We have successfully designed, fabricated, installed, and tested a super compact X-band SLAC Energy Doubler system at SLAC. It is composed of an elegant 3 dB coupler-mode converter-polarizer coupled to a single spherical energy storage cavity with high Q 0 of 94000 and a diameter less than 12 cm. The available rf peak power of 50 MW can be compressed to a peak average power of more than 200 MW in order to double the kick for the electron bunches in a rf transverse deflector system and greatly improve the measurement resolution of both the electron bunches and the x-ray free-electron laser pulses. The design physics and fabrication as well as the measurement results will be presented in detail. High-power operation has demonstrated the excellent performance of this rf compression system without rf breakdown, sign of pulse heating, and rf radiation.
We consider the means to damp the wakefield left behind ultrarelativistic charges. In particular, we focus on a pair of traveling wave accelerators operating at an X-band frequency of 11.424 GHz. In order to maximize the efficiency of acceleration, in the context of a linear collider, multiple bunches of charged particles are accelerated within a given pulse of the electromagnetic field. The wakefield left behind successive bunches, if left unchecked, can seriously disturb the progress of trailing bunches and can lead to an appreciable dilution in the emittance of the beam. We report on a method to minimize the influence of the wakefield on trailing bunches. This method entails detuning the characteristic mode frequencies which make up the electromagnetic field, damping the wakefield, and interleaving the frequencies of adjacent accelerating structures. Theoretical predictions of the wakefield and modes, based on a circuit model, are compared with experimental measurements of the wakefield conducted within the ASSET facility at SLAC. Very good agreement is obtained between theory and experiment and this allows us to have some confidence in designing the damping of wakefields in a future linear collider consisting of several thousand of these accelerating structures.
The shape of an rf pulse is distorted due to dispersion encountered in acceleration through travelingwave linear accelerator structures. Simulations are made to ascertain the severity of this distortion in cavities designed to operate at various group velocities. The pulse suffers maximum degradation when propagated through accelerating cavities with a phase advance per cell in the vicinity of , where the group velocity reaches its minimum value. Several cavities are simulated to study the pulse distortion and compared with experiments performed on a high phase advance structure H60VG3, which has a phase advance of 5=6 per cell. A circuit model and a mode matching code are used to perform these simulations on accelerating structures consisting of multiple cells. Beam loading is taken into account and the implications on energy dispersion are also analyzed. Means of mitigating for this energy deviation are discussed.
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