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Injection into a circular machine with a KV distribution

Description: In order to achieve a maximum space charge limit in the IPNS-II synchrotron it is desirable to inject a Kapchinskij-Vladimirskij (KV) distribution (1). We rederive the KV distribution, first starting from a smoothed Hamiltonian and then for the full alternating gradient case. The microcanonical distribution can be generalized slightly so as to allow one to alter the aspect ratio of the beam ellipse. The KV distribution requires that the injected particles all have the same total transverse oscillation energy, and also that they are distributed uniformly throughout the entire energy shell. This requires painting the injected beam uniformly in the three independent dimensions of the energy shell. We have devised two scenarios for doing this, one involving a suitable variation of the x and y injected amplitudes during the injection process, and the second involving introducing a small coupling between the x and y motions. We have written a program to simulate the injection process which includes the turn-to-turn forces between the (500) injected turns. If we omit the turn-to-turn forces then the resulting space charge density distributions are indeed very nearly uniform within a circular beam cross section for either KV injection scenario, but are neither uniform nor circular for other plausible scenarios. With turn-to-turn forces included, the interturn scattering can be fairly important and the resulting density distributions tend to develop lower density halos. If we add a gradient bump to simulate magnetic quadrupole errors in the lattice, then the effects of half-integral resonances can be clearly seen. When the space charge forces between turns depress the tune to a resonance, beam growth keeps the tunes constant at the edge of the stop band, unless the resonance is crossed quickly.
Date: December 31, 1995
Creator: Crosbie, E. & Symon, K.
Partner: UNT Libraries Government Documents Department

Topping up experiments at SRRC

Description: In an operation of a synchrotron radiation facility, it is very desirable to be able to provide beam with almost constant intensity. This has considerable advantage in terms of calibration and normalization of detectors, heat load of optical components,and the duration of data taking time. To achieve that goal, the topping up mode injection has been tested at SRRC. The experiment was performed to fill automatically the stored beam current up to 200 mA whenever it was decreased to a present low limit value. The following items were examined: reproducibility of the bunch train structure of the injected beam, stability of the storage ring pulsed injection magnets, injection startup and bucket address system. Effects on the stored beam stability will be studied and methods to minimize disruption to research program during injection time will be investigated.
Date: October 1, 1996
Creator: Ueng, T.S.; Hsu, K.T.; Chen, J.; Lin, K.K. & Weng, W.T.
Partner: UNT Libraries Government Documents Department

Automated tuning of the advanced photon source booster synchrotron

Description: The acceleration cycle of the Advanced Photon Source (APS) booster synchrotron is completed within 223 ms and is repeated at 2 Hz. Unless properly corrected, transverse and longitudinal injection errors can lead to inefficient booster performance. In order to simplify daily operation, automated tuning methods have been developed. Through the use of beam position monitor (BPM) reading, transfer line corrector magnets, magnet ramp timing, and empirically determined response functions, the injection process is optimized by correcting the first turn trajectory to the measured closed orbit. These tuning algorithms and their implementation are described here along with an evaluation of their performance.
Date: August 1, 1997
Creator: Biedron, S.G. & Milton, S.V.
Partner: UNT Libraries Government Documents Department

