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Register a new userPhase I results with the Large Angle Beamstrahlung Monitor (LABM) with SuperKEKB beams
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We report on the SuperKEKB Phase I operations of the Large Angle Beamstrhalung Monitor (LABM). The detector is described and its performance characterized using the synchrotron radiation backgrounds from the last Beam Line magnets. The backgrounds are also used to determine the expected position of the Interaction Point (IP), and the expected background rates during Phase II.
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First beam commissioning of SuperKEKB (Phase-1), which is an asymmetry double ring collider of 7-GeV electron and 4-GeV positron beams, which had started from February, has been successfully accomplished at the end of June 2016, and the desired beam current for Phase-1 was achieved in both rings. This paper summarize the operation results related to low level RF (LLRF) control issues during the Phase-1 commissioning, including the system tuning, the coupled bunch instability and the bunch gap transient effect. RF system of SuperKEKB consists of about thirty klystron stations in both rings. Newly developed LLRF control systems were applied to the nine stations among the thirty for Phase-1. The RF reference signal distribution system has been also upgraded for SuperKEKB. These new systems worked well without serious problem and they contributed to smooth progress of the commissioning. The old existing systems, which had been used in the KEKB operation, were still reused for the most stations, and they also worked as soundly as performed in the KEKB operation.
The relative center-of-mass energy spread at $e^+e^-$ colliders is about $10^{-3}$, which is much larger than the widths of narrow resonances produced in the s-channel in $e^+e^-$ collisions. This circumstance greatly lowers the resonance production rates of J/Psi, Upsilon(1S), Upsilon(2S), Upsilon(3S) and makes it extremely difficult to observe resonance production of the Higgs boson. Thus, a significant reduction of the center-of-mass energy spread would open up great opportunities in the search for new physics in rare decays of narrow resonances, the search for new narrow states with small $Gamma_{e^+e^-}$, the study of true muonium and tauonium, etc. The existing monochromatization scheme is only suitable for head-on collisions, while $e^+e^-$ colliders with crossing angles (the so-called Crab Waist collision scheme) can provide significantly higher luminosity due to reduced collision effects. In this paper, we propose a new monochromatization method for colliders with a large crossing angle. The contribution of the beam energy spread to the spread of the center-of-mass energy is canceled by introducing an appropriate energy-angle correlation at the interaction point; $sigma_W/W sim (3-5)10^{-6}$ appears possible. Limitations of the proposed method are also considered.
This paper presents one of the case studies of the Gamma Factory initiative -- a proposal of a new operation scheme of ion beams in the CERN accelerator complex. Its goal is to extend the scope and precision of the LHC-based research by complementing the proton-proton collision programme with the high-luminosity nucleus-nucleus one. Its numerous physics highlights include studies of the exclusive Higgs-boson production in photon-photon collisions and precision measurements of the electroweak (EW) parameters. There are two principal ways to increase the LHC luminosity which do not require an upgrade of the CERN injectors: (1) modification of the beam-collision optics and (2) reduction of the transverse emittance of the colliding beams. The former scheme is employed by the ongoing high-luminosity (HL-LHC) project. The latter one, applicable only to ion beams, is proposed in this paper. It is based on laser cooling of bunches of partially stripped ions at the SPS flat-top energy. For isoscalar calcium beams, which fulfil the present beam-operation constrains and which are particularly attractive for the EW physics, the transverse beam emittance can be reduced by a factor of $5$ within the $8$ seconds long cooling phase. The predicted nucleon-nucleon luminosity of $L_{NN}= 4.2 times 10^{34},$s$^{-1}$cm$^{-2}$ for collisions of the cooled calcium beams at the LHC top energy is comparable to the levelled luminosity for the HL-LHC proton-proton collisions, but with reduced pile-up background. The scheme proposed in this paper, if confirmed by the future Gamma Factory proof-of-principle experiment, could be implemented at CERN with minor infrastructure investments.
The readout electronics for the resonant beam position monitors (BPMs) in the Fermilab Switchyard (SY) have been upgraded, utilizing a low noise amplifier transition board and Fermilab designed digitizer boards. The stripline BPMs are estimated to have an average signal output of between -110 dBm and -80 dBm, with an estimated peak output of -70 dBm. The external resonant circuit is tuned to the SY machine frequency of 53.10348 MHz. Both the digitizer and transition boards have variable gain in order to accommodate the large dynamic range and irregularity of the resonant extraction spill. These BPMs will aid in auto-tuning of the SY beamline as well as enabling operators to monitor beam position through the spill.
The radiation reaction (beamstrahlung) effect on particle dynamics during interaction of oppositely charged beams is studied. It is shown that the beam focusing can be strongly enhanced due to beamstrahlung. An approximate analytical solution of the motion equation including the radiation reaction force is derived. The disruption parameter is calculated for classical and quantum regime of beamstrahlung. The analytical model is verified by QED-PIC simulations. The model for head-on collision of long beams undergoing a number of betatron oscillation during interaction is also developed. It is demonstrated that the beamstrahlung-enhanced disruption effect can play a significant role in future lepton colliders with high-current particle beams.
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