Search

We present the first use of a tunable superconducting radio frequency cavity to perform a scan search for dark photon dark matter with novel data analysis strategies. We mechanically tuned the resonant frequency of a cavity embedded in the liquid helium with a temperature of $2$ K, scanning the dark photon mass over a frequency range of $1.37$ MHz centered at $1.3$ GHz. By exploiting the superconducting radio frequency cavity's considerably high quality factors of approximately $10^{10}$, our results demonstrate the most stringent constraints to date on a substantial portion of the exclusion parameter space, particularly concerning the kinetic mixing coefficient between dark photons and electromagnetic photons $\epsilon$, yielding a value of $\epsilon < 2.2 \times 10^{-16}$., Comment: 11 pages, 7 figures

The photocathode RF gun is one of the most critical components for high quality electron beam sources. The asymmetric multi-pole field contributes to the transverse emittance growth and degrades the beam quality. In order to overcome the problem, we propose a novel rotationally symmetric 1.6 cell RF gun to construct the symmetric field in this paper. The concrete proposal is that a coaxial cell cavity with a symmetrical distribution of four grooves is concatenated to the photocathode end of the traditional 0.6 cell cavity to form the novel 0.6 cell cavity. Through the detailed design study, the profile of the RF gun is optimized to improve the shunt impedance and mode separation and make the surface peak electric field at the photocathode end. Considering the filling time, a coupling slot is designed to couple input power into the RF gun. The RF cavity is machined by numerical control machine tool, and the tuning and low power RF measurement are carried out. The experimental results are consistent with the simulation results., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

In this paper, we study the microwave characteristics of 500 MHz RF cavity, including the optimization of cavity structure, the simulation design of high-order mode (HOM) absorption structure and the design of coupler. The cavity structure is simulated by CST. The absorption waveguide is designed and optimized. The coupler is designed., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Multi-bend achromat lattices with unit cells have been used in diffraction-limited storage ring designs. The longitudinal gradient bend can reduce the horizontal emittance below the theoretical minimum of a given magnet structure, and generally the horizontal emittance reduces with the peak field grows. Therefore superconducting longitudinal gradient bend (SLGB) can produce higher peak field value and quasi-hyperbolic field profile to minimize emittance at location of radiation and generate better hard X-rays. NbTi conductor, rather than Nb₃Sn conductor, is selected to keep the design and manufacture of SLGB magnet as simple as possible. In this paper, how the field profiles of race-track type coil and solenoid coil change with their geometric parameters is studied, and multi-objective genetic algorithm is used to optimize SLGB magnet structure considering Hefei Advanced Light Facility lattice design demand and NbTi critical current., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

In this paper, we propose a novel electron gun based on THz acceleration and field emission to generate femtosecond electron bunches. The field emission cathode is placed in the center of the cavity, and the standing wave field is established in the cavity to achieve the field emission conditions and extract the electron beam. Because the period of THz band is about picosecond, the femtosecond bunch is formed by controlling the field strength and the pulse width of the extracted beam. We analyzed the feasibility of field emission and the length of the pulse beam. The surface peak field intensity of the structure of the cavity with different emitters are simulated by CST software., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The layout of the THz source based on FEL was de-scribed in this paper. The THz source was based on a FEL which was composed of a compact 8-14MeV LINAC, undulator, optical resonance, THz wave measurement system and so on. The facility was designed in 2013 and the typical running parameter got in 2017 were as the following: energy is of 12.7MeV, energy spread is of 0.3%, macro-pulse is of 4 μs, pulse length of micro-pulse is of 6ps, emittance is of 24 mm.mrad. After that the ma-chine was commissioning for production THz radiation. In November 2018, the THz wave was test and got THz wave signal, the spectrum was also got. This year, we plan to measure the output power of the THz source., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