Advanced photoinjector laser and microwave technologies. Final report

Description: An overview of the design parameters of the compact, high gradient, high luminosity X-band (8.568 GHz) photoinjector facility currently being developed as a collaborative effort between LLNL and UC Davis, is followed by a more detailed description of each of its major subsystems : X-band rf gun, GHz repetition rate synchronously modelocked AlGaAs quantum well laser oscillator, and 8-pass Ti: Al{sub 2}O{sub 3} chirped pulse laser amplifier. The photoinjector uses a high quantum efficiency ({approx}5%) Cs{sub 2}Te photocathode, and will be capable of producing high charge (> 1 nC), relativistic (5 MeV), ultrashort (< 1 ps) electron bunches at 2.142 GHz repetition rate in burst mode (100 photoelectron bunches). Design studies indicate that a normalized rms transverse emittance {epsilon}{sub n} = 0.75 {pi} mm-mrad is possible at 0.1 nC charge, while 2.5 {pi} mm-mrad can be obtained at 1 nC. A complete status report of our progress in the development and implementation of the design discussed herein is then given, together with initial experimental data concerning the performance of the 15 MW SLAC X-band klystron amplifier. Finally, the phase noise and jitter characteristics of the laser and rf systems of the high gradient X-band photoinjector have been measured experimentally. In this case, the laser oscillator is a self-modelocked Titanium:Sapphire system operating at the 108th subharmonic of the rf gun. The X-band signal is produced from the laser by a phase-locked dielectric resonance oscillator, and amplified by a pulsed TWT. A comparison between the TWT phase noise and the fields excited in the rf gun demonstrates the filtering effect of the high Q cavity resonant structure, thus indicating that the rf gun can be used as a master oscillator, and could be energized by either a magnetron or a cross-field amplifier.
Date: January 1, 1997
Creator: Hartemann, F.V.; Luhmann, N.C. Jr. & Talley, W.K.
Partner: UNT Libraries Government Documents Department

Beam test of a superconducting cavity for the Fermilab high-brightness electron photo-injector

Description: An electron photo-injector facility has been constructed at Fermilab for the purpose of providing a 14�18 MeV elec-tron beam with high charge per bunch (8 nC), short bunch length (1 mm RMS), and small transverse emittance [1]. The facility was used to commission a second-generation photo-cathode RF gun for the TeSLA Test Facility (TTF) Linac at DESY [2, 3]; in the future, the Fermilab electron beam will be used for R & D in bunch length compres-sion, beam diagnostics, and new acceleration techniques. Acceleration beyond 4 MeV is provided by a 9-cell super-conducting cavity (see Figure 1). The cavity also provides a longitudinal position-momentum correlation for subse-quent bunch length compression. We report on the RF tests and a first beam test of this cavity.
Date: May 4, 1999
Creator: W. Hartung, J.P. Carneiro, M. Champion, H. Edwards, J. Fuest, K. Koepke and M. Kuchnir
Partner: UNT Libraries Government Documents Department

Optimization criteria for standing wave transverse magnetic deflection cavities

Description: An important linear accelerator requirement, in order to demonstrate narrow energy spectra, is the injection of electron bunches of narrow phase spread and negligible inter-bunch current. This can be achieved by r-f transverse modulation and clipping of the beam by an aperture prior to injection into the accelerator waveguide, i.e., chopper operation. By magnetically biasing the beam to one side of the centerline, it is possible to arrange for transmission into the accelerator at a time during each r-f cycle when the radial momentum imparted to the beam by the chopper cavity is passing through zero. The low efficiency of beam utilization normally associated with this type of operation, because of the high ratio of collected to transmitted current, can be considerably improved by combining the transverse chopping action with a suitably phased longitudinal velocity modulating field as obtained from a simple prebunching cavity. Transverse r-f deflection techniques also enable sub-harmonic bunch selection and injection into linear accelerators which are used as injectors for electron synchrotrons. This is achieved by driving the chopper cavity at the same frequency as the synchrotron r-f system (which is maintained at a precise sub-multiple of the linear accelerator fundamental frequency) and then prebunching the chopped beam at the fundamental frequency prior to injection into the linear accelerator.
Date: August 1, 1995
Creator: Haimson, J.
Partner: UNT Libraries Government Documents Department

High current plasma electron emitter

Description: A high current plasma electron emitter based on a miniature plasma source has been developed. The emitting plasma is created by a pulsed high current gas discharge. The electron emission current is 1 kA at 300 V at the pulse duration of 10 ms. The prototype injector described in this paper will be used for a 20 kA electrostatic current injection experiment in the Madison Symmetric Torus (MST) reversed-field pinch. The source will be replicated in order to attain this total current requirement. The source has a simple design and has proven very reliable in operation. A high emission current, small size (3.7 cm in diameter), and low impurity generation make the source suitable for a variety of fusion and technological applications.
Date: July 1, 1995
Creator: Fiksel, G.; Almagri, A.F. & Craig, D.
Partner: UNT Libraries Government Documents Department

The drive laser for the APS LEUTL FEL RF photoinjector.

