RF Design of a High Average Beam-Power SRF Electron Source

The International Linear Collider (ILC) main linac comprises a series of 12 m-long cryomodules. The cryomodule contains eight 9-cell superconducting (SC) RF (SRF) cavities and an SC quadrupole magnet combined with dipole correctors to focus and steer electron and positron beams. The magnets are installed between the SRF cavity string and at the longitudinal center of a common cryomodule/cryostat. These magnets are conductively cooled by pure aluminum channels thermally connected to a 2 K two-phase helium pipe for cooling the SRF cavities. A recent study shows that field-emitted electrons, so-called “dark current” initiated in the SRF cavities, are transmitted through the SRF cavity string and reach the SC magnet. The energy is inevitably absorbed in the SC coil due to the magnetic field, resulting in risks of a quench caused by the coil heating. We are investigating alternate magnet designs by using Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{MgB}_{2}$</tex-math></inline-formula> SC and by adding the dark current absorber surrounding the beam-pipe to realize sustainable magnet operation under the dark current heating. We report the design study of the magnet system and interfaces to the cryomodule accommodating it with the SRF cavities.

The European Spallation Source (ESS) is one of Europe’s largest planned research infrastructures. The project is funded by a collaboration of 17 European countries and is under design and construction in Lund, Sweden. Three families of Superconducting Radio-Frequency (SRF) cavities are being prototyped, counting the spoke resonators with a geometric beta of 0.5, medium-beta elliptical cavities (β=0.67) and high beta elliptical cavities (β=0.86). The ESS linac will produce 2.86 ms long proton pulses with a repetition rate of 14 Hz (4 % duty cycle), a beam current of 62.5 mA and an average beam power of 5 MW. A control system is being developed to operate the different accelerator systems. All operating modes of the superconducting linac shall ensure a safe operation of the accelerator. This paper presents the preliminary functional analysis and the operating modes of the 704 MHz SRF linac.

State of the art high-current superconducting accelerators require efficient RF sources with a fast dynamic phase and power control. This allows for compensation of the phase and amplitude deviations of the accelerating voltage in the Superconducting RF (SRF) cavities caused by microphonics, etc. Efficient magnetron transmitters with fast phase and power control are attractive RF sources for this application. They are more cost effective than traditional RF sources such as klystrons, IOTs and solid-state amplifiers used with large scale accelerator projects. However, unlike traditional RF sources, controlled magnetrons operate as forced oscillators. Study of the impact of the controlling signal on magnetron stability, noise and efficiency is therefore important. This paper discusses experiments with 2.45 GHz, 1 kW tubes and verifies our analytical model which is based on the charge drift approximation.

CEPC is a circular electron positron collider operating at 240 GeV center-of-mass energy as a Higgs factory, recently proposed by the Chinese high energy physics community. The CEPC study group, together with the FCC and ILC community, will contribute to the development of future high energy colliders and experiments which will ensure that the elementary particle physics remain a vibrant and exciting field of fundamental investigation for decades to come. Superconducting RF (SRF) system is one of the most important technical systems of CEPC and is a key to achieving its design energy and luminosity. It will dominate, with the associated RF power source and cryogenic system, the overall machine cost, efficiency and performance. The CEPC SRF system will be one of the largest and most powerful SRF accelerator installations in the world. The preliminary conceptual design of the CEPC SRF system is summarized in this paper, including the machine layout, key parameter choices and some critical issues such as HOM damping, emphasizing the new technology requirement and R&D focuses.

The Advanced Superconducting Test Accelerator (ASTA) is in the early stage of commissioning. The front-end consists of a 1.5 cell normal conducting RF Gun resonating at 1.3 GHz with a gradient of up to 40 MV/m, a cesium telluride (Cs2Te) cathode for photoelectron production, a pulsed 263 nm ultra-violet (UV) laser delivery system, and a diagnostic area for measuring the characteristics of the photoelectron beam. We report on the design, construction, and early experience of the UV Laser Delivery and Diagnostic Platform and the Photocathode Imaging System.

