system have been measured using a spectrometer and CCD camera system in order to gain insight into the nature of field emissions sites. Spectra were measured from between 2 ridged parallel copper electrodes with a gap ranging from 60µm to 100µm and a bias voltage of up to 8000V under high vacuum conditions. A strong correlation between the light intensity of the spectra and the measured field emitted current was observed as a function of applied voltage. A characteristic broadband spectrum ranging from 550nm and 850nm wavelength was observed but there were important features which varied as a function of observation angle, polarity, and conditioning state and also with time. Possible causes of the optical spectra being considered include black body radiation, optical transition radiation and cathode luminescence of copper. Further experiments are ongoing with an improved optical setup to increase optical alignment for measurements with different materials of electrodes, developing further understanding of the cause of the optical spectra, to provide understanding into characteristics and evolution of emission sites., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Published
2021

45. Development of 36 GHz RF Systems for RF Linearisers

Author

Castilla, Alejandro, Behtouei, Mostafa, Burt, Graeme, Cai, Jinchi, Cross, Adrian, Latina, Andrea, Liu, Xingguang, Nix, Laurence, Spataro, Bruno, Syratchev, Igor, Wu, Xiaowei, Wuensch, Walter, Zhang, Liang, Lin, Liu, Byrd, John M., Neuenschwander, Regis, Picoreti, Renan, Schaa, Volker R. W., Lin, Liu (Ed.), Byrd, John M. (Ed.), Regis Neuenschwander (Ed.), Picoreti, Renan (Ed.), and Schaa, Volker R. W. (Ed.)

Subjects
CompactLight, X-ray Free Electron Lasers, MC7: Accelerator Technology, X-band RF technologies, Accelerators and Storage Rings, RF Linearisers, QC, Accelerator Physics
Abstract

As part of the deign studies, the CompactLight project plans to use an injector in the C-band. Which constitutes a particular complication for the harmonic system in charge of linearising the beam’s phase space, since it means its operation frequency could be higher than the standard X-band RF technologies. In the present work, we investigated a 36 GHz (Ka-band) as the ideal frequency for the harmonic system. A set of structure designs are presented as candidates for the lineariser, based on different powering schemes and pulse compressor technologies. The comparison is made both in terms of beam dynamics and RF performance. Given the phase stability requirements for the MW class RF sources needed for this system, we performed careful studies of a Gyro-Klystron and a multi-beam klystron as potential RF sources, with both showing up to 3 MW available power using moderate modulator voltages. Alternatives for pulse compression at Ka-band are also discussed in this work., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Published
2021
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46. High-Gradient Breakdown Studies of an X-Band Accelerating Structure Operated in the Reversed Taper Direction

Author

Wu, Xiaowei, Boronat, Marça, Castilla, Alejandro, Catalán Lasheras, Nuria, Edwards, Amelia, Grudiev, Alexej, McMonagle, Gerard, Millar, William, Syratchev, Igor, and Wuensch, Walter

Subjects
MC7: Accelerator Technology, Accelerators and Storage Rings, Accelerator Physics
Abstract

The results of high-gradient tests of a tapered X-band traveling-wave accelerator structure powered in reversed direction are presented. Powering the tapered structure from the small aperture, normally output, at the end of the structure provides unique conditions for the study of gradient limits. This allows high fields in the first cell for a comparatively low input power and a field distribution that rapidly falls off along the length of the structure. A maximum gradient of 130 MV/m in the first cell at a pulse length of 100 ns was reached for an input power of 31.9 MW. Details of the conditioning and operation at high-gradient are presented. Various breakdown rate measurements were conducted at different power levels and rf pulse widths. The structure was standard T24 CLIC test structure and was tested in Xbox-3 at CERN., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Published
2021

47. The Southern Hemisphere’s First X-Band Radio-Frequency Test Facility at the University of Melbourne

Author

Volpi, Matteo, Boland, Mark, Catalán Lasheras, Nuria, Dowd, Rohan, Gonzalez Anton, Sergio, McMonagle, Gerard, Rassool, Roger, Sheehy, Suzanne, Stapnes, Steinar, Taylor, Geoffrey, Williams, Scott, Wuensch, Walter, and Zingre, Karl

Subjects
MC7: Accelerator Technology, Accelerators and Storage Rings, Accelerator Physics
Abstract

