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Performance of photocathode rf gun electron accelerators

Description: In Photo-Injectors (PI) electron guns, electrons are emitted from a photocathode by a short laser pulse and then accelerated by intense rf fields in a resonant cavity. The best known advantage of this technique is the high peak current with a good emittance (high brightness). This is important for short wavelength Free-Electron Lasers and linear colliders. PIs are in operation in many electron accelerator facilities and a large number of new guns are under construction. Some applications have emerged, providing, for example, very high pulse charges. PIs have been operated over a wide range of frequencies, from 144 to 3000 MHz (a 17 GHz gun is being developed). An exciting new possibility is the development of superconducting PIs. A significant body of experimental and theoretical work exists by now, indicating the criticality of the accelerator elements that follow the gun for the preservation of the PI's performance as well as possible avenues of improvements in brightness. Considerable research is being done on the laser and photocathode material of the PI, and improvement is expected in this area.
Date: January 1, 1993
Creator: Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department

Computation of emittance growth in a focusing wiggler FEL (Free Electron Laser)

Description: Computed electron trajectories in a free electron laser show significant emittance growth in the wiggle plane when there are wiggler field gradients. For a low gain free electron laser using a focusing planar wiggler, phase space plots show the development of this 3-dimensional effect as well as rotation of the phase space region occupied by the beam due to betatron oscillations in the focusing wiggler field. Matching the input electron beam to the wiggler eliminates emittance growth. 3 refs., 5 figs., 1 tab.
Date: January 1, 1988
Creator: Ben-Zvi, I. & Wachtel, J.M.
Partner: UNT Libraries Government Documents Department

On the future of BNL user facilities

Description: The purpose of this document is to portray the emerging technology of high-power high-brightness electron beams. This new technology will impact several fields of science and it is essential that BNL stay abreast of the development. BNL has a relative advantage and vital interest in pursuing this technology that will impact its two major facilities, the NSLS and RHIC. We have a sensible development path towards this critical future technology, in which BNL will gradually acquire a strong basis of Superconducting Radio Frequency (SRF) technology while executing useful projects. The technology of high-power AND high-brightness (HPHB) electron beams is based of the convergence of two extant, but relatively recent technologies: Photoinjectors and superconducting energy-recovering linacs. The HPHB technology presents special opportunities for the development of future BNL user facilities for High-Energy and Nuclear Science (HE-NP) and Basic Energy Science (BES). In HE-NP this technology makes it possible to build high-energy electron cooling for RHIC in the short range and a unique linac-based electron-ion collider (eRHIC). In BES, we can build short pulse, coherent FIR sources and high flux femtosecond hard x-ray sources based on Compton scattering in the short range and, in the longer range, femtosecond, ultra-high brightness synchrotron light sources and, ultimately, an X-ray Free-Electron Laser (FEL).
Date: August 1, 2010
Creator: Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department

Superconducting Storage Cavity for RHIC

Description: This document provides a top-level description of a superconducting cavity designed to store hadron beams in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. It refers to more detailed documents covering the various issues in designing, constructing and operating this cavity. The superconducting storage cavity is designed to operate at a harmonic of the bunch frequency of RHIC at a relatively low frequency of 56 MHz. The current storage cavities of RHIC operate at 197 MHz and are normal-conducting. The use of a superconducting cavity allows for a high gap voltage, over 2 MV. The combination of a high voltage and low frequency provides various advantages stemming from the resulting large longitudinal acceptance bucket.
Date: January 2, 2009
Creator: Ben-Zvi,I.
Partner: UNT Libraries Government Documents Department

ELECTRON COOLING AND ELECTRON-ION COLLIDERS AT BNL.

Description: Superconducting Energy Recovery Linacs (ERL) have significant potential uses in various fields, including High Energy Physics and Nuclear Physics. Brookhaven National Laboratory (BNL) is pursuing some of the potential applications in this area and the technology issues that are associated with these applications. The work addressed in this paper is carried out at BNL towards applications in electron cooling of high-energy hadron beams and electron-nucleon colliders. The common issues for these applications are the generation of high currents of polarized or high-brightness unpolarized electrons, high-charge per bunch and high-current. One must address the associated issue of High-Order Modes generation and damping. Superconducting ERLs have great advantages for these applications as will be outlined in the text.
Date: October 3, 2007
Creator: BEN-ZVI,I.
Partner: UNT Libraries Government Documents Department

Engineering Design and Fabrication of an Ampere-Class Superconducting Photocathode Electron Gun

