We report observations of an intense, multi-band, sub-THz and THz radiation extracted from a similar to 2-3 MeV electron beam with a flat transverse profile propagating in an oversized rectangular waveguide placed into a 3.25 mm gap of a planar undulator having 1.3 cm period and similar to 20 cm length. Radiation outcoupling is accomplished using a horn antenna and a miniature permanent in-vacuum magnet separating the mm-sub-mm-waves and electron beam. A table-top experiment utilizes a radio frequency thermionic electron gun delivering a thousand momentum-chirped microbunches per macropulse and an alpha-magnet producing microbunches of a sub-mm length. Total radiated energy of a sub-millijoule per a microsecond radio frequency macropulse is demonstrated with flux more than ten micro-Joules per centimeter squared. With 1 THz filter the energy measured is about 1 microjoule and flux of a few micro-Joules per centimeter squared.

Next-generation, high-performance storage ring (SR) light sources based on multibend achromat optics will require on-axis injection because of the extremely small dynamic aperture. Injectors will need to supply full-current bunch replacement in the SR with high single-bunch charge for swap-out. For upgrades of existing light sources, such as the Advanced Photon Source Upgrade (APS-U), it is economical to retain the existing injector infrastructure and make appropriate improvements. The challenges to these improvements include achieving high single-bunch charge in the presence of instabilities, beam loading, charge stability and reliability. In this paper, we discuss the rationale for the injector upgrades chosen for APS-U, as well as backup and potential alternate schemes. To date, we have achieved single-bunch charge from the injectors that doubles the original design value, and have a goal to achieve about three times the original design value.

Design features and some past experimental results are presented for a sub-THz wave source employing the Advanced Photon Source's RF thermionic electron gun. The setup includes a compact alpha-magnet, four quadrupoles, a novel radiator, a THz transport line, and THz diagnostics. The radiator is composed of a dielectricfree, planar, over-sized structure with gratings. The gratings are integrated into a combined horn antenna and ~90° permanent bending magnet. The magnetic lattice enables operation in different modes, including conversion to a flat beam for efficient interaction with the radiating structure. The experiment described demonstrated the generation of narrow bandwidth THz radiation from a compact, laser and undulator-free, tabletop system. This concept could be scaled to create a THzsub-THz source capable of operating in long-pulse, multibunch, and CW modes. Additionally, the system can be used to remove unwanted time-dependent energy variations in longitudinally compressed electron bunches or for various time-dependent beam diagnostics. Plans for future experiments and upgrades are also discussed.

The Advanced Photon Source (APS) injector complex includes an option for rf photocathode (PC) gun beam injection into the 450-MeV S-band linac. At the 150-MeV point, a four-dipole chicane was used to compress the micropulse bunch length from a few ps to sub-0.5 ps (FWHM). Noticeable enhancements of the optical transition radiation (OTR) signal sampled after the APS chicane were then observed as has been reported in the Linac Coherent Light Source (LCLS) injector commissioning. A far-infrared (FIR) coherent transition radiation detector and interferometer were used to monitor the bunch compression process and correlate the appearance of localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam-image footprint. We have performed spectral-dependency measurements at 375 MeV with a series of bandpass filters centered in 50-nm increments from 400 to 700 nm and with an imaging spectrometer and observed a broadband enhancement in these spikes. Mitigation concepts of the observed coherent OTR, which exhibits an intensity enhancement in the red part of the visible spectrum as compared to incoherent OTR, are described.

The Advanced Photon Source (APS) injector complex includes an option for rf photocathode (PC) gun beam injection into the 450-MeV S-band linac. At the 150-MeV point, a 4-dipole chicane was used to compress the micropulse bunch length from a few ps to sub 0.5 ps (FWHM). Noticeable enhancements of the optical transition radiation (OTR) signal sampled after the APS chicane were then observed as has been reported in LCLS injector commissioning. A FIR CTR detector and interferometer were used to monitor the bunch compression process and correlate the appearance of localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam image footprint. We have done spectral dependency measurements at 375 MeV with a series of band pass filters centered in 50-nm increments from 400 to 700 nm and with an imaging spectrometer and observed a broadband enhancement in these spikes. Mitigation concepts of the observed COTR which has more of a red component than OTR are described. rgy, Office of Science, Office of High Energy Physics, nder Contract No. DE-AC02-06CH11357. TERIZATION AND MITIGATION OF COTR SI ELECTRON BEAM* A.H. Lumpkin, Fermilab, Batavia, IL U.S.A. 60510 N.S. Sereno, W. Berg, M. Borland, Y. Li, and S. Pasky *Work supported by U.S. Department of Ene u FERMILAB-PUB-09-051-AD

