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Stochastic cooling of high-energy bunched beams
Abstract
Stochastic cooling of 100 GeV/nucleon bunched beams has been achieved in the Relativistic Heavy Ion Collider (RHIC). The physics and technology of the longitudinal cooling system are discussed, and plans for a transverse cooling system are outlined.
... Emittance growth from IBS at injection might be mitigated by implementing a stochastic cooling system [17] but such a project will require study and a lead time for development of hardware. A sufficiently powerful system might even improve integrated luminosity at collision energy as has been done so successfully at RHIC. ...
The 2011 lead-lead run of the LHC not only exceeded all expectations for luminosity but also yielded very valuable information on future performance limits. An additional highlight was the partial demonstration of the feasibility of proton-lead collisions, the first upgrade of the LHC. Although uncertainties still remain, this operating mode has been adopted for the 2012 heavy ion run. The implications of running at special energies choice of bunch spacing and filling scheme are discussed. An outline of the future heavy-ion programme up to 2022 (between LS1 and LS3) is given.
... Given our experience with stochastic cooling in both transverse and longitudinal planes from previous runs, components were redesigned and repaired to improve reliability as well as allow for simultaneous operation of all planes in both rings [4]. A horizontal system was not in place for this run, but the vertical system accomplishes cooling in both transverse planes via coupling. ...
Following the Fiscal Year (FY) 2010 (Run-10) Relativistic Heavy Ion Collider (RHIC) Au+Au run, RHIC experiment upgrades sought to improve detector capabilities. In turn, accelerator improvements were made to improve the luminosity available to the experiments for this run (Run-11). These improvements included: a redesign of the stochastic cooling systems for improved reliability; a relocation of 'common' RF cavities to alleviate intensity limits due to beam loading; and an improved usage of feedback systems to control orbit, tune and coupling during energy ramps as well as while colliding at top energy. We present an overview of changes to the Collider and review the performance of the collider with respect to instantaneous and integrated luminosity goals. At the conclusion of the FY 2011 polarized proton run, preparations for heavy ion run proceeded on April 18, with Au+Au collisions continuing through June 28. Our standard operations at 100 GeV/nucleon beam energy was bracketed by two shorter periods of collisions at lower energies (9.8 and 13.5 GeV/nucleon), continuing a previously established program of low and medium energy runs. Table 1 summarizes our history of heavy ion operations at RHIC.
... This filter has the transfer function , where is the revolution period, is the pickup to kicker delay, and is the difference between the drive frequency and the nearest revolution line. With the 2/3 of a turn delay of the fiber optic link and the one-turn filter, the cooling force has the correct sign for kHz [2]. For gold beam with = 107 and 4 MV on the RF storage cavities at h = 2520 the ___________________________________________ *Work performed by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. ...
A new microwave link has been developed for the longitudinal stochastic cooling system, replacing the fiberoptic link used for the transmission of the beam signal from the pickup to the kicker. This new link reduces the pickup to kicker delay from 2/3 of a turn to 1/6 of a turn, which greatly improves the phase margin of the system and allows operation at higher frequencies. The microwave link also introduces phase modulation on the transmitted signal due to variations in the local oscillators and time of flight. A phase locked loop tracks a pilot tone generated at a frequency outside the bandwidth of the cooling system. Information from the PLL is used to calculate real-time corrections to the cooling system at a 10 kHz rate. The design of the pilot tone system is discussed and results from commissioning are described.
The Relativistic Heavy Ion Collider (RHIC) is designed to provide luminosity over a wide range of beam energies and species, including heavy ions, polarized protons, and asymmetric beam collisions. In the first seven years of operation there has been a rapid increase in the achieved peak and average luminosity, substantially exceeding design values. Work is presently underway to achieve the enhanced design parameters. Planned major upgrades include the Electron Beam Ion Source (EBIS), RHIC-II, and construction of an electron-ion collider (eRHIC). We review the expected RHIC upgrade performance. Electron cooling and its impact on the luminosity both for heavy ions and protons are discussed in detail.
