10 research outputs found
Plasma Cleaning of LCLS-II-HE verification cryomodule cavities
Plasma cleaning is a technique that can be applied in superconducting
radio-frequency (SRF) cavities in situ in cryomodules in order to decrease
their level of field emission. We developed the technique for the Linac
Coherent Light Source II (LCLS-II) cavities and we present in this paper the
full development and application of plasma processing to the LCLS-II High
Energy (HE) verification cryomodule (vCM). We validated our plasma processing
procedure on the vCM, fully processing four out of eight cavities of this CM,
demonstrating that cavities performance were preserved in terms of both
accelerating field and quality factor. Applying plasma processing to this
clean, record breaking cryomodule also showed that no contaminants were
introduced in the string, maintaining the vCM field emission-free up to the
maximum field reached by each cavity. We also found that plasma processing
eliminates multipacting (MP) induced quenches that are typically observed
frequently within the MP band field range. This suggests that plasma processing
could be employed in situ in CMs to mitigate both field emission and
multipacting, significantly decreasing the testing time of cryomodules, the
linac commissioning time and cost and increasing the accelerator reliability.Comment: 11 pages, 10 figure
FIELD EMISSION MITIGATION VIA IN-SITU PLASMA PROCESSING IN 1.3 GIGAHERTZ 9-CELL LCLS-II CAVITIES
Field emission (FE) is one of the limiting factors in superconducting radiofrequency cavities' performance. It is known that even a few monolayers of surface adsorbed
contaminants can lower the niobium work function and increase the FE.
In order to address the field emission that may arise once the accelerator is already
assembled, it was decided to develop plasma processing for the Linac Coherent Light
Source II, a method to mitigate field emission in-situ.
Starting from Doleans's successful experience with plasma processing for high beta
cavities, Fermi National Accelerator Laboratory is developing plasma cleaning
for TESLA shaped 1.3 GHz 9-cell cavities. A new method of ignition based on the
higher order modes and couplers was developed, along with a detection procedure
that allows to identify the location of the plasma inside the cavity. In this work are
presented the results of plasma processing applied to 1.3 GHz cavities, both single-cell
and 9-cells. The cavities were contaminated with multiple sources, naturally or artificially, and their performance was measured through cryogenic RF tests before and
after plasma cleaning. These experiments proved that plasma processing successfully
removed hydrocarbon-related field emission from cavities artificially contaminated,
but also from a cavity with natural and unknown FE source. In some cases of more
extreme contamination through vacuum failure simulation conducted in air (not in a
cleanroom), plasma processing was not able to recover the cavity's performance. An
ongoing analysis of the cavity contaminants is presented here, explaining the reason
why some contaminated cavities showed little improvement after plasma processing.
A microscopic study of the effect of plasma processing on the niobium surface
is also presented. Niobium samples prepared with different surface treatments were
analyzed using X-ray photoelectron spectroscopy, scanning electron microscopy and
energy-dispersive X-ray spectroscopy. The samples were subjected to plasma processing and analyzed again, in order to draw a comparison and identify possible surface
changes caused by the reactive oxygen contained in the glow discharge. The samples
were prepared with different surface treatments in order to understand if plasma processing
may affect them differently. This study showed a possible increase in the oxide
thickness after plasma processing and a reduction of the energy difference between the
pentoxide and the metal peaks. In preparation for this study, the near-surface region
of one niobium sample was investigated with X-ray photoelectron spectroscopy at
various steps of sputtering and subsequent oxide regrowth in air. The results showed
that the majority of the oxide is composed of Nb2O5, however, the presence of two
suboxides (NbO, NbO2) is observed, plus an additional peak (attributed to Nb2O)
measured both during sputtering and oxide regrowth
Neuro-Behçet’s Disease presenting as an isolated progressive cognitive and behavioral syndrome
Behçet’s disease is a chronic inflammatory disorder manifesting as a vasculitis that affects arteries and veins of any size. Up to 44% of cases may also present with neurological symptoms, thus defining
Neuro-Behçet’s disease. We describe a case of Neuro-Behçet’s disease characterized by progressive behavioral and cognitive deterioration prevailing over other neurological symptoms, without evident
systemic involvement