Description: Over the past three years, Advanced Energy Systems and Brookhaven National Laboratory (BNL) have been collaborating on the design of an Ampere- class superconducting photocathode electron gun. BNL performed the physics design of the overall system and RF cavity under prior programs. Advanced Energy Systems (AES) is currently responsible for the engineering design and fabrication of the electron gun under contract to BNL. We will report on the engineering design and fabrication status of the superconducting photocathode electron gun. The overall configuration of the cryomodule will be reviewed. The layout of the hermitic string, space frame, shielding package, and cold mass will be discussed. The engineering design of the gun cavity and removable cathode will be presented in detail and areas of technical risk will be highlighted. Finally, the fabrication sequence and fabrication status of the gun cavity will be discussed.
Date: November 17, 2008
Creator: Ben-Zvi,I.
Partner: UNT Libraries Government Documents Department

Final Report for May 1 2004 to April 30 2005 and renewal request for the experiment # 1042511 Electro-optical detection for the temporal characterization of sub-picosecond beam bunch

Description: To develop a novel, single-shot, non-destructive method of determining the time structure of the relativistic electron bunch length in the sub-picosecond resolution. Using an electro-optical flash (EO-flash) detection technique, we will demonstrate that the electron bunch length can be converted from time to spatial information. An additional task added for the continuation is advanced topics of particle acceleration in vacuum with high-power lasers.
Date: May 1, 2005
Creator: Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department

Quench propagation in the HOM damper of the 56 MHz cavity

Description: The aim of this report is to summarize a study of the propagation of a quench in a HOM damper probe of the 56 MHz superconducting storage cavity for RHIC and provide guidance for machine protection. The 56 MHz cavity [1] is designed to operate as a beam-driven superconducting quarter-wave resonator in the RHIC ring. Four Higher Order Mode (HOM) dampers [2] are used to prevent beam instabilities [3] in RHIC. These are inserted in the back wall of the cavity (the high magnetic field region) through ports that also serve for rinsing the cavity with high-pressure deionized water as well as the fundamental power coupler and pick-up ports. Figure 1 shows the outline of the cavity [4,5]. The HOM damper probe has a magnetic coupling loop which penetrates the cavity as shown in Figure 2 [5]. The loop is cooled by conduction to the 4.3K helium system, thus any sudden, significant amount of heat dumped on the loop will cause local heating. The peak magnetic field on the loop can reach about 7.4 x 10{sup 4} amperes per meter at a cavity voltage of 2.5 MV [5]. The scenario we present here is that a small region on the loop quenches. We can calculate the current driving the cavity using the RHIC parameters and get the magnetic field as a function of the current, the cavity's intrinsic Q and detuning parameter, however it turns out that within the time relevant for the quench development (a fraction of a second) the cavity field does not change sufficiently to warrant this extra computation. Thus we can assume that the field over the loop is constant. The damper loop dimensions are not so important, however its cross section is. In the following we assume that the loop's cross-section is 2 cm by ...
Date: August 1, 2009
Creator: Ben-Zvi,I.
Partner: UNT Libraries Government Documents Department

THE ERL HIGH-ENERGY COOLER FOR RHIC.

Description: Electron cooling [1] entered a new era with the July 2005 cooling of the Tevatron recycler ring [2] at Fermilab, using {gamma} = 9.5. Considering that the cooling rate decreases as faster than {gamma}{sup 2} and the electron energy forces higher electron currents, new acceleration techniques, high-energy electron cooling presents special challenges to the accelerator scientists and engineers. For example, electron cooling of RHIC at collisions requires electron beam energy up to about 54 MeV at an average current of between 50 to 100 mA and a particularly bright electron beam. The accelerator chosen to generate this electron beam is a superconducting Energy Recovery Linac (ERL) with a superconducting RF gun with a laser-photocathode.
Date: June 23, 2006
Creator: BEN-ZVI, I.
Partner: UNT Libraries Government Documents Department

Polarized gun and ERL R and D for eRHIC

Description: At Jefferson Laboratory charge density and charge lifetime during electron beam delivery are over 2 x 10{sup 5} C/cm{sup 2} and 200 C, respectively. A 200 C charge lifetime at 2 mA corresponds to 10{sup 5} seconds. In a more recent result, charge lifetimes of about an order of magnitude larger were achieved by a load-lock gun with a larger cathode area.
Date: May 27, 2009
Creator: Ben-Zvi,I.
Partner: UNT Libraries Government Documents Department

