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Selective suppression of high order axial modes of the gyrotron backward-wave oscillator (gyro-BWO) is investigated in theory and in experiment. The gyro-BWO interaction is much more efficient in a down-tapered interaction structure, while it is also more susceptible to the problem of axial mode competition in such a structure. Because higher order axial modes (at a higher oscillation frequency) penetrate deeper into the interaction structure, application of distributed wall loss at the downstream end of the interaction structure is shown in theory to be effective for selective suppression of these modes without degrading the efficiency of the desired fundamental axial mode. A stable gyro-BWO operating in a single mode throughout the entire beam pulse is demonstrated on the basis of this principle. Theoretical and experimental results are found to be in good agreement.

A 10MW L-band Multi-Beam Klystron (MBK) has been developed and tested by Toshiba, Japan for the European XFEL and a future linear collider projects. The Toshiba MBK has six low-perveance beams operated at low voltage of 115 kV (for 10MW) and six ring-shaped cavities to enable a higher efficiency than a single-beam klystron for a similar power. After the successful acceptance testing at the Toshiba Nasu factory in March 2006, attended by a DESY stuff, the final acceptance test was done at DESY laboratory in June 2006. In these tests, the output power of 10.2MW, more than the design goal (10MW), has been demonstrated at the standard beam voltage of 115 kV at the RF pulse length of 1.5 ms and the beam pulse of 1.7 ms at 10 Hz. The efficiency was 66%. The robustness of the tube was also demonstrated by being operated continuously more than 24 hours above 10MW. Total time of operation on the test stand at DESY already exceeds 750 hours (up to date February 4, 2007). A horizontal version of the Toshiba MBK is now under construction.

Summary form only given. The rise- and fall-time behavior of a pulsed microwave oscillator is of importance to radar and other applications because it can be a transient source of unwanted oscillations and hence the cause of leading/trailing edge jitters during the pulse. Here we present a study of such behavior in the gyrotron backward-wave oscillator (gyro-BWO). The gyro-BWO interaction processes are distinctively different from those of the resonator-based gyrotron oscillator. For the latter device, the oscillation frequency is largely fixed by the resonator structure. Consequently, voltage and pitch-angle variations of the electron beam in the rise and fall portions of the pulse lead to transit angle variations for a number of modes, and each of these modes can be excited over a duration in which its transit angle transitions through the optimum value (~pi). For the gyro-BWO, however, there are no cold resonant modes. The oscillation frequency is free to assume any value over a continuous range and identities of the axial modes are determined entirely by the electron dynamics rather than by the interaction structure. As a result, it has been shown that the (hot) axial modes are linearly characterized by a discrete set of optimum transit angles Theta separated by ~2pi where Theta is the accumulated phase variation of the wave as observed by the electron in traversing the interaction space. The current study reveals theoretically that, during the rise and fall of the beam pulse, the frequency of a given gyro-BWO mode varies in such a way that the transit angle remains at the optimum value for the mode. However, mode competition and mode switching can still occur due to the characteristic asymmetry of the axial mode profiles. A Ka-band gyro-BWO experiment has been carried out to examine the rise/fall-time behavior. Time-frequency analyses of the output pulses show excellent agreement with theoretical predictions. These understandings are expected to provide a useful guide for the design of a stable gyro-BWO operating at a single mode throughout the pulse

The Spallation Neutron Source (SNS) accelerator systems will deliver a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of a 1 GeV linear accelerator, an accumulator ring and associated transport lines. The SNS diagnostics platform is mostly PC-based running Windows XP Embedded for its OS and LabVIEW as its programming language. Coordinating timing among the various diagnostics instruments with the generation of the beam pulse is a challenging task that we have chosen to divide into three phases. First, timing was derived from VME based systems. The second phase, described in this paper, timing pulses were generated by an in house designed, PCI timing card installed in ten diagnostics PCs. Because each timing card has up to four available triggers and we could duplicate triggers using a distribution fan out module, enough triggers were generated for all instruments. This paper describes how the Timing NAD (Network Attached Device) was rapidly developed using our NAD template, LabVIEW’s PCI driver wizard, and LabVIEW Channel Access test screens. The NAD was successfully commissioned and has reliably provided triggers to the instruments. This work supports the coming third phase where every NAD will have its own timing card.