This paper describes the physics design of a S-band (2856 MHz) linear accelerator (linac) with variable energy tuning. The system consists of a DC gun for generating electron, prebuncher for velocity modulation and two travelling wave (TW) accelerating sections for acceleration. The accelerating structure is a 2'Ð/3 mode constant gradient TW structure, which comprises TW buncher cells, followed by uniform cells. The structure is designed to accelerate 45 keV electron beam from the electron gun to 3.2 MeV, and then 10 MeV. An important feature of the TW linac is that the RF output power of the first linac is as the RF input power of the second linac. Three dimensional transient simulations of the accelerating structure along with the input and output couplers have been performed to explicitly demonstrate this feature. Beam dynamics is performed to calculate the beam parameter., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The photocathode RF gun is one of the most critical components for high quality electron beam sources. The asymmetric multi-pole field contributes to the transverse emittance growth and degrades the beam quality. In order to overcome the problem, we propose a novel rotationally symmetric 1.6 cell RF gun to construct the symmetric field in this paper. The concrete proposal is that a coaxial cell with a symmetrical distribution of four grooves is concatenated to the first 0.6 cell at the photocathode end to form a new resonant cell (NRC) to mantain the symmetric multi-pole field in 1.6 cell. Our simulations indicate that 3D multi-pole fields of NRC are with the perfect symmetry. After that, the profile of the RF gun is optimized to improve the shunt impedance and mode separation and make the surface peak electric field at the photocathode end. Our simulations demonstrate promising outlook of using coaxial cell for photocathode RF guns with various applications., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

For discovering structure at atomic scale and getting more details of chemical material and biological tissue, an ultrafast electron microscopy (UEM) has been developed and applied in plenty of subjects and studies. This paper described a C-band photocathode electron gun which will be working at 5712MHz to produce ultrashort electron beams with better dynamic parameters. The RF gun is using coaxial coupler to decrease the size of the gun and keep better symmetry of the field in the photocathode gun so that the beam emittance and energy spread can be reduce a lot. The photocathode rf gun will be a important part of the ultrafast electron microscopy (UEM). Using CST MWS and superfish code to simulate design the gun. After dynamic simulation, the beam parameters as the following: Energy is of 3MeV, Normal emittance of 0.12mm-mrad in boin direction, energy spread is of 5.8·10⁻⁴, which are better enough for an UEM., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China

A novel side coupling standing-wave (SW) accelerat-ing tube for low energy medical linac has been designed that operating frequency is 2998 MHz, operating mode is ', final energy is 6 MeV and beam current is 130 mA. A novel bridge hole between an accelerating cavity and coupling cavity has been utilized to reduce the mutual effect between two cavities and improve the anti-jamming capability and the long term stability. The inner end plate of the inlet of the first accelerating cavity in-cludes the nose cone to realize self-focusing in transverse to improve the beam quality. The simulation of the elec-tromagnetic field of structure and beam dynamic has been carried out with the SUPERFISH, CST Microwave studio and Parmela, respectively., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

Commissioning the compact LINAC of 14Mev for a THz source based on FEL Y.J.Pei National Synchrotron Radiation laboratory, University of Science & Technology of China Abstract The compact LINAC of 14MeV is designed for a FEL which will produce a THz radiation through 30μm to 300μm. The LINAC was composed of a novel EC-ITC-RF gun, constant gradient travelling wave accelerator with a collinear absorbing load, focusing system, RF power system, beam diagnostic system, vacuum system, control system and so on. The LINAC was installed on November of 2014. Last year, we finished the install of the undulator and the optical resonance cavities. Now the LINAC has been testing and commissioning for THz radiation test. So far, the running beam parameters of the LINAC are as the following: Energy is of 13.58MeV macro pulse current is of 655mA macro pulse length of 1.2μsμpulse beam current is of 59A beam length of theμpulse is of 4ps energy spread of 0.33% normal beam emmitance is of 24.1mm.mrad., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

The characteristics of asymmetric iris between first cell and second cell of 1.6 cell photocathode gun are studied. For π-mode, the RF radial field of two sides of the iris is non anti-symmetric. Thus, the RF transverse force at the iris is not negligible. In this paper, we present the status of the optimization simulations, using the SUPERFISH and PARMELA particle-in-cell code. Numerical results of beam dynamics show that it can improve the emittance at the exit of the gun., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