Recent progress in photo-injectors

Description: In photoinjector electron guns, electrons are emitted from a photocathode by a short laser pulse and then accelerated by intense RF fields in a resonant cavity. Photoinjectors are very versatile tools. Normally we think of them in terms of the production of high electron density in 6-D phase space, for reasons such as injection to laser accelerators, generation of x-rays by Compton scattering and short wavelength FELs. Another example for the use of photo-injectors is the production of a high charge in a short time, for wake- field acceleration, two-beam accelerators and high-power, long-wavelength FELs. There are other potential uses, such as the generation of polarized electrons, compact accelerators for industrial applications and more. Photoinjectors are in operation in many electron accelerator facilities and a large number of new guns are under construction. The purpose of this work is to present some trend setting recent results that have been obtained in some of these laboratories. In particular the subjects of high density in 6-D phase space, new diagnostic tools, photocathode advances and high-charge production will be discussed.
Date: October 1, 1996
Creator: Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department

ELECTRON COOLING FOR RHIC.

Description: The Accelerator Collider Department (CAD) at Brookhaven National Laboratory is operating the Relativistic Heavy Ion Collider (RHIC), which includes the dual-ring, 3.834 km circumference superconducting collider and the venerable AGS as the last part of the RHIC injection chain. CAD is planning on a luminosity upgrade of the machine under the designation RHIC II. One important component of the RHIC II upgrade is electron cooling of RHIC gold ion beams. For this purpose, BNL and the Budker Institute of Nuclear Physics in Novosibirsk entered into a collaboration aimed initially at the development of the electron cooling conceptual design, resolution of technical issues, and finally extend the collaboration towards the construction and commissioning of the cooler. Many of the results presented in this paper are derived from the Electron Cooling for RHIC Design Report [1], produced by the, BINP team within the framework of this collaboration. BNL is also collaborating with Fermi National Laboratory, Thomas Jefferson National Accelerator Facility and the University of Indiana on various aspects of electron cooling.
Date: May 13, 2001
Creator: BEN-ZVI,I.
Partner: UNT Libraries Government Documents Department

High-brightness electron beam diagnostics at the ATF

Description: The Brookhaven Accelerator Test Facility (ATF) is a dedicated user facility for accelerator physicists. Its design is optimized to explore laser acceleration and coherent radiation production. To characterize the low-emittance, picoseconds long electron beam produced by the ATF`s photocathode RF gun, we have installed electron beam profile monitors for transverse emittance measurement, and developed a new technique to measure electron beam pulse length by chirping the electron beam energy. We have also developed a new technique to measure the ps slice emittance of a 10 ps long electron beam. Stripline beam position monitors were installed along the beam to monitor the electron beam position and intensity. A stripline beam position monitor was also used to monitor the timing jitter between the RF system and laser pulses. Transition radiation was used to measure electron beam energy, beam profile and electron beam bunch length.
Date: July 1, 1996
Creator: Wang, X.J. & Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department

ADVANCED DIAGNOSTICS FOR DEVELOPING HIGH-BRIGHTNESS ELECTRON BEAMS.

Description: The production of high-brightness particle beams calls for the development of advanced beam diagnostics. High brightness beams, meaning beams with a high density in phase space, are important for many applications, such as short-wavelength Free-Electron Lasers and advanced accelerator systems. A diagnostic that provides detailed information on the density distribution of the electron bunch in multi-dimensional phase-space is an essential tool for obtaining small emittance at a high charge. This diagnostic system has been developed at Brookhaven National Laboratory. One component of the system is the measurement of a slice emittance which provides a measurement of transverse beam properties (such as emittance) as a function of the longitudinal position. Changing the laser pulse profile of a photocathode RF gun has been suggested as one way to achieve non-linear emittance compensation and improve the brightness and that can be diagnosed by the slice emittance system. The other element of the diagnostic is the tomographic reconstruction of the transverse phase. In our work we give special attention to the accuracy of the phase space reconstruction and present an analysis using a transport line with nine focusing magnets and techniques to control the optical functions and phases. This high precision phase space tomography together with the ability to modify the radial charge distribution of the electron beam presents an opportunity to improve the emittance and apply non-linear radial emittance corrections. Combining the slice emittance and tomography diagnostics leads to an unprecedented visualization of phase space distributions in 5 dimensional phase-space and an opportunity to perform high-order emittance corrections. This should lead to great improvements in the beam brightness.
Date: November 24, 1998
Creator: BEN-ZVI,I.
Partner: UNT Libraries Government Documents Department

