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Zenghai Li

Publications and source records attributed to Zenghai Li.

15 recordsLinked to original sources
arXiv2025

A Prototype Hybrid Mode Cavity for Heterodyne Axion Detection

In the heterodyne approach to axion detection, axion dark matter induces transitions between two modes of a microwave cavity, resulting in a parametrically enhanced signal power. We describe the fabrication and characterization of a prototype normal conducting cavity specifically optimized for heterodyne detection. Corrugations on the cavity walls support linearly polarized hybrid modes which maximize the signal power while strongly suppressing noise. We demonstrate tuning mechanisms which allow one mode's frequency to be scanned across a 4 MHz range, while suppressing cross-coupling noise by at least 80 dB. A future superconducting cavity with identical geometry to our prototype would have the potential to probe orders of magnitude beyond astrophysical bounds.

physics.ins-det↗
arXiv2025

ESPPU INPUT: C$^3$ within the "Linear Collider Vision"

The Linear Collider Vision calls for a Linear Collider Facility with a physics reach from a Higgs Factory to the TeV-scale with $e^+e^{-}$ collisions. One of the technologies under consideration for the accelerator is a cold-copper distributed-coupling linac capable of achieving high gradient. This technology is being pursued by the C$^3$ collaboration to understand its applicability to future colliders and broader scientific applications. In this input we share the baseline parameters for a C$^3$ Higgs-factory and the energy reach of up to 3 TeV in the 33 km tunnel foreseen under the Linear Collider Vision. Recent results, near-term plans and future R\&D needs are highlighted.

physics.acc-ph↗
arXiv2024

Integrated simulation of cavity design and radiation transport codes (ACE3P + Geant4)

A simulation workflow has been developed to study dark current (DC) radiation effects using ACE3P and Geant4. The integrated workflow interfaces particle data transfer and geometry between the electromagnetic (EM) cavity simulation code ACE3P and the radiation code Geant4, targeting large-scale problems using high-performance computing. The process begins by calculating the operating mode in the vacuum region of an accelerator structure and tracking field-emitted electrons influenced by the EM fields of the mode calculated by ACE3P. It then transfers particle data at the vacuum-wall interface for subsequent radiation calculations within the wall enclosure materials through Geant4 calculation. The whole integrated simulation workflow will be demonstrated through large-scale dark current radiation calculations for the KEK 56-cell traveling-wave structure, and the efficiency of performing these simulations on the NERSC supercomputer Perlmutter will be presented.

physics.comp-ph↗
arXiv2023

An Integrated Simulation Tool for Dark Current Radiation Effects Using ACE3P and Geant4

A simulation workflow is under development to interface particle data transfer and matching of geometry between the electromagnetic (EM) cavity simulation code ACE3P and radiation code Geant4. The target is to simulate dark current (DC) radiation effects for the KEK 56-cell S-band accelerating structure using ACE3P and Geant4, and benchmark against KEK experiment data. As a first step, ACE3P DC simulations using a 7-cell structure have been performed by first calculating the operating mode in the structure and then tracking field-emitted electrons under the influence of the EM fields of the mode. The ACE3P simulation results agree well with the EM software CST for an accelerating gradient of 21.8 MV/m. The reader/writer I/O in ACE3P and the transfer of particle data from Track3P to Geant4 for DC radiation effects studies have been implemented. The simulation workflow between the two codes will be demonstrated with the goal of performing large-scale simulations for the KEK 56-cell structure. In addition to modeling DC effects in linacs, the integrated simulation workflow will be applicable to studying positron source and capture structure for future lepton colliders.

hep-ex↗
arXiv2021

C$^3$: A "Cool" Route to the Higgs Boson and Beyond

We present a proposal for a cold copper distributed coupling accelerator that can provide a rapid route to precision Higgs physics with a compact 8 km footprint. This proposal is based on recent advances that increase the efficiency and operating gradient of a normal conducting accelerator. This technology also provides an $e^{+}e^{-}$ collider path to physics at multi-TeV energies. In this article, we describe our vision for this technology and the near-term R&D program needed to pursue it.

hep-ex↗
arXiv2018

Distributed Coupling Accelerator Structures: A New Paradigm for High Gradient Linacs

We present a topology for linear accelerators (linacs) that permits larger degrees of freedom for the optimization of individual cavity shapes. The power is distributed to the cavities through a waveguide with periodic apertures that guarantees the correct phases and amplitudes along the structure. This topology optimizes the power consumption and efficiency and allows the manipulation of the surface fields for high gradient operation. It also provides a possibility for low-temperature manufacturing techniques for use with novel materials. This greatly enhanced performance for both normal and superconducting linacs. We present a design and an experimental demonstration of this linac.

physics.acc-ph↗
arXiv2018

An Advanced NCRF Linac Concept for a High Energy e$^+$e$^-$ Linear Collider

We have explored a concept for an advanced Normal-Conducting Radio-Frequency (NCRF) C-band linear accelerator (linac) structure to achieve a high gradient, high power e$^+$e$^-$ linear collider in the TeV class. This design study represents the first comprehensive investigation for an emerging class of distributed coupling accelerator topology exploring nominal cavity geometries, frequency and temperature of operation. The structure features internal manifolds for distributing RF power separately to each cell, permitting the full structure geometry to be designed for high shunt impedance and low breakdown. Optimized within operational constraints, we find that it is advantageous for the structure to be cooled directly by liquid nitrogen (LN), further increasing the shunt impedance. A crucial part of this design process has been cost optimization, which is largely driven by the cost of peak RF power. The first operation of a distributed coupling structure at cryogenic temperatures and the nominal operating gradient 120 MeV/m is also presented, demonstrating the feasibility of achieving high-gradient performance with a cryogenically-cooled normal-conducting accelerating structure.

