Equivalent circuit for postcoupler stabilization in a drift tube linac

Abstract

Postcouplers (PCs) are devices used in order to reduce the effect of perturbations on the operating mode of a drift tube linac (DTL), using the resonant coupling stabilization method. In this article an equivalent circuit for a DTL equipped with PCs is presented, together with a 3D simulation analysis, which can explain the principle of postcoupler stabilization and define a new tuning strategy for DTL cavities. The PC tuning procedure based on the equivalent circuit and on frequency measurements has been tested and validated with measurements on the Linac4 DTL aluminum model, present at CERN.

Straightforward and accurate technique for post-coupler stabilization in drift tube linac structures

“…It is shown that zero admittance leads to a stabilized field distribution. The same stabilization point is found in [16] by a transport matrix notation. There the numerical model is fitted to modal measurements by adjusting the post-coupler parameters.…”

“…In order to better understand the cavity behavior, equivalent-circuit models have been derived and its parameters extracted [5,[13][14][15][16]. Two resonance conditions are discussed in [5] with zero and infinite coupling admittance that will be rediscussed in this paper.…”

“…In the present article, a new straightforward and accurate technique to find optimum post-coupler lengths is discussed. It is based on a combination of results of earlier publications in that it (a) analyzes tilt-sensitivity slope [2,10], (b) using an equivalent-circuit model [13,16], and (c) focusing on the conditions of resonance on the postcoupler [5,16]. The extraction of the optimum point (d) uses the resonance investigated in [11] however (e) for each post-coupler individually [6].…”

rf measurements and tuning of the 750 MHz radio frequency quadrupole

“…In order to perform the field tuning a relation needs to be made between the desired and measured fields of the cavity and the dimensions of the tuners. In general many tuner algorithms for accelerator cavities are based on equivalent circuit models [5][6][7]. This is also the case for RFQs, where the measurable field errors, usually obtained using the standard bead-pulling technique, are described as elements of the circuit [8][9][10].…”

Analyzing the effects of post couplers in DTL tuning by the equivalent circuit model

“…References [7][8][9] propose an equivalent circuit model for the DTL with the symmetrical PCs, further, this article improves the model so that field distribution and stabilization with asymmetrical PCs will be analyzed and the rate of the tilting field can be estimated. 2 The equivalent circuit for general periodic structure Figure 2, which is composed of equivalent parallel admittance Y n and series impedance Z n .…”