73541758
PLS RF system operation during the commissioning
The storage ring of the Pohang Light Source (PLS) is designed to store 100s mA of 2 GeV electrons injected from the full energy linear accelerator. To compensate for the synchrotron radiation loss three RF cavities were installed in one of the straight sections powered by three 60 kW-TV transmitters independently. Phase and amplitude are controlled by the separate low level systems. During the commissioning, since the beam lifetime is limited by the vacuum pressure, various accelerating voltages were set to investigate the system characteristics. Even one cavity is enough to store 100 mA of beam, whereas the vacuum-limited lifetime is few minutes at 1 mTorr. The cavity HOM-induced multi-bunch instabilities were observed at certain condition and cured to some extent by shifting phase and water temperature. General description of RF system performance and trouble-shoots during the commissioning are presented.
56441588
RF noise driven dipole mode parametric resonance
In the Pohang Light Source (PLS) storage ring, we have occasionally experienced the abnormal spontaneous beam. lifetime reduction and strong longitudinal damping. Due to the abnormal beam lifetime reduction, available beam time is reduced substantially. From the recent data analysis of the PLS longitudinal feedback system (LFS) and the streak camera, we have found that the abnormal phenomena can be generated by the RF noise via the dipole mode parametric resonance of the RF phase modulation. We describe the observation of the dipole mode parametric resonance driven by the RF noise and compare it with a simulation result in the PLS storage ring.
26940755
Ultra-low noise single-photon detector based on Si avalanche photodiode.
We report operation and characterization of a lab-assembled single-photon detector based on commercial silicon avalanche photodiodes (PerkinElmer C30902SH, C30921SH). Dark count rate as low as 5 Hz was achieved by cooling the photodiodes down to -80 °C. While afterpulsing increased as the photodiode temperature was decreased, total afterpulse probability did not become significant due to detector's relatively long deadtime in a passively-quenched scheme. We measured photon detection efficiency >50% at 806 nm.
67819097
Fast beam-ion instability driven longitudinal damping
In the Pohang Light Source storage ring, we empty 68 buckets of total 468 buckets to cure the conventional ion trapping. However, the fast beam-ion instability is occasionally generated at higher beam current. Immediately after the strong vertical beam shaking due to the fast beam-ion instability, the longitudinal coupled bunch mode instabilities are substantially damped down without any active feedback system. We have described the fast beam-ion instability driven longitudinal damping and its mechanism in the Pohang Light Source storage ring.
54856298
Low frequency longitudinal relaxation oscillation
From the recent data analysis of the longitudinal feedback system and the streak camera, we have found a longitudinal relaxation beam oscillation whose frequency is a multiple of 36 Hz. When the relaxation oscillation is generated, horizontally oscillating wide beams are observed at the diagnostic beamline, and the beam lifetime is fluctuated. The strength of the longitudinal coupled bunch mode instabilities is also modulated sinusoidally. We have described the observed longitudinal relaxation oscillation in the Pohang Light Source storage ring.
122988282
A method of closed orbit correction under constraint conditions
We have developed the correction algorithm of the closed orbit distortion (COD) under the constraint condition where beam positions at particular points are not changed. The new algorithm is based on the modified PSINOM algorithm including the regularization process in order to avoid the inversion problem of the ill-posed response matrices. We have confirmed that the COD is well corrected with no orbit leak in the simulation and is in good agreement with the experiment.
13118121
Lorentz Boosts as Squeeze Transformations and Coherence Problems
The quark model and the parton model are known to be two different manifestations of the same covariant entity. However, the interaction amplitudes of partons are incoherent while they are coherent in the quark model. According to Feynman, this is due to the dilation of the interaction time among the quarks. We present a quantitative analysis of this time-dilation problem using Lorentz boosts as squeeze transformations.
43997367
New generation digital longitudinal feedback system for Duke FEL and HIγS facilities
To cure harmful longitudinal coupled-bunch mode beam instabilities during high-current and multi-bunch beam operations at the Duke free electron laser (FEL) and high intensity gamma-ray source (HIgammaS) facilities, we have been developing a new generation digital bunch-by-bunch longitudinal feedback (LFB) system which is based on an Integrated gigasample processor (iGp-64F). In this paper, we describe the new generation digital longitudinal feedback system for the Duke FEL and HIgammaS facilities.
18963275
Heavy quarkonium in a holographic QCD model
Encouraged by recent developments in AdS/QCD models for the light quark system, we study heavy quarkonium in the framework of the AdS/QCD models. We calculate the masses of cc vector meson states using the AdS/QCD models at zero and at finite temperature. Among the models adopted in this work, we find that the soft-wall model describes the low-lying heavy quark meson states at zero temperature relatively well. At finite temperature, we observe that once the bound state is above T{sub c}, its mass will increase with temperature until it dissociates at a temperature of around 494 MeV. It is shown that the dissociation temperature is fixed by the infrared cutoff of the models. The present model serves as a unified nonperturbative model to investigate the properties of bound quarkonium states above T{sub c}.
14420331
Harmonic Oscillators as Bridges between Theories: Einstein, Dirac, and Feynman
Other than scattering problems where perturbation theory is applicable, there are basically two ways to solve problems in physics. One is to reduce the problem to harmonic oscillators, and the other is to formulate the problem in terms of two-by-two matrices. If two oscillators are coupled, the problem combines both two-by-two matrices and harmonic oscillators. This method then becomes a powerful research tool to cover many different branches of physics. Indeed, the concept and methodology in one branch of physics can be translated into another through the common mathematical formalism. Coupled oscillators provide clear illustrative examples for some of the current issues in physics, including entanglement, decoherence, and Feynman's rest of the universe. In addition, it is noted that the present form of quantum mechanics is largely a physics of harmonic oscillators. Special relativity is the physics of the Lorentz group which can be represented by the group of by two-by-two matrices commonly called $SL(2,c)$. Thus the coupled harmonic oscillators can therefore play the role of combining quantum mechanics with special relativity. Both Paul A. M. Dirac and Richard P. Feynman were fond of harmonic oscillators, while they used different approaches to physical problems. Both were also keenly interested in making quantum mechanics compatible with special relativity. It is shown that the coupled harmonic oscillators can bridge these two different approaches to physics.
13722156
Enhancement of the ATLAS trigger system with a hardware tracker finder FTK
The existing three-level ATLAS trigger system is deployed to reduce the event rate from the bunch crossing rate of 40 MHz to ~ 200 Hz for permanent storage at the LHC design luminosity of 1034 cm−2 s−1. When the LHC exceeds the design luminosity, the load on the Level-2 trigger system will significantly increase due both to the need for more sophisticated algorithms to suppress background and the larger event sizes. The Fast Tracker is a proposed upgrade to the current ATLAS trigger system that will operate at the full Level-1 accepted rate of 100 kHz and provide high quality tracks at the beginning of processing in the Level-2 trigger, by performing track reconstruction in hardware with massive parallelism of associative memories. The concept design is being advanced and justified with the performance in important physics areas, b-tagging, τ-tagging and lepton isolation. The prototyping with current technology is underway and R&D with new technologies has been started.