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Beam matching and halo control

Description: We present an overview of the status of ongoing work on physics models describing beam matching and halo control for particle accelerators, particularly high power ion linacs. We consider moments and various new variables that more naturally describe beam halo evolution. We compute matched beams and ``mode invariants`` (analogs of moment invariants) using primarily symbolic techniques.
Date: September 1, 1997
Creator: Lysenko, W. & Parsa, Z.
Partner: UNT Libraries Government Documents Department

DML and Foil Measurements of ETA Beam Radius

Description: Simultaneous measurements of the ETA beam radius have been made with a quartz foil and a diamagnetic loop (DML). While the measurements agreed at some settings they diverged at others. While the DML measures the rms radius of the total beam, the foil measures mainly the core and the divergence can be explained by the presence of a low density halo. Evidence of such a halo from other measurements is presented.
Date: May 11, 2005
Creator: Nexsen, W & Weir, J
Partner: UNT Libraries Government Documents Department


Description: Within the halo experiment presently being conducted at the Low Energy Demonstration Accelerator at Los Alamos National Laboratory, specific beam instruments that acquire horizontally and vertically projected particle-density distributions out to greater than 10{sup 5}:1 dynamic range are located throught the 52-magnet halo lattice.
Date: January 1, 2001
Creator: Gilpatrick, J. D. (John Douglas); Barr, D. S. (Dean S.); Day, L. A. (Lisa A.); Kerstiens, D. M. (Debora M.); Stettler, M. W. (Matthew W.); Valdiviez, R. (Robert) et al.
Partner: UNT Libraries Government Documents Department

Results from Vernier scans during the RHIC 2008 PP Run

Description: Using the vernier scan or Van der Meer scan technique, where one beam is swept stepwise across the other while measuring the collision rate as a function of beam displacement, the transverse beam profiles, the luminosity and the effective cross section of the detector in question can be measured. This report briefly recalls the vernier scan method and presents results from the 100 GeV 2008 RHIC polarized proton (pp) run.
Date: May 4, 2009
Creator: Drees,A. & D Ottavio, T.
Partner: UNT Libraries Government Documents Department

Transverse Beam Profile Measurement Using Scrape Scans

Description: A scraper scan - sending a scraper through a particle beam while measuring the intensity as a function of scraper position - is a common method of determining the profile of the beam. At first glance, this seems to be a rather simple procedure. Nevertheless, some care is required in the acquisition of the data and in the analysis if one is going to achieve an accurate result.
Date: September 13, 2001
Creator: Werkema, Steven J.
Partner: UNT Libraries Government Documents Department

Beam profile analysis for the C{ampersand}MS B231 electron beam welding machines

Description: The electron beams produced by two different welders were examined using computer assisted tomographic (CT) analysis. The machines used are Hamilton Standard welders with 150 kV/50mA maximum. One machine uses a ribbon filament while the other uses a hairpin filament. The objective of this study was to characterize the beam power distribution on each machine to see if weld parameters could easily be transferred between machines. Beam focus, voltage, and current settings were pre-selected to duplicate the welding conditions used in LLNL program applications. The results show that the actual beam currents measured by Faraday cup are 5 to 10% higher for the first machine and 30% lower for the second. The CT analysis of the beam shapes shows that the hairpin filament welder produces an elliptical beam shape in the sharp focus condition that defocuses to a diamond shape. The ribbon filament welder produced less of an elliptical beam shape in the sharp focus condition, but when defocused, acquires an elliptical shape. CT analysis of the effects of defocus on the peak power density shows that the hairpin filament drops in peak power density much more quickly than the ribbon filament for a given amount of defocus. Furthermore, it was more difficult to find and repeat the sharp focus condition for the hairpin filament, particularly at higher beam currents.
Date: June 12, 1997
Creator: Elmer, J. W.; Teruya, A.T. & Gauthier, M.
Partner: UNT Libraries Government Documents Department

Electron Bunch Length Diagnostic With Coherent Smith-Purcell Radiation

Description: The authors have designed a new technique for measuring subpicosecond electron bunch lengths using coherent Smith-Purcell radiation. This new diagnostic technique involves passing the electron beam in close proximity of a grating with a period comparable to the electron bunch length. The emitted Smith-Purcell radiation will have a coherent component whose angular position and distribution are directly related to the electron bunch length and longitudinal profile, respectively. This new diagnostic technique is inherently simple, inexpensive and non-intercepting. The authors show that the new technique is also scaleable to femtosecond regime.
Date: May 12, 1997
Creator: Nguyen, D.C.
Partner: UNT Libraries Government Documents Department

