Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTMCI with Resonator Wakes
93
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Transverse mode-coupling instability (TMCI) with a high-frequency resonator wake is examined by the Nested Head-Tail Vlasov solver (NHT), where a Gaussian bunch in a parabolic potential (GP model) is represented by concentric rings in the longitudinal phase space. It is shown that multiple mode couplings and decouplings make impossible an unambiguous definition of the threshold, unless Landau damping is taken into account. To address this problem, instead of a single instability threshold, an interval of thresholds is suggested, bounded by the low and high intensity ones. For the broadband impedance model, the high intensity threshold is shown to follow Zotters scaling, but smaller by about a factor of two. The same scaling, this time smaller than Zotters by a factor of four, is found for the ABS model (Air Bag Square well).
rate research
Read More
Transverse mode-coupling instability (TMCI) is known to limit bunch intensity. Since space charge (SC) changes coherent spectra, it affects the TMCI threshold. Generally, there are only two types of TMCI with respect to SC: the vanishing type and the strong space charge (SSC) type. For the former, the threshold value of the wake tune shift is asymptotically proportional to the SC tune shift, as it was first observed twenty years ago by M. Blaskiewicz for exponential wakes. For the latter, the threshold value of the wake tune shift is asymptotically inversely proportional to the SC, as it was shown by one of the authors. In the presented studies of various wakes, potential wells, and bunch distributions, the second type of instability was always observed for cosine wakes; it was also seen for the sine wakes in the case of a bunch within a square potential well. The vanishing TMCI was observed for all other wakes and distributions we discuss in this paper: always for the negative wakes, and always, except the cosine wake, for parabolic potential wells. At the end of this paper, we consider high-frequency broadband wake, suggested as a model impedance for CERN SPS ring. As expected, TMCI is of the vanishing type in this case. Thus, SPS Q26 instability, observed at strong SC almost with the same bunch parameters as it would be observed without SC, cannot be TMCI.
We develop analytical models of the longitudinal and transverse wakes, on and off axis for realistic structures, and then compare them with numerical calculations, and generally find good agreement. These analytical first order formulas approximate the droop at the origin of the longitudinal wake and of the slope of the transverse wakes; they represent an improvement in accuracy over earlier, zeroth order formulas. In example calculations for the RadiaBeam/LCLS dechirper using typical parameters, we find a 16% droop in the energy chirp at the bunch tail compared to simpler calculations. With the beam moved to 200~$mu$m from one jaw in one dechiper section, one can achieve a 3~MV transverse kick differential over a 30~$mu$m length.
Numerical and experimental analysis of high power microwave generation in photonic BWO, which uses foil photonic crystal, is presented. Single frequency excitation of the below cutoff modes in the photonic BWO is analyzed and demonstrated.
Studies were made into the arise and an evolution of the beam breakup (BBU) instability in a rectangular dielectric resonator under excitation by a sequence of relativistic electron bunches. The dielectric resonator is a metal rectangular waveguide $R_{26}$ $(45mmtimes 90mm)$ with Teflon dielectric slabs $8.2mm$ thick (dielectric constant $varepsilon=2.051$) located along the wide side of the resonator. The wavelength of the $LM_{21}$ operating mode having a symmetric profile of the longitudinal electric field component is $53.2mm$. The electron energy of bunches is $4.5MeV$ , the charge of each bunch is $6.4nC$, the bunch repetition period is equal to twice the wavelength of the $LM_{21}$ mode. By the use of numerical PIC simulations, the charge losses of electron bunches on the dielectric plates were investigated as the bunches were displaced relative to the cavity axis. It is found that the charge losses on the dielectric slabs due to the BBU instability do not exceed $5%$. When the bunch repetition period is changed to a multiple of another eigenfrequency (e.g., the $LM_{11}$ mode), the charge losses of drive bunches do not change appreciably.
Current theories of the origin of the Universe, including string theory, predict the existence of a multiverse containing many bubble universes. These bubble universes will generically collide, and collisions with ours produce cosmic wakes that enter our Hubble volume, appear as unusually symmetric disks in the cosmic microwave background (CMB) and disturb large scale structure (LSS). There is preliminary observational evidence consistent with one or more of these disturbances on our sky. However, other sources can produce similar features in the CMB temperature map and so additional signals are needed to verify their extra-universal origin. Here we find, for the first time, the detailed three-dimensional shape and CMB temperature and polarization signals of the cosmic wake of a bubble collision in the early universe consistent with current observations. The predicted polarization pattern has distinctive features that when correlated with the corresponding temperature pattern are a unique and striking signal of a bubble collision. These features represent the first verifiable prediction of the multiverse paradigm and might be detected by current experiments such as Planck and future CMB polarization missions. A detection of a bubble collision would confirm the existence of the Multiverse, provide compelling evidence for the string theory landscape, and sharpen our picture of the Universe and its origins.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
