P. Den Hartog

The magnetic and diagnostics systems for the Advanced Photon Source self-amplified spontaneously emitting FEL

A self-amplified spontaneously emitting (SASE) free-electron laser (FEL) for the visible-to-ultraviolet spectral range is under construction at the Advanced Photon Source at Argonne National Laboratory. The amplifier part of the FEL consists of twelve identical 2.7-meter-long sections. Each section includes a 2.4-meter-long, 33-mm-period hybrid undulator, a quadruple lens, and a set of electron beam and radiation diagnostics equipment. The undulatory will operate at a fixed magnetic gap (approx. 9.3 mm) with K=3.1. The electron beam position will be monitored using capacitive beam position monitors, YAG scintillators with imaging optics, and secondary emission detectors. The spatial distribution of the photon beam will be monitored by position sensitive detectors equipped with narrow-band filters. A high-resolution spectrograph will be used to observe the spectral distribution of the FEL radiation.

Measurements of nonlinear harmonic generation at the Advanced Photon Source's SASE FEL

SASE saturation was recently achieved at the Advanced Photon Sources SASE FEL in the low-energy undulator test line (LEUTL) at 530 nm and 385 nm. The electron beam microbunching becomes more and more prominent until saturation is achieved. This bunching causes nonlinear harmonic emission that extends the usefulness of a SASE system in achieving shorter FEL wavelengths for the same electron beam energy. They have investigated the intensity of the fundamental and second-harmonic undulator radiation as a function of distance along the undulator line and present the experimental results and compare them to numerical simulations. In addition, they have measured the single-shot second harmonic spectra as well as the simultaneous fundamental and second harmonic spectra and present the experimental results.

Radiation effects studies at the Advanced Photon Source

At the Advanced Photon Source (APS) concern for radiation-induced demagnetization of the insertion devices (IDs) in the storage ring and in the free-electron laser has initiated systematic radiation effects studies towards the development of efficient techniques for ID protection. The studies include radiation dose monitoring, parametric study of the radiation-induced demagnetization, as well as, potentially, a dedicated radiation effects testbed at the APS providing GeV electron beams. Such studies could also be directly applicable to future generation facilities, such as the Linac Coherent Light Source (LCLS). Results and discussion of the radiation damage studies at APS are presented.

Planned use of pulsed crab cavities for short X-ray pulsed generation at the Advanced Photon Source

Recently, we have explored application to the Advanced Photon Source (APS) of Zholents[1] crab cavity scheme for production of short x-ray pulses. We assumed use of superconducting (SC) cavities in order to have a continuous stream of crabbed bunches and flexibility of operating modes. The challenges of the SC approach are related to the size, cost, and development time of the cavities and associated systems. A good case can be made [2] for a pulsed system using room-temperature cavities. APS has elected to pursue such a system in the near term, with the SC-based system planned for a later date. This paper describes the motivation for the pulsed system and gives an overview of the planned implementation and issues. Among these are overall configuration options and constraints, cavity design options, frequency choice, cavity design challenges, tolerances, instabilities, and diagnostics plans.

APS undulator radiation—first results

The first undulator radiation has been extracted from the Advanced Photon Source (APS). The results from the characterization of this radiation are very satisfactory. With the undulator set at a gap of 15.8 mm (K=1.61), harmonics as high as the 17th were observed using a crystal spectrometer. The angular distribution of the third-harmonic radiation was measured, and the source was imaged using a zone plate to determine the particle beam emittance. The horizontal beam emittance was found to be 6.9 {plus_minus} 1.0 nm-rad, and the vertical emittance coupling was found to be less than 3%. The absolute spectral flux was measured over a wide range of photon energies, and it agrees remarkably well with the theoretical calculations based on the measured undulator magnetic field profile and the measured beam emittance. These results indicate that both the emittance of the electron beam and the undulator magnetic field quality exceed the original specifications.

Present status and recent results from the APS SASE FEL

The Low-Energy Undulator Test Line (LEUTL) at the Advanced Photon Source, Argonne National Laboratory, is intended to demonstrate the basic operation of a SASE-based free-electron laser. Goals include comparison of experimental results With theoretical predictions and scaling laws, identification of problems relevant to fourth-generation light source construction and operation and the means of addressing them, the development of operational and diagnostic techniques to optimize SASE FEL performance and increase repeatability from run to run. and performance of initial pioneering experiments capable of exploiting the unique properties of the laser. The basic layout and operational philosophy of the LEUTL experiment is presented. A summary of past results, including saturation, is reviewed, and a description of recent results is presented. We conclude with future plans, which include pressing to shorter wavelengths and incorporating user experiments into the LEUTL experimental program. (Less)

An electromagnetic helical undulator for polarized x-rays

Linearly and circularly polarized x-rays have been very successfully applied to the study of the properties of materials. Many applications can benefit from the availability of energy-turnable, high-brilliance x-ray beams with adjustable polarization properties. A helical undulator that can generate beams of variable (linear to circular) polarization has been designed and built by the Budker Institute of Nuclear Physics and the Advanced Photon Source. The first harmonic of this 12.8-cm-period device will cover the energy range from 0.4 keV to 3.5 keV. An important feature of this fully electromagnetic device is that it will allow one to generate 100% horizontally (K{sub x}=O)or vertically (K{sub y}=O) plane-polarized radiation, which will enable many experiments otherwise not technically feasible. With symmetric deflection parameters (K{sub x}=K{sub y}), the on-axis radiation will be circularly polarized, with a user-selectable handedness. The polarization can be changed at rates up to 10 Hz.

Radiation doses to insertion devices at the advanced photon source

Dose measurements made on and around the insertion devices (IDs) at the Advanced Photon Source are reported. Attempts are made to compare these dose rates to dose rates that have been reported to cause radiation-induced demagnetization, but comparisons are complicated by such factors as the particular magnet material and the techniques used in its manufacture, the spectrum and type of radiation, and the demagnetizing field seen by the magnet. The spectrum of radiation at the IDs has been measured and found to include a large high-energy (7 GeV) component, at least during some runs. Lead shielding installed immediately upstream of the IDs has been found to decrease the dose to the upstream ends of the IDs. It has almost no effect on the dose to the downstream ends of the IDs, however, since much of the radiation travels through the ID vacuum chamber and cannot be readily shielded. Opening the gaps of the IDs during injection and at other times also helps decrease the radiation exposure.

STATUS OF THE ATLAS ACCELERATOR

The construction of the ATLAS superconducting heavy‐ion linear accelerator is complete. The first beam acceleration occurred on March 22, 1985. The first experiment with the ATLAS linac took place during the week of October 7, 1985. The project was completed on time and within budget. Initial system performance has met our expectations.

Advanced Photon Source experience with vacuum chambers for insertion devices

During the last five years, a new approach to the design and fabrication of extruded aluminum vacuum chambers for insertion devices was developed at the Advanced Photon Source (APS). With this approach, three different versions of the vacuum chamber, with vertical apertures of 12 mm, 8 mm, and 5 mm, were manufactured and tested. Twenty chambers were installed in the storage ring and successfully integrated into the APS vacuum system. All have operated with beam, and 16 have been coupled with insertion devices. Two different vacuum chambers with vertical apertures of 16 mm and 11 mm were developed for the BESSY-II storage ring and 3 of the 16 mm chambers were manufactured.