Optical diagnostics on ETA-II for x-ray spot size

Description: Improvements have been made in the performance of the ETA-II accelerator that allow a nominal 2 kA, 6 MeV beam to be focused to a spot size less that 1 mm in diameter. The improvements include reducing the energy sweep to less than +/- 0.5 & over 40 ns of the pulse using a real time energy diagnostic and improving the magnetic tune of the accelerator to reduce the emittance to 8 cm-mrad. Finally, an automated tuning system (MAESTRO) was run to minimize the time dependent centroid motion (corkscrew) by adjusting the steering dipoles over the focusing solenoids. The corkscrew motion was reduced to less than +/- 0.5 mm at the output of the accelerator.
Date: March 22, 1999
Creator: Richardson, R A
Partner: UNT Libraries Government Documents Department

Experiment and simulations of sub-ps electron bunch train generation at Fermilab photoinjectors

Description: Recently the generation of electron bunch trains with sub-picosecond time structure has been experimentally demonstrated at the A0 photoinjector of Fermilab using a transverse-longitudinal phase-space exchange beamline. The temporal profile of the bunch train can be easily tuned to meet the requirements of the applications of modern accelerator beams. In this paper we report the A0 bunch-train experiment and explore numerically the possible extension of this technique to shorter time scales at the Fermilab SRF Accelerator Test Facility, a superconducting linear electron accelerator currently under construction in the NML building.
Date: October 1, 2011
Creator: Sun, Y.-E; Church, M.; /Fermilab; Piot, P.; Prokop, C.R. & U., /Fermilab /Northern Illinois
Partner: UNT Libraries Government Documents Department

Emittance measurements using Vernier Scans during Run 09 (pp at 250 GeV)

Description: Emittance measurements using the vernier scan technique give reliable results for 250 GeV protons even though the transverse beam profiles have non-Gaussian tails. Those non-Gaussian tails were observed for the first time this run at the 250 GeV beam energy. The vernier scan measurements are in excellent agreement with the emittances derived from collision rates and show practically no fill to fill scatter if compared to the latter. The results are consistent with a {beta}* of 0.7 m and round beams. The IPM measurements show a discrepancy of up to 80% compared with the vernier scan data and a fill to fill scatter of up to 30%. If an uncertainty in the beta-function at the location of the IPM is the root cause, this uncertainty seems to be quite large. In any case, such an uncertainty could not explain the fill to fill variations of up to 30% which indicate yet another underlying reason that could explain fill to fill variations (candidates could be beam intensity issues with the IPM, beam position at the IPM, varying background etc.).
Date: November 1, 2010
Creator: Drees, A.
Partner: UNT Libraries Government Documents Department

A laser-wire beam-energy and beam-profile monitor at the BNL linac

Description: In 2009 a beam-energy monitor was installed in the high energy beam transport (HEBT) line at the Brookhaven National Lab linac. This device measures the energies of electrons stripped from the 40mA H{sup -} beam by background gas. Electrons are stripped by the 2.0x10{sup -7}torr residual gas at a rate of {approx}1.5x10{sup -8}/cm. Since beam electrons have the same velocities as beam protons, the beam proton energy is deduced by multiplying the electron energy by m{sub p}/m{sub e}=1836. A 183.6MeV H{sup -} beam produces 100keV electrons. In 2010 we installed an optics plates containing a laser and scanning optics to add beam-profile measurement capability via photodetachment. Our 100mJ/pulse, Q-switched laser neutralizes 70% of the beam during its 10ns pulse. This paper describes the upgrades to the detector and gives profile and energy measurements.
Date: March 28, 2011
Creator: Connolly, R.; Degen, C.; DeSanto, L.; Meng, W.; Michnoff, R.; Minty, M. et al.
Partner: UNT Libraries Government Documents Department