شناخت آسیب پذیری جمعیت و گروه های انسانی به عنوان اقدامی ابزاری در راستای پیشگیری از زایش فاجعه مبتنی بر زیستن در نواحی پر خطر مطرح است. تحلیل آسیب پذیری کانون‌های جمعیتی واقع در عرصه های خطر اقدامی علمی برای فراهم سازی زیر ساخت اطلاعاتی مناسب از درجه و میزان خطرپذیری از رخداد مخاطره است. بر اساس چنین دیدگاهی مسئله تحلیل آسیب پذیری ناشی از مخاطرات ژئومورفولوژیک فرونشست در جنوب شهر تهران مورد توجه قرار گرفته است. بدین منظور در ابتدا با استفاده از تکنیک تداخل سنجی راداری نرخ و دامنه فرونشست در محدوده مورد مطالعه استخراج گردید. سپس برای تولید نقشه فضایی عرصه های پر مخاطره نرخ و دامنه فرونشست به عنوان فاکتور عامل در زایش مخاطره به تحلیل گر سیستم در محیط GIS وارد گردید. نقشه خروجی معرف سلول‌های واجد ارزش متفاوت از فاکتور زایش مخاطره است. استخراج عرصه متعلق پهنه در معرض مخاطره نشان داد که از مجموع مساحت محدوده 7/12 درصد در پهنه های بسیار پرخطر، 7/14 در عرصه پرخطر،5/15 در عرصه نسبتاً پرخطر بیش از نیمی از محدوده (57درصد) در عرصه نسبتاً کم خطر قرار گرفته‌اند. برای ارزیابی میزان خطرپذیری، الگوی توزیع فضایی تأسیسات و ساخت‌وساز های موجود با نقشه عرصه های در معرض خطر هم نهاد گردید. مبتنی بر این اطلاعات و با استفاده از پیمایش میدانی اقدام به بررسی آسیب پذیری جمعیت ،مساکن و تأسیسات موجود در محدوده مورد مطالعه صورت پذیرفت. یافته های تحقیق موید آسیب پذیر بودن اکثر سکونت گاه‌ها و جمعیت ساکن درآنهاو تأسیسات موجود در محدوده می‌باشد. همچنین بر اساس پایش های میدانی صورت گرفته مشخص گردید که اکثر ساخت و سازهای موجود در منطقه غیر اصولی بوده که این امر باعث فراهم آوری زیرساخت آسیب پذیری برای مستحدثات در شرایط خطرپذیر است.

The Coherent Electron Cooling Proof of Principle (CeC PoP) system is being installed in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. It will demonstrate the ability of relativistic electrons to cool a single bunch of heavy ions in RHIC. This technique may increase the beam luminosity by as much as tenfold. Within the scope of this experiment, a 112 MHz 2 MeV Superconducting Radio Frequency (SRF) electron gun coupled with a cathode stalk mechanism, two normal conducting 500 MHz single-cell bunching cavities, a 704 MHz 20 MeV 5-cell SRF cavity and a helical undulator will be used. In this paper, we provide an overview of the engineering design for this project, test results and discuss project status and plansd.

eRHIC project requires construction of a FFAG ring to accelerate electrons and connect to the existing ion ring of Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. This new ring will have the same radius as the RHIC ring. Synchrotron radiation lost in the electron ring should be compensated by a CW superconducting radio frequency (SRF) cavity. Here we propose an 845 MHz single cell harmonic cavity. This cavity will experience a high average current (∼0.7 A) passing through it. With this consideration, this cavity design requires optimization to reduce higher order mode power. On the other hand, the cavity will operate at relatively high gradient up to 18 MV/m. Current design requires fundamental couplers to handle 400 kW forward RF power and HOM couplers to extract 2.5 kW HOM power.