High precision beam alignment of electromagnetic wigglers

Description: The performance of Free-Electron Lasers depends critically on the quality of the alignment of the electron beam to the wiggler's magnetic axis and the deviation of this axis from a straight fine. The measurement of the electron beam position requires numerous beam position monitors in the wiggler, where space is at premium. The beam position measurement is used to set beam steerers for an orbit correction in the wiggler. The authors propose an alternative high precision alignment method in which one or two external Beam Position Monitors (BPM) are used. In this technique, the field in the electro-wiggler is modulated section by section and the beam position movement at the external BPM is detected in synchronism with the modulation. A beam offset at the modulated beam section will produce a modulation of the beam position at the detector that is a function of the of the beam offset and the absolute value of the modulation current. The wiggler errors produce a modulation that is a function of the modulation current. It will be shown that this method allows the detection and correction of the beam position at each section in the presence of wiggler errors with a good resolution. Furthermore, it allows one to measure the first and second integrals of the wiggler error over each wiggler section. Lastly, provided that wiggler sections can be degaussed effectively, one can test the deviation of the wiggler's magnetic axis from a straight line.
Date: January 1, 1993
Creator: Ben-Zvi, I. & Qiu, X.Z.
Partner: UNT Libraries Government Documents Department

Ultraviolet Free Electron Laser Facility preliminary design report

Description: This document, the Preliminary Design Report (PDR) for the Brookhaven Ultraviolet Free Electron Laser (UV FEL) facility, describes all the elements of a facility proposed to meet the needs of a research community which requires ultraviolet sources not currently available as laboratory based lasers. Further, for these experiments, the requisite properties are not extant in either the existing second or upcoming third generation synchrotron light sources. This document is the result of our effort at BNL to identify potential users, determine the requirements of their experiments, and to design a facility which can not only satisfy the existing need, but have adequate flexibility for possible future extensions as need dictates and as evolving technology allows. The PDR is comprised of three volumes. In this, the first volume, background for the development of the proposal is given, including descriptions of the UV FEL facility, and representative examples of the science it was designed to perform. Discussion of the limitations and potential directions for growth are also included. A detailed description of the facility design is then provided, which addresses the accelerator, optical, and experimental systems. Information regarding the conventional construction for the facility is contained in an addendum to volume one (IA).
Date: February 1, 1993
Creator: Ben-Zvi, I. (ed.)
Partner: UNT Libraries Government Documents Department

Towards short wavelengths FELs workshop

Description: This workshop was caged because of the growing perception in the FEL source community that recent advances have made it possible to extend FEL operation to wavelengths about two orders of magnitude shorter than the 240 nm that has been achieved to date. In addition short wavelength FELs offer the possibilities of extremely high peak power (several gigawatts) and very short pulses (of the order of 100 fs). Several groups in the USA are developing plans for such short wavelength FEL facilities. However, reviewers of these plans have pointed out that it would be highly desirable to first carry out proof-of-principle experiments at longer wavelengths to increase confidence that the shorter wavelength devices will indeed perform as calculated. The need for such experiments has now been broadly accepted by the FEL community. Such experiments were the main focus of this workshop as described in the following objectives distributed to attendees: (1) Define measurements needed to gain confidence that short wavelength FELs will perform as calculated. (2) List possible hardware that could be used to carry out these measurements in the near term. (3) Define a prioritized FEL physics experimental program and suggested timetable. (4) Form collaborative teams to carry out this program.
Date: December 1, 1993
Creator: Ben-Zvi, I. & Winick, H.
Partner: UNT Libraries Government Documents Department

Characterization of an SRF gun: a 3D full wave simulation

Description: We characterized a BNL 1.3GHz half-cell SRF gun is tested for GaAs photocathode. The gun already was simulated several years ago via two-dimensional (2D) numerical codes (i.e., Superfish and Parmela) with and without the beam. In this paper, we discuss our investigation of its characteristics using a three dimensional (3D) full-wave code (CST STUDIO SUITE{trademark}).The input/pickup couplers are sited symmetrically on the same side of the gun at an angle of 180{sup o}. In particular, the inner conductor of the pickup coupler is considerably shorter than that of the input coupler. We evaluated the cross-talk between the beam (trajectory) and the signal on the input coupler compared our findings with published results based on analytical models. The CST STUDIO SUITE{trademark} also was used to predict the field within the cavity; particularly, a combination of transient/eigenmode solvers was employed to accurately construct the RF field for the particles, which also includes the effects of the couplers. Finally, we explored the beam's dynamics with a particle in cell (PIC) simulation, validated the results and compare them with 2D code result.
Date: March 28, 2011
Creator: Wang, E.; Ben-Zvi, I. & Wang, J.
Partner: UNT Libraries Government Documents Department

