Abstract
We discuss $X$-band rf power production and deceleration in the two-beam test stand of the CLIC test facility at CERN. The rf power is extracted from an electron drive beam by a specially designed power extraction structure. In order to test the structures at high-power levels, part of the generated power is recirculated to an input port, thus allowing for increased deceleration and power levels within the structure. The degree of recirculation is controlled by a splitter and phase shifter. We present a model that describes the system and validate it with measurements over a wide range of parameters. Moreover, by correlating rf power measurements with the energy lost by the electron beam, as measured in a spectrometer placed after the power extraction structure, we are able to identify system parameters, including the form factor of the electron beam. The quality of the agreement between model and reality gives us confidence to extrapolate the results found in the present test facility towards the parameter regime of CLIC.
Highlights
The Compact Linear Collider, CLIC [1], is a candidate for a multi-TeV linear collider
Both points are addressed in the two-beam acceleration scheme for CLIC [2], where a moderate energy, but high-intensity electron beam excites electromagnetic fields inside so-called power extraction and transfer structures (PETS) which are transferred to acceleration structures where a second beam is accelerated to TeV energies
The experimental verification of the two-beam acceleration scheme is the central task of the two-beam test stand (TBTS) [3] in the CLIC Test Facility 3 (CTF3) [4] at CERN
Summary
The Compact Linear Collider, CLIC [1], is a candidate for a multi-TeV linear collider. In order to better understand the measurements of the rf power levels and the energy loss of the drive beam that can be measured in a spectrometer beam line, we have constructed a recirculation model that permits one to determine with high precision relevant parameters of the combined system of the beam and rf fields These include the power splitter and phase shifter settings, but more importantly the coupling of the beam to the fields inside the PETS, which depends strongly on the bunch length via the bunch form factor. We correlate rf power extraction with deceleration measurements by calculating the total pulse energy loss using two different methods
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