On the Evolution of Ion Bunch Profile in the Presence of Longitudinal Coherent Electron Cooling

In the presence of longitudinal coherent electron cooling, the evolution of the line-density profile of a circulating ion bunch can be described by the 1-D Fokker-Planck equation. We show that, in the absence of diffusion, the 1-D equation can be solved analytically for certain dependence of cooling force on the synchrotron amplitude. For more general cases with arbitrary diffusion, we solved the 1-D Fokker-Planck equation numerically and the numerical solutions have been compared with results from macro-particle tracking

Formation of thin film Cr-N composites under ion bombardment at low rates of chromium deposition

One of peculiar features of the IBAD technology consists in that the damage level and concentration of implanted ions are distributed nonuniformly in the depth of deposited material. The calculations, we have done earlier [1], showed that the highest degree of nonequilibrium is realized in the first 50 nm of a coating. However, just in this thickness the nucleation and formation of the material structure is observed. The peculiarities of chromium coating formation without assisted irradiation and under bombarding with nitrogen ions having the energy of 30 keV were studied. The rates of chromium deposition were low, 0,05…0,1 nm/s. During the experiment the vacuum was maintained at a level of 4·10⁻³ Pa and was determined, in main, by the content of nitrogen molecules arriving from the discharging chamber of the ion source. The thickness within the range from 3 to 10 nm was investigated. The results have shown that at the earliest stages of the film growth solely chromium nitride CrN is formed. Sizes of visible nuclei are in the range from 1 to 4 nm, and their density is 1…3·10¹²cm⁻² . As the film thickness increases, the nuclei are growing, then their coalescence occurs and a uniform coating is formed. Chromium deposition without irradiation, but at the same nitrogen pressure, resulted in formation of chromium hcp structure with the following crystallographic parameters: a = 0,315 nm; c = 0,492 nm. The grain size was 3…4 nm. After reaching the coating continuity, the hcp structure was transformed into the bcc structure with the parameter a = 0,261 nm.Проведено сравнительное исследование начальных стадий формирования хромового покрытия в условиях бомбардировки ионами азота с энергией 30 кэВ и без ассистированного облучения, но при повышенном содержании азота в рабочей камере. Скорости осаждения были выбраны небольшими – 0,05...0,1 нм/с. Вакуум в камере был на уровне 4•10⁻³ Па и определялся в основном азотом, который напускался в разрядную камеру ионного источника. Толщина исследуемых объектов была в интервале 3…10 нм. Результаты показали, что при ионной бомбардировке происходит образование нитрида хрома CrN, начиная с самых ранних стадий роста пленки. Размер видимых зародышей находится в диапазоне 1…4 нм, плотность – 3•10¹² см⁻². С увеличением толщины пленки происходит коалесценция малых зародышей, образование свободных зон и зарождение на них новой популяции зерен. Осаждение хрома без ионного облучения приводит к формированию ГПУ-структуры с параметрами решетки а=0,315 нм и с=0,492 нм. При достижении сплошности у пленки происходит трансформация ГПУ-структуры в ОЦК с параметром а=0,261 нм.Проведено порівняльне вивчення початкової стадії формування хромового покриття в умовах бомбардування іонами азоту з енергією 30 кеВ та без асистуючого опромінення, але при підвищеному тиску азоту. Швидкості осадження були підібрані невеликі – 0,05…0,1 нм/с. Вакуум у камері був на рівні 4·10⁻³ Па та обумовлювався азотом, який напускався в розрядову камеру іонного джерела. Товщина досліджених плівок – 3…10 нм. Результати показали, що при іонному бомбардуванні має місце створення нітриду хрому CrN починаючи з самих початкових стадій. Розмір зародків знаходиться у діапазоні 1…4 нм, щільність – 3·10¹² см⁻². Зі збільшенням товщини має місце коалесценція зародків, створення вільних зон та зародження на них нової популяції зерен. Осадження хрому без іонного опромінення призводить до формування ГПУ-структури хрому з параметрами гратки а=0,315 нм та с=0,492 нм. При появленні сполошної плівки має місце трансформування ГПУ-структури у ОЦК з параметром а=0,261нм

Formation of thin film Cr-N composites under ion bombardment at low rates of chromium deposition