RF Accelerator Technology R&D: Report of AF7-rf Topical Group to Snowmass 2021
Accelerator radio frequency (RF) technology has been and remains critical for modern high energy physics (HEP) experiments based on particle accelerators. Tremendous progress in advancing this technology has been achieved over the past decade in several areas highlighted in this report. These achievements and new results expected from continued R&D efforts could pave the way for upgrades of existing facilities, improvements to accelerators already under construction (e.g., PIP-II), well-developed proposals (e.g., ILC, CLIC), and/or enable concepts under development, such as FCC-ee, CEPC, C3, HELEN, multi-MW Fermilab Proton Intensity Upgrade, future Muon Colloder, etc. Advances in RF technology have impact beyond HEP on accelerators built for nuclear physics, basic energy sciences, and other areas. Recent examples of such accelerators are European XFEL, LCLS-II and LCLS-II-HE, SHINE, SNS, ESS, FRIB, and EIC. To support and enable new accelerator-based applications and even make some of them feasible, we must continue addressing their challenges via a comprehensive RF R&D program that would advance the existing RF technologies and explore the nascent ones
Searches for New Particles, Dark Matter, and Gravitational Waves with SRF Cavities
International audienceThis is a Snowmass white paper on the utility of existing and future superconducting cavities to probe fundamental physics. Superconducting radio frequency (SRF) cavity technology has seen tremendous progress in the past decades, as a tool for accelerator science. With advances spear-headed by the SQMS center at Fermilab, they are now being brought to the quantum regime becoming a tool in quantum science thanks to the high degree of coherence. The same high quality factor can be leveraged in the search for new physics, including searches for new particles, dark matter, including the QCD axion, and gravitational waves. We survey some of the physics opportunities and the required directions of R&D. Given the already demonstrated integration of SRF cavities in large accelerator systems, this R&D may enable larger scale searches by dedicated experiments
Efficacy of lamivudine prophylaxis in preventing hepatitis B virus reactivation in patients with resolved infection undergoing allogeneic SCT and receiving rituximab
Gerstmann-Sträussler-Scheinker Disease
Gerstmann-Sträussler-Scheinker disease (GSS) is a hereditary form of prion disease. GSS, in particular the form caused by the PRNP gene P102L mutation, is transmissible to primates and rodents. Thus, GSS is a unique disease that is both genetic and transmissible; however, the exact nature of the transmissible agent is not clear. The clinical picture of GSS comprises cerebellar ataxia, dementia and pyramidal and extrapyramidal signs and symptoms. However, the disease is heterogeneous and in different families and different mutations the clinical picture may vary. The neuropathological picture is characterized by the presence of amyloid plaques – mainly multicentric plaques. There are several models of GSS in transgenic mice and in Drosophila sp. In mice produced with an overexpressed transgene that carries the P101L mutation (corresponding to the P102L mutation in humans), “spontaneous” neurodegeneration is observed and this, in turn, is transmissible but to transgenic mice with a low copy number. In contrast, P101L transgenic mice produced by means of reciprocal recombination show no spontaneous neurodegeneration, but instead become more susceptible to transmission of human GSS following inoculation.Choroba Gerstmanna-Sträusslera-Scheinkera (GSS) jest genetycznie uwarunkowaną chorobą wywoływaną przez priony. Jest ona unikalna, ponieważ udało się przepasażować GSS na naczelne i gryzonie przynajmniej z mózgu obarczonego mutacją kodonu 102. Tym samym jest to jedyne schorzenie jednocześnie genetycznie uwarunkowane i zakaźne, aczkolwiek natura czynnika infekcyjnego (prionu) nadal stanowi przedmiot dyskusji. W obrazie klinicznym GSS dominuje postępująca ataksja móżdżkowa z towarzyszącym otępieniem i objawami piramidowo-pozapiramidowymi. Jest to jednak choroba heterogenna, o różnym obrazie klinicznym u nosicieli różnych mutacji, a nawet u nosicieli tej samej mutacji. Obraz neuropatologiczny obejmuje obecność PrPd – immunododatnich złogów amyloidu pod postacią blaszek, zwłaszcza tzw. blaszek wielordzeniowych. Istnieje kilka modeli GSS. U myszy transgenicznych z nadekspresją zmutowanego genu kodującego PrP obserwuje się spontaniczną chorobę zwyrodnieniową, pasażowalną na myszy transgeniczne o niskiej liczbie transgenu. U myszy transgenicznych uzyskanych drogą wzajemnej rekombinacji, a więc bez nadeskpresji, nie występuje choroba spontaniczna, niemniej stają się one wrażliwe na zakażenie GSS
Italian Neurological Society guidelines for the diagnosis of dementia: Revision l
This paper presents the Italian guidelines for the diagnosis of dementi