After the last successful RHIC Au-Au run in 2004 (Run-4), RHIC experiments now require significantly enhanced luminosity to study very rare events in heavy ion collisions. RHIC has demonstrated its capability to operate routinely above its design average luminosity per store of 2times10<sup>26</sup> cm<sup>-2</sup> s<sup>-1</sup>. In Run-4 we already achieved 2.5 times the design luminosity in RHIC. This luminosity was achieved with only 40% of the total possible number of bunches filled, and with beta* = 1 m. However, the goal is to reach 4 times the design luminosity, an average of 8times10<sup>26</sup> cm<sup>-2</sup> s<sup>-1</sup>, by reducing the beta* value and increasing the number of bunches to the accelerator maximum of 111. In addition, the average time at store was expected to be increased by a factor of 1.1 to about 60% of calendar time. We present an overview of the changes that increased the instantaneous luminosity, luminosity lifetime and integrated luminosity of RHIC Au-Au operations during Run-7 even though the goal of 60% time at store could not be reached.
Three-dimensional stochastic cooling of 100 GeV/nucleon gold beams has been achieved in the Relativistic Heavy Ion Collider (RHIC). We discuss the physics and technology of the cooling systems and present results with a beam. A factor of 2 increase in luminosity was achieved and another factor of 2 is expected.
It is generally accepted that longitudinal stochastic cooling of bunched beams is not possible without a synchrotron frequency spread. Experiments in the Fermilab Recycler storage ring demonstrate the opposite: with an antiproton bunch in a parabolic potential well (no synchrotron frequency spread), the cooling was almost as efficient as in a trapezoidal potential well (with a relative synchrotron frequency spread of ˜100%). A possible explanation is that, at Recycler parameters, diffusion processes are sufficient to provide particle mixing.
The longitudinal equilibrium distribution of electrons stored in a ring is computed in the general case of a nonlinear accelerating
field. From this is derived an equation which gives the exact longitudinal density in the presence of longitudinal fields
generated by the circulating particles. A method for solving numerically this equation is given and the exact solution is
compared to the lowest-approximation solution when self-fields are proportional to the derivative of the bunch density.
Si calcola la distribuzione di equilibrio longitudinale degli elettroni immagazzinati in un anello nel caso generale di un
campo accelerators non lineare. Da ciò si deduce un’equazione che dà l’esatta densità longitudinale in presenza di campi longitudinali
generati dalle particelle circolanti. Si espone un metodo per risolvere numericamente questa equazione e si confronta la soluzione
esatta con la soluzione di minima approssimazione quando gli autocampi sono proporzionali alla derivata della densità del
pacchetto.
В общем случае нелине йного ускоряющего поля вычисляется про дольное равновесное распределение элект ронов, накопленных в
к ольце. И распределение элект ронов, накопленных в к ольце. Из этого выводи тся уравнение, которо е дает точную продоль ную
плотность при нал ичии продольны этого выводится урав нение, которое дает то чную продольную плот ность при наличии про дольных
полей, образо ванных вращающимися частицами. Приводитс я метод для численног о решения этого уравн продольную плотност ь при
наличии продоль ных полей, образованн ых вращающимися част ицами. Приводится мет од для численного реш ения этого уравнения.
Точное решение сравн ивается с приближенн ым решением, когда соб ственные поля пропор циональны образованных вращаю щимися
частицами. При водится метод для чис ленного решения этог о уравнения. Точное ре шение сравнивается с приближенным решени
ем, когда собственные поля пропорциональн ы производной от плот ности сгустка. метод для численного решения этого уравне ния.
Точное решение ср авнивается с приближ енным решением, когда собственные поля про порциональны произв одной от плотности сг
устка. решение сравниваетс я с приближенным реше нием, когда собственн ые поля пропорционал ьны производной от пл отности
сгустка. собственные поля про порциональны произв одной от плотности сг устка. плотности сгустка.
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