The Advanced Photon Source (APS) injector complex includes an option for photocathode (PC) gun beam injection into the 450-MeV S-band linac. At the 150-MeV point, a 4-dipole chicane was used to compress the micropulse bunch length from a few ps to sub 0.5 ps (FWHM). Noticeable enhancements of the optical transition radiation (OTR) signal sampled after the APS chicane were then observed as has been reported in LCLS injector commissioning. A FIR CTR detector and interferometer were used to monitor the bunch compression process and correlate the appearance of localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam image footprint. We have done spectral dependency measurements at 375 MeV with a series of band pass filters centered in 50-nm increments from 400 to 700 nm and observed a broadband enhancement in these spikes. Discussions of the possible mechanisms will be presented.

Adjustment of the rf phase in a linear accelerator is crucial for maintaining optimal performance. If phasing is incorrect, the beam will in general have an energy error and increased energy spread. While an energy error can be readily detected and corrected using position readings from beam position monitors at dispersion locations, this is not helpful for correcting energy spread in a system with many possible phase errors. Uncorrected energy spread results in poor capture efficiency in downstream accelerators, such as the Advanced Photon Source's (APS's) particle accumulator ring (PAR) or booster synchrotron. To address this issue, APS has implemented beam-to-rf phase detectors in the linac, along with software for automatic correction of phase errors. We discuss the design, implementation, and performance of these detectors and how they improved APS top-up operations.

Operational goals for the Advanced Photon Source (APS) facility include 97% availability and a mean time between unscheduled beam losses (faults) of 70 hours, with more than 5000 user hours of scheduled beam per year. To meet this objective, our focus has been maximizing the mean time between faults (MTBF). We have made various hardware and software improvements to better operate and monitor the injector power supply systems. These improvements have been challenging to design and implement in light of the facility operating requirements but are critical to maintaining maximum reliability and availability of beam for user operations. This paper presents actions taken as well as future plans to continue improving injector power supply hardware and software to meet APS user operation goals.

The Advanced Photon Source (APS) has constructed an injector test stand (ITS) for high-brightness electron beam research. The test stand includes three rf ports with independent phase and power control, beamline supports designed for rapid reconfiguration, and a control and diagnostics system based on the design of the APS linac. The beamline design features a high-resolution electron spectrometer that includes provision for operation as a dispersion-free dogleg, and a rapidly reconfigurable gun-to-spectrometer transport line. Picosecond and nanosecond photocathode drive lasers are available; the room shielding is also adequate for the high average beam powers typically produced by thermionic-cathode rf guns. The initially installed gun is a ballistic-compression gun, which requires all three rf ports to be connected to the gun. Plans include the installation of a higher-order mode photoinjector, requiring one rf connection; this will free the other ports to provide power to a small TW linac section and deflector cavity for bunch-length measurements. The test stand is also capable of being used as an operator training facility, and serves as a validation facility and test bed for the APS main injector rf guns.

The Advanced Photon Source (APS), a premier third-generation synchrotron radiation source, presently operates in top-up mode during most user run time. During top-up mode, charge is injected into the storage ring at approximately 2-minute intervals to stabilize the stored beam current to within 0.1%. Top-up mode requires the dedicated use of the entire APS injector system, severely limiting time available for operator training. The APS injector test stand (ITS) is presently configured to operate a ballistic bunch compression (BBC) rf gun, which uses three independently powered and phased rf cavities, and either a thermionic cathode or a photocathode. Operation of the BBC gun requires cavity phasing and input rf power selection analogous to the operation of a high-energy linac. In conjunction with the ITS beamline components (quadrupoles, dipoles, diagnostics, correctors), this provides an effective analog to the APS linac. Operators can therefore practice accelerator tuning and control methods with a live beam and -real components, rather than simulations, while top-up operation is ongoing.

In recent years many changes have been made to the Advanced Photon Source (APS) linear accelerator (linac) to support multiple tasks. The primary purpose of the linac is to provide beam to fill the APS storage ring, which is done using thermionic cathode rf guns. At the same time we provide support for research projects, including a new facility that will be used for future operator training and testing of injector components. With each task requiring a different lattice and timing configuration, while at the same time using common rf systems, the complexity of operations has increased significantly with even greater demands being made on reliability and performance. In addition, personnel safety and equipment protection concerns have become more complex. We approached these challenges by developing three new subsystems: a highly automated linac operation using APS's Procedure Execution Manager (PEM) software; a new interlock system based on programmable logic controllers; and an automated S-band rf switching system. In this paper, we discuss how these developments have improved the flexibility and reliability of the APS linac, and how we intend to conduct operator training and test new injector components while maintaining storage ring injections.

