High Q Operation of SRF Cavities The Impact of Thermocurrents on the RF Surface Resistance

We present a study concerning the operation of a superconducting RF cavity non doped niobium in horizontal testing with the focus on understanding the thermoelectrically induced contribution to the surface resistance. Starting in 2009, we suggested a means of reducing the residual resistance by warming up a cavity after initial cooldown to about 20 K and cooling it down again [1]. In subsequent studies we used this technique to manipulate the residual resistance by more than a factor of 2 [2]. We postulated that thermocurrents during cooldown generate additional trapped magnetic flux that impacts the cavity quality factor. Since several questions remained open, we present here a more extensive study including measurement of two additional passband modes of the 9 cell cavity that confirms the effect. We also discuss simulations that substantiate the claim. While the layout of the cavity LHe tank system is cylindrically symmetric, we show that the temperature dependence of the material parameters result in a non symmetric current distribution. Hence a significant amount of magnetic flux can be generated at the RF surface resulting in an increased surface resistance [3]

High Q Cavity Operation Study on the Thermoelectrically Induced Contribution to RF Surface Resistance

We present a study concerning the operation of a superconducting RF cavity non doped niobium in horizontal testing with the focus on understanding the thermoelectrically induced contribution to the surface resistance. Starting in 2009, we suggested a means of reducing the residual resistance by warming up a cavity after initial cooldown to about 20 K and cooling it down again [1]. In subsequent studies we used this technique to manipulate the residual resistance by more than a factor of 2 [2]. We postulated that thermocurrents during cooldown generate additional trapped magnetic flux that impacts the cavity quality factor. Since several questions remained open, we present here a more extensive study including measurement of two additional passband modes of the 9 cell cavity that confirms the effect. We also discuss simulations that substantiate the claim. While the layout of the cavity LHe tank system is cylindrically symmetric, we show that the temperature dependence of the material parameters result in a non symmetric current distribution. Hence a significant amount of magnetic flux can be generated at the RF surface resulting in an increased surface resistance [3

Process approach: the way to improve the quality of high-tech products

В статье представлен процесс регламентации бизнес-процесса «Изготовление источников питания», описанного с использованием методологии IDEF0 и программного продукта Business Studio 4.0 на примере подразделения, которое занимается разработкой и изготовлением сварочных источников тока. При моделировании процесса изготовления источников питания была построена матрица атрибутов, в которой определены цели и задачи процессов, владельцы на каждом этапе процесса, несущие ответственность за ход и за результат, определены входы и выходы (документы) процесса, а также критерии результативности и/или эффективности процесса, для осуществления оперативного управления на всех этапах изготовления конечной продукции. В результате работы был разработан комплект документов, в состав которого вошли: регламент процесса изготовления источников тока, положение о подразделении, должностные инструкции сотрудников, участвующих в процессе. Деятельность по регламентации процесса проводилась в рамках подготовки подразделения к сертификации в соответствии с требованиями стандарта ГОСТ РВ 0015-002-2012 «Система разработки и постановки продукции на производство военной техники. Системы менеджмента качества. Общие требования» в системе добровольной сертификации «Военный регистр»

Impact of geometry on flux trapping and the related surface resistance in a superconducting cavity

In order to minimize the surface resistance in superconducting cavities, a deeper understanding of residual resistance due to trapped magnetic flux is necessary. For that purpose, a combined temperature and magnetic field mapping system is employed to map magnetic flux trapped in a superconducting cavity, and the related increase in surface resistance. By cooling down a 1.3 GHz TESLA single cell cavity several times with externally applied static magnetic fields with different orientations with respect to the cavity, a statement can be made about how the angle between the applied magnetic field and the cavity s surface affects flux trapping, and surface resistance. For example, a significantly higher increase in surface resistance is observed when the applied magnetic field is perpendicular to the cavity s surface compared to when it is paralle

Ecological Niche Modeling of Francisella tularensis Subspecies and Clades in the United States

Two subspecies of Francisella tularensis are recognized: F. tularensis subsp. tularensis (type A) and F. tularensis subsp. holartica (type B). Type A has been subdivided further into A1a, A1b, and A2, which differ geographically and clinically. The aim of this work was to determine whether or not differences among subspecies and clades translate into distinct ecological niches. We used 223 isolates from humans and wildlife representing all six genotypes (type A, B, A1, A2, A1a, or A1b). Ecological-niche models were built independently for each genotype, using the genetic algorithm for rule-set prediction. The resulting models were compared using a non-parametric multivariate analysis-of-variance method. A1 and A2 are ecologically distinct, supporting the previously observed geographic division, whereas ecological niches for types A and B overlapped notably but A1a and A1b displayed no appreciable differences in their ecological niches

BERLinPro A Compact Demonstrator ERL for High Current and Low Emittance Beams

The HZB previously BESSY was the first institution in Germany to build and operate a dedicated synchrotron light source BESSY I . About 10 years ago BESSY II, a third generation synchrotron light source, was commissioned and is very successfully running since that time. Due to its expertise in development and operation of accelerator facilities HZB is ideally suited to realize new accelerator concepts. Therefore HZB is proposing to build a demonstrator ERL facility BERLinPro that will realize high current and low emittance operation at 100 MeV. BERLinPro is intented to bring ERL technology to maturity. This paper presents an overview of the project and the key components of the facilit

Results from Beam Commissioning of an SRF Plug Gun Cavity Photoinjector

Superconducting rf photo electron injectors SRF photoinjectors hold the promise to deliver high brightness, high average current electron beams for future light sources or other applications demanding continuous wave operation of an electron injector. This paper discusses results from beam commissioning of a hybrid SRF photoinjector based on a Pb coated plug and a Nb rf gun cavity for beam energies up to 2.5MeV at Helmholtz Zentrum Berlin HZB . Emittance measurements and transverse phase space characterization with solenoid scan and slitmask methods will be presente

Mitigation of parasitic losses in thequadrupole resonator enabling directmeasurements of low residual resistancesof SRF samples

The quadrupole resonator QPR is a dedicated sample test cavity for the RF characterization of superconducting samples in a wide temperature, RF field, and frequency range. Its main purpose is high resolution measurements of the surface resistance with direct access to the residual resistance, thanks to the low frequency of the first operating quadrupole mode. In addition to the well known high resolution of the QPR, a bias of measurement data toward higher values has been observed, especially in higher harmonic quadrupole modes. Numerical studies show that this can be explained by parasitic RF losses on the adapter flange used to mount samples into the QPR. Coating several micrometers of niobium on those surfaces of the stainless steel flange that are exposed to the RF fields significantly reduced this bias, enabling a direct measurement of a residual resistance smaller than 5 n amp; 937; at 2 K and 413 MHz. A constant correction based on simulations was not feasible due to deviations from one measurement to another. However, this issue is resolved given these new result