Design of the Compact Linear Collider main linac accelerating structure made from two halves

Milling on two longitudinally split halves is one method to manufacture accelerating structures. This method is simple and allows one to avoid electromagnetic fields at bonding joints, making it attractive in manufacturing high-gradient accelerating structures. An X-band structure design with strong wakefield damping based on this manufacturing approach is studied in this work as an alternative design for the Compact Linear Collider (CLIC) main linac accelerating structures. The geometry of the structure is optimized to greatly reduce the surface fields, improve the efficiency, and suppress the wakefield. This structure features the baseline design of the CLIC main linac with additional advantages. This study may serve as a reference for designing other high frequency-band corrugated structures.

Figure 1

Conventional way of manufacturing an accelerating structure.

Figure 2

Manufacturing accelerating structure by milling on two halves of copper plate (HFSS model [8]).

Figure 3

Wakefield suppression of CLIC-T24-Open: (a) philosophy; (b) time-domain wakefield potential (CLIC-G* is the baseline main linac accelerating structure design).

Figure 4

New open geometry structure with full damping scheme.

Figure 5

Suppression of the HOMs in two polarizations.

Figure 6

Geometric parameters of the single cell: (a) Cut view of YZ plane; (b) view of the disk in the XY plane. See Fig. 4 for the orientation of each view.

Figure 7

Magnetic field distribution vs wall profile.

Figure 8

$Sc$ vs wall profile.

Figure 9

Transverse wakefield of the proposed structure.

Figure 10

Dependence of wakefield ($Wx$) on $\mathrm{\Delta }b$.

Figure 11

Detuning the 23 GHz mode ($d$ is the iris thickness defined in Fig. 6): (a) Spectrum ($Wx$) of single cell; (b) spectrum ($Wx$) of the full structure.

Figure 12

Dependence of wakefield suppression on the iris matching step ($g_m$ in Fig. 6): (a) $Wx$; (b) $Wy$. The solid point represents the optimum choice.

Figure 13

Dependence of wakefield suppression ($Wy$) on the waveguide matching step ($w_m$ in Fig. 6); the solid point represents the optimum choice.

Figure 14

Geometry of the coupler cell and the full tapered structure. Only one half is shown.

Figure 15

Field distribution of structure cells (solid line: loaded $100\mathrm{MV}/\mathrm{m}$; dashed line: unloaded $100\mathrm{MV}/\mathrm{m}$).

Figure 16

Geometry of the HOM damping loads.

Figure 17

Wakefield simulation results of CLIC-HDS-A: (a) Enveloped wake in log scale; (b) wake in linear scale.

Figure 18

Phase of quadruple field component and accelerating component.

Figure 19

Off-axis distribution of transverse deflection strength [$\mathrm{MV}/\mathrm{m}$] to the beam: (a) $G_x$; (b) $G_y$.

Figure 20

Amplitude of quadruple components versus iris geometry.

Figure 21

Amplitude of quadruple components versus wall geometry.

Figure 22

Setup of rotating two consecutive structure units by 90 degrees.