| 1. |
- Bhattacharyya, Anirban, et al.
(författare)
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ESS RF Source and Spoke Cavity Test Plan
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report describes the test plan for the first high power RF source, ESS prototype double spoke cavity and ESS prototype cryomodule at the FREIA Laboratory.
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| 2. |
- Courtney Mustaphi, Colin, et al.
(författare)
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A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya
- 2017
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 12:9
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Tidskriftsartikel (refereegranskat)abstract
- High-elevation ecosystems, such as those on Mount Kenya are undergoing significant changes, with accelerated glacial ice losses over the twentieth century creating new space for alpine plants to establish. These ecosystems respond rapidly to climatic variability and within decades of glacial retreat, Afroalpine pioneering taxa stabilize barren land and facilitate soil development, promoting complex patches of alpine vegetation. Periglacial lake sediment records can be used to examine centennial and millennial scale variations in alpine and montane vegetation compositions. Here we present a 5300-year composite pollen record from an alpine tarn (4370 m asl) in the Hausberg Valley of Mount Kenya. Overall, the record shows little apparent variation in the pollen assemblage through time with abundant montane forest taxa derived and transported from mid elevations, notably high abundances of aerophilous Podocarpus pollen. Afroalpine taxa included Alchemilla, Helichrysum and Dendrosenecio-type, reflecting local vegetation cover. Pollen from the ericaceous zone was present throughout the record and Poaceae percentages were high, similar to other high elevation pollen records from eastern Africa. The Oblong Tarn record pollen assemblage composition and abundances of Podocarpus and Poaceae since the late Holocene (similar to 4000 cal yr BP-present) are similar to pollen records from mid-to-high elevation sites of nearby high mountains such as Mount Elgon and Kilimanjaro. These results suggest a significant amount of uphill pollen transport with only minor apparent variation in local taxa. Slight decreasing trends in alpine and ericaceous taxonomic groups show a long-term response to global late Holocene cooling and a step decrease in rate of change estimated from the pollen assemblages at 3100 cal yr BP in response to regional hydroclimatic variability. Changes in the principal component axis scores of the pollen assemblage were coherent with an independent mid-elevation temperature reconstruction, which supported the strong influence of uphill pollen transport from montane forest vegetation and association between temperatures and montane vegetation dynamics. Pollen accumulation rates showed some variability related to minerogenic sediment input to the lake. The Oblong Tarn pollen record provides an indication of long term vegetation change atop Mount Kenya showing some decreases in local alpine and ericaceous taxa from 5300-3100 cal yr BP and minor centennial-scale variability of montane taxa from mid elevation forests. The record highlights potentials, challenges and opportunities for the use of proglacial lacustrine sediment to examine vegetation change on prominent mountain massifs.
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| 3. |
- Goryashko, Vitaliy, 1982-, et al.
(författare)
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Proposal for Design and Test of a 352 MHz Spoke RF Source
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- More than a dozen of spoke resonators prototypes (SSR, DSR, TSR) have been constructed and tested worldwide. None have accelerated beam until now and the ESS LINAC will be the first accelerator to operate with spoke cavities. Experience with other types of superconducting cavities indicates that high-power test is vital for reliable operation of the cavity in an accelerator. Although characteristics of a bare cavity can be obtained in a low-power test some important features of a `dressed' cavity like the electroacoustic stability and tuning system can be studied only in a high-power test stand. The ESS LINAC is a pulsed machine and the Lorentz detuning originating from the electromagnetic pressure on the cavity walls is expected to be strong. The Lorentz force along with the cavity sensitivity to mechanical excitations at some resonant frequencies may lead to self-sustained mechanical vibrations which make cavity operation dicult. Practical experience shows that increasing the boundary stiness will decrease the static Lorentz force detuning but not necessarily the dynamic one. Therefore, the FREIA group at Uppsala University is building a high-power test stand able to study performance of the ESS spoke cavity at high power. The RF test stand will be able to drive the cavity not only in the self-excitation mode but also with closed RF loop and fixed frequency. The later technique will be used to reproduce the shape of the cavity voltage pulse as it is expected to be in the cavity operating in the ESS LINAC such that the cavity tuning compensation system will be tested under realistic conditions.
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| 4. |
- Jobs, Magnus, 1984-, et al.
