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Yuan He

Publications and source records attributed to Yuan He.

178 records · Page 10Linked to original sources
arXiv2018

Magnetic properties and hydrides precipitation observation of nitrogen doping niobium used for accelerator applications

Nitrogen doping study on niobium (Nb) samples used for the fabrication of the superconducting radio frequency (SRF) cavities has been carried out. The samples' surface treatment was attempted to replicate that of the SRF cavities, which includes heavy electropolishing (EP), nitrogen doping and the subsequent EP with different amounts of material removal. The magnetization curves of both the doped and the un-doped samples have been measured, from which the field of the first flux penetration and the upper critical field were extracted. The thermodynamic critical field, the the Ginzburg-Landau parameter, the penetration depth, the coherence length and the superheating field were calculated from the determined reversible magnetization curves. The superheating field of the doped samples is obviously smaller than that of the un-doped samples. Direct observation of hydrides precipitation on both the doped and the un-doped samples has been carried out using Scanning Electron Microscope (SEM) with a cold stand at 80K, which showed that the amount of hydrides precipitation on the doped samples was reduced to varying degrees with different amounts of material removal. Under our doping recipe, the doped sample with subsequent EP material removal of 7-9 microns corresponds to the minimum nitrogen concentration that can effectively reduce the amounts of hydrides precipitation.

physics.acc-ph↗
arXiv2018

XPS studies of nitrogen doping niobium used for accelerator applications

Nitrogen doping study on niobium (Nb) samples used for the fabrication of superconducting radio frequency (SRF) cavities was carried out. The samples' surface treatment was attempted to replicate that of the Nb SRF cavities, which includes heavy electropolishing (EP), nitrogen doping and the subsequent EP with different amounts of material removal. The surface chemical composition of Nb samples with different post treatments has been studied by XPS. The chemical composition of Nb, O, C and N was presented before and after Gas Cluster Ion Beam (GCIB) etching. No signals of poorly superconducting nitrides NbNx was found on the surface of any doped Nb sample with the 2/6 recipe before GCIB etching. However, in the depth range greater than 30nm, the content of N element is below the XPS detection precision scope even for the Nb sample directly after nitrogen doping treatment with the 2/6 recipe.

physics.acc-ph↗
arXiv2017

Analytical Solution to the Transient Beam Loading Effects of the Superconducting Cavity

Transient beam loading effect is one of the key issues in any superconducting accelerators, which needs to be carefully investigated. The core problem in the analysis is to obtain the time evolution of cavity voltage under the transient beam loading. To simplify the problem, the second order ordinary differential equation describing the behavior of the cavity voltage is intuitively simplified to a first order one, with the aid of the two critical approximations lacking the proof for their validity. In this paper, the validity is examined mathematically in some specific cases, resulting in a criterion for the simplification. It's popular to solve the approximated equation for the cavity voltage numerically, while this paper shows that it can also be solved analytically under the step function approximation for the driven term. With the analytical solution to the cavity voltage, the transient reflected power from the cavity and the energy gain of the central particle in the bunch can also be calculated analytically. The validity of the step function approximation for the driven term is examined by direct evaluations. After that, the analytical results are compared with the numerical ones.

physics.acc-ph↗
arXiv2016

Read-Write Memory and k-Set Consensus as an Affine Task

The wait-free read-write memory model has been characterized as an iterated \emph{Immediate Snapshot} (IS) task. The IS task is \emph{affine}---it can be defined as a (sub)set of simplices of the standard chromatic subdivision. It is known that the task of \emph{Weak Symmetry Breaking} (WSB) cannot be represented as an affine task. In this paper, we highlight the phenomenon of a "natural" model that can be captured by an iterated affine task and, thus, by a subset of runs of the iterated immediate snapshot model. We show that the read-write memory model in which, additionally, $k$-set-consensus objects can be used is, unlike WSB, "natural" by presenting the corresponding simple affine task captured by a subset of $2$-round IS runs. Our results imply the first combinatorial characterization of models equipped with abstractions other than read-write memory that applies to generic tasks.

cs.DC↗
arXiv2016

Measuring Transport Difficulty of Data Dissemination in Large-Scale Online Social Networks: An Interest-Driven Case

