Broadband electromagnetic characterization of a100  Ωtraveling-wave electrode by measuring scattering parameters

Abstract

The Single Bunch Selector (SBS) will be used on the Spiral2 linear accelerator to reduce the rate of high energy bunches reaching the target with, in principle, no residual particles from the suppressed bunches. For this purpose, a pulsed electromagnetic wave will travel along the 100 microstrip meander line electrode of the SBS. In this work we describe the broadband accurate characterization of the electrode electromagnetic features. The method applied here leads to the analytical determination of complex characteristic impedance, propagation constant, and group velocity from a measurement of the 50 scattering parameters on the meander transmission line. Particular care is given to the de-embedding phase of the transitions required to connect the meander electrode to the measurement device.

Proton beam commissioning of the SPIRAL2 Single Bunch Selector

“…The TW structure was preferred to capacitive electrodes driven by switching devices to grant the fast transient times required to select a single bunch, while the ceramic substrate could provide more acceptance to beam loss. The required voltages being much higher than those of CERN Linac4, a higher characteristic impedance (𝑍 𝑠 = 100 Ω) was chosen to minimize the pulser power, and specific R&D and prototyping was initiated to design the meander plate, to evacuate RF loss and to design the feedthroughs, as already reported in [6][7][8][9].…”

Fast chopper for single radio-frequency quadrupole bunch selection for neutron time-of-flight capabilities

“…Di Giacomo et al [10] report on the development of a single bunch selection to be used at the Spiral II [11] accelerator complex planned for the Neutrons for Science (NFS) facility [12]. This technique relies on very fast HV pulses rise and fall time, approximately 5 ns or less, with the goal of no residual particles from the suppressed bunches [13]. A similar technique has been discussed by Madrack and Wildman [14] for single bunch selection following the 2.5 MeV 325 MHz RFQ at Fermilab, which includes a pulse delaying microstrip structure for deflecting the beam, with high voltage (1.2 kV) and fast (ns rise time) pulsers.…”