Beam Line Parameters Research Articles

Recent advances in software for beamline design, accelerator operations and personnel training

Accelerators are finding new applications in research, industry, medicine, as well as other fields, and there is a growing need for new tools to improve the productivity of scientists and engineers involved with these emerging accelerator applications. Several advances in computer software have been made that focus on meeting those needs. This paper summarizes recent work in the development of a unique software framework designed specifically to support the accelerator community: the Multi-Platform Shell for Particle Accelerator Related Codes (SPARC MP). SPARC MP includes a sophisticated beamline object model, an extensive library of GUI components, and supports a variety of particle optics codes and add-on tools. This framework has been used to create the Particle Beam Optics Laboratory (PBO Lab TM) family of software applications. PBO Lab has been used for beamline design, as a computer aid for teaching particle optics, and to support accelerator operations. Several popular charged particle optics programs, including MARYLIE, TRANSPORT, TURTLE and TRACE 3-D, have been integrated with a new version of PBO Lab. The modeling and simulation capabilities of these codes allow PBO Lab to support a wide spectrum of accelerator types. New external data interface tools are available to import beamline parameters from other sources, for example, to utilize magnet strengths generated by a control system. An overview of the new version of PBO Lab is presented.

Ray tracing studies of a complete plane grating monochromator beam line

Optical design of a plane grating monochromator beam line for X-ray spectroscopic studies to be installed on INDUS-1 is studied using ray tracing technique. The main components of the beam line are pre- and post-elliptical mirrors and the plane mirror-grating dispersing system. The ideal positions of the optical components are decided by using our analytical formulation of the Riemer’s kinetic principle for reflecting synchrotron radiation onto the same spot of the dispersing grating. The program is developed indigenously and can be used on a PC. The tangent error and microroughness of the mirrors is explicitly accounted for in the program. The wavelength dependent absorption of radiation at the different reflecting surfaces is also included for calculations of the optical throughput. The dependence of the final image line shape and resolution on various beam line parameters is calculated. The results are useful in deciding the tolerances of the various beam line components and their positions.

Synchrotron radiation beamline for x-ray lithography

We designed a synchrotron radiation (SR) beamline for x-ray lithography and optimized the beamline based on ray-tracing calculations. For a beamline with a single toroidal mirror, the intensity uniformity in the horizontal direction can be improved by making the meridian radius different from that of the general focal condition. We used this method to determine beamline parameters. Converging the SR beam gave an intensity gain of about 4, and we reduced the nonuniformity of intensity distribution to less than 3%. We also estimated the overlay error due to incorrect mirror parameters to be a maximum of 14 nm with a gap of 20 μm. We calculated an exposure-gap diagram using simulation codes; the calculation accounted for absorbed energy distribution due to Fresnel diffraction, penumbral blur, electron ranges of the secondary electrons in the resist, and development properties. We found that there is a dose margin of at least ±5% to achieve ±10% linewidth control for 0.15 μm feature size for gaps below 20 μm. We made preliminary measurements of spectra and intensity distributions for the constructed beamline, and showed that the performance is as predicted by our calculations.

Electron beam sensitivity study of the Los Alamos advanced free-electron laser beam line

A sensitivity study that used the particle tracking code PARMELA was performed on the Advanced Free-Electron Laser (AFEL). The tolerances on the alignment of the beam-line elements and the magnetic-field strengths were examined. Two base-line configurations were determined at the beginning of the study. The electron beam was then matched into the wiggler. The optimized beam-line parameters were varied independently and their sensitivities were judged with the criterion that the free-electron laser (FEL) effective-detuning parameter should not fluctuate more than 10%. The results of this study set the specifications for the alignment, for the sensitivity of the steering magnets, and for the accuracy of the magnetic field in the quadrupoles and dipoles. 5 figs., 3 figs., 3 tabs.

GALOPR, a beam transport program with space charge and bunching

Abstract GALOPR is a first-order beam transport code including three-dimensional space-charge forces and the beam bunching process. It deals with usual optical devices (bending magnets, lenses, solenoids, drift spaces, bunchers) and can take into account any special optical device represented by its transfer matrix with space charge (the “Muller” and the “Pabot-Belmont” inflectors were recently introduced as one of these devices). The beam can be continuous, bunched or undergoing a bunching or debunching process. The beam-line parameters can be optimized to fit any elements of the 6 × 6 transfer and/or covariance matrices in order to obtain the maximum transmission efficiency. The results are presented with a complete set of printouts and graphical displays. This code has been used to optimize the 100 kV axial injection beam line at GANIL.

6-m TGM implementation at the Wisconsin Synchrotron Radiation Center (SRC)

We recently commissioned the SRC/Vanderbilt University 6-m toroidal grating monochromator beamline. The problems with mirror heating, signal normalization, monochromator control, and scattered light reduction have led to several innovations on this line, making for a better user interface and adding to the stability and reliability of the final image. We discuss these innovations, and how they affect the user. They include a built-in laser alignment system, a sapphire windowed gate valve, entrance mirror temperature stabilization, computer automation and control, a beam-chopper, and the capability of real-time monitoring of the photon flux during the experiment. We have used noble gas resonance lines to carefully characterize the wavelength resolution of the beamline as a function of energy over a range of beamline parameters. The results demonstrate that by limiting the horizontal width of the image at the slits, and by masking outer portions of the gratings, the flux/bandwidth ratio can be improved at the points where the exit slit location does not coincide with the Rowland circle. These same resonance lines, in conjunction with accurate measurements of the grating rotation angle as a function of scan-drive displacement, are used to correct for imperfections in the surface of the drive-flat and thus obtain a precise and accurate determination of wavelength versus scan-drive displacement.

Thermal problems on high flux beam lines

Wiggler and undulator magnets can provide very intense photon flux densities to beam line components. This paper addresses some thermal/materials consequences due to such impingement. The LBL/Exxon/SSRL hybrid-wiggler beam line VI [1] now nearing operation will be able to provide up to ∼ 7 kW of total photon power at planned SPEAR operating conditions. The first masks are located at 6.5 m from the source and may receive a peak power density (transverse to the beam) exceeding 20 kW/cm 2. Significantly, this heat transfer rate exceeds that radiated from the sun's surface (7 kW/cm 2) and is comparable to that if welding torches. Clearly, cooling and configuration are of critical importance. Configurations for the first mask, the movable mask and the pivot mask on this beam line are presented together with considerations of thermal stress fatigue and of heat transfer by conduction to water-cooling circuits. Some preliminary information on the heating of crystals and mirrors is also presented. For the future, many additional intense wiggler/undulator beam lines are contemplated at several storage rings. The design of these beamlines would be enhanced by faster and more accurate computational techniques. LBL is developing a computer code which will be capable of giving photon power densities onto impinged surfaces for a wide range of source and beam line parameters. These include electron beam energy, current, emittance and orbit deviations; wiggler/undulator length, period and magnetic field; photon energy and angular distribution; reflection/absorption at intermediate impinged surfaces; defining apertures and focusing by mirrors. Three-dimensional computer programs for temperature, stress and strain have been available for some years, but “user friendly” versions are being sought. Other items to pursue are also suggested.

Control of Machine Functions or Transport Systems

A computer code, COMFORT, has been developed at SLAC for on-line calculation of the strengths of magnetic elements in an electron storage ring or transport beam line, subject to first order fitting constraints on the ring or beam line parameters. This code can also be used off-line as an interactive lattice or beam line design tool.