Description: A beam of D{sup -} ions has been produced at 7-13 keV, with currents up to 2.2 {angstrom}, using charge exchange in sodium vapor. The beam profile is bi-Gaussian with angular divergence 0.7{sup o} x 2.8{sup o} and peak current density 15 mA/cm{sup 2}. The characteristics of the beam are in excellent agreement with predictions based on atomic cross sections. The sodium vapor target is formed by a jet directed across the beam. The sodium density drops rapidly in the beamline downstream from the charge exchange region, decreasing three orders of magnitude in 15 cm. Measurement and analysis of the plasma accompanying the beam demonstrate that plasma densities nearly equal to the beam density are obtained 1 m from the charge exchange medium. The plasma produced in the sodium is thus well confined to the charge exchange region and does not propagate along the beam.
Date: February 1, 1981
Creator: Hooper, E.B.; Poulsen, P. & Pincosy, P.A.
Partner: UNT Libraries Government Documents Department

Negative Transconductance in Apertured Electron Guns

Description: Passing an electron beam through an aperture can serve to reduce the beam current or change the transverse beam profile. For a sufficiently intense beam, space charge will drive a radial expansion of the beam, which may cause the current passing through the aperture to increase even though the current arriving at the aperture is decreasing. When a gridded electron gun is used, this may be expressed by stating that the transconductance of the apertured gun is negative. Here we explain this effect, and explore some of the key factors governing when it can occur and influencing its strength.
Date: September 21, 2007
Creator: Harris, J R & O'Shea, P G
Partner: UNT Libraries Government Documents Department

Correction of unevenness in recycler beam profile

Description: A beam confined between two rf barriers in the Fermilab Recycler Ring exhibits very uneven longitudinal profile. This leads to the consequence that the momentum-mined antiproton bunches will have an intolerable variation in bunch intensity. The observed profile unevenness is the result of a tiny amount of rf imperfection and rf beam-loading. The profile unevenness can be flattened by feeding back the uneven rf fan-back gap voltage to the low-level rf.
Date: May 1, 2006
Creator: Crisp, J.; Hu, M.; Ng, K.Y. & /Fermilab
Partner: UNT Libraries Government Documents Department

LCLS Spontaneous Radiation with Reflection along the Beam Line in the Undulator Pipes

Description: Some commissioning and alignment procedures for XTOD may rely on the use of the spontaneous radiation. Therefore we have modeled the spontaneous radiation between the Undulator and the Near Experimental Hall to derive numerical values of the expected beam width and of the energy deposition. The values are then used to determine aperture sizes and detector sensitivities. We performed the calculations in three stages. The first was to generate an appropriate distribution of photons within the Undulator. The second was to simulate the emergence of the photons from the Undulator. The third was to propagate the photons (without any obstructing objects) to various points along the Z-axis up to the Near Experimental Hall entrance. We performed the simulations for low and high energies based on the spectral flux data supplied by Sven Reiche. These data sets were at 71 meters from the end of the Undulator for 4.5 and 14.08 GeV electrons.
Date: September 7, 2005
Creator: Fong, K W
Partner: UNT Libraries Government Documents Department

Techniques and use of a tunable, laser-based, MeV-Class Compton scattering light source

Description: A Compton scattering {gamma}-ray source, capable of producing photons with energies ranging from 0.1 MeV to 0.9 MeV has been commissioned and characterized, and then used to perform nuclear resonance fluorescence (NRF) experiments. The key source parameters are the size (0.01 mm{sup 2}), horizontal and vertical divergence (6 x 10 mrad{sup 2}), duration (10 ps), spectrum and intensity (10{sup 5} photons/shot). These parameters are summarized by the peak brightness, 1.5 x 10{sup 15} photons/mm{sup 2}/mrad{sup 2}/s/0.1%bandwidth, measured at 478 keV. Additional measurements of the flux as a function of the timing difference between the drive laser pulse and the relativistic photoelectron bunch, {gamma}-ray beam profile, and background evaluations are presented. These results are systematically compared to theoretical models and computer simulations. NRF measurements performed on {sup 7}Li in LiH demonstrate the potential of Compton scattering photon sources to accurately detect isotopes in situ.
Date: June 30, 2009
Creator: Albert, F; Anderson, S G; Gibson, D J; Hagmann, C A; Johnson, M S; Messerly, M et al.
Partner: UNT Libraries Government Documents Department