In this paper, we aim to model the formation of data dissemination in online social networks (OSNs), and measure the transport difficulty of generated data traffic. We focus on a usual type of interest-driven social sessions in OSNs, called \emph{Social-InterestCast}, under which a user will autonomously determine whether to view the content from his followees depending on his interest. It is challenging to figure out the formation mechanism of such a Social-InterestCast, since it involves multiple interrelated factors such as users' social relationships, users' interests, and content semantics. We propose a four-layered system model, consisting of physical layer, social layer, content layer, and session layer. By this model we successfully obtain the geographical distribution of Social-InterestCast sessions, serving as the precondition for quantifying data transport difficulty. We define the fundamental limit of \emph{transport load} as a new metric, called \emph{transport complexity}, i.e., the \emph{minimum required} transport load for an OSN over a given carrier network. Specifically, we derive the transport complexity for Social-InterestCast sessions in a large-scale OSN over the carrier network with optimal communication architecture. The results can act as the common lower bounds on transport load for Social-InterestCast over any carrier networks. To the best of our knowledge, this is the first work to measure the transport difficulty for data dissemination in OSNs by modeling session patterns with the interest-driven characteristics.

cs.SI↗
arXiv2016

Study on transient beam loading compensation for China ADS proton linac injector II

Significant transient beam loading effects were observed during beam commissioning tests of prototype II of the injector for the Accelerator Driven Sub-critical (ADS) system, which took place at the Institute of Modern Physics, Chinese Academy of Sciences, between October and December 2014. During these tests experiments were performed with CW operation of the cavities with pulsed beam current, and the system was configured to make use of a prototype digital low level radio frequency (LLRF) controller. The system was originally operated in pulsed mode with a simple PID feedback control algorithm, which was not able to maintain the desired gradient regulation during pulsed 10 mA beam operations. A unique simple transient beam loading compensation method which made use of a combination of PI feedback and feedforward control algorithm was implemented in order to significantly reduce the beam induced transient effect in the cavity gradients. The superconducting cavity field variation was reduced to less than 1.7% after turning on this control algorithm. The design and experimental results of this system are presented in this paper.

physics.acc-ph↗
arXiv2015

On the modeling and simulation of reaction-transfer dynamics in semiconductor-electrolyte solar cells

The mathematical modeling and numerical simulation of semiconductor-electrolyte systems play important roles in the design of high-performance semiconductor-liquid junction solar cells. In this work, we propose a macroscopic mathematical model, a system of nonlinear partial differential equations, for the complete description of charge transfer dynamics in such systems. The model consists of a reaction-drift-diffusion-Poisson system that models the transport of electrons and holes in the semiconductor region and an equivalent system that describes the transport of reductants and oxidants, as well as other charged species, in the electrolyte region. The coupling between the semiconductor and the electrolyte is modeled through a set of interfacial reaction and current balance conditions. We present some numerical simulations to illustrate the quantitative behavior of the semiconductor-electrolyte system in both dark and illuminated environments. We show numerically that one can replace the electrolyte region in the system with a Schottky contact only when the bulk reductant-oxidant pair density is extremely high. Otherwise, such replacement gives significantly inaccurate description of the real dynamics of the semiconductor-electrolyte system.

math.AP↗
arXiv2015

Design Study on Medium beta SC Half-Wave Resonator at IMP

A superconducting half-wave resonator has been designed with the frequency of 325 MHz and beta of 0.51. Different geometry parameters and shapes of inner conductors (racetrack, ring-shape and elliptical-shape) were optimized to decrease the peak electromagnetic fields to obtain higher accelerating gradients and minimize the dissipated power on the cavity walls. To suppress the operation frequency shift caused by the helium pressure fluctuations and maximize the tuning ranges, the frequency shifts and mechanical properties were studied on the electric and magnetic areas separately. At the end, the helium vessel was also designed to keep the mechanical structure as robust as possible. The fabrication and test of the prototype will be completed in the beginning of 2016.

physics.acc-ph↗
arXiv2015

Group Mutual Exclusion in Linear Time and Space

We present two algorithms for the Group Mutual Exclusion (GME) Problem that satisfy the properties of Mutual Exclusion, Starvation Freedom, Bounded Exit, Concurrent Entry and First Come First Served. Both our algorithms use only simple read and write instructions, have O(N) Shared Space complexity and O(N) Remote Memory Reference (RMR) complexity in the Cache Coherency (CC) model. Our first algorithm is developed by generalizing the well-known Lamport's Bakery Algorithm for the classical mutual exclusion problem, while preserving its simplicity and elegance. However, it uses unbounded shared registers. Our second algorithm uses only bounded registers and is developed by generalizing Taubenfeld's Black and White Bakery Algorithm to solve the classical mutual exclusion problem using only bounded shared registers. We show that contrary to common perception our algorithms are the first to achieve these properties with these combination of complexities.

cs.DC↗
arXiv2013

Radiation field simulation of C-ADS Injector II

The injector of C-ADS (Chinese Accelerator Driven Sub-critical System) project is a high current, fully super-conducting proton accelerator. Meanwhile, a BLM system is indispensable to this facility, especially in low energy segments. This paper presents some basic simulations for 10MeV proton by Monte Carlo program FLUKA, as well as the distributions on different secondary particles in three aspects: angular, energy spectrum and current. These results are beneficial to selecting the detector type and its location and determining its dynamic range matching different requirements for both fast and slow beam loss. Further, the major impact of the background is analyzed, such as superconducting cavity X radiation and radiation caused by material activation, in this paper as well. This work is meaningful in BLM system research.

