M. Lynch

Optical performance of the Los Alamos free-electron laser

During a year of oscillator experiments, the Los Alamos free-electron laser has demonstrated high-power and diffraction-limited output capabilities with a factor-of-4 wavelength tunability in the infrared. A conventional, L -band RF linear accelerator produced a 100 μs long, 2000 pulse train of 35 ps wide electron-beam pulses with peak currents to 50 A and nominal energy of 20 MeV. Small-signal gain in excess of 40 percent was generated in a 1 m, plane-polarized, uniform-period undulator for wavelengths between 9 and 11 μm. Best performance included an electron-energy extraction efficiency of 1 percent, 10 MW peak output power, and a corresponding average power of 6 kW over a 90 μs pulse train. A Strehl ratio of 0.9 characterized the output spatial beam quality. By reducing the electron energy by a factor of 2, the wavelength was tuned continuously from 9 to 35 μm.

The effects of linear-accelerator noise on the Los Alamos free-electron laser

The optical power produced by the Los Alamos free-electron laser has been flawed by a peristent instability. This instability appears as fluctuations in output power in a frequency band centered around 100 kHz. We have found that the fluctuations are dependent on the strength of the lasing and on variations in the electron micropulses arrival time. When the lasing is strong, the fluctuations are small; when the lasing is weak, the fluctuations are large. The variations in the electron micropulses arrival time primarily are due to fluctuations in the accelerator gradients. The primary noise sources in the accelerator are the electron gun and the klystron amplifier chain. In addition, this noise is uncontrolled because of a lack of bandwidth in the feedback controls for the RF system. Appropriate improvements are being made to eliminate these fluctuations in optical power.

The Los Alamos free electron laser: Accelerator performance☆

The Los Alamos free electron (FEL) laser oscillator has successfully operated over a wavelength range from 9 to 11 ..mu..m with a peak output power of 5 MW and an average output power of 6 kW over a 70-..mu..s pulse length. The FEL is driven by a conventional rf linear accelerator operating at 1.3 GHz with a nominal energy of 20 MeV. Particularly important parts of the beamline are the electron gun, the subharmonic and fundamental-bunching systems, the accelerator, the feedback controllers, the steering and focusing systems, the Cherenkov radiators used as beam-position monitors, and the slow and fast deflectors used with the diagnostic spectrometer at the exit of the beamline. We will discuss problems and present the performance of these components. 10 references, 12 figures, 2 tables.

The SNS linac high power RF system design, status, and results

The Spallation Neutron Source being built at the Oak Ridge National Lab in Tennessee requires a 1 GeV proton linac. Los Alamos has responsibility for the RF systems for the entire linac. The linac requires 3 distinct types of RF systems: 2.5-MW peak, 402.5 MHz, RF systems for the RFQ and DTL (7 systems total); 5-MW peak, 805 MHz systems for the CCL and the two energy corrector cavities (6 systems total); and 550-kW peak, 805 MHz systems for the superconducting sections (81 systems total). The design of the SNS Linac RF system was presented at the 2001 Particle Accelerator Conference in Chicago. Vendors have been selected for the klystrons (3 different vendors), circulators (1 vendor), transmitter (1 vendor), and high power RF loads (3 different vendors). This paper presents the results and status of vendor procurements, test results of the major components of the Linac RF system and our installation progress.

Uncertain system modeling of SNS RF control system

This paper addresses the modeling problem of the linear accelerator RF system for SNS. The cascade of the klystron and the cavity is modeled as a nominal system. In the real world, high voltage power supply ripple, Lorentz force detuning, microphonics, cavity RF parameter perturbations, distortions in RF components, and loop time delay imperfection exist inevitably, which must be analyzed. The analysis is based on the accurate modeling of the disturbances and uncertainties. In this paper, modern control theory is applied for modeling the disturbances, uncertainties, and for analyzing the closed loop system robust performance.