Land surface processes and land-atmosphere interactions are hot research focuses of the earth science,and the coupling soil heat and water dynamics in the near surface is the critical link between these processes and interactions.Analysis of the soil heat and water dynamics in Qilian Mountains was quite limited,primarily because there was no enough long-term monitoring data.This situation has been moderated,more or less,with a lot of automatic recording field station been established over the past decade.Pailugou forest station is among the stations with the longest periods of observations(10 years) in this region.By using the long-term field monitoring dataset(measured via ENVIS system from Jun 1,2002 to May 31,2008),we analyzed the relationships between soil temperature,soil moisture dynamics and other meteorological factors in the forest-grassland ecotone of Qilian Mountains.The results were shown as follows: 1) the changing patterns and trends of the soil temperature are largely consistent with the air temperature at different temporal scale,while a lag phase between them was observed which increase with soil depth.2) Soil moisture dynamics is much more complex compared with the temperature dynamics,and strongly affected by the precipitation / evaporation and melting / freezing processes.Generally,the variability of soil moisture is relatively more intense at the depths of 20—80 cm and less intense at the depths of 80—160 cm in the soil profile.Moreover,small differences exist between the evolution trends in the soil moisture dynamics at the different depths,for example,soil moisture slightly decreased at the 40 cm and 80 cm,while increased at the other depths of the soil profile during the study period.3) Energy budget at the soil surface significantly controlled the seasonal melting of the top-layer frozen soil(0—20 cm),while the liquid water infiltrated from the precipitation and melting water in the top-layers also contributed a lot to the melting processes of low-layer frozen soil(20—80 cm).4) At the daily time scale,soil temperature is highly related with the air temperature,while the soil moisture is also highly related with the net solar radiation beside the air temperature.At the monthly time scale,soil temperature is mainly controlled by the air temperature and relative air humidity,and soil moisture dynamics is controlled by the air temperature,saturated vapor pressure differences(VPD),and net solar radiation.Better statistical relationships between soil temperature and meteorological factors was observed at month-scale rather than a daily time scale,and as a result,the relationships built at monthly time scale can be used to get a better prediction of temperature in the top soil layers,i.e.20 cm,40 cm and 60 cm.The results derived from this study clearly indicate that precipitation and air temperature are among the most important environmental factors that affect soil heat and water dynamics in Qilian Mountains.More modeling efforts are needed to quantify and qualify these effects for the fragile alpine ecosystem in the arid northwest China,especially under future climate scenarios and under regional disturbance regimes.

With the aim to obtain short-pulse bunches with high peak current for a terahertz radiation source, an FEL-based LINAC is employed in HUST THz-FEL, and the LINAC consists of an EC-ITC RF gun, a disk-loaed waveguide structure with a constant gradient and collinear absorbing loads with focusing coils surrounded and so on. To achieve a balance between compactness and high performance, beam diagnostic system should be simple and high-precision. So that a cost-effective measurement scheme for the high-brightness beam extracted by the LINAC is needed. This paper will describe the beam line and beam diagnostic system of the LINAC in the HUST THz-FEL in detail and give corresponding assembly scheme. In addition, online monitor system is introduced., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

The construction of a compact high-power THz source based on the free electron laser(FEL), which is constructed in HUST, is undergoing. Before the end of 2014, we have installed most of the key components, completed conditioning of the LINAC-based FEL injector, and performed first beam experiment. During last 5 months, we have established a high efficient beam diagnostic system with a reliable online monitor platform and precise data processing methods. At present, longitudinal properties such as the micro-pulse width and the energy spread are kept to a reasonable level, while transverse emittance compensation by adjusting focusing parameters is still undergoing. In this paper, we will give the summary on the commissioning schedule, detailed commissioning plan, the development of the commissioning and first performance of the LINAC, etc., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

A compact medical standing-wave (SW) electron accelerating tube has been designed that operating frequency is 2998MHz, operating mode is π/2, final energy is 6MeV and beam current is 100mA based on genetic algorithm (GA)’s optimal calculation. It employed a bi-periodic structure with nose cone shape. We performed the simulation experiment which proved that GA was feasible and gave a set of geometric parameter with higher shunt impedance. We performed tuning of the whole tube by CST MICROWAVE STUDIO and SUPERFISH and calculation of beam dynamics by ASTRA and Parmela in this paper. The total length of the tube is less than 300mm., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany