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Performance of 1300 Mhz KEK-type single cell niobium cavities

Description: Four single cell niobium cavities fabricated from Tokyo-Denkai material of RRR=200 have been tested repeatedly with the purpose to evaluate different fabrication and processing techniques used at KEK and Jefferson Lab, respectively. Two cavities--K-15 and K-16--have been manufactured completely at KEK prior to shipment to Jefferson Lab. In addition, K-16 had received a barrel polishing treatment at KEK, resulting in the removal of 40 {mu}m of material from the surface. Cavity K-17 was electron-beam welded at Jefferson Lab; the deep drawing of the half cells and the trimming of the cups for electron-beam welding were done at KEK, however. Cavity JL-1 was completely fabricated at Jefferson Lab. Often, some processing field levels related to electronic activity in the cavities, possibly multipacting, have been seen at KEK and the purpose of this investigation is a verification of such observations. In addition, a comparison of different fabrication procedures and surface treatments are of interest for optimizing cost and performance for larger scale application. In several cavities, accelerating gradients between 20 MV/m {<=} E{sub acc} {<=} 27 MV/m have been measured with only little field emission loading. In one of the cavities, resonant electron loading was ''provoked'' by rinsing it with oil contaminated acetone. The observed multipacting levels at E{sub acc}=13 MV/m and 25 MV/m could be identified with the help of simulation calculations as 1-point and 2-point multipacting across the equator of the cavity. There is - as previously reported - a rather strong dependence of the quench field levels on the amount of material removed from the surface, confirming a picture of a surface damage layer which becomes depleted of defects as more and more of it is removed.
Date: October 1, 1997
Creator: Kneisel, P.; Saito, K. & Parodi, R.
Partner: UNT Libraries Government Documents Department

Measurements of Martin-Puplett Interferometer Limitations using Blackbody Source

Description: Frequency domain measurements with Martin-Puplett interferometer is one of a few techniques capable of bunch length measurements at the level of ~ 100 fs. As the bunch length becomes shorter, it is important to know and be able to measure the limitations of the instrument in terms of shortest measurable bunch length. In this paper we describe an experiment using a blackbody source with the modified Martin-Puplett interferometer that is routine- ly used for bunch length measurements at the JLab FEL, as a way to estimate the shortest, measurable bunch length. The limitation comes from high frequency cut-off of the wire-grid polarizer currently used and is estimated to be 50 fs RMS. The measurements are made with the same Golay cell detector that is used for beam measure- ments. We demonstrate that, even though the blackbody source is many orders of magnitude less bright than the coherent transition or synchrotron radiation, it can be used for the measurements and gives a very good signal to noise ratio in combination with lock-in detection. We also compare the measurements made in air and in vacuum to characterize the very strong effect of the atmospheric absorption.
Date: June 1, 2013
Creator: Evtushenko, Pavel E. & Klopf, John M.
Partner: UNT Libraries Government Documents Department

High Dynamic Range Beam Imaging with Two Simultaneously Sampling CCDs

Description: Transverse beam profile measurement with sufficiently high dynamic range (HDR) is a key diagnostic to measure the beam halo, understand its sources and evolution. In this contribution we describe our initial experience with the HDR imaging of the electron beam at the JLab FEL. On contrary to HDR measurements made with wire scanners in counting mode, which provide only two or three 1D projections of transverse beam distribution, imaging allows to measure the distribution itself. That is especially important for non-equilibrium beams in the LINACs. The measurements were made by means of simultaneous imaging with two CCD sensors with different exposure time. Two images are combined then numerically in to one HDR image. The system works as an online tool providing HDR images at 4 Hz. An optically polished YAG:Ce crystal with the thickness of 100 {micro}m was used for the measurements. When tested with a laser beam images with the DR of about 10{sup 5} were obtained. With the electron beam the DR was somewhat smaller due to the limitations in the time structure of the tune-up beam macro pulse.
Date: June 1, 2013
Creator: Evtushenko, Pavel E. & Douglas, David R.
Partner: UNT Libraries Government Documents Department

High Dynamic Range Beam Imaging with Two Simultaneously Sampling CCDs

Description: Transverse beam profile measurement with sufficiently high dynamic range (HDR) is a key diagnostic to measure the beam halo, understand its sources and evolution. In this contribution we describe our initial experience with the HDR imaging of the electron beam at the JLab FEL. On contrary to HDR measurements made with wire scanners in counting mode, which provide only two or three 1D projections of transverse beam distribution, imaging allows to measure the distribution itself. That is especially important for non-equilibrium beams in the LINACs. The measurements were made by means of simultaneous imaging with two CCD sensors with different exposure time. Two images are combined then numerically in to one HDR image. The system works as an online tool providing HDR images at 4 Hz. An optically polished YAG:Ce crystal with the thickness of 100 {micro}m was used for the measurements. When tested with a laser beam images with the DR of about 10{sup 5} were obtained. With the electron beam the DR was somewhat smaller due to the limitations in the time structure of the tune-up beam macro pulse.
Date: May 1, 2013
Creator: Evtushenko, Pavel; Douglas, David R.; Legg, Robert A. & Tennant, Christopher D.
Partner: UNT Libraries Government Documents Department

APPLICATION OF NEURAL NETWORK ALGORITHMS FOR BPM LINEARIZATION

Description: Stripline BPM sensors contain inherent non-linearities, as a result of field distortions from the pickup elements. Many methods have been devised to facilitate corrections, often employing polynomial fitting. The cost of computation makes real-time correction difficult, particulalry when integer math is utilized. The application of neural-network technology, particularly the multi-layer perceptron algorithm, is proposed as an efficient alternative for electrode linearization. A process of supervised learning is initially used to determine the weighting coefficients, which are subsequently applied to the incoming electrode data. A non-linear layer, known as an “activation layer,” is responsible for the removal of saturation effects. Implementation of a perceptron in an FPGA-based software-defined radio (SDR) is presented, along with performance comparisons. In addition, efficient calculation of the sigmoidal activation function via the CORDIC algorithm is presented.
Date: November 1, 2012
Creator: Musson, John C.; Seaton, Chad; Spata, Mike F. & Yan, Jianxun
Partner: UNT Libraries Government Documents Department

1.1 Simulations of a Free-Electron Laser Oscillator at Jefferson Lab Lasing in the Vacuum Ultraviolet

Description: The UVFEL at Jefferson Lab has provided a 10 eV photon beam for users by outcoupling the coherent third harmonic of the UVFEL operated at 372 nm. This can provide up to tens of milliwatts of power in the VUV. Operation of the FEL at the fundamental might enhance this power by up to a factor of 1000. With minor upgrades to the accelerator now underway and a new undulator proposed by Calabazas Creek Research, Inc. we show that we can lase in the fundamental at 124 nm. The predicted output is higher by four orders of magnitude on an average power basis and six orders of magnitude on a peak fluence basis than the Advanced Light Source at Lawrence Berkeley National Laboratory.
Date: April 1, 2013
Creator: Shinn, Michelle D. & Benson, Stephen V.
Partner: UNT Libraries Government Documents Department

Design Concept of a Gamma-gamma Higgs Factory Driven by Thin Laser Targets and Energy Recovery Linacs

Description: A gamma-gamma collider has long been considered an option for a Higgs Factory. Such photon colliders usually rely on Compton back-scattering for generating high energy gamma photons and further Higgs bosons through gamma-gamma collisions. The presently existing proposals or design concepts all have chosen a very thick laser target (i.e., high laser photon intensity) for Compton scatterings. In this paper, we present a new design concept of a gamma-gamma collider utilizing a thin laser target (i.e., relatively low photon density), thus leading to a low electron to gamma photon conversion rate. This new concept eliminates most useless and harmful low energy soft gamma photons from multiple Compton scattering so the detector background is improved. It also greatly relaxes the requirement of the high peak power of the laser, a significant technical challenge. A high luminosity for such a gamma-gamma collider can be achieved through an increase of the bunch repetition rate and current of the driven electron beam. Further, multi-pass recirculating linac could greatly reduce the linac cost and energy recovery is required to reduce the needed RF power.
Date: June 1, 2013
Creator: Zhang, Yuhong
Partner: UNT Libraries Government Documents Department

A Program for Optimizing SRF Linac Costs

Description: Every well-designed machine goes through the process of cost optimization several times during its design, production and operation. The initial optimizations are done during the early proposal stage of the project when none of the systems have been engineered. When a superconducting radio frequency (SRF) linac is implemented as part of the design, it is often a difficult decision as to the frequency and gradient that will be used. Frequently, such choices are made based on existing designs, which invariably necessitate moderate to substantial modifications so that they can be used in the new accelerator. Thus the fallacy of using existing designs is that they will frequently provide a higher cost machine or a machine with sub-optimal beam physics parameters. This paper describes preliminary results of a new software tool that allows one to vary parameters and understand the effects on the optimized costs of construction plus 10 year operations of an SRF linac, the associated cryogenic facility, and controls, where operations includes the cost of the electrical utilities but not the labor or other costs. It derives from collaborative work done with staff from Accelerator Science and Technology Centre, Daresbury, UK [1] several years ago while they were in the process of developing a conceptual design for the New Light Source project. The initial goal was to convert a spread sheet format to a graphical interface to allow the ability to sweep different parameter sets. The tools also allow one to compare the cost of the different facets of the machine design and operations so as to better understand the tradeoffs.
Date: April 1, 2013
Creator: Powers, Thomas J.
Partner: UNT Libraries Government Documents Department

FINAL TECHNICAL REPORT FOR DE-FG02-05ER64097 Systems and Methods for Injecting Helium Beams into a Synchrotron Accelerator

Description: A research grant was approved to fund development of requirements and concepts for extracting a helium-ion beam at the LLUMC proton accelerator facility, thus enabling the facility to better simulate the deep space environment via beams sufficient to study biological effects of accelerated helium ions in living tissues. A biologically meaningful helium-ion beam will be accomplished by implementing enhancements to increase the accelerator’s maximum proton beam energy output from 250MeV to 300MeV. Additional benefits anticipated from the increased energy include the capability to compare possible benefits from helium-beam radiation treatment with proton-beam treatment, and to provide a platform for developing a future proton computed tomography imaging system.
Date: September 30, 2008
Creator: Bush, David A
Partner: UNT Libraries Government Documents Department