Abstract 2 LINAC AUTOMATED OPERATIONS In recent years, many changes have been made to the Advanced Photon Source (APS) linear accelerator (linac) to support multiple tasks. The primary purpose of the linac is to provide beam to fill the APS storage ring, which is done using new thermionic cathode rf guns. At the same time, we have had to provide support for research, including the free-electron laser (FEL) project and a new facility for testing injector components. With each operating gun and research project requiring a different lattice and timing configuration, while at the same time using a common rf system, the complexity of operations increased significantly with even greater demands on reliability and performance. In addition, personnel safety and equipment protection concerns grew as the machine operation became more complex. Our approach to these challenges involved three developments: a high degree of automation in linac operation, using APS’s Procedure Execution Manager (PEM) software; a new interlock system based on programmable logic controllers; and use of an automated S-band rf switching system. In this paper, we discuss how these developments have or will improve the flexibility and reliability of linac operations. The APS linac is made up of five modulators and klystrons, three SLEDs, three electron guns, and a complex diagnostic and lattice arrangement. In addition, there are various subsystems, like water, vacuum, and timing, that are incorporated into various operating screens that hold hundreds of read-backs and controls for every aspect of operation. Originally, when making changes in the linac, the operators had to switch back and forth among many control screens and perform procedures from memory or with the aid of written procedures. To say the least, this was a very time-consuming, error-prone task. PEM software procedures [1,2], when configured properly, follow the same steps an operator would take during equipment start-ups and reconfiguration. The main difference is that PEM has the ability to repeat steps faster, more consistently, and with less possibility of error. After implementing the PEM system for the linac, linac operators found it provided the ability to make changes to linac configuration while maintaining safe operation of the subsystem equipment. When using PEM procedures, the operator no longer has to open numerous control screens and work on one task at a time. Rather, the PEM is able to efficiently use multitasking to alleviate the burden on the operators in what can often be a stressful situation. The operators can read corresponding descriptions and view the steps of a PEM procedure to become familiar with it. This is not intended to reduce operator training, but it does serve as an additional source of information that may be valuable to operators.

Exponential growth of self-amplified spontaneous emission at 530nm was first experimentally observed at the Advanced Photon Source low-energy undulator test line in December 1999. Since then, further detailed measurements and analysis of the results have been made. Here, we present the measurements and compare these with calculations based on measured electron beam properties and theoretical expectations.

The S-band linear accelerator (linac), which was built to be the electron source and the front end of the Advanced Photon Source (APS) injector, is now also being used to support a low-energy undulator test line (LEUTL) to drive a free-electron laser (FEL). The APS linac system employs five units of pulsed high-power klystrons (35-MW class) as the main rf sources. The matching pulse modulators provide high-voltage pulses running at 280 kV and 300 A with 3.5-μs pulse width and a nominal pulse repetition rate of 30 Hz. The system availability of the entire APS linac during the last run period of calendar year 2000 was estimated to be slightly over 95%. We present a discussion of the reliability and various fault statistics of the klystron-modulator system together with the key features of the system hardware

The Advanced Photon Source (APS) linear accelerator has two thermionic cathode rf guns and one photocathode rf gun. The thermionic guns are used primarily for APS operations while the photocathode gun is used as a free-electron laser (FEL) driver. With each gun requiring a different lattice and timing configuration, the need to change quickly between guns puts great demands on the accelerator operators. Using the Procedure Execution Manager (PEM), a software environment for managing automated procedures, we have made start-up and switch-over of the linac systems both easier and more reliable. The PEM is a graphical user interface written in Tcl/Tk that permits the user to invoke "machine procedures" and control their execution. It allows construction of procedures in a hierarchical, parallel fashion, which makes for efficient execution and development. In this paper, we discuss the features and advantages of the PEM environment as well the specifics of our procedures for the APS linac.

An S-band linear accelerator is the source of particles and the front end of the Advanced Photon Source injector. In addition, it supports a low-energy undulator test line (LEUTL) and drives a free-electron laser (FEL). A waveguide-switching and distribution system is now under construction. The system configuration was revised to be consistent with the recent change to electron-only operation. There are now six modulator-klystron subsystems, two of which are being configured to act as hot spares for two S-band transmitters each, so that no single failure will prevent injector operation. The two subsystems are also used to support additional LEUTL capabilities and off-line testing. Design considerations for the waveguide-switching subsystem, topology selection, control and protection provisions, high-power test results, and current status are described