Novel deflecting cavity design for eRHIC

Description: To prevent significant loss of the luminosity due to large crossing angle in the future ERL based Electron Ion Collider at BNL (eRHIC), there is a demand for crab cavities. In this article, we will present a novel design of the deflecting/crabbing 181 MHz superconducting RF cavity that will fulfil the requirements of eRHIC. The quarter-wave resonator structure of the new cavity possesses many advantages, such as compact size, high R{sub t}/Q, the absence of the same order mode and lower order mode, and easy higher order mode damping. We will present the properties and characteristics of the new cavity in detail. As the accelerator systems grow in complexity, developing compact and efficient deflecting cavities is of great interest. Such cavities will benefit situations where the beam line space is limited. The future linac-ring type electron-ion collider requires implementation of a crab-crossing scheme for both beams at the interaction region. The ion beam has a long bunches and high rigidity. Therefore, it requires a low frequency, large kicking angle deflector. The frequency of the deflecting mode for the current collider design is 181 MHz, and the deflecting angle is {approx}5 mrad for each beam. At such low frequency, the previous designs of the crab cavities will have very large dimensions, and also will be confronted by typical problems of damping the Lower Order Mode (LOM), the Same Order Mode (SOM), and as usual, the Higher Order Modes (HOM). In this paper we describe how one can use the concept of a quarter-wave (QW) resonator for a deflecting/crabbing cavity, and use its fundamental mode to deflect the beam. The simplicity of the cavity geometry and the large separation between its fundamental mode and the first HOM make it very attractive.
Date: July 25, 2011
Creator: Wu, Q.; Belomestnykh, S. & Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department

The fundamental power coupler and pick-up of the 56 MHz SRF cavity for RHIC

Description: A fundamental power coupler (FPC) is designed to provide fast tuning the 56MHz SRF cavity in RHIC. The FPC will be inserted from one of the chemical cleaning ports at the rear end of the cavity with magnetic coupling to the RF field. The size and the location of the FPC are decided based on the required operational external Q of the cavity. The cavity is beam driven, and the FPC is designed with variable coupling that would cover a range of power levels. It is thermally isolated from the base temperature of the cavity, which is 4.2K. A 1kW power amplifier will be used to close an amplitude control feedback loop. In this paper, we discuss the coupling factor of the FPC with the chosen design.
Date: March 28, 2011
Creator: Wu, Q.; Bellavia, S.; Ben-Zvi, I. & Pai, C.
Partner: UNT Libraries Government Documents Department

Simulation of the High-Pass Filter for 56MHz Cavity for RHIC

Description: The 56MHz Superconducting RF (SRF) cavity for RHIC places high demands High Order Mode (HOM) damping, as well as requiring a high field at gap with fundamental mode frequency. The damper of 56MHz cavity is designed to extract all modes to the resistance load outside, including the fundamental mode. Therefore, the circuit must incorporate a high-pass filter to reflect back the fundamental mode into the cavity. In this paper, we show the good frequency response map obtained from our filter's design. We extract a circuit diagram from the microwave elements that simulate well the frequency spectrum of the finalized filter. We also demonstrate that the power dissipation on the filter over its frequency range is small enough for cryogenic cooling.
Date: May 23, 2010
Creator: Wu, Q. & Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department

Simulations for preliminary design of a multi-cathode DC electron gun for eRHIC

Description: The proposed electron ion collider, eRHIC, requires a large average polarized electron current of 50 mA, which is more than 20 times higher than the present experimental output of a single, highly polarized electron source, based on cesiated super-lattice GaAs. To meet eRHIC's requirement for current, we designed a multicathode DC electron gun for injection. The twenty-four GaAs cathodes emit electrons in sequence, then are combined on axis by a rotating field (or 'funnelled'). In addition to its ultra-high vacuum requirements, the multicathode DC electron gun will place high demand on the electric field symmetry, the magnetic field shielding, and on preventing arcing. In this paper, we discuss our results from a 3D simulation of the latest model for this gun. The findings will guide the actual design in future. Their preliminary design of a multi-cathode electron source for eRHIC demonstrated tolerable fields and reasonable results in both field and particle simulations.
Date: May 23, 2010
Creator: Wu, Q.; Ben-Zvi, I.; Chang, X. & Skaritka, J.
Partner: UNT Libraries Government Documents Department