I. Vasserman

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.

FEL development at the Advanced Photon Source

Construction of a single-pass free-electron laser (FEL) based on the self-amplified spontaneous emission (SASE) mode of operation is nearing completion at the Advanced Photon Source (APS) with initial experiments imminent. The APS SASE FEL is a proof-of-principle fourth-generation light source. As of January 1999 the undulator hall, end-station building, necessary transfer lines, electron and optical diagnostics, injectors, and initial undulators have been constructed and, with the exception of the undulators, installed. All preliminary code development and simulations have also been completed. The undulator hall is now ready to accept first beam for characterization of the output radiation. It is the project goal to push towards full FEL saturation, initially in the visible, but ultimately to UV and VUV, wavelengths.

The elliptical multipole wiggler project

The elliptical multipole wiggler (EMW) has been designed, constructed, and installed in the X13 straight section of the NSLS X-ray Ring. The EMW generates circularly polarized photons in the energy range of 0.1-10 keV with AC modulation of polarization helicity. The vertical magnetic field of 0.8 T is produced by a hybrid permanent magnet structure with a period of 16 cm. The horizontal magnetic field of 0.22 T is generated by an electromagnet, the core of which is fabricated from laminated iron to operate with a switching frequency up to 100 Hz. There are dynamic compensation trim magnets at the wiggler ends to control the first and second field integrals with very high accuracy throughout the AC cycle. The residual closed orbit motion due to the electromagnet AC operation is discussed.

Search for possible radiation damage on a NdFeB permanent magnet structure after two years of operation

Recently there has been some concern about possible radiation damage due to ionizing particles present in high energy storage rings such as multi‐GeV electrons, fast neutrons, or hard photons. Partial demagnetization has been observed on undulators after mis‐steering of the injected electron beam. Our interest was focused to possible radiation damage of a permanent magnet insertion device during routine operation of a storage ring. Therefore, we repeated the magnetic measurements on one of the three 4.0 m long x‐ray wigglers used at place ♯2 in DORIS III. This device is in operation since 1991. The results were compared to the data taken before installation. The total dose was determined from measurements with thermoluminescence dosimeters and the known number of stored ampere hours. The results which show no significant degradation of the magnetic performance are presented and discussed.

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.

Optimization of the design for the LCLS undulator line

The Linac Coherent Light Source (LCLS) undulator line will consist of undulator segments separated by breaks of various lengths. Focusing quadrupoles, in a FODO lattice, and electron-beam diagnostics will be located in the breaks, and every third break will be longer to also accommodate photon diagnostics. The electron-beam beta function and the undulator period were selected to minimize the saturation length. The FEL simulation code RON has been used to optimize parameters such as the length of the undulators and the break lengths between undulators. Different break lengths after the first three undulators have been found to help reduce the overall undulator line saturation length. Tolerances for individual undulators have also been determined. r 2001 Elsevier Science B.V. All rights reserved. PACS: 41.60. Cr

ELLIPTICAL MULTIPOLE WIGGLER FACILITY AT THE ADVANCED PHOTON SOURCE

The use of circularly polarized radiation is advantageous for the study of magnetic materials using x‐ray scattering techniques. The APS is an ideal source of x‐ray radiation for such studies. We present a description of the elliptical multipole wiggler (EMW) [S. Yamamoto, H. Kawata, H. Kitamura, and M. Ando, Phys. Rev. Lett. 62, 2672 (1989)] to be constructed at the APS. This device has been chosen for reasons of tunability and special polarization properties. This insertion device is capable of producing circularly polarized x rays on axis. The EMW period will be λu=16 cm, the number of full strength poles in the hybrid structure is 31, and the device length is 2.8 m. The hybrid magnetic structure produces a peak vertical magnetic field with Ky=14 and the electromagnet provides horizontal magnetic field with Kx=1–2. The frequency of the horizontal field change is up to 10 Hz. The beamline will consist of three stations operating in tandem with only one station receiving x rays at any one time. The three...

A Design Concept for a Planar Superconducting Undulator for the APS

A superconducting planar undulator is under development at the Advanced Photon Source. The R&D phase culminated in the successful testing of several short magnetic structure prototypes. Work is now focused on a complete design for the first undulator. The conceptual designs for its superconducting magnet, the cooling system, and the cryostat are described in this paper.

Phase errors and predicted spectral performance of a prototype undulator

A prototype undulator (3.3 cm period, permanent‐magnet hybrid device) has been used to study different magnetic end configurations and shimming techniques for straightening the beam trajectory. Field distributions obtained by Hall‐probe measurements were analyzed in terms of trajectory, phase errors, and on‐axis brightness for the purpose of correlating predicted spectral intensity with the calculated phase errors. An rms phase error of less than 3° is found and 87% of the ideal value of the on‐axis brightness for the third harmonic (nominal gap is 11.5 mm and derived effective K is 2.25) is predicted. The gap dependence of the phase errors and spectral brightness was also analyzed and it was found that the rms phase error remains small at all gap settings.

RaD of Short-Period NBTI and Nb 3 Sn Superconducting Undulators for the APS

Superconducting undulators (SCUs) with a period of 14.5 mm are under development for the Advanced Photon Source (APS). The undulators have been designed to achieve a peak field on the beam axis higher than 0.8 T with an 8 mm pole gap and current densities over 1 kA/mm2in the NbTi and Nb 3 Sn coils. Upper-half NbTi SCUs of short sections have been fabricated and were charged up to near the critical current density of 1.43 kA/mm2to achieve a peak field about 1 T. The stability margin of the SCU was measured by imposing steady-state heat fluxes on the pole/coil face of the SCU in a pool-boiling liquid He (LHe) dewar at 4.2 K. Near the critical current density, where the temperature stability margin is minimal, the heat flux density to quench the SCU was about 1.3 mW/mm2, of which 60% was attributed to LHe at the interface of the SCU and the vacuum chamber. The peak fields of the SCU were mapped along the beam axis using a Hall probe in a vertical dewar. The first test of a Nb 3 Sn short-section SCU was charged to an average current density of 1.45 kA/mm2, slightly higher than the critical current density for the NbTi SCU.