The first Southern Hemisphere X-band Laboratory for Accelerators and Beams (X-LAB) is under construction at the University of Melbourne, and it will operate CERN X-band test stand containing two 12GHz 6MW klystron amplifiers. By power combination through hybrid couplers and the use of pulse compressors, up to 50 MW of peak power can be sent to any of 2 test slots at pulse repetition rates up to 400 Hz. The test stand is dedicated to RF conditioning and testing CLIC’s high gradient accelerating structures beyond 100 MV/m. It will also form the basis for developing a compact accelerator for medical applications, such as radiotherapy and compact light sources. Australian researchers working as part of a collaboration between the University of Melbourne, international universities, national industries, the Australian Synchrotron -ANSTO, Canadian Light Source and the CERN believe that creating a laboratory for novel accelerator research in Australia could drive technological and medical innovation., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Published
2021

48. Machine Learning Models for Breakdown Prediction in RF Cavities for Accelerators

Author

Obermair, Christoph, Apollonio, Andrea, Cartier-Michaud, Thomas, Catalán Lasheras, Nuria, Felsberger, Lukas, Millar, William, Pernkopf, Franz, and Wuensch, Walter

Subjects
MC7: Accelerator Technology, Physics::Accelerator Physics, Accelerators and Storage Rings, Accelerator Physics
Abstract

Radio Frequency (RF) breakdowns are one of the most prevalent limits in RF cavities for particle accelerators. During a breakdown, field enhancement associated with small deformations on the cavity surface results in electrical arcs. Such arcs degrade a passing beam and if they occur frequently, they can cause irreparable damage to the RF cavity surface. In this paper, we propose a machine learning approach to predict the occurrence of breakdowns in CERN’s Compact LInear Collider (CLIC) accelerating structures. We discuss state-of-the-art algorithms for data exploration with unsupervised machine learning, breakdown prediction with supervised machine learning, and result validation with Explainable-Artificial Intelligence (Explainable AI). By interpreting the model parameters of various approaches, we go further in addressing opportunities to elucidate the physics of a breakdown and improve accelerator reliability and operation., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Published
2021
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49. S-Band Transverse Deflecting Structure Design for CompactLight

Author

Wu, Xiaowei, Di Mitri, Simone, Thompson, Neil, Wuensch, Walter, Lin, Liu (Ed.), Byrd, John M. (Ed.), Regis Neuenschwander (Ed.), Picoreti, Renan (Ed.), and Schaa, Volker R. W. (Ed.)

Subjects
CompactLight, X-ray Free Electron Lasers, X-band Technologies, MC2: Photon Sources and Electron Accelerators, Physics::Accelerator Physics, S-Band Transverse Deflecting Structure, Accelerators and Storage Rings, Accelerator Physics
Abstract

The CompactLight project is currently developing the design of a next generation hard X-ray FEL facility, which is based on high-gradient X-band (12 GHz) structures. However, to carry out pump-and-probe experiments in the project, two-bunch operation with a spacing of 10 X-band rf cycles is proposed. A sub-harmonic transverse deflecting structure working at S-band is proposed to direct the two bunches into two separate FEL lines. The two FEL pulses will have independently tunable wavelengths and can be combined in a single experiment with a temporal delay between pulses of ± 100 fs. The rf design of the transverse deflector is presented in this paper., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Published
2021

50. Statistical Analysis of Field-Emission Currents

Author

Lachmann, Sagy, Jacewicz, Marek, Profatilova, Iaroslava, Paszkiewicz, Jan, Wuensch, Walter, Ashkenazy, Yinon, Lachmann, Sagy, Jacewicz, Marek, Profatilova, Iaroslava, Paszkiewicz, Jan, Wuensch, Walter, and Ashkenazy, Yinon

Abstract

The current due to cold tunneling of electrons from a metallic surface exposed to high electric fields, regularly named "dark current," is commonly described in modern literature using an analytical approximate solution provided by Murphy and Good [Phys. Rev. 102, 1464 (1956)]. This expression, which corrects earlier work by Fowler and Nordheim, is a Fowler-Nordheim-type equation: I similar to E2 exp(-a/E), where I is the dark current, E is the local electric field, and a is a system-specific constant. In this paper, a numerical approximation, rather than the analytical one given by Murphy and Good, is presented. This approximation is accurate over a wide range of fields, and is used to derive the effective field enhancement factor ,B. On the basis of this approximation, and considering local field and current fluctuations, two alternative methods for ,B estimation are presented. These methods allow instantaneous field-specific estimation of ,B, rather than the average estimate derived with current methods. The applicability of fluctuation-based methods is demonstrated by numerical simulation in a variety of conditions. The methods are applied to estimate ,B using fluctuation analysis in experimental measurements that were not dedicated for this purpose. An open-source code for the implementation of fluctuation-derived ,B estimation is provided, with an analysis of possible future experimental opportunities using dedicated experiments.

Published
2021
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