59 Matching Results

Search Results

Advanced search parameters have been applied.

Calculation of longitudinal and transverse wake-field effects in dielectric structures

Description: The electro-magnetic radiation of a charged particle passing through a dielectric structure has many applications to accelerator physics. Recently a new acceleration scheme, called the dielectric wake field accelerator, has been proposed. It also can be used as a pick up system for a storage ring because of its slow wave characteristics. In order to study these effects in detail, in this paper we will calculate the wake field effects produced in a dielectric structure by a charged particle. 8 refs., 2 figs.
Date: January 1, 1989
Creator: Gai, W.
Partner: UNT Libraries Government Documents Department

Design of a high charge (10 - 100 nC) and short pulse (2 - 5 ps) rf photocathode gun for wakefield acceleration.

Description: In this paper we present a design report on a 1-1/2 cell, L Band RF photocathode gun that is capable of generating and accelerating electron beams with peak currents >10 kA. We have performed simulation for bunch intensities in the range of 10-100 nC with peak axial electrical field at the photocathode of 30-100 MV/m. Unlike conventional short electron pulse generation, this design does not require magnetic pulse compression. Based on numerical simulations using SUPERFISH and PARMELA, this design will produce 20-100 nC beam at 18 MeV with rms bunch length 0.6-1.25 mm and normalized transverse emittance 30-108 mm mrad. Applications of this beam for wakefield acceleration is also discussed.
Date: July 16, 1998
Creator: Gai, W.
Partner: UNT Libraries Government Documents Department

High-power testing of 11.424 GHz dielectric-loaded accelerating structures.

Description: The design, construction, and bench testing of an X-band travelling-wave accelerating structure loaded with a permittivity=20 dielectric has been published recently by the Argonne Advanced Accelerator Group [1]. Here we describe a new program to build a test accelerator using this structure. The accelerator will be powered using high-power 11.424-GHz radiation available at the Magnicon Facility at the Naval Research Lab [2]. The magnicon is expected to provide up to 30 MW from each of two WR-90 output waveguide arms in pulses of up to 1-{micro}s duration, permitting tests of the dielectric-loaded X-band device at gradients of {approximately}40 MV/m. The use of higher power pulses (100-500 MW) eventually available at the output of an active pulse compressor [3] driven by the magnicon will permit gradients in excess of 100 MV/m to be achieved.
Date: July 16, 2001
Creator: Gold, S. H. & Gai, W.
Partner: UNT Libraries Government Documents Department

Field analysis of a dielectric-loaded rectangular waveguide accelerating structure.

Description: In this paper, we present a detailed analysis of the modes of a dielectric-loaded rectangular waveguide accelerating structure. In general, the acceleration field in a synchronous acceleration mode is non-uniform in the two transverse dimensions. However, we could use an array of these structures rotated alternatively by 90 degrees to get a focusing-defocusing force continuously as a simple FODO lattice, while maintaining uniform energy gain. The expressions of characteristic parameters such as R/Q, group velocity and attenuation constant are given. The longitudinal wake field experienced by a relativistic charged particle beam in the structure is also presented. These analytical results are also compared with numerical calculations using the MAFIA code suite demonstrating the validity of our analytic approach.
Date: July 16, 2001
Creator: Xiao, L.; Gai, W. & Sun, X.
Partner: UNT Libraries Government Documents Department

Design of dielectric accelerator using TE-TM mode converter.

Description: A new design for X band dielectric accelerator using a TE-TM mode converter has been proposed and studied. It first converts RF from TE to TM mode in a pure metal section, then a tapered transition section is used for high efficiency transmission to the dielectric accelerator section. Because there is no dielectrics near the RF coupler, this scheme has potential to overcome RF breakdown problems near the coupling holes in the dielectric based accelerators, as it happened in the older designs. A detailed design study shows that high conversion efficiency ({approx}100%) can be achieved for both single and dual coupling ports and it is less sensitive to machine errors than previous designs. Another advantage of this design is that it can be made to different modules thus greatly reduce the R&D cycles.
Date: August 29, 2002
Creator: Liu, W. & Gai, W.
Partner: UNT Libraries Government Documents Department

Mixing, staging, and phasing for a proton-driven wake field accelerator

Description: This paper expands on a few important details of the Wakeatron concept. This is a device where electrons can be accelerated by the wake field of short intense proton bunches travelling along the axis of an rf structure. Specifically, we have examined the consequences of the longitudinal dynamics of both the electron and the proton bunches. Included were ''mixing'' in the proton bunches (crucial to the overall concept) and phase shifts (electron bunches relative to proton bunches) in the acceleration process. Because of the deterioration of the proton bunches, due to the ''mixing'' process, it is required that the Wakeatron is indeed staged in a number of consecutive sections.
Date: January 1, 1987
Creator: Gai, W.; Ruggiero, A.G. & Simpson, J.D.
Partner: UNT Libraries Government Documents Department

The Argonne Wakefield Accelerator (AWA) laser system and its associated optics

Description: Generating a 100 nC, 15 ps pulse length electron beam at the AWA requires a stable laser system capable of producing 1--3 ps, 5 mJ at 248 nm with the ability to shape the wave front. We have installed a combined Coherent ultra fast 702 dye laser and Lambda Physik excimer pulsed amplification system which meets these requirements. A device has been built to produce shaped laser pulses. Detailed characterizations of the laser system, its associated optics development, and timing/amplitude stabilization are presented.
Date: July 1, 1992
Creator: Gai, W.; Konecny, R. & Power, J.
Partner: UNT Libraries Government Documents Department

Limiting Effects in the Transverse-to-Longitudinal Emittance Exchange Technique for Low Energy Relativistic Electron Beams

Description: Transverse to longitudinal phase space manipulation hold great promises, e.g., as a potential technique for repartitioning the emittances of a beam. A proof-of-principle experiment to demonstrate the exchange of a low longitudinal emittance with a larger transverse emittance is in preparation at the Argonne Wakefield Accelerator using a {approx}12 MeV electron beam. In this paper we explore the limiting effects of this phase space manipulation method including high order and collective effects. A realistic start-to-end simulation of the planned proof-of-principle experiment including sensitivity studies is also presented.
Date: May 1, 2009
Creator: Rihaoui, M. M.; Piot, P.; Power, J. G. & Gai, W.
Partner: UNT Libraries Government Documents Department

Measurement and Simulation of Space Charge Effects in a Multi-Beam Electron Bunch from an RF Photoinjector

Description: We report on a new experimental study of the space charge effect in a space-charge-dominated multi-beam electron bunch. A 5 MeV electron bunch, consisting of a variable number of beamlets separated transversely, was generated in a photoinjector and propagated in a drift space. The collective interaction of these beamlets was studied for different experimental conditions. The experiment allowed the exploration of space charge effects and its comparison with three-dimensional particle-in-cell simulations. Our observations also suggest the possible use of a multibeam configuration to tailor the transverse distribution of an electron beam.
Date: May 1, 2009
Creator: Rihaoui, M. M.; Piot, P.; Power, J. G.; Yusof, Z. & Gai, W.
Partner: UNT Libraries Government Documents Department

Verification of the AWA Photoinjector Beam Parameters Required for a Transverse-to-Longitudinal Emittance Exchange Experiment

Description: A transverse-to-longitudinal emittance exchange experiment is in preparation at the Argonne Wakefield Accelerator (AWA). The experiment aims at exchanging a low ({var_epsilon}{sub z} < 5 {micro}m) longitudinal emittance with a large ({var_epsilon}{sub x} > 15 {micro}m) transverse horizontal emittance for a bunch charge of {approx}100 pC. Achieving such initial emittance partitioning, though demonstrated via numerical simulations, is a challenging task and needs to be experimentally verified. In this paper, we report preliminary emittance measurements of the beam in the transverse and longitudinal planes performed at {approx}12 MeV. The measurements are compared with numerical simulations.
Date: May 1, 2009
Creator: Rihaoui, M. M.; Piot, P.; Power, J. G.; Mihalcea, D. & Gai, W.
Partner: UNT Libraries Government Documents Department

Experimental measurement of nonlinear plasma wake-fields

Description: We report direct high resolution observation of nonlinear steepened plasma waves excited in the wake of an intense, self-pinched electron beam. Oscillators in both accelerating and deflecting fields are measured, and analyzed in the context of linear and nonlinear plasma wave theory. The degree of nonlinearity in the wake-fields is shown to be consistent with analytical predictions of the beam self-pinching. The impact of these results on plasma acceleration and focusing schemes is discussed. 15 refs., 4 figs.
Date: January 1, 1989
Creator: Rosenzweig, J.B.; Schoessow, P.; Cole, B.; Gai, W.; Konecny, R.; Norem, J. et al.
Partner: UNT Libraries Government Documents Department

Transformer ratio enhancement using a ramped bunch train in a collinear wakefield accelerator.

Description: We present a practical method for achieving a transformer ratio (R) greater than 2 with any collinear wakefield accelerator--i.e. with either plasma or structure based wakefield accelerators. It is known that the transformer ratio cannot generally be greater than 2 for a symmetric drive bunch in a collinear wakefield accelerator. However, using a ramped bunch train (RBT) where a train of n electron drive bunches, with increasing (ramping) charge, one can achieve R = 2n after the bunch train. We believe this method is feasible from an engineering standpoint. We describe a proof of principle experiment using an disk-loaded waveguide, of frequency 13.65 GHz, driven by a RBT of 4 electron bunches. We expect to achieve R > 6 using 4 electron bunches. Details of the simulation and experimental design are presented.
Date: July 19, 2001
Creator: Power, J. G.; Gai, W.; Sun, X. & Kanareykin, A.
Partner: UNT Libraries Government Documents Department

A hybrid dielectric and iris loaded periodic accelerating structure.

Description: One disadvantage of conventional iris-loaded accelerating structures is the high ratio of the peak surface electric field to the peak axial electric field useful for accelerating a beam. Typically this ratio E{sub s}/E{sub a} {ge} 2. The high surface electric field relative to the accelerating gradient may prove to be a limitation for realizing technologies for very high gradient accelerators. In this paper, we present a scheme that uses a hybrid dielectric and iris loaded periodic structure to reduce E{sub s}/E{sub a} to near unity, while the shunt impedance per unit length r and the quality factor Q compare favorably with conventional metallic structures. The analysis based on MAFIA simulations of such structures shows that we can lower the peak surface electric field close to the accelerating gradient while maintaining high acceleration efficiency as measured by r/Q. Numerical examples of X-band hybrid accelerating structures are given.
Date: July 17, 2001
Creator: Zou, P.; Xiao, L.; Sun, X. & Gai, W.
Partner: UNT Libraries Government Documents Department

Design and construction of a high charge and high current 1-1/2 cell L-Band RF photocathode gun.

Description: The Argonne Wakefield Accelerator has been successfully commissioned and used for conducting wakefield experiments in dielectric loaded structures and plasmas. Although the initial wakefield experiments were successful, higher drive beam quality would substantially improve the wakefield accelerating gradients. In this paper we present a new 1-1/2 cell L-band photocathode RF gun design. This gun will produce 10-100 nC beam with 2-5 ps rms pulse length and normalized emittance less than 100 mm mrad. The final gun design and numerical simulations of the beam dynamics are presented.
Date: March 26, 1999
Creator: Conde, M. E.; Gai, W.; Konecny, R.; Power, J. G. & Schoessow, P.
Partner: UNT Libraries Government Documents Department

Construction and testing of an 11.4 GHz dielectric structure based travelling wave accelerator.

Description: One major challenge in constructing a dielectric loaded traveling wave accelerator powered by an external rf power source is the difficulty in achieving efficient coupling. In this paper, we report that we have achieved high efficiency broadband coupling by using a combination of a tapered dielectric section and a carefully adjusted coupling slot. We are currently constructing an 11.4 GHz accelerator structure loaded with a permitivity=20 dielectric. Bench testing has demonstrated a coupling efficiency in excess of 95% with bandwidth of 600 MHz. The final setup will be tested at high power at SLAC using an X-band klystron rf source.
Date: March 26, 1999
Creator: Gai, W.; Konecny, R.; Wong, T. & Zou, P.
Partner: UNT Libraries Government Documents Department

Wakefield excitation in multimode structures by a train of electron bunches.

Description: We discuss wakefield excitation and propagation in dielectric structures, particularly concentrating on the case of multiple drive beam excitation in multimode structures. We emphasize calculations of the energy loss of the drive bunch train, the amplitude of the wakefield, and the relation between power flow and stored energy in the dielectric wakefield device. We show that for a collinear multimode structure the amplitude of the wakefield generated by a bunch train is less than or equal to the wakefield generated by a single bunch of the same total charge. Furthermore, the transformer ratio, R, is shown to be always less than 2, even in the multiple drive beam case. Plans for an experiment to measure wakes in a multimode structure at AWA are presented.
Date: March 26, 1999
Creator: Conde, M. E.; Gai, W.; Konecny, R.; Power, J. G. & Schoessow, P.
Partner: UNT Libraries Government Documents Department

Initial tests of the dual-sweep streak camera system planned for APS particle-beam diagnostics

Description: Initial tests of a dual-sweep streak system planned for use on the Advanced Photon Source (APS) have been performed using assets of the Argonne Wakefield Accelerator (AWA) facility. The short light pulses from the photoelectric injector drive laser in both the visible ({lambda}=496 nm, {Delta}t{approximately}1.5 ps (FWHM)), and the ultraviolet ({lambda}=248 nm, {Delta}t{approximately}5 ps (FWHM)) were used. Both a UV-visible S20 photocathode streak tube and a UV-to-x-ray Au photocathode streak tube were tested. Calibration data with an etalon were also obtained. A sample of dual-sweep streak data using optical synchrotron radiation on the APS injector synchrotron is also presented.
Date: July 1, 1995
Creator: Lumpkin, A.; Yang, B.; Gai, W. & Cieslik, W.
Partner: UNT Libraries Government Documents Department

Accelerating field step-up transformer in wake-field accelerators

Description: In the wake-field scheme of particle acceleration, a short, intense drive bunch of electrons passes through a slow-wave structure, leaving behind high rf power in its wake field. The axial accelerating electric field associated with the rf can be quite large, > 100 MeV/m, and is used to accelerate a much less intense witness'' beam to eventual energies > 1 TeV. The rf power is deposited predominantly in the fundamental mode of the structure, which, for dielectric-lined waveguide as used at Argonne, is the TM{sub 01} mode. In all likelihood on the field amplitude will be limited only by rf breakdown of the dielectric material, the limit of which is currently unknown in the short time duration, high frequency regime of wake-field acceleration operation. To obtain such strong electric fields with given wake-field rf power, the dimensions of the dielectric-lined waveguide have to be fairly small, OD of the order of a cm and ID of a few mm, and this gives rise to the generation of strong deflection modes with beam misalignment. While a scheme exists to damp such deflection modes on a bunch-to-bunch time scale, head-tail beam deflection could still be a problem and BNS damping as well as FODO focusing are incomplete cures. Presented here are details of a scheme by which the rf power is generated by in a large-diameter wake-field tube, where deflection mode generation by the intense drive beam is tolerable, and then fed into a small-diameter acceleration tube where the less intense witness beam is accelerated by the greatly enhanced axial electric field. The witness beam generates little deflection-mode power itself, even in the small acceleration tube, thus a final high-quality, high-energy electron beam is produced.
Date: January 1, 1991
Creator: Chojnacki, E.; Gai, W.; Schoessow, P. & Simpson, J.
Partner: UNT Libraries Government Documents Department

Argonne plasma wake-field acceleration experiments

Description: Four years after the initial proposal of the Plasma Wake-field Accelerator (PWFA), it continues to be the object of much investigation, due to the promise of the ultra-high accelerating gradients that can exist in relativistic plasma waves driven in the wake of charged particle beams. These wake-fields are of interest both in the laboratory, for acceleration and focusing of electrons and positrons in future linear colliders, and in nature as a possible cosmic ray acceleration mechanism. The purpose of the present work is to review the recent experimental advances made in PWFA research at Argonne National Laboratory. Some of the topics discussed are: the Argonne Advanced Accelerator Test Facility; linear plasma wake-field theory; measurement of linear plasma wake-fields; review of nonlinear plasma wave theory; and experimental measurement of nonlinear plasma wake-fields. 25 refs., 11 figs.
Date: March 14, 1989
Creator: Rosenzweig, J.B.; Cole, B.; Gai, W.; Konecny, R.; Norem, J.; Schoessow, P. et al.
Partner: UNT Libraries Government Documents Department

Proposed RF Breakdown Studies at the AWA

Description: A study of breakdown mechanism has been initiated at the Argonne Wakefield Accelerator (AWA). Breakdown may include several factors such as local field enhancement, explosive electron emission, Ohmic heating, tensile stress produced by electric field, and others. The AWA is building a dedicated facility to test various models for breakdown mechanisms and to determine the roles of different factors in the breakdown. We plan to trigger breakdown events with a high-powered laser at various wavelengths (IR to UV) to determine the role of explosive electron emission in the breakdown process. Another experimental idea follows from the recent work on a Schottky-enabled photoemission in an RF photoinjector [1] that allows us to determine in situ the field enhancement factor on a cathode surface. Monitoring the field enhancement factor before and after the breakdown can shed some light on a number of observations such as the crater formation process.
Date: March 21, 2007
Creator: Antipov, S.; Conde, M.; Gai, W.; Power, J. G.; Spentzouris, L.; Yusof, Z. et al.
Partner: UNT Libraries Government Documents Department

High gradient dielectric wakefield device measurements at the Argonne wakefield accelerator

Description: The Argonne Wakefield Accelerator (AWA) is a facility designed to investigate high gradient wakefield acceleration techniques. Wakefields are excited using a drive beam produced by a 14 MeV high current photoinjector-based linac. A second photocathode gun generates a 4 MeV witness beam which is used as a probe of the wakefields in the device under test. The delay of the witness bunch with respect to the drive bunch can be continuously varied from -100 ps to >1 ns. The drive and witness bunches propagate along collinear or parallel trajectories through the test section. A dipole spectrometer is then used to measure the energy change of the witness beam. The complete wakefield measurement system has been commissioned and wakefield experiments using dielectric structures are underway. Initial experiments have focused on collinear wakefield device geometries where the drive and witness bunches traverse the same structure. For attaining very high gradients we will construct and study step-up transformer structures in which the rf pulse generated by the drive beam is compressed transversely and longitudinally.
Date: October 1997
Creator: Schoessow, P.; Conde, M.; Gai, W.; Konecny, R.; Power, J. & Simpson, J.
Partner: UNT Libraries Government Documents Department

Performance of the Argonne Wakefield Accelerator Facility and initial experimental results

Description: The Argonne Wakefield Accelerator facility has begun its experimental program. It is designed to address advanced acceleration research requiring very short, intense electron bunches. It incorporates two photocathode based electron sources. One produces up to 100 nC, multi-kiloamp `drive` bunches which are used to excite wakefields in dielectric loaded structures and in plasma. The second source produces much lower intensity `witness` pulses which are used to probe the fields produced by the drive. The drive and witness pulses can be precisely timed as well as laterally positioned with respect to each other. This paper discusses commissioning, initial experiments, and outline plans for a proposed 1 GeV demonstration accelerator.
Date: October 1, 1996
Creator: Gai, W.; Conde, M.; Cox, G.; Konecny, R.; Power, J.; Schoessow, P. et al.
Partner: UNT Libraries Government Documents Department