Evaluation of predictive correlation between flux expulsion and grain growth for superconducting radio frequency cavities

A series of experiments were carried out in an effort to develop a simple method for predicting magnetic flux expulsion behavior of high purity niobium used to fabricate superconducting radio frequency (SRF) cavities. Using conventional metallographic characterizations in conjunction with high spatial resolution electron backscattered diffraction-orientation imaging microscopy (EBSD-OIM), we found that the flux expulsion behavior of 1.3 GHz single cell SRF Nb cavities is significantly associated with the grain growth of the Nb material during heat treatment. Most of Nb grains rapidly grew during 900C heat treatment, and likely full-recrystallized with 1000C HT. With comparison of the magnetic flux expulsion ratio (Bsc/Bnc) at dT = 5 K, the flux expulsion efficiency of the cavities increases along with increasing of grain size. Most interestingly, 900C HT shows a roughly linear trend that suggests this criterion could be used to predict appropriate heat treatment temperature for sufficient flux expulsion behavior in SRF-grade Nb. This result would be used to see if flux expulsion can be predicted by examining the materials coming from the Nb vendor, prior to cavity fabrication

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

The Grizzly, October 30, 1990

Ursinus Honored at Governor\u27s Mansion • Sam Stretton To Speak • Glassmoyer Retires • Heefner New Board President • The Gender of Speech: A Tri-Lambda Lecture • Career Day November 6th • Forbes to Speak to Clergy • Animal Lovers Unite • Mock DWI A Hit • Student Camp Experience • David is Great!! • Presenting Protheatre: The Changeling • Crutcher Leads Team• Muhlenberg Falls • Swimmers Open Season at Relay Meet • Women Running To MAC\u27s • Men Go for MAC Title • Soccer • Letters: Keep Ursinus Clean; Quad Keys Revoked?; Signs Stolen; Security, Please Hold • Environmentally Concerned? Get Active • Bush\u27s Environmental Lip Service • This Time for Real • Nature Versus Nurture: A Step in Solving the Puzzlehttps://digitalcommons.ursinus.edu/grizzlynews/1262/thumbnail.jp

The Grizzly, February 18, 1992

Fraternity Pledging in Full Swing • Commencement Speaker Chosen • Today\u27s Health • Energy-Savers • Tau Sig Clothing Drive • Jolly Green Giants • Frederick Douglass Now • A Capella Entertainment • Movie Review: Thelma and Louise • Japan Bashing: Justified or Not? • Laff-a-Lympics • Letters: Can I Graduate?; Pepe\u27s Problem • Hoopsters Continue to Get Dunked • Hoop-A-Holics Come out on Top • Lady Bears Break Team Record • Aquabears End Season with a Splashhttps://digitalcommons.ursinus.edu/grizzlynews/1290/thumbnail.jp

Conservation and Promotion of Neglected and Underutilized Crop Species in West Africa: Policy and Governance

Neglected and underutilized crop species (NUCS/NUS) are claimed to contribute to sustainable development. However, many scholars argue that enabling policies and appropriate governance are needed to operationalize such a potential contribution. Therefore, this systematic review analyzes the literature dealing with the relationships between policy and governance aspects and the promotion of NUS in West Africa. It draws upon 45 eligible articles identified through a search conducted on the Web of Science in December 2023. The existing literature focuses on Nigeria and a few NUS, especially cassava. The addressed policy domains include biodiversity conservation; subsidies; seed systems; food security, self-sufficiency and sovereignty; trade and import substitution; food safety and health; climate change and energy; land use; research, innovation and development; and support and assistance systems. Meanwhile, the main governance domains are (1) inclusiveness and participation and (2) institutional capacity. The analysis suggests that NUS development is also affected by sectoral policy coherence and consistency as well as the policy–governance interplay. Future studies should widen the scope in terms of geographical coverage in West Africa and NUS addressed to allow for more comparisons. Furthermore, there is a need for further research to understand the synergies and trade-offs between sectoral policies affecting NUS promotion and development

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Measurement of the very rare K+→π+ννˉK^+ \to \pi^+ \nu \bar\nu decay

The decay K+→π+νν¯ , with a very precisely predicted branching ratio of less than 10−10 , is among the best processes to reveal indirect effects of new physics. The NA62 experiment at CERN SPS is designed to study the K+→π+νν¯ decay and to measure its branching ratio using a decay-in-flight technique. NA62 took data in 2016, 2017 and 2018, reaching the sensitivity of the Standard Model for the K+→π+νν¯ decay by the analysis of the 2016 and 2017 data, and providing the most precise measurement of the branching ratio to date by the analysis of the 2018 data. This measurement is also used to set limits on BR(K+→π+X ), where X is a scalar or pseudo-scalar particle. The final result of the BR(K+→π+νν¯ ) measurement and its interpretation in terms of the K+→π+X decay from the analysis of the full 2016-2018 data set is presented, and future plans and prospects are reviewed

Narrow Bandwidth Active Noise Control for Microphonics Rejection in Superconducting Cavities at LCLS-II

LCLS-II is an X-Ray Free Electron Laser (XFEL) com-missioned in 2022, being the first Continuous Wave (CW) hard XFEL in the world to come into operation. To accelerate the electron beam to an energy of 4 GeV, 280 TESLA type superconducting RF (SRF) cavities are used. A loaded quality factor $(_ )$ of $4×10^7$ is used to drive the cavities at a power level of a few kilowatts. For this _ , the RF cavity bandwidth is 32 Hz. Therefore, keeping the cavity resonance frequency within such bandwidth is imperative to avoid a significant increase in the required drive power. In superconducting accelerators, resonance frequency variations are produced by mechanical microphonic vibrations of the cavities. One source of microphonic noise is rotary machinery such as vacuum pumps or HVAC equipment. A possible method to reject these disturbances is to use Narrowband ActiveNoise Control (NANC) techniques. Such a technique was already tested at DESY/CMTB [1] and Cornell/CBETA [2].This proceeding presents the implementation of a NANC controller adapted to the LCLS-II Low Level RF (LLRF) control system. Tests showing the rejection of LCLS-II microphonic disturbances are also presented