Description: The APS LEUTL free-electron laser (FEL) is a high-gain, short-wavelength device requiring a high-current, low-emittance beam. An rf photoinjector driven by a laser is used to provide the requisite beam. The drive laser consists of a diode-pumped Nd:Glass oscillator and a chirped pulse amplification (CPA) system consisting of a grating stretcher, a flashlamp-pumped Nd:Glass regenerative amplifier, and a grating compressor. The system generates 4-mj pulses in the R with a pulse length as short as 2 ps FWHM and a repetition rate of 6 Hz. Nonlinear doubling crystals are used to generate fourth-harmonic output of {approx}500 {micro}J in the UV (263 nm), which is required to exceed the work function of the copper cathode in the gun. This paper describes the drive laser as well as the extensive controls implemented to allow for remote operation and monitoring. Performance measurements as well as the operating experience are presented.
Date: September 1, 1999
Creator: Arnold, N.; Koldenhoven, R. & Travish, G.
Partner: UNT Libraries Government Documents Department

Location of Maximum Credible Beam Losses in LCLS Injector

Description: The memo describes the maximum credible beam the LCLS injector can produce and lose at various locations along the beamline. The estimation procedure is based upon three previous reports [1, 2, 3]. While specific numbers have been updated to accurately reflect the present design parameters, the conclusions are very similar to those given in Ref 1. The source of the maximum credible beam results from the explosive electron emission from the photocathode if the drive laser intensity exceeds the threshold for plasma production. In this event, the gun's RF field can extract a large number of electrons from this plasma which are accelerated out of the gun and into the beamline. This electron emission persists until it has depleted the gun of all its energy. Hence the number of electrons emitted per pulse is limited by the amount of stored RF energy in the gun. It needs to be emphasized that this type of emission is highly undesirable, as it causes permanent damage to the cathode.
Date: December 13, 2010
Creator: Mao, Stan
Partner: UNT Libraries Government Documents Department

Wakefield Calculations for Radiation Stopper 1 (RST1)

Description: The main result of this note is that no wakefield mitigation is required for the Radiation Stopper (RST1) in the LCLS injector. The RST1 geometry is not symmetric in the vertical direction, and we derive a slight modification to the diffraction model wake for a cylindrically symmetric (2D) cavity that can be used for this problem. Performing a full 3D MAFIA calculation for the nominal 1 mm (rms) long bunch, we show that the modified diffraction model well describes the wakefields generated in RST1. The results imply an on-axis emittance growth of 0.0075%, well below the 0.5% tolerance threshold. To reach the 0.5% threshold the beam would need to be mis-steered by a large amount - 7 mm - from the axis. One reason that the effect is small is that the beta functions at the RST1 are small.
Date: December 13, 2010
Creator: Limborg-Deprey, C.
Partner: UNT Libraries Government Documents Department

Wakefield Computations for the Injector (Part I)

Description: In this document, we report on basic wakefield computations used to establish the impedance budget for the LCLS injector. Systematic comparisons between analytic formulae and results from ABCI are done. Finally, a comparison between 2D and 3D wakefield calculations are given for a cross. The three parts of the document are presented as follows: (1) ABCI computations for a few structures (Flange, Bellows...); (2) Comparison analytic with ABCI runs; and (3) Comparison Cross and Cavity using MAFIA.
Date: December 13, 2010
Creator: Limborg-Deprey, C.
Partner: UNT Libraries Government Documents Department

