G. Portmann

Automated beam based alignment of the ALS quadrupoles

Knowing the electrical offset of the storage ring beam position monitors (BPM) to an adjacent quadrupole magnetic center is important in order to correct the orbit in the ring. We describe a simple, fast and reliable technique to measure the BPM electrical centers relative to the quadrupole magnetic centers. By varying individual quadrupole magnets and observing the effects on the orbit we were able to measure the BPM offsets in half the horizontal and vertical BPMs (48) in the ALS. These offsets were measured to an accuracy of better than 50 /spl mu/m. The technique is completely automated and takes less than 3 hours for the whole ring.

First undulators for the Advanced Light Source

The first three undulators, each 4.6 m in length, for the Advanced Light Source (ALS) at Lawrence Berkeley Laboratory (LBL), are near completion and are undergoing qualification tests before installation into the storage ring. Two devices have 5.0-cm period lengths, 89 periods, and achieve an effective field of 0.85 T at the 14 mm minimum magnetic gap. The other device has a period length of 8.0 cm, 55 periods, and an effective field of 1.2 T at the minimum 14 mm gap. Measurements on the first 5 cm period device show the uncorrelated field errors to be 0.23%, which is less than the required 0.25%. Measurements of gap control show reproducibility of /spl plusmn/5 microns or better. The first vacuum chamber, 5.0 m long, is flat to within 0.53 mm over the 4.6 m magnetic structure section and a 4/spl times/10/sup -11/ Torr pressure was achieved during vacuum tests. Device description, fabrication, and measurements are presented.<<ETX>>

Reduction of nonlinear resonance excitation from insertion devices in the ALS

Theoretical studies of Lawrence Berkeley Laboratorys Advanced Light Source (ALS) storage ring predict strong field insertion devices will break the rings symmetry, increasing resonance excitation that may reduce the dynamic aperture and thus the beam lifetime. We have embarked on an experimental program to study the strength of nonlinear resonance excitation in the ALS when insertion devices are present. We observe an enhancement in the resonance excitation of a third-order resonance when the gap of the insertion device is narrowed. We also find that it is possible to suppress this resonance by detuning two quadrupoles on either side of the insertion device. The results of this study are presented in this paper.

Wigglers at the Advanced Light Source

Two 3.4 m long wigglers are being designed and constructed at Lawrence Berkeley Laboratorys (LBL) Advanced Light Source (ALS). A 19 period planar wiggler with 16.0 cm period length is designed to provide photons up to 12.4 keV for protein crystallography. This device features a hybrid permanent magnet structure with tapered poles and designed to achieve 2.0 T at a 1.4 cm magnetic gap. An elliptical wiggler is being designed to provide circularly polarized photons in the energy range of 50 eV to 10 keV for magnetic circular dichroism spectroscopy. This device features vertical and horizontal magnetic structures of 14 and 14 1/2 periods respectively of 20 cm period length. The vertical magnetic structure is a 2.0 T hybrid permanent magnet configuration. The horizontal structure is an iron core electromagnetic design, shifted longitudinally 1/4 period with respect to the vertical magnetic structure. A maximum horizontal peak field of 0.1 T at an oscillating frequency up to 1 Hz will be achieved by excitation of the horizontal poles with a trapezoidal current waveform.

The VHF-Gun, the LBNL High-Brightness Electron Photo-Injector for MHz-Class Repetition-Rate Applications

Science needs are pushing the development of MHz-class repetition-rate linac-based facilities generating high-brightness electron beams. The successful lower repetition-rate RF gun schemes cannot be scaled up to MHz rates. At LBNL, we developed the VHF-Gun, a room-temperature RF gun designed for CW operation and high-brightness beam performance.

APEX Present Experimental Results

The APEX electron source at LBNL combines highrepetition-rate and high beam brightness typical of photoguns, delivering low emittance electron pulses at MHz frequency. Proving the high beam quality of the beam is an essential step for the success of the experiment. It would enable high repetition rate operations for brightness-hungry applications such as X-Ray FELs, and MHz ultrafast electron diffraction. A full 6D characterization of the beam phase space at the gun beam energy (750 keV) is foreseen in the first phase of the project. Diagnostics for low and high current measurements have been installed and tested, measuring the performances of different cathode materials in a RF environment with mA average current. A double-slit system allows the characterization of beam emittance at high charge and full current (mA). An rf deflecting cavity is being installed, and a high precision spectrometer allow the characterization of the longitudinal phase space. Here we present the latest results at low and high repetition rate, discussing the tools and techniques used.

Observation of nonlinear resonances in the advanced light source

Observations of nonlinear resonances in the Advanced Light Source have been made by scanning betatron tunes and observing count rates in a beam‐loss radiation monitor placed down stream of a beam scraper. We have found that it is possible to see structural resonances which are unallowed as well as those which are allowed by the ring’s natural 12‐fold symmetry. By systematically breaking the amount of symmetry we see that the widths of the unallowed resonances grow while the widths of the allowed resonances do not. In this paper we briefly discuss the importance of symmetry and its effect on resonances in the design of the ALS. Next we describe our experimental setup and discuss the performance of the beam loss monitor which we used to view the resonances. We then present scans of the tune space where one can see the presence of the structural resonances and their evolution when the lattice symmetry is systematically broken.