One of peculiar features of the IBAD technology consists in that the damage level and concentration of implanted ions are distributed nonuniformly in the depth of deposited material. The calculations, we have done earlier [1], showed that the highest degree of nonequilibrium is realized in the first 50 nm of a coating. However, just in this thickness the nucleation and formation of the material structure is observed. The peculiarities of chromium coating formation without assisted irradiation and under bombarding with nitrogen ions having the energy of 30 keV were studied. The rates of chromium deposition were low, 0,05…0,1 nm/s. During the experiment the vacuum was maintained at a level of 4•10⁻³ Pa and was determined, in main, by the content of nitrogen molecules arriving from the discharging chamber of the ion source. The thickness within the range from 3 to 10 nm was investigated. The results have shown that at the earliest stages of the film growth solely chromium nitride CrN is formed. Sizes of visible nuclei are in the range from 1 to 4 nm, and their density is 1…3•10¹²cm⁻² . As the film thickness increases, the nuclei are growing, then their coalescence occurs and a uniform coating is formed. Chromium deposition without irradiation, but at the same nitrogen pressure, resulted in formation of chromium hcp structure with the following crystallographic parameters: a = 0,315 nm; c = 0,492 nm. The grain size was 3…4 nm. After reaching the coating continuity, the hcp structure was transformed into the bcc structure with the parameter a = 0,261 nm.Проведено сравнительное исследование начальных стадий формирования хромового покрытия в условиях бомбардировки ионами азота с энергией 30 кэВ и без ассистированного облучения, но при повышенном содержании азота в рабочей камере. Скорости осаждения были выбраны небольшими – 0,05...0,1 нм/с. Вакуум в камере был на уровне 4•10⁻³ Па и определялся в основном азотом, который напускался в разрядную камеру ионного источника. Толщина исследуемых объектов была в интервале 3…10 нм. Результаты показали, что при ионной бомбардировке происходит образование нитрида хрома CrN, начиная с самых ранних стадий роста пленки. Размер видимых зародышей находится в диапазоне 1…4 нм, плотность – 3•10¹² см⁻² . С увеличением толщины пленки происходит коалесценция малых зародышей, образование свободных зон и зарождение на них новой популяции зерен. Осаждение хрома без ионного облучения приводит к формированию ГПУ-структуры с параметрами решетки а=0,315 нм и с=0,492 нм. При достижении сплошности у пленки происходит трансформация ГПУ-структуры в ОЦК с параметром а=0,261 нм.Проведено порівняльне вивчення початкової стадії формування хромового покриття в умовах бомбардування іонами азоту з енергією 30 кеВ та без асистуючого опромінення, але при підвищеному тиску азоту. Швидкості осадження були підібрані невеликі – 0,05…0,1 нм/с. Вакуум у камері був на рівні 4•10⁻³ Па та обумовлювався азотом, який напускався в розрядову камеру іонного джерела. Товщина досліджених плівок – 3…10 нм. Результати показали, що при іонному бомбардуванні має місце створення нітриду хрому CrN починаючи з самих початкових стадій. Розмір зародків знаходиться у діапазоні 1…4 нм, щільність – 3•10¹² см⁻² . Зі збільшенням товщини має місце коалесценція зародків, створення вільних зон та зародження на них нової популяції зерен. Осадження хрому без іонного опромінення призводить до формування ГПУ-структури хрому з параметрами гратки а=0,315 нм та с=0,492 нм. При появленні сполошної плівки має місце трансформування ГПУ-структури у ОЦК з параметром а=0,261нм

Petroleum-related hydrocarbons in deep and subsurface sediments from South-Western Barents Sea

Subsurface sediments from a pockmark area in South-Western Barents Sea have been earlier found to contain elevated levels of petroleum-related polycyclic aromatic hydrocarbons. This work describes a comprehensive analysis of various biomarkers, including the highly source-specific hopanes, in a 4.5 m long gravity core from the same area, together with subsurface sediment samples from other areas in the region without pockmarks present (“background samples”). A clear difference between the pockmark gravity core and the background sediment cores was found, both with regard to genesis and the level of transformation of organic matter. A number of indicator parameters, such as methylphenanthrene index (MPI-1), point towards a significantly higher maturity of hydrocarbons in the pockmark core throughout its length as compared to the other sampled locations. Higher contents of microbial hopanoids (hopenes) may indicate the former presence of petroleum. These findings confirm the hypothesis of a natural hydrocarbon source in the deeper strata present in the studied location with pockmarks

A Statistical Study on the Morphology of Rays and Dynamics of Blobs in the Wake of Coronal Mass Ejections