Cornell relativistic electron coil experiment (RECE). Progress report, January 1, 1973--June 30, 1973

Description: Measurements on the RECE-Berta facility indicate that strong relativistic electron rings can withstand ( self-heal'') considerably larger irregularities in the externally applied magnetic field than had been assumed in the past. At the same time, energy measurements on the trapped electrons showed that the energy losses of these electrons are dominated by classical collisions with the background gas and do not seem seriously enhanced by collective effects. Similarly, a more detailed theoretical analysis of the absolute decay rates of our rings done in this period reaffirms that the decay of our rings can be fully explained by classical collisions without anomalous effects. In another small pilot facility, a different injection scheme -injection of the electron beams through a magnetic cusp--was successfully tested and led to the generation of field-reversing electron rings. These rings exhibited life times of up to 9 mu sec and general characteristics very similar to those observed on the RECE-Berta rings. The acceptance tests for the new 5-MeV electron accelerator were successfully completed and the machine is in operation. So far, excellent operational and maintenance characteristics were observed, and no problems were encountered. The new RECE-Christa facility was put into operation amd experiments on it started. Some unexpected problems were encountered in the propagation of the new high-energy beams through the beam injector. However, first trapping experiments still led to the generation of almost-fieldreversing electron rings. The general characteristics of these rings again are very similar to those observed in the other machines. However, life times increased to up to 125 mu sec, i.e., about five times over those found in RECE-Berta. Very encouragingly, these life times agree well with extrapolations of the RECE- Berta results based on a purely collisional scaling. (auth)
Date: January 1, 1973
Creator: Fleischmann, H.H.
Partner: UNT Libraries Government Documents Department

Cold Test Measurements on the GTF Prototype RF Gun

Description: The SSRL Gun Test Facility (GTF) was built to develop a high brightness electron injector for the LCLS and has been operational since 1996. Based on longitudinal phase space measurements showing a correlated energy spread the gun was removed and re-characterized in 2002. The low power RF measurements performed on the gun are described below. Perturbative bead measurements were performed to determine the field ratio in the two-cell gun, and network analyzer measurements were made to characterize the mode structure. A second probe was installed to monitor the RF field in the first cell, and a diagnostic was developed to monitor the high-power field ratio. Calibration of the RF probes, a model for analyzing RF measurements, and Superfish simulations of bead and RF measurements are described.
Date: December 3, 2010
Creator: Gierman, S.M.
Partner: UNT Libraries Government Documents Department

Summary of QM02 Measurements

Description: This note summarizes both the beam-based and various laboratory measurements of quadrupole magnets, units 387 and 428, used for QM02 in the LCLS Injector. These were undertaken because of a consistent discrepancy between accelerator model predictions and beam observations which seemed to indicate a weak QM02. A report 'QM02 Strength Measurement', by Welch and Wu, describes the discrepancy and beam-based measurements on unit 387. Subsequently, unit 387 was replaced by unit 428, refinements were made to analysis of the beam-based measurements were made, and additional magnetic measurements were made on unit 387 in the lab. These new results are summarized in this note. The principle results are: (1) Laboratory measurements of integrated gradient for the same magnet, or for different magnets of the same type, are all within 1% of each other at gradients of interest. These cases cover three independent types of measurements, disassembly/reassembly of the units, and extended periods of time between measurements. (2) Standardization, or lack thereof, can cause integrated gradient errors of approximately 0.2 kG, which can amount to a few percent of the strength of the magnet depending on the setting. (3) Model-independent beam-based measurements indicate the magnets are actually weaker than expected by about 2 percent, but these measurements are subject to the uncertainty of the BPMS1 location. (4) The standardization cycle is effective. (5) The stainless steel BPM vacuum chamber inside the magnets has no significant effect on the beam. The discrepancy between the accelerator model predictions and the actual orbit response is not resolved, but the evidence points away from magnetic strength errors as the source. Differences between the model locations and effective locations of BPM's is a possible culprit. This idea is explored in Section 2. Table 1 summarizes the measurement activities that were performed on the units. The dates listed ...
Date: December 3, 2010
Creator: Fisher, Andrew
Partner: UNT Libraries Government Documents Department

Beam monitoring and conditioning working group 4 report

Description: The highlights of Seventh Advanced Accelerator Concepts (AAC) working group IV (Beam Monitoring, Conditioning and Control at High Frequencies and Ultrafast Timescales) are presented in this report. The talks given at the working group covered wide range of subjects of beam monitoring. They including a new technique of measuring sub- picosecond electron beam bunch length, optical stochastic cooling experiment, timing jitter measurement of photocathode injector, and proposed experiment of measuring micro-bunching of IFEL accelerator. Working group IV also carried out extensive discussion on the longitudinal and transverse emittance characterization of short (sub- picosecond) low emittance (normalized rms emittance < 1 mm-mrad) electron beam, and beam diagnostics requirements for Muon collider.
Date: January 1, 1997
Creator: Wang, X.J.
Partner: UNT Libraries Government Documents Department

Debugging real accelerators

Description: Particle losses and emittance growth in the injection process can result form mismatched injected beams arising from quadrupole errors in the ring and injection line. We describe a method, based on carefully analyzing the BPM-corrector response matrix, which allows the accurate determination of quadrupole errors and, at the same time, determines BPM and corrector calibration errors as well as the BPM resolution. Results from SPEAR, NSLS, ALS, and CELSIUS will be briefly described.
Date: December 1, 1996
Creator: Corbett, W.J.; Robin, D.; Safranek, J. & Ziemann, V.
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

Table top, pulsed, relativistic electron gun with GV/m gradient

Description: We present the design and performance characteristics of a compact high voltage pulser with 150 ps rise time, 0.2 to 2 ns adjustable flat top and up to 1 MV amplitude on a 80 Ohm load or up to 0.5 W on a 20 Ohm load, at 1 Hz repetition rate. Combination of a laser triggered SF{sub 6} and a liquid cap is used to form the fast rising pulse and maintain a low jitter between the laser, external trigger, and the high voltage pulsed output. The dark current and breakdown studies with this pulse applied between the electrodes of a diode indicate that fields up to 1 GV/m could be supported by stainless steel and copper cathodes without breaking down. The dark current from a conditioned cathode in a background pressure of 10{sup -7} Torr is below the detection limit of 0.5 mA of our system. Photoemission studies had been conducted with 300 kV applied between copper cathode and stainless steel anode separated by 2 mm. KrF laser of 5 eV photon energy and 20 ns FWHM was used to irradiate the cathode. In these preliminary measurements, 3 nC charge and corresponding quantum efficiency of 3.5 x 10{sup -4} have been obtained. Future plans include increasing the gradient to GV/m range, decreasing the laser pulse duration to ps and subps range and increasing the electron energy to a few MeV.
Date: October 1, 1996
Creator: Srinivasan-Rao, T. & Smedley, J.
Partner: UNT Libraries Government Documents Department

Conceptual design for an electron-beam heated hypersonic wind tunnel

Description: There is a need for hypersonic wind-tunnel testing at about mach 10 and above using natural air and simulating temperatures and pressures which are prototypic of flight at 50 km altitude or below. With traditional wind-tunnel techniques, gas cooling during expansion results in exit temperatures which are too low. Miles, et al., have proposed overcoming this difficulty by heating the air with a laser beam as it expands in the wind-tunnel nozzle. This report discusses an alternative option of using a high-power electron beam to heat the air as it expands. In the e-beam heating concept, the electron beam is injected into the wind-tunnel nozzle near the exit and then is guided upstream toward the nozzle throat by a strong axial magnetic field. The beam deposits most of its power in the dense air near the throat where the expansion rate is greatest. A conceptual design is presented for a large-scale system which achieves Mach 14 for 0.1 seconds with an exit diameter of 2.8 meters. It requires 450 MW of electron beam power (5 MeV at 90 A). The guiding field is 500 G for most of the transport length and increases to 100 kG near the throat to converge the beam to a 1.0-cm diameter. The beam generator is a DC accelerator using a Marx bank (of capacitors) and a diode stack with a hot cathode. 14 refs. 38 figs., 9 tabs.
Date: July 1, 1997
Creator: Lipinski, R.J. & Kensek, R.P.
Partner: UNT Libraries Government Documents Department

Establishing the operational durability of polymer light-emitting diodes

Description: This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Recent research has made it clear that polymer light-emitting diodes (PLEDs) have all the necessary device attributes (efficiency, emission colors, operating voltage) required to build a successful display technology. This project was initiated to establish meaningful device operating lifetimes and to understand PLED failure mechanisms in order to control device reliability and ultimately produce a viable commercial product. A PLED lifetime testing capability was established to measure the change in PLED light output and drive voltage at constant current bias as a function of time for different current bias levels, operating temperatures and device (polymer) thickness. The dominant failure mechanism of the polymer light emitting diodes, occurring at less than 1000 hours of operation, was identified as delamination of the electron-injecting metal contact. A new electroabsorption technique to measure the electric field distribution inside the PLEDs was developed and then used to assess relative device reliability. 2 figs.
Date: December 31, 1998
Creator: Campbell, I.H.; Davids, P.S. & Heller, C.M.
Partner: UNT Libraries Government Documents Department

Radiation chemistry of alternative fuel oxygenates -- Substituted ethers

Description: The electron beam process, an advanced oxidation and reduction technology, is based in the field of radiation chemistry. Fundamental to the development of treatment processes is an understanding of the underlying chemistry. The authors have previously evaluated the bimolecular rate constants for the reactions of methyl tert-butyl ether (MTBE) and with this study have extended their studies to include ethyl tert-butyl ether (ETBE), di-isopropyl ether (DIPE) and tert-amyl methyl ether (TAME) with the hydroxyl radical, hydrogen atom and solvated electron using pulse radiolysis. For all of the oxygenates the reaction with the hydroxyl radical appears to be of primary interest in the destruction of the compounds in water. The rates with the solvated electron are limiting values as the rates appear to be relatively low. The hydrogen atom rate constants are relatively low, coupled with the low yield in radiolysis, they concluded that these are of little significance in the destruction of the alternative fuel oxygenates (and MTBE).
Date: November 15, 1999
Creator: Mezyk, S. P.; Cooper, W. J.; Bartels, D. M.; Tobien, T. & O'Shea, K. E.
Partner: UNT Libraries Government Documents Department

The Advanced Photon Source injection timing system

Description: The Advanced Photon Source consists of five accelerators. The injection timing system provides the signals required to cause a bunch emitted from the electron gun to navigate through intermediate accelerators to a specific bucket (1 out of 1296) within the storage ring. Two linacs and a positron accumulator ring operate at 60Hz while a booster synchrotron ramps and injects into the storage ring at 2Hz. The distributed, modular VME/VXI-based injection timing system is controlled by two EPICS-based input/output controllers (IOCs). Over 40 VME/VXI cards have been developed to implement the system. Card types range from 352MHz VXI timing modules to VME-based fiber optic fanouts and logic translators/drivers. All timing is distributed with fiber optics. Timing references are derived directly from machine low-level rf of 9.77MHz and 352MHz. The timing references provide triggers to programmable delay generators. Three grades of timing are provided. Precision timing is derived from commercial digital delay generators, intermediate precision timing is obtained from VXI 8-channel digital delay generators which provide timing with 25ns peak-to-peak jitter, and modest precision timing is provided by the APS event system. The timing system is fully integrated into the APS EPICS-based control system.
Date: December 31, 1995
Creator: Lenkszus, F.R. & Laird, R.
Partner: UNT Libraries Government Documents Department