Spectrometers for RF breakdown studies for CLIC Jacewicz, M.; Ziemann, V.; Ekelöf, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2016, Volume:
828
Journal Article
Peer reviewed
Open access
An e+e− collider of several TeV energy will be needed for the precision studies of any new physics discovered at the LHC collider at CERN. One promising candidate is CLIC, a linear collider which is ...based on a two-beam acceleration scheme that efficiently solves the problem of power distribution to the acceleration structures. The phenomenon that currently prevents achieving high accelerating gradients in high energy accelerators such as the CLIC is the electrical breakdown at very high electrical field. The ongoing experimental work within the CLIC collaboration is trying to benchmark the theoretical models focusing on the physics of vacuum breakdown which is responsible for the discharges. In order to validate the feasibility of accelerating structures and observe the characteristics of the vacuum discharges and their eroding effects on the structure two dedicated spectrometers are now commissioned at the high-power test-stands at CERN.
First, the so called Flashbox has opened up a possibility for non-invasive studies of the emitted breakdown currents during two-beam acceleration experiments. It gives a unique possibility to measure the energy of electrons and ions in combination with the arrival time spectra and to put that in context with accelerated beam, which is not possible at any of the other existing test-stands.
The second instrument, a spectrometer for detection of the dark and breakdown currents, is operated at one of the 12GHz stand-alone test-stands at CERN. Built for high repetition rate operation it can measure the spatial and energy distributions of the electrons emitted from the acceleration structure during a single RF pulse. Two new analysis tools: discharge impedance tracking and tomographic image reconstruction, applied to the data from the spectrometer make possible for the first time to obtain the location of the breakdown inside the structure both in the transversal and longitudinal direction thus giving a more complete picture of the vacuum breakdown phenomenon.
Understanding the effects of rf breakdown in high-gradient accelerator structures on the accelerated beam is an extremely relevant aspect in the development of the Compact Linear Collider (CLIC) and ...is one of the main issues addressed at the Two-beam Test Stand at the CLIC Test Facility 3 at CERN. During a rf breakdown high currents are generated causing parasitic magnetic fields that interact with the accelerated beam affecting its orbit. The beam energy is also affected because the power is partly reflected and partly absorbed thus reducing the available energy to accelerate the beam. We discuss here measurements of such effects observed on an electron beam accelerated in a CLIC prototype structure. Measurements of the trajectory of bunch trains on a nanosecond time scale showed fast changes in correspondence of breakdown that we compare with measurements of the relative beam spots on a scintillating screen. We identify different breakdown scenarios for which we offer an explanation based also on measurements of the power at the input and output ports of the accelerator structure. Finally we present the distribution of the magnitude of the observed changes in the beam position and we discuss its correlation with rf power and breakdown location in the accelerator structure.
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Status of the cylindrical-GEM project for the KLOE-2 inner tracker Balla, A.; Bencivenni, G.; Cerioni, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2011, Volume:
628, Issue:
1
Journal Article
Peer reviewed
Open access
The status of the R&D on the Cylindrical-GEM (CGEM) detector foreseen as inner tracker for KLOE-2, the upgrade of the KLOE experiment at the
DA
Φ
NE
φ
-factory
, is presented. The R&D includes ...several activities: (i) the construction and complete characterization of the full-size CGEM prototype, equipped with
650
μ
m
pitch 1-D longitudinal strips; (ii) the study of the 2-D readout with XV patterned strips and operation in magnetic field (up to 1.5
T), performed with small planar prototypes in a dedicated test at the H4-SPS beam facility; (iii) the characterization of the single-mask GEM technology for the realization of large-area GEM foils.
We present a precise measurement of the ratio RK=Γ(K→eν(γ))/Γ(K→μν(γ)) and a study of the radiative process K→eνγ, performed with the KLOE detector. The results are based on data collected at the ...Frascati e+e− collider DAΦNE for an integrated luminosity of 2.2 fb−1. We find RK=(2.493±0.025stat±0.019syst)×10−5, in agreement with the Standard Model expectation. This result is used to improve constraints on parameters of the Minimal Supersymmetric Standard Model with lepton flavor violation. We also measured the differential decay rate dΓ(K→eνγ)/dEγ for photon energies 10<Eγ< 250 MeV. Results are compared with predictions from theory.
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