Experimental and discrete element methods were used to investigate the effects of distance between two preexisting cracks, bridge area (The length of the bridge area) and its angularities on the shear behaviour of bridge area. A punchthrough shear test was used to model the gypsum (concrete like) cracks under shear loading. Gypsum samples (concrete like) with dimension of 120 mm × 120 mm × 50 mm were prepared in the laboratory. Within the specimen model and near its four corners, four vertical notches were provided. Three different configuration systems were prepared for notches; i.e., paralell and in plane, inside echelon and outside echelon configuration systems, respectively. In these configurations, the length of cracks were taken as 2 cm, 4 cm and 6 cm based on the cracks configuration systems. Then, 9 specimens with different lengths of the bridge area and bridge area angles were prepared. Assuming a plane strain condition, special rectangular models were prepared with dimensions of 100 mm × 100 mm. similar to those for cracks configuration systems in the experimental tests i.e., 9 models with different lengths of the bridge area and bridge area angularities were prepared. The axial load was applied to the punch through the central portion of the model. This testing showed that the failure process was mostly governed by the lengths of the bridge area and bridge area angularities. The shear strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the lengths of the bridge area. The strength of samples decreases by increasing the crack length. Also, the outside echelon crack configuration system has the maximum value of strength while the inside echelon crack configuration system has the minimum value of specimen's tensile strength. The failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

Ideas about retrieval of memories are based largely on localization of function inferred after brain damage. On the other hand, communication in the cerebral cortex occurs through an intricate network of connections, suggesting highly distributed circuits. Loss of memory after lesions thus affects not only the damaged area, but also its rich inputs and outputs. The discussion here is based on a structural model of neural communication that can help explain the process of recruiting highly distributed relevant signals for conceptual and sensory recognition and memory. Discussion of cortical communication has traditionally been sensory-centric, based on the flow of information from the periphery to primary sensory areas and beyond, or in the reverse direction. However, visual signals often do not activate areas along a sequential route as predicted by a hierarchical model, exemplified by the fact that some visual signals activate prefrontal areas earlier than some visual association areas. On the other hand, the structural model for connections is based on the fundamental principle of systematic variation in laminar architecture of the cortex and applies to all cortical systems. The structural model is relational: it predicts that laminar-specific connections in the cortex depend on the structural (laminar) relationship between linked areas. Thus, connections that link an area with simpler laminar structure originate mainly – but not exclusively – in the deep layers and terminate mainly in the upper layers of an area with more elaborate laminar structure. In the opposite direction, connections originate in the upper layers and terminate in the middle-deep layers. Because the laminar architecture across cortical areas is graded, so is the distribution of connections within layers. The structural model holds for connections in all cortical systems and diverse species. Moreover, laminar-specific connections as predicted by the structural model terminate within inhibitory microenvironments that also differ by the distribution of functionally distinct classes of inhibitory neurons that can dynamically shift activity among layers and change cortical rhythms. The relational nature of the structural model and predictions of graded patterns of connections thus suggest that distributed areas and layers are recruited dynamically to meet task demands, including recollection of concepts and events.

Several future accelerator projects at Brookhaven for the Relativistic Heavy Ion Collider (RHIC) are based on energy recovery linacs (ERLs) with high-charge high-current electron beams. Their stable operation mandates effective higher-order-mode (HOM) damping. The development of HOM dampers for these projects is pursued actively at this laboratory. Strong HOM damping was experimentally demonstrated both at room and at superconducting (SC) temperatures in a prototype research and development (R) five-cell niobium superconducting rf (SRF) cavity with ferrite dampers. Two room-temperature mock-up five-cell copper cavities were used to study various damper configurations with emphasis on capacitive antenna dampers. An innovative type of ferrite damper over a ceramic break for an R SRF electron gun also was developed. For future SRF linacs longer cryomodules comprised of multiple superconducting cavities with reasonably short intercavity transitions are planned. In such a configuration, the dampers, located closer to the cavities, will be at cryogenic temperatures; this will impose additional constraints and complications. This paper presents the results of simulations and measurements of several damper configurations.