An overview of the Low Energy Demonstration Accelerator (LEDA) project RF systems

Successful operation of the Accelerator Production of Tritium (APT) plant will require that accelerator downtime be kept to an absolute minimum. Over 230 separate 1 MW RF systems are expected to be used in the APT plant, making the efficiency and reliability of these systems two of the most critical factors in plant operation. The Low Energy Demonstration Accelerator (LEDA) being constructed at Los Alamos National Laboratory will serve as the prototype for APT. The design of the RF systems used in LEDA has been driven by the need for high efficiency and extremely high system reliability. We present details of the high voltage power supply and transmitter systems as well as detailed descriptions of the waveguide layout between the klystrons and the accelerating cavities. The first stage of LEDA operations will use four 1.2 MW klystrons to test the RFQ and supply power to one test stand. The RFQ will serve as a power combiner for multiple RF systems. We present some of the unique challenges expected in the use of this concept.

Accelerator production of tritium 700 MHz and 350 MHz klystron test results

The Accelerator Production of Tritium project (APT) utilizes a 1,700 MeV, 100 mA proton Linac. The radio frequency (RF) power is provided by 244 continuous wave (CW) klystron amplifiers at 350 MHz and 700 MHz. All but three of the klystrons operate at a frequency of 700 MHz. The 350 MHz klystrons have a nominal output power of 1.2 MW at a DC-to-RF conversion efficiency of 65%. They are modulating-anode klystrons and operate at a beam voltage and current of 95 kV and 20 A. The design is based on the CERN klystron. The 700 MHz klystron is a new development for APT. Three 700 MHz klystrons are currently under development. Two vendors are each developing a baseline klystron that has a nominal output power of 1.0 MW at a DC-to-RF conversion efficiency of 65%. A 700 MHz klystron is also under development that promises to provide an efficiency in excess of 70%. The 700 MHz klystrons operate at a maximum beam voltage of 95 kV and a maximum beam current of 17 A. The test results of these klystrons will be presented and the design features will be discussed.

The BEAR accelerator

The Beam Experiments Aboard Rocket (BEAR) accelerator is the major component of an experiment designed to demonstrate the operation of an ion accelerator in space and to characterize the exoatmospheric propagation of a neutral particle beam. It is designed to produce a 10-mA (equivalent), 1-MeV, neutral hydrogen beam in 50- mu s pulses at 5 Hz. The accelerator consists of a 30-kV, H/sup -/ injector, a 1-MeV radiofrequency quadrupole, two 425-MHz RF amplifiers, a gas-cell neutralizer, beam optics, a vacuum system, diagnostics, and controls. The design has been constrained by the need for a light-weight rugged system that would operate autonomously. The accelerator has undergone extensive environmental and operational laboratory testing in preparation for launch. The results of testing on the ground test stand are reported.<<ETX>>

Reliability and availability considerations in the RF systems of ATW‐class accelerators

In an RF‐driven, ion accelerator for waste transmutation or nuclear material production, the overall availability is perhaps the most important specification. The synchronism requirements in an ion accelerator, as contrasted to an electron accelerator, cause a failure of an RF source to have a greater consequence. These large machines also are major capital investments, so the availability determines the return on this capital. RF system design methods to insure a high availability without paying a serious cost penalty are the subject of this paper. The overall availability goal in our present designs is 75% for the entire ATW complex, and from 25 to 35% of the unavailability is allocated to the RF system, since it is one of the most complicated subsystems in the complex. The allowed down time for the RF system (including the linac and all other subsystems) is then only 7 to 9% of the operating time per year, or as little as 613 hours per year, for continuous operation. Since large accelerators consume la...

Lansce RF System Refurbishment

The Los Alamos Neutron Science Center (LANSCE) is in the planning phase of a refurbishment project that will sustain reliable facility operations well into the next decade. The linear accelerator was constructed in the late 1960s and commissioned as the Los Alamos Meson Physics Facility (LAMPF) in 1972. As the mission changed, LANSCE became a national user facility that provides pulsed protons and spallation neutrons for defense and civilian research and applications. The upgrade will replace all of the 201.25 MHz RF systems and a substantial fraction of the 805 MHz RF systems and high voltage systems. This paper will provide the design details of the new RF and high voltage systems.