physics.acc-ph↗
arXiv2018

Operation of normal-conducting RF cavities in multi-tesla magnetic fields for muon ionization cooling: a feasibility demonstration

Ionization cooling is the preferred method for producing bright muon beams. This cooling technique requires the operation of normal conducting, radio-frequency (RF) accelerating cavities within the multi-tesla fields of DC solenoid magnets. Under these conditions, cavities exhibit increased susceptibility to RF breakdown, which can damage channel components and imposes limits on channel length and transmission efficiency. We present a solution to the problem of breakdown in strong magnetic fields. We report, for the first time, stable high-vacuum, copper cavity operation at gradients above 50 MV/m and in an external magnetic field of three tesla. This eliminates a significant technical risk that has previously been inherent in ionization cooling channel designs.

physics.acc-ph↗
arXiv2015

The Development of the Linac Coherent Light Source RF Gun

The Linac Coherent Light Source (LCLS) is the first x-ray laser user facility based upon a free electron laser (FEL). In addition to many other stringent requirements, the LCLS XFEL requires extraordinary beam quality to saturate at 1.5 angstroms within a 100 meter undulator.[1] This new light source is using the last kilometer of the three kilometer linac at SLAC to accelerate the beam to an energy as high as 13.6 GeV and required a new electron gun and injector to produce a very bright beam for acceleration. At the outset of the project it was recognized that existing RF guns had the potential to produce the desired beam but none had demonstrated it. This paper describes the analysis and design improvements of the BNL/SLAC/UCLA s-band gun leading to achievement of the LCLS performance goals.

physics.acc-ph↗
arXiv2015

Design, prototyping and testing of a compact superconducting double quarter wave crab cavity

A novel design of superconducting Crab Cavity was proposed and designed at Brookhaven National Laboratory. The new cavity shape is a Double Quarter Wave or DQWCC. After fabrication and surface treatments, the niobium proof-of-principle cavity was cryogenically tested in a vertical cryostat. The cavity is extremely compact yet has a low frequency of 400 MHz, an essential property for service for the Large Hadron Collider luminosity upgrade. The electromagnetic properties of the cavity are also well matched for this demanding task. The demonstrated deflecting voltage of 4.6 MV is well above the requirement for a crab cavity in the future High Luminosity LHC of 3.34 MV. In this paper we present the design, prototyping and test results of the DQWCC.

physics.acc-ph↗
arXiv2011

RF thermal and new cold part design studies on TTF-III input coupler for Project-X

RF power coupler is one of the key components in superconducting (SC) linac. It provides RF power to the SC cavity and interconnects different temperature layers (1.8K, 4.2K, 70K and 300K). TTF-III coupler is one of the most promising candidates for the High Energy (HE) linac of Project X, but it cannot meet the average power requirements because of the relatively high temperature rise on the warm inner conductor, some design modifications will be required. In this paper, we describe our simulation studies on the copper coating thickness on the warm inner conductor with RRR value of 10 and 100. Our purpose is to rebalance the dynamic and static loads, and finally lower the temperature rise along the warm inner conductor. In addition, to get stronger coupling, better power handling and less multipacting probability, one new cold part design was proposed using 60mm coaxial line; the corresponding multipacting simulation studies have also been investigated.

physics.acc-ph↗
arXiv2001

Analytic Formula for Weak Multi-Bunch Beam Break-Up in a Linac

In designing linear accelerator structures for multi-bunch applications we are often interested in estimating the effect of relatively weak multi-bunch beam break-up (BBU), due to the somewhat complicated wakefields of detuned structures. This, for example, is the case for the injector linacs of the JLC/NLC linear collider project. Deriving an analytical formula for such a problem is the subject of this report.

physics.acc-ph↗
arXiv2001

Obtaining the Wakefield Due to Cell-to-Cell Misalignments in a Linear Accelerator Structure

A linear accelerator structure, such as will be used in the linacs of the JLC/NLC collider, is composed of on the order of 100 cells. The cells are constructed as individual cups that are brazed together to form a structure. Fabrication error will result in slight cell-to-cell misalignments along the finished structure. In this report we derive an approximation to the transverse wakefield of a structure with cell-to-cell misalignments in terms of the eigenfunctions and eigenvalues of the error-free structure.

physics.acc-ph↗
arXiv2000

Dipole Mode Detuning in the Injector Linacs of the NLC

The injector linacs of the JLC/NLC project include the prelinac, the e+ drive linac, the $e- booster, and the $e+ booster. The first three will be S-band machines, the last one, an L-band machine. We have demonstrated that by using detuning alone in the accelerator structure design of these linacs we will have acceptable tolerances for emittance growth due to both injection jitter and structure misalignments, for both the nominal (2.8ns) and alternate (1.4ns) bunch spacings.

physics.acc-ph↗