The JLAB UV Undulator

Description: Recently the JLAB FEL has demonstrated 150 W at 400 nm and 200 W at 700 nm using a 33mm period undulator designed and built by STI Optronics. This paper describes the undulator design and performance. Two key requirements were low phase error, zero steering and offset end fields and small rms trajectory errors. We will describe a new genetic algorithm that allowed phase error minimization to 1.8 degrees while exceeding specifications. The mechanical design, control system and EPICS interface will also be summarized.
Date: May 1, 2013
Creator: Gottschalk, Steven C.; Benson, Steven V. & Moore, Steven Wesley
Partner: UNT Libraries Government Documents Department

Improvements to Existing Jefferson Lab Wire Scanners

Description: This poster will detail the augmentation of selected existing CEBAF wire scanners with commercially available hardware, PMTs, and self created software in order to improve the scanners both in function and utility.
Date: June 1, 2013
Creator: McCaughan, Michael D.; Tiefenback, Michael G. & Turner, Dennis L.
Partner: UNT Libraries Government Documents Department

A Test Facility for MEIC ERL Circulator Ring Based Electron Cooler Design

Description: An electron cooling facility which is capable to deliver a beam with energy up to 55 MeV and average current up to 1.5 A at a high bunch repetition rate up to 750 MHz is required for MEIC. The present cooler design concept is based on a magnetized photo-cathode SRF gun, an SRF ERL and a compact circulator ring. In this paper, we present a proposal of a test facility utilizing the JLab FEL ERL for a technology demonstration of this cooler design concept. Beam studies will be performed and supporting technologies will also be developed in this test facility.
Date: May 1, 2013
Creator: Zhang, Yuhong; Derbenev, Yaroslav S.; Douglas, David R.; Hutton, Andrew M.; Krafft, Geoffrey A. & Nissen, Edward W.
Partner: UNT Libraries Government Documents Department

Rf System Requirements for JLab’s MEIC Collider Ring

Description: The Medium-energy Electron Ion Collider (MEIC), proposed by Jefferson Lab, consists of a series of accelerators. At the top energy are the electron and ion collider rings. For the ion ring, it accelerates five long ion bunches to colliding energy and rebunches ions into a train of very short bunches before colliding. A set of low frequency RF system is needed for the long ion bunch energy ramping. Another set of high frequency RF cavities is needed to rebunch ions. For the electron ring, superconducting RF (SRF) cavities are needed to compensate the synchrotron radiation energy loss. The impedance of the SRF cavities must be low enough to keep the high current electron beam stable. The preliminary design requirements of these RF cavities are presented.
Date: June 1, 2013
Creator: Wang, Shaoheng; Li, Rui; Rimmer, Robert A.; Wang, Haipeng & Zhang, Yuhong
Partner: UNT Libraries Government Documents Department

Use of Multipass Recirculation and Energy Recovery In CW SRF X-FEL Driver Accelerators

Description: We discuss the use of multipass recirculation and energy recovery in CW SRF drivers for short wavelength FELs. Benefits include cost management (through reduced system footprint, required RF and SRF hardware, and associated infrastructure - including high power beam dumps and cryogenic systems), ease in radiation control (low drive beam exhaust energy), ability to accelerate and deliver multiple beams of differing energy to multiple FELs, and opportunity for seamless integration of multistage bunch length compression into the longitudinal matching scenario. Issues include all those associated with ERLs compounded by the challenge of generating and preserving the CW electron drive beam brightness required by short wavelength FELs. We thus consider the impact of space charge, BBU and other environmental wakes and impedances, ISR and CSR, potential for microbunching, intra-beam and beam-residual gas scattering, ion effects, RF transients, and halo, as well as the effect of traditional design, fabrication, installation and operational errors (lattice aberrations, alignment, powering, field quality). Context for the discussion is provided by JLAMP, the proposed VUV/X-ray upgrade to the existing Jefferson Lab FEL.
Date: August 1, 2010
Creator: Douglas, David; Akers, Walt; Benson, Stephen V.; Biallas, George; Blackburn, Keith; Boyce, James et al.
Partner: UNT Libraries Government Documents Department

GPU-optimized Code for Long-term Simulations of Beam-beam Effects in Colliders

Description: We report on the development of the new code for long-term simulation of beam-beam effects in particle colliders. The underlying physical model relies on a matrix-based arbitrary-order symplectic particle tracking for beam transport and the Bassetti-Erskine approximation for beam-beam interaction. The computations are accelerated through a parallel implementation on a hybrid GPU/CPU platform. With the new code, a previously computationally prohibitive long-term simulations become tractable. We use the new code to model the proposed medium-energy electron-ion collider (MEIC) at Jefferson Lab.
Date: June 1, 2013
Creator: Roblin, Yves; Morozov, Vasiliy; Terzic, Balsa; Aturban, Mohamed A.; Ranjan, D. & Zubair, Mohammed
Partner: UNT Libraries Government Documents Department