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The Drift Tube (DT) accelerating structure is very well known, developed and widely used in existent proton linacs. Nevertheless, in the development of new projects all time arise the problem to estimate rf parameters of the structure for particular case given. This paper is the first report about activity in the creation of the data library for accelerating structures development. Basing on particularities of codes, which were developed early in INR (CPU time to calculate in 2D approximation one variant of the cell is several seconds with modern computer) and later were added with the shell to change automatically cell dimensions and tune to the frequency given, we store one time extremely large number of variants. The ranges of the cell dimensions overlap all known and another reasonably interesting variants of the DT structure application (both with focusing lenses inside drift tubes and without lenses). The main (cells dimensions, quality factor, shunt impedance, transit time factor) and additional results (the distribution of rf losses and so on) are stored in the file and provide the data base for further treatment. Using the data base obtained, we can with scaling and interpolation consider and compare, without additional calculations, rf parameters of the structure at different frequencies and with different limitations, finding either optimal or compromise solution for the structure. Introduction All times in design of the accelerating structure there is the problem to find reasonable compromise between different requirements. It may be internal problem in the structure design how to choose dimensions to have effective shunt impedanceZe as high as possible and to keep electrical field at the surfaceEsmax (usually in parts of the Kilpatric limit Ek) in reasonable limits. The increasing of an aperture radius is good for beam dynamic, but leads to the reduction in the Ze. The manufacturing processes will be simpler if a set of dimensions will be constant through the structure, but it means that will be deviation from optimal parameters. As a role, dependencies of parameters from dimensions qualitatively are known, but, if the problem arises to have a number (to estimate “the price” of the solution), the designer needs to do estimation or additional calculations. To simplify the design procedure for the DTL structure, this work has been performed. The Data Base Storage Several years ago the set of very powerful 2D codes [1] was developed in INR. With modern “middle power” computers, like DEC ALFA 2000, one run takes of order 3 ÷ 5 sec CPU time from mesh generation to physical postprosessing with high precision of results. Later, this set of codes was added with several simple codes to provide the system, which allows to perform automatically the set of similar calculations. The idea and realization of the data base are not so complicated. The cell of the accelerating structure may be specified with several independent parameters (for example length, aperture radius, gap ratio and so on) and one dependent to tune the cell for the operating frequency given f0. Two options of the DTL structure have been considered (Fig. 1). The first one is a conventional DTL with the possibility to place focusing lenses inside drift tubes. The second option has small drift tubes without lenses and is intended for high frequency DTL application Bridge Coupled DTL (BCDTL) [2]. Figure 1: The field distribution and drift tube shape for the conventional DTL option and for the BCDTL one. The cell of the DTL for both options is specified with six independent parameters and the cell radius Rc as dependent one. The limits of the independent parameters in normalized type (in parts of operating wavelength λ0) are listed in Table 1. Several steps with each parameters were done during the data base storage. As a role, the dependencies of the structure rf parameters vrs dimensions are smooth enough and not so many points are needed to approximate any curve using cubic spline interpolation. It is evident, that accuracy of this interpolation is better for larger number of points. But, if we have M independent parameters and are going to doN steps with each parameter, number of variants to be calculated isM . As the results of the compromise between accuracy of the interpolation and the total number of variants for calculations, from 4 to 7 steps for each parameter were chosen, depending on influence of the parameter given on the structure rf characteristics. Table 1 The ranges of the DTL cells dimensions. Conv. DTL BCDTL β 0.05÷ 0.57 0.05÷ 0.57 Aperture rad. a/λ0 0.0023÷ 0.0223 0.01÷ 0.09 Low. DT rad. r1/λ0 0.002÷ 0.01 0.002÷ 0.01 Upp. DT rad. r2/λ0 0.004÷ 0.04 0.0066÷ 0.036 DT radius rt/λ0 0.033÷ 0.067 DT angle φ 0.0◦ ÷ 30.0◦ Gap ratio to 0.5 to 0.5 It is not so difficult to develop algorithm for this work and to pass this long routine job to computer, for which it is directly intended. The system takes one variant, tunes it to frequency specified, stores results and goes to next variant automatically. The results of this job are M -dimensional arrays in direct access file. For every variant are stored: a) the cell dimensions, b) general parameters of the structure transit time factor T , quality factor Q, effective shunt impedance Ze, maximum electric field at the surface Esmax/(E0T ) ratio, maximum magnetic field at the surface Hsmax/(E0T ) ratio. The surface of the cell is divided in several segments. For each segment are stored: c) the relative part of rf losses (with respect to losses in total cell), d) frequency shift due to possible displacement of this segment, e) maximum electric field at the segment -Esimax/(E0T ) ratio. As the particularities of the DTL structure, frequency shift and additional rf losses in the stem together with additional rf losses in the end wall are calculated and stored. The Data Treatment and Applications The data base stored is the main value of the system. The procedure of the application is also simple. First of all, the designer should specify DTL option and the operating frequency. The data base will be extracted, scaled to the frequency specified and the available ranges of the cell dimensions will be displayed. There is a large variety of the data base applications for the DTL design. The simplest one is the comparison of different DTL variants. For this purpose the designer should specify the cells dimensions under interest. After each specification, using standard methods of the cubic spline interpolation, dimensions of data arrays will be reduced at 1. At the end of this procedure the values of rf parameters, corresponding to the cell dimensions specified, will be displayed. For example, at Fig. 2 and Fig. 3 the plots of Ze and E0T for different BCDTL operating frequencies, assuming a = 15 mm, r1 = 3 mm, r2 = 7.5 mm, φ = 0 are shown. If the dimensions of the drift tube are fixed, especially aperture radius, the increasing of the operating frequency do not leads to the increasing in shunt impedance. 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 0 50 100 150 200 E ffe ct iv e sh un t i m pe da nc e Z e, M O hm /m Proton energy, MeV 400 MHz

The Data Library for Accelerating Structures Development. RF Parameters of the Drift Tube Accelerating Structure