The Spallation Neutron Source accelerator systems will deliver a 1 GeV, 1.44 MW proton beam to a mercury target for neutron production. The beam commissioning of the accelerator systems is taking place in modules, as components are installed and tested. To date there have been four beam commissioning runs, the H-injector, Drift Tube Linac Tank 1, Drift Tube Linac Tanks 1-3 and Drift Tube Linac Tanks 4-6 plus CCL modules 1-3. Among the critical performance goals have been achieved are, demonstration of design 38 mA beam peak current, 1 msec long beam pulse, and 1 mA average beam. Results of accelerator availability during beam commissioning program are presented.

3 pp. (2005)., ophisticated beam-based alignment is essential in future linear colliders to preserve the beam emittance during the transport through the main linac. One such method is dispersion free steering. In this paper different options to implement this method are discussed, based on the use of different accelerating gradients, RF phases and bunch particle types during a beam pulse.

The Spallation Neutron Source (SNS) accelerator systems will provide a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron production. In order to satisfy the accelerator systems' portion of the critical decision 4 (CD-4) commissioning goal (which marks the completion of the construction phase of the project), a beam pulse with intensity greater than 1/spl times/10/sup 13/ protons must be accumulated in the ring, extracted in a single turn and delivered to the target. A commissioning plan has been formulated for bringing into operation and establishing nominal operating conditions for the various ring and transport line subsystems as well as for establishing beam conditions and parameters which meet the commissioning goal.

Summary form only given. The Spallation Neutron Source (SNS) accelerator system includes a nominally 1000 MeV, 1.4 mA average current linac consisting of a radio frequency quadrupole (RFQ), drift tube linac (DTL), coupled cavity linac (CCL), a medium and high beta super conducting (SC) linac, and two buncher cavities for beam transport to an accumulator ring. The average proton beam power of the accelerator is 1.4 MW. Los Alamos is responsible for the RF systems for all sections of the linac. The SNS linac is a pulsed proton linac and the RF system must support a 1 msec beam pulse at up to a 60 Hz repetition rate. The RFQ and DTL utilize seven, 2.5 MW klystrons and operate at 402.5 MHz. The CCL,SC, and buncher cavities operate at 805 MHz. Six, 5 MW klystrons are utilized for the CCL and buncher cavities while eighty-one 550 kW klystrons are used for the SC cavities.

Summary form only given, as follows. The hard-tube MILO (magnetically insulated transmission line oscillator) is a multigigawatt cross-field microwave tube powered by a 500-kV, 60-kA electron beam. During the initial experiments with a 300-ns beam pulse, a simple velvet cathode configuration was used. However, after extending the beam pulse to 600 ns, problems mainly involving cathode flares compelled cathode design changes to be made. We report on modifications made to the velvet cathode as well as on recent results using a CsI-coated, graphite-fiber cathode. The performance characteristics and relative merits of each cathode are presented.

The phenomenon of beam pulse shortening phenomenon associated with the RF electron gun is reported. The author believes that the beam loading effect plays an important role. The interaction between the electron beam and the deflecting mode is another important factor. >

Summary form only given. A 1-MV accelerator column composed of aperture lenses that focus and accelerate K/sup +/ ions from a hot-plate is being studied experimentally at Lawrence Berkeley Laboratory. The source must provide adequate current with a sufficiently low temperature so that the beam can be focused to the required small spot at the target. Time-independent codes provide design insight but fail to give any information about beam transients. HIF applications require careful control of the entire beam pulse. Continued refinement of the time-dependent code GYMNOS now allows detailed comparison with experiment and provides guidance for the evolution of the column design.