J. Safranek

Low alpha mode for SPEAR3

In the interest of obtaining shorter bunch length for shorter X-ray pulses, we have developed a low-alpha operational mode for SPEAR3. In this mode the momentum compaction factor is reduced by a factor of 21 or more from the usual achromat mode by introducing negative dispersion at the straight sections. We successfully stored 100 mA with the normal fill pattern at a lifetime of 30 hrs. The bunch length was measured to be 6.9 ps, compared to 17 ps in the normal mode. In this paper we report our studies on the lattice design and calibration, orbit stability, higher order alpha measurement, lifetime measurement and its dependence on the sextupoles, injection efficiency, longitudinal stability and bunch lengths.

Measurement of transient atomic displacements in thin films with picosecond and femtometer resolution.

We report measurements of the transient structural response of weakly photo-excited thin films of BiFeO3, Pb(Zr,Ti)O3, and Bi and time-scales for interfacial thermal transport. Utilizing picosecond x-ray diffraction at a 1.28 MHz repetition rate with time resolution extending down to 15 ps, transient changes in the diffraction angle are recorded. These changes are associated with photo-induced lattice strains within nanolayer thin films, resolved at the part-per-million level, corresponding to a shift in the scattering angle three orders of magnitude smaller than the rocking curve width and changes in the interlayer lattice spacing of fractions of a femtometer. The combination of high brightness, repetition rate, and stability of the synchrotron, in conjunction with high time resolution, represents a novel means to probe atomic-scale, near-equilibrium dynamics.

The 3 GeV synchrotron injector for SPEAR

A dedicated 3-GeV injector synchrotron for the storage ring SPEAR has been constructed at the Stanford Synchrotron Radiation Laboratory, SSRL. The injector consists of an RF-gun, a 120-MeV linear accelerator, a 3-GeV booster synchrotron, and associated beam transport lines. General design features and special new developments for this injector are presented, together with operational performance.<<ETX>>

The linac and booster RF systems for a dedicated injector for SPEAR

A 120 MeV, 2856 MHz, traveling wave linear accelerator (linac), with a microwave gun, alpha magnet, and chopper, has been built at the Stanford Synchrotron Radiation Laboratory (SSRL) as a preinjector for and along with a 3 GeV, 358.54 MHz, booster synchrotron ring. The resulting injector will be available on demand to fill the Stanford Positron-Electron Accelerator Ring (SPEAR), which is a storage ring now dedicated to synchrotron light production. A description is given of the injectors two separate and different frequency RF systems. Synchronization of the two, non-harmonic systems is achieved through the linacs chopper. Some of the interesting mechanical and electrical details are discussed and the operating characteristics of the linac and ring RF are highlighted.<<ETX>>

Bunch length measurements in SPEAR3

A series of bunch length measurements were made in SPEAR3 for two different machine optics. In the achromatic optics the bunch length increases from the low-current value of 16.6 ps rms to about 30 ps at 25 ma/bunch yielding an inductive impedance of -0.17 Omega. Reducing the momentum compaction factor by a factor of ~60 [1] yields a low-current bunch length of ~4 ps rms. In this paper we review the experimental setup and results.

The SSRL injector beam position monitoring systems

The authors describe the software and processing electronics of the systems used to measure electron beam trajectories for the new Stanford Synchrotron Radiation Laboratory (SSRL) injector and for the Stanford Positron Electron Accelerator Ring (SPEAR). The focus is on the use of the electron beam position monitors (BPMs) to measure electron trajectories in the injector transport lines and the booster ring. There are three different BPM systems in the injector. One system consists of a set of five BPMs located on the injection transport line from the linac to the booster. There is a second system of six BPMs located on the ejection transport line. Finally, there is an array of 40 BPMs installed on the main booster ring itself. The injector beam position monitor systems have successfully been used to measure electron orbits and to diagnose configuration problems. The booster BPM system has proved capable of measuring orbits at intervals of 2 milliseconds during the ramp every two seconds.<<ETX>>

Commissioning the SSRL injector

The SSRL injector has been commissioned and already fills SPEAR (Stanford Positron Electron Asymmetric Ring) at rates which are comparable to those obtained using the SLAC (Stanford Linear Accelerator Center) linac. The design goals for the injector are presented along with the best achieved performance levels and routine performance levels.<<ETX>>

A Design Report of the Baseline for PEP-X: an Ultra-Low Emittance Storage Ring

Over the past year, we have worked out a baseline design for PEP-X, as an ultra-low emittance storage ring that could reside in the existing 2.2-km PEPII tunnel. The design features a hybrid lattice with double bend achromat (DBA) cells in two arcs and theoretical minimum emittance (TME) cells in the remaining four arcs. Damping wigglers are used to reduce the horizontal emittance to 86 pm-rad at zero current for a 4.5 GeV electron beam. At a design current of 1.5 A, the horizontal emittance increases, due to intrabeam scattering, to 164 pm-rad when the vertical emittance is maintained at a diffraction limited 8 pm-rad. The baseline design will produce photon beams achieving a brightness of 10{sup 22} (ph/s/mm{sup 2}/mrad{sup 2}/0.1% BW) at 10 keV in a 3.5-m conventional planar undulator. Our study shows that an optimized lattice has adequate dynamic aperture, while accommodating a conventional off-axis injection system. In this report, we present the results of study, including the lattice properties, nonlinear dynamics, intra-beam scattering and Touschek lifetime, RF system, and collective instabilities. Finally, we discuss the possibility of partial lasing at soft X-ray wavelengths using a long undulator in a straight section.

Enhanced performance of the Advanced Light Source through periodicity restoration of the linear lattice

An essential feature of third generation storage ring based light sources is the magnetic lattice is designed with a high degree of periodicity. Tracking simulations show that if the periodicity is perturbed (by focusing errors for example), non-linear resonances become excited, which causes a reduction in the dynamic aperture. Therefore it is important to have a method to measure and correct perturbed periodicity. In this paper we study the effect of broken and restored periodicity at an actual third generation light source: the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. First we show that it is possible to accurately determine the storage ring optic and thus the perturbation of the periodicity by fitting measured orbit response matrices. This method allows us to determine individual field gradient errors in quadrupoles and closed orbit errors in sextupoles. By varying individual quadrupole field strengths it is possible to correct the optic, largely restoring the lattice periodicity. A comparison is made of the performance of the ALS before and after the optic is corrected. Measurements of the electron beam tails and the synchrotron light image reveal a large suppression in resonance excitation after the optic is corrected. Correcting the optic also improves the injection efficiency and lifetime.

Dynamic aperture studies for SPEAR 3

The Stanford Synchrotron Radiation Laboratory is investigating an accelerator upgrade project that would replace the present 130 nm⋅rad FODO lattice with an 18 nm⋅rad double bend achromat (DBA) lattice: SPEAR 3. The low emittance design yields a high brightness beam, but the stronger focusing in the DBA lattice increases chromaticity and beam sensitivity to machine errors. To ensure efficient injection and long Touschek lifetime, an optimization of the design lattice and dynamic aperture has been performed. In this paper, we review the methods used to maximize the SPEAR 3 dynamic aperture including necessary optics modifications, choice of tune and phase advance, optimization of sextupole and coupling correction, and modeling effects of machine errors, wigglers and lattice periodicity.