(författare)
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DB Science 400 kW RF Station Site Acceptance Test
- 2017
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Rapport (populärvet., debatt m.m.)abstract
- The manufactured and delivered DB-Science 400 kW RF station was tested on site at FREIA during 2016. The station can successfully deliver continuous pulse-trains with a power-level up to 400 kW, however during most of the on-site measurements and testing the total combiner output power was limited to 360 kW due to unusually high G2 currents measured in one of the spare TH595 tetrode tubes used in the station. Each of the stations 200 kW tetrode based amplifier sections were mounted with TH595 tetrode tubes from Thales and tuned for optimal performance. The gain of the tetrode amplifiers were roughly 15 dB with some variation between the two amplifier sections and the overall gain was approximately 74 dB maximum. Amplitude and phase pulse variations were within the specified levels.
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| 5. |
- Jobs, Magnus, et al.
(författare)
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Itelco-Electrosys 400 kW RF Station Site Acceptance Test
- 2015
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Rapport (populärvet., debatt m.m.)abstract
- The manufactured and delivered Itelco-Electrosys 400 kW RF station was tested on site at FREIA, in Uppsala August 31 through September 4 2015. The station could successfully deliver continuous pulsetrains with a power-level up to 400 kW. Each of the stations 200 kW tetrode based amplifier sections were mounted with TH-595 tetrode tubes from Thales and tuned for optimal performance. The gain of the tetrode amplifiers were roughly 15 dB with some variation between the two amplifier sections andthe overall gain was approximately 85 dB maximum.Some droop and phase distortion on the combined output pulse was measured caused primarily by a limited response time of the screen-grid power supply.
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| 6. |
- Kaufman, Darrell, et al.
(författare)
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A global database of Holocene paleotemperature records
- 2020
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format.
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| 7. |
- Li, Han, et al.
(författare)
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Characterization of a beta=0.5 double spoke cavity with a fixed power coupler
- 2019
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 927, s. 63-69
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Tidskriftsartikel (refereegranskat)abstract
- ESS, the European Spallation Source, will adopt a single family of double spoke cavities for accelerating the beam from the normal conducting section to the first family of the elliptical superconducting cavities. It will be the first double spoke cavities in the world to be commissioned for a high power proton accelerator. The first double spoke cavity for the ESS project was tested with high power in the HNOSS cryostat at Uppsala University. A pulse-mode test stand based on a self-excited loop was used in this test. The qualification of the cavity package involves a double-spoke superconducting cavity, a fixed fundamental power coupler, tuner, a low-level radiofrequency (LLRF) system and a high-power radiofrequency (RF) station. The test represents an important verification milestone before the module assembly. This cavity had unfortunately a high dynamic loss of 12W @ 9 MV/m, where potential causes for such a high value have been studied and corresponding suggestions are listed. This paper presents the test configuration, RF conditioning history, first high power performance and experience of this cavity package.
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| 8. |
- Li, Han, et al.
(författare)
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ESS Spoke Cavity Conditioning at FREIA
- 2017
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Ingår i: Proceedings of IPAC2017. - 9783954501823 ; , s. 1074-1076
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The first ESS double spoke cavity installed with RF power coupler was tested in the HNOSS cryostat at the FREIA Laboratory. Power coupler and cavity conditioning have been optimized in order to reach high efficiency and high availability by reducing the time and effort of the overall conditioning process. Meanwhile, an optimal procedure for ESS conditioning is studied. This paper presents the study result and experience of the RF conditioning procedure for the first ESS double spoke cavity.
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| 9. |
- Li, Han, et al.
(författare)
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First High Power Test of the ESS Double Spoke Cavity
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The first double spoke cavity for ESS project was tested with high power in the HNOSS cryostat at FREIA Laboratory. This cavity is designed for 325.21MHz, a pulse mode with 14 Hz repetition rate, up to peak power of 360 kW. The qualification of the cavity package in a high power test, involved a spoke superconducting cavity, a fundamental power coupler, LLRF system and a RF station, represented an important verification before the module assembly. This report presents the test configuration, RF conditioning history and first high power performance of this cavity package.
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| 10. |
- Li, Han, et al.
(författare)
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First High Power Test of the ESS High Beta Elliptical Cavity package
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The first high-beta elliptical cavity for ESS project was tested with high power in the HNOSS cryostat at FREIA Laboratory. This cavity is designed for 704.42 MHz, a pulse mode with 14 Hz repetition rate, up to peak power of 1.5 MW. The qualification of the cavity package in a high power test, involved an elliptical superconducting cavity, a fundamental power coupler, cold tuning system, LLRF system and klystron system, represented an important verification before the module assembly. This report presents the test configuration, RF conditioning history and first high power performance of this cavity package.
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