G. Wiemerslage

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.

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)

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.

New insertion device vacuum chambers at the Advanced Photon Source

Six new types of insertion device vacuum chambers have been designed at the Advanced Photon Source (APS). One chamber has been designed for the APS canted undulator beamlines, two for the Canadian Light Source (CLS), and three for BESSY II. For the double canted undulators and CLS, a new extrusion shape with an oval aperture (not elliptical as usual) was developed and extruded. That required a thorough stress analysis and some compromise, which included a small increase of the vacuum chamber wall thickness. The details of the stress analyses and design of the chambers, along with lessons learned, are presented.

UV-VUV diagnostics for the Advanced Photon Source SASE FEL

The Advanced Photon Source self-amplified spontaneous emission (SASE) free-electron laser (FEL) uses diagnostics between undulator sections to characterize the light and the electron beam. These diagnostics enable z-dependent measurements of the exponential growth of the radiation and of the microbunching. The original diagnostics were designed for visible light. To enable measurements down to 265 nm, UV-enhanced cameras and fused-silica lenses have been installed. We have now designed a diagnostics suite that will enable us to continue measurements down to 50 nm using reflective optics and back-illuminated CCD cameras operating in vacuum. We describe the enhancements to the diagnostics for operation in the UV and VUV.

The vacuum chambers for the VUV SASE FEL at the TESLA Test Facility (TTF FEL) at DESY

A vacuum chamber for the VUV SASE FEL undulators at the TESLA Test Facility (TTF) was designed, a prototype was built and tested, and seven complete chambers were manufactured. The chambers use the aluminum extrusion technology developed for the insertion device vacuum chambers of the Advanced Photon Source. Each chamber is 4.5 m long with a beam aperture of 9.5 mm and an external thickness of 11.5 mm. Three of the chambers include ports for integral beam position monitors (10 horizontal and vertical pairs) inserted into the chambers, and all of the chambers include grooves for mounting correction coils. Bimetallic flanges (stainless steel to aluminum) are welded to the ends of the chamber for connection to the beamline. Special processing was performed to meet. The stringent vacuum and particle-free requirements of the TTF.

The vacuum system for insertion devices at the Advanced Photon Source

A vacuum system for the insertion devices at the Advanced Photon Source was designed, and chambers of this design were successfully manufactured and tested. Three different versions of the vacuum chamber have been developed with vertical apertures of 12 mm, 8 mm, and 5 mm, respectively. The chambers are fabricated by extruding 6063 aluminum alloy to form a tube with the desired internal shape and machining the exterior to finish dimensions. The wall thickness of the completed chamber at the beam orbit position is 1 mm. The design utilizes a rigid strongback that limits deflection of the chamber under vacuum despite the thin wall. Chambers with lengths of 2.2 m and 5.2 m have been fabricated. Pumping is accomplished by a combination of lumped and distributed non-evaporable getters and ion pumps. An ultimate pressure of 5.1/spl times/10/sup -11/ torr was achieved with the 12-mm vertical aperture prototype. Alignment of the vacuum chamber on its support stand can be made with a precision of /spl plusmn/25 /spl mu/m in the vertical plane, which allows minimum insertion device pole gaps of 14.5 mm, 10.5 mm, and 7.5 mm.

A study of the minimum wall thickness for an extruded aluminum vacuum chamber

Decreasing an ID vacuum chamber wall thickness is a way to achieve a smaller ID gap and a higher magnetic field without decreasing the clear beam aperture of the chamber. Multiple extruded aluminum ID vacuum chambers with 1-mm wall thickness were developed and fabricated at Argonne for the APS and several other synchrotron radiation facilities [1]. Thinner walls have been avoided due to fear that porosity and defects from the extrusion process would result in vacuum leaks. There were also concerns that thinner walls may have excessive deformation or may not withstand the stresses. Recently, several extrusions have been machined to a wall thickness of less than 1 mm to determine the practical limits. Using the extrusion for the insertion device vacuum chamber (ID VC) for the DESY FEL project with a 9.5-mm inner diameter and the LCLS test vacuum chamber extrusion, we decreased the wall thickness to 0.6, 0.5, and 0.4 mm to test the vacuum integrity for a thin wall in these extrusions. Structural analysis and test results are presented.

Mechanical Design of a Front End for Canted Undulators at the Advanced Photon Source

At the Advanced Photon Source, three new beamlines will use an undulator configuration enabling the simultaneous use of two photon beams from a single straight section. To accommodate this configuration, a new front end was designed that is capable of handling the power of two undulators, with a beam separation of 1 mrad and a stored beam current of 200 mA at 7 GeV. Commissioning of the first front end took place early this summer. The design and major benefits of the new front‐end components will be discussed in this paper.

Self-amplified spontaneous emission saturation at the Advanced Photon Source free-electron laser (abstract) (invited)

Today, many bright photon beams in the ultraviolet and x-ray wavelength range are produced by insertion devices installed in specially designed third-generation storage rings. There is the possibility of producing photon beams that are orders of magnitude brighter than presently achieved at synchrotron sources, by using self-amplified spontaneous emission (SASE). At the Advanced Photon Source (APS), the low-energy undulator test line (LEUTL) free-electron laser (FEL) project was built to explore the SASE process in the visible through vacuum ultraviolet wavelength range. While the understanding gained in these experiments will guide future work to extend SASE FELs to shorter wavelengths, the APS FEL itself will become a continuously tunable, bright light source. Measurements of the SASE process to saturation have been made at 530 and 385 nm. A number of quantities were measured to confirm our understanding of the SASE process and to verify that saturation was reached. The intensity of the FEL light was me...