physics.acc-ph↗
arXiv2013

Identities involving the $\left(h,q\right)$-Genocchi polynomials and $\left(h,q\right)$-Zeta-type function

The fundamental objective of this paper is to obtain some interesting properties for $\left(h,q\right)$-Genocchi numbers and polynomials by using the fermionic $p$-adic $q$-integral on $\mathbb{Z}_{p}$ and mentioned in the paper $q$-Bernstein polynomials. By considering the $q$-Euler zeta function defined by T. Kim, which can also be obtained by applying the Mellin transformation to the generating function of $\left(h,q\right)$-Genocchi polynomials, we study $\left(h,q\right)$-Zeta-type function. We derive symmetric properties of $\left(h,q\right)$-Zeta function and from these properties we give symmetric property of $\left(h,q\right)$-Genocchi polynomials.

math.NT↗
arXiv2013

Study on the frequency tuning of half-wave resonator at IMP

A 162.5 MHz superconducting half-wave resonator (HWR) with geometry beta of 0.09 is being developed for Injector II of China Accelerator Driven Sub-critical System (CADS) Project at the Institute of Modern Physics (IMP). The HWR section composed of 16 HWR cavities will accelerate the proton beam from 2.1 MeV to 10 MeV. The RF and mechanical coupled analysis are essential in geometry design in order to predict the deformation of the cavity walls and the frequency shift caused by the deformation. In this paper, the detuning caused by both bath helium pressure and Lorentz force is analysed and a tuning system has been investigated and designed to compensate the detuning by deforming the cavity along the beam axis. The simulations performed with ANSYS code show that the tuning system can adjust and compensate the frequency drift due to external vibrations and helium pressure fluctuation during operation.

physics.acc-ph↗
arXiv2013

Mechanical design and analysis for a low beta squeezed half-wave resonator

A superconducting half-wave resonator (HWR) of frequency=162.5 MHz and β=0.09 has been developed at Institute of Modern Physics. Mechanical stability of the low beta HWR cavity is a big challenge in cavity design and optimization. The mechanical deformations of a radio frequency superconducting cavity could be a source of instability, both in continues wave(CW) operation or in pulsed mode. Generally, the lower beta cavities have stronger Lorentz force detuning than that of the higher beta cavities. In this paper, a basic design consideration in the stiffening structure for the detuning effect caused by helium pressure and Lorentz force has been presented. The mechanical modal analysis has been investigated with finite element method(FEM). Based on these considerations, a new stiffening structure has been promoted for the HWR cavity. The computation results concerning the frequency shift show that the low beta HWR cavity with new stiffening structure has low frequency sensitivity coefficient, Lorentz force detuning coefficient KL and stable mechanical property.

physics.acc-ph↗
arXiv2012

Identities involving q-Genocchi numbers and polynomials

In this paper, we focus on the q-Genocchi numbers and polynomials. We shall introduce new identities of the q-Genocchi numbers and polynomials by using the fermionic p-adic integral on Zp which are very important in the study of Frobenius-Genocchi numbers and polynomials. Also, we give Cauchy-integral formula for the q-Genocchi polynomials and moreover by using measure theory on p-adic integral we derive the distribution formula q-Genocchi polynomials. Finally, we present a new definition of q-Zeta-type function by using Mellin transformation which is the interpolation function of the q-Genocchi polynomials at negative integers.

math.NT↗
arXiv2012

Triggercast: Enabling Wireless Collisions Constructive

It is generally considered that concurrent transmissions should be avoided in order to reduce collisions in wireless sensor networks. Constructive interference (CI) envisions concurrent transmissions to positively interfere at the receiver. CI potentially allows orders of magnitude reductions in energy consumptions and improvements on link quality. In this paper, we theoretically introduce a sufficient condition to construct CI with IEEE 802.15.4 radio for the first time. Moreover, we propose Triggercast, a distributed middleware, and show it is feasible to generate CI in TMote Sky sensor nodes. To synchronize transmissions of multiple senders at the chip level, Triggercast effectively compensates propagation and radio processing delays, and has $95^{th}$ percentile synchronization errors of at most 250ns. Triggercast also intelligently decides which co-senders to participate in simultaneous transmissions, and aligns their transmission time to maximize the overall link PRR, under the condition of maximal system robustness. Extensive experiments in real testbeds reveal that Triggercast significantly improves PRR from 5% to 70% with 7 concurrent senders. We also demonstrate that Triggercast provides on average $1.3\times$ PRR performance gains, when integrated with existing data forwarding protocols.

cs.DC↗