Optimal cells for TESLA accelerating structure

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

Geng

Kirchgessner

et al.

Self Cite

The accelerating gradient performance of superconducting niobium cavities is rapidly progressing as a result of reduced field emission due to improvement in surface preparation techniques. Beyond the field emission limitation, there exists a fundamental limit imposed by the critical magnetic field of niobium. One way to tackle this limit is to reduce the ratio of the peak magnetic field to the accelerating gradient so that a higher accelerating gradient is possible while the cavity is still superconducting. New cavity shapes of reentrant type have been proposed and optimized [1]. A single cell 1300MHz cavity of this new class of shapes has been fabricated. Because of the reentrant geometry, the fabrication and surface cleaning of the cavity becomes challenging. In this paper, we present some calculation prerequisites and the fabrication and preparation results for this new cavity.

“…Between other approaches we examined [1], one was done with use of two elliptic arcs. The problem of a cavity electric strength led to the iris edge in a shape of an ellipse long ago [4].…”

Section: The Code and Geometry For Calculationsmentioning

confidence: 99%

“…One way to tackle this limit is to reduce the ratio of the peak magnetic field to the accelerating gradient so that a higher accelerating gradient is possible while the cavity is still superconducting. New cavity shapes of reentrant type have been proposed and optimized [1]. A single cell 1300MHz cavity of this new class of shapes has been fabricated.…”

mentioning

confidence: 99%

An optimized shape cavity for TESLA: concept and fabrication

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

Geng

Kirchgessner

et al.

Self Cite

“…One of results of this evolution is the reentrant elliptic cavity that has now a record achieved acceleration rate [3,4]. The relationship between the parameters of these arcs is a subject of cavity optimization in search of the best consistency between maxima of the surface electric and magnetic fields that defines the maximal acceleration achievable in the cavity.…”

Section: Introductionmentioning

confidence: 99%

“…If no limitations are used for the wall slope angle α, we will come to the reentrant shape having the minimal H pk =E acc from all possible for given E pk =E acc and R a [3]. It is worthy to note that H pk =E acc is a monotone function of any of these three parameters: it decreases for smaller α and R a , and for bigger E pk =E acc .…”

Section: Introductionmentioning

confidence: 99%

Analytical relationships between elliptic accelerating cavity shape and fields

Phys. Rev. ST Accel. Beams

Hoffstaetter

2014

Here we describe some relationships between cavity shape and fields on and near its surface that can be used for better understanding of the surface field properties. The problem of accelerating cavity optimization lies in the search of the shape with minimal peak magnetic or electric field for a given acceleration rate. This problem became especially important due to widespread use of superconducting cavities where the maximal magnetic field appeared to have a hard limit. The peak magnetic field can be lowered if one can increase the peak electric field but the electric field is also limited because of field emission. The problem of minimal losses in a cavity is very close to the problem of minimal peak magnetic field, though it is not the same, it relates to the lowest average field for a given acceleration rate. The field configuration on the cavity surface is also responsible for the phenomenon of multipactor. Cavities with these properties-minimal peak fields, minimal losses, and absence of multipactor-are found within the set of elliptic cavities. Further improvement of these properties is possible if we step out of the limits of elliptic shapes.

“…For example, let us consider the trajectory obtained in multipacting calculations for a cavity [1], Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

Multipactor in crossed rf fields on the cavity equator

Phys. Rev. ST Accel. Beams

2013

Multipactor discharge in an accelerating superconducting elliptic cavity occurs usually near its equator. As simulations show, the dimensions of the trajectories of multipacting electrons are very small compared to the dimensions of a cavity. This feature gives a way for solving explicit equations of motion instead of cumbersome simulations. Electric and magnetic fields near the cavity equator are presented in a form of expansions up to the third power of coordinates. Comparisons with numerical calculations of fields made with the SLANS code for the TESLA cavity cells, as well as with the analytical solution for a spherical cavity, are done. These fields are used for solving the equations of motion of electrons in crossed rf fields near the equator. Based on the analysis of these equations, general features of multipacting in this area are obtained. Results are compared with simulations and experimental data. The experimental formulas for multipacting zones are explained and their dependence on the cavity geometries is shown. Because of small sizes of electron trajectories, the influence of the weld seams is taken into account. This suggests a possible explanation of multipacting in a cavity which was not found by simulations. The developed approach allows evaluation of multipacting in a cavity without its simulations but after an analysis of fields in the equatorial region. These fields can be computed by any code used for cavity calculation.