Over the past several decades, extreme drought events have become increasingly frequent in Central Serbia and have affected vast areas of land. In agriculture, the impact of drought is dramatic, especially if the soils in the affected area are shallow, like in most of the Sumadija Region where field crops, fruits and grapevines are traditionally rainfed. Exceptionally dry years have a multiple-year effect. Investment in irrigation is imminent but not feasible without state subsidies. To arrive at an impartial decision as to which part of a region should be given priority, it is extremely important to study the spatial distribution and severity of drought. Assessments made to date have resulted in the identification of areas with similar precipitation patterns. However, these assessments are rather crude and have classified parts of Serbia by precipitation depth or climatological precipitation deficit; as such, they are not accurate enough for agricultural purposes. Present-day needs call for more detailed analyses on a smaller scale for specific purposes such as plant production. It is a well-known fact that drought does not simultaneously affect an entire region. It is generally more severe in a certain area, less severe in another area, and may leave parts of the region unaffected. The objective of this research was to conduct a statistical analysis to determine the homogeneity of drought within a region, in spatial and temporal terms. Towards that end, the Standardized Precipitation Index (SPI) of the growing season was studied in 12 areas over a monitoring period of 60 years. Applying the Principle Component Analysis (PCA) method, a single dominant component with a total variance of 69.47% was determined, to which all sites contributed equally. Varimax rotation was then applied and resulted in the identification of three areas. Based on this study of the spatial distribution of drought in the considered region, only one area to the east could be reliably identified as experiencing neither extreme drought nor excessive moisture, while no such claim could be made about two other areas which were assessed. Consequently, drought mitigation measures may be based on separate, homogeneous units. Key words: Agricultural drought, principal component analysis (PCA), standardize precipitation index (SPI).

The sand quarry activities in Cikalahang Village, District of Dukuhpuntang, Cirebon Regency had been illegally mined by hundreds of people. The land properties are owned by the Cikalahang Village. Those mine areas are close to the Telaga Remis (Remis Lake) , which is administratively included in the Kuningan Regency. The existence of illegal mining has disturbed both of local government and people community. In the regional government point of view, the illegal mining will not significantly contribute to generate regional income, whilst for many people their mining activities will produce a destruction to the environment. These can be seen from the objection of the people that request the government to stop all of mine activities because of disturbance to environmental condition of the Telaga Remis (Remis Lake) as one of the water resources for the Cirebon Regency. Based on the intensity of the people requirements, the government of Cirebon Regency had decided to close all of activities of the illegal mining in those area in 2006. According to the decision of Cirebon Regent and the Office of Environment, Forestry and Mining Cirebon Regency, it had prepared planning for rehabilitation and restoration to recover the natural and environmen- tal capability in the mined out areas with respect to the regional spatial planning, land utilization and community demand. The intention of study is to analyse the currently condition of environment in those area including people perception and then making further evaluation to obtain the properly environmental pic- tures for determining the real and strategic action. Data resources to support the study were collected through primary and secondary data. The primary data of physical-chemical component can be obtained by taking instantaneous samples of soil and surface water in the area of study. To identify the people perception, some questioners have been spreaded out to the various strata of people in order to obtain their perception and also direct interview will be applied in this study. The secondary data required for this study such as regional spatial planning, regional landuse and regional regulations will be taken from some institutions in Cirebon Regency. Result analyses showed that the soil characteristics in mined out area were poor because of lack of nutrient and high porousity and the water of Telaga Remis and mine out area could be used as fishing cultivation and household water. The final study shows that the mined out area can potentially be developed as tourism resort in accordance with people request. The other consideration this area is adjacent to Telaga Remis with the background of the beautiful panorama of Mount Ciremai.