In this paper, with a survey through the Large Angle and Spectrometric Coronagraph (LASCO) data from 1996 to 2009, we present 11 events with plasma blobs flowing outwards sequentially along a bright coronal ray in the wake of a coronal mass ejection. The ray is believed to be associated with the current sheet structure that formed as a result of solar eruption, and the blobs are products of magnetic reconnection occurring along the current sheet. The ray morphology and blob dynamics are investigated statistically. It is found that the apparent angular widths of the rays at a fixed time vary in a range of 2.1-6.6 (2.0-4.4) degrees with an average of 3.5 (2.9) degrees at 3 (4) Rs, respectively, and the observed durations of the events vary from 12 h to a few days with an average of 27 h. It is also found, based on the analysis of blob motions, that 58% (26) of the blobs were accelerated, 20% (9) were decelerated, and 22% (10) moved with a nearly-constant speed. Comparing the dynamics of our blobs and those that are observed above the tip of a helmet streamer, we find that the speeds and accelerations of the blobs in these two cases differ significantly. It is suggested that these differences of the blob dynamics stem from the associated magnetic reconnection involving different magnetic field configurations and triggering processes.Comment: 12 pages, 6 figures, accepted by Solar Physic

Stratigraphy of Late Cenozoic sediments of the western Chukchi Sea: New results from shallow drilling and seismic-reflection profiling

The Quaternary history of Beringia and of the Arctic–Pacific marine connection via the Bering Strait is poorly understood because of the fragmentary stratigraphic record from this region. We report new borehole and seismic-reflection data collected in 2006 in the southwestern Chukchi Sea. Sediment samples were analyzed for magnetic properties, grain size, heavy minerals, and biostratigraphic proxies (spores and pollen, foraminifers, ostracodes, diatoms, and aquatic palynomorphs). Two shallow boreholes drilled between the Chukotka Peninsula and the Wrangel Island recovered sediments of two principal stratigraphic units with a distinct unconformity between them. Based on predominantly reverse paleomagnetic polarity of the lower unit and pollen spectra indicative of forested coasts and climate warmer than present, the age of this unit is estimated as Pliocene to early Pleistocene (broadly between ca. 5 and 2 Ma). Attendant sedimentary environments were likely alluvial to nearshore marine. These deposits can be correlated to the seismic unit infilling valleys incised into sedimentary bedrock across much of the study area, and possibly deposited during a transgression following the opening of the Bering Strait. The upper unit from both boreholes contains Holocene 14C ages and is clearly related to the last, postglacial transgression. Holocene sediments in Borehole 2 indicate fast deposition at the early stages of flooding (between ca. 11 and 9 ka) to very low deposition, possibly related to expansive sea ice. Closer to shore, deposition at Borehole 1 resumed much later (ca. 2 ka), likely due to a change in the pattern of coastal erosional processes and/or the demise of a landbridge between the Chukotka Peninsula and the Wrangel Island inferred from studies on mammoth distribution

VORPAL simulations relevant to coherent electron cooling

Coherent electron cooling (CEC) [1] combines the best features of electron cooling and stochastic cooling, via free-electron laser technology [2], to offer the possibility of cooling high-energy hadron beams with order-of-magnitude shorter cooling times. Many technical difficulties must be resolved via full-scale 3D simulations, before the CEC concept can be validated experimentally. VORPAL is the ideal code for simulating the modulator and kicker regions, where the electron and hadron beams will co-propagate as in a conventional electron cooling section. Unlike previous VORPAL simulations [3] of electron cooling physics, where dynamical friction on the ions was the key metric, it is the details of the electron density wake driven by each ion in the modulator section that must be understood, followed by strong amplification in the FEL. We present some initial simulation results

Small gap magnet prototype measurements for eRHIC

In this paper we present the design and prototype measurement of small gap (5mm to 10 mm aperture) dipole and quadrupole for the future high energy ERL (Energy Recovery Linac). The small gap magnets have the potential of largely reducing the cost of the future electron-ion collider project, eRHIC, which requires a 10GeV to 30 GeV ERL with up to 6 energy recovery passes (3.8 km each pass). We also studied the sensitivity of the energy recovery pass and the alignment error in this small magnets structure and countermeasure methods

Digital receivers for low-frequency radio telescopes UTR-2, URAN, GURT

This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. Since 1998, digital receivers performing on-the-fly dynamic spectrum calculations or waveform data recording without data loss have been used at the UTR-2 radio telescope, the URAN VLBI system, and the GURT new generation radio telescope. Here we detail these receivers developed for operation in the strong interference environment that prevails in the decameter wavelength range. Data collected with these receivers allowed us to discover numerous radio astronomical objects and phenomena at low frequencies, a summary of which is also presented.Comment: 24 pages, 15 figure