Abstract
Shortening the pulse length of input power is a possible approach to raise the accelerating gradient limit of normal conducting structures. We present a novel design of a parallel-coupled structure that operates at ultrashort input power pulses. The principle of the design is to shorten the filling time of the whole structure by feeding the cells individually so that the duration of power transmission between cells can be saved. An X-band (11.994 GHz) parallel-coupled structure design with a 10 ns pulse length is presented in this work. Previous high-power tests of X-band structure prototypes show that a gradient of $120\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ could be achieved for a 200 ns pulse length. Based on the law requiring that ${E}^{30}{t}^{5}=\text{constant}$, this 10-ns-structure design should be able to reach a gradient of $200\text{ }\text{ }\mathrm{MV}/\mathrm{m}$. A detailed circuit model and real-time electromagnetic field simulation methods for designing the parallel-coupling structure are also presented and discussed in this paper.
Highlights
High-gradient normal conducting structures have been studied for several decades as promising candidates for linear accelerator projects such as the compact linear collider (CLIC) and free-electron lasers [1,2,3,4,5,6,7]
Where E is the accelerating gradient and t is the input pulse length. This equation indicates that a higher accelerating gradient may be achievable with a shorter pulse length
The estimated parameters of this modified CLIC-T24 design as well as of the nominal design are shown in Table I, which seem less attractive for practical use
Summary
High-gradient normal conducting structures have been studied for several decades as promising candidates for linear accelerator projects such as the compact linear collider (CLIC) and free-electron lasers [1,2,3,4,5,6,7]. The estimated parameters of this modified CLIC-T24 design as well as of the nominal design are shown, which seem less attractive for practical use Another approach to shortening the filling time is to reduce the number of cells per input coupler. Since the power coupling between neighboring cells is avoided, the parallel structure can prevent severe rf breakdowns near the beam aperture and has more design space to improve the performance in terms of, e.g., the shunt impedance [29]. This work studies a conceptual parallel-coupled highgradient structure for ultrashort input power pulses. Significant advantages are presented for the parallel-coupled structure operating at ultrashort pulses, and the search for a high gradient is shown to be promising. The reflection coefficient s00 could be calculated from b0=a0 and the coefficients of power division s0n are equal to cn=a0, as shown in Eq (8) below
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