Workbench-size particle accelerators, enabled by Nb3Sn-based superconducting radio-frequency (SRF) cavities, hold the potential of driving scientific discovery by offering a widely accessible and affordable source of high-energy electrons and x-rays. Thin-film Nb3Sn RF superconductors with high quality factors, high operation temperatures, and high-field potentials are critical for these devices. However, surface roughness, non-stoichiometry, and impurities in Nb3Sn deposited by conventional Sn-vapor diffusion prevent them from reaching their theoretical capabilities. Here we demonstrate a seed-free electrochemical synthesis that pushes the limit of chemical and physical properties in Nb3Sn. Utilization of electrochemical Sn pre-deposits reduces the roughness of converted Nb3Sn by five times compared to typical vapor-diffused Nb3Sn. Quantitative mappings using chemical and atomic probes confirm improved stoichiometry and minimized impurity concentrations in electrochemically synthesized Nb3Sn. We have successfully applied this Nb3Sn to the large-scale 1.3 GHz SRF cavity and demonstrated ultra-low BCS surface resistances at multiple operation temperatures, notably lower than vapor-diffused cavities. Our smooth, homogeneous, high-purity Nb3Sn provides the route toward high efficiency and high fields for SRF applications under helium-free cryogenic operations.

A novel TiO2/Fe0 composite as water treatment chemical: Zerovalent iron (ZVI) and titanium dioxide (TiO2) have been considered potent reagents in the degradation of organic pollutants. However, the diminishing reactivity with time has obstructed their wide applications, due to the building-up of oxide layer on the surface of ZVI and the electron-hole recombination in TiO2. This study proposed to used the reduction potential of photocatalytic TiO2 (-0.2 to 3.0 eV) to retard the formation of the surface oxide layer and to retard the electron-hole recombination phenomena in TiO2. By this theory, a novel TiO2/Fe0 composite (NTFC) has been developed. This study is comprised of the synthesis of the NTFC, the testing and optimization of NTFC reactivity efficiency by using Acid Black-24 (AB-24) as the target compound, the enhanced degradation of TOC by the compound UV/NTFC/H2O2 system, the choice of light source in the UV/VIS/NTFC system, and the mechanisms of NTFC. The nanoscaled neutral TiO2 sol and nanoscaled zerovalent irons (nZVI) were prepared separately. Surface characterization confirmed that the NTFC is a composite of TiO2 and ZVI with partial core shell structure. The composite is with high specific surface area and microporous structure, with strong binding between TiO2 and ZVI. Moreover, The NTFC which has good strong binding structure strength can be recycled by magnets. Results showed that NTFC was highly efficient in degrading AB-24. The NTFC of highest reactivity was obtained when the TiO2 and Fe0 ratio was 1 to 10. And the optimal pH for reaction was discovered between 3 and 7. Experimental result with color removal of AB-24 showed that the NTFC can be excited by visible lights with the possibility of combining cold cathode fluorescent light (CCFL) and light emitted diode (LED). Tests by the combined UV/NTFC/H2O2 system indicated that the color of the AB-24 containing wastewater was removed by the Fe0 in the beginning and the TOC was degraded by UV/H2O2. The results from the analysis of Electron Paramagnetic Resonance (EPR) and Electrochemical impedance spectroscopy (EIS) confirmed that the NTFC can retard the formation of the oxide layers on the Fe0 and the recombination of electron-hole in TiO2. High concentration of ferrous ions can be maintained in the reaction, and the hydrogen peroxide and free radicals can be produced resulting in Fenton reaction. The TiO2-iron oxide/Fe0 core shell was formed, which resulted in the adsorption of pollutants and the Galvanic cell effect. The mechanism of NTFC reaction can be summarized as: (1) strong reduction in the first stage, (2) oxidation in the second stage, (3) adsorption on the core-shell and Galvanic cell effect in the final stage. The reaction of AB-24 in the NTFC began with the N=N bonds breaking which released the chromophores and auxochromic groups and resulted in decoloration. The moieties from AB-24 bond breaking containing functional groups such as sulfonic acid and N=N bonds were adsorbed on the surface of Fe0 ready for further treatment.