The vacuum system of KEKB
21 Feb 2003-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment (North-Holland)-Vol. 499, Iss: 1, pp 66-74
TL;DR: In this paper, two rings with a circumference of 3016 m, mainly made of copper, were constructed for the KEK B-factory, and the design of pump layout was aimed to realize 100 l s −1 m −1.
Abstract: For the KEK B-factory, two rings with a circumference of 3016 m , mainly made of copper, were constructed. A gap between the flanges is filled using Helicoflex as a vacuum seal. The contact force of an RF finger in a bellows is assured by using a spring finger. Pumping slots are backed by crossing bars to prevent the penetration of beam-induced fields. To obtain a pressure of 10 −9 Torr with the beam when the photo-desorption coefficient reaches 10−6, the design of pump layout is aimed to realize 100 l s −1 m −1 . NEG strips are used as the main pump. Chemical polishing is applied to clean the extruded surface of a copper chamber. Almost all chambers were baked before installation. Only ion pumps were baked in situ. The photo-desorption coefficient at the start of commissioning was slightly higher than expected, but a decrease of the coefficient is as expected on the whole. At high currents, some bellows were found to be warmed by the TE mode of beam induced fields. The effect of the electron cloud became evident, especially in the LER. Direct damage by the beam is seen at the surface of the movable mask.
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KEK1
15 Jan 2006-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the secondary electron and photoelectron yields of a TiN coating were studied with an intense positron beam at the KEK B-Factory (KEKB), following up their previous study on a NEG (Ti-Zr-V) coating.
Abstract: In order to investigate a way to suppress the electron-cloud instability (ECI), the secondary electron and photoelectron yields (SEY and PEY) of a TiN coating were studied with an intense positron beam at the KEK B-Factory (KEKB), following up our previous study on a NEG (Ti–Zr–V) coating. A TiN-coated chamber was installed at an arc section of the KEKB positron ring, where photons with a line density of 6.5×1014 photons m−1 s−1 mA−1 were directly irradiated. The number of electrons around the positron bunches was measured by a special electron-current monitor, up to a stored beam current of about 1700 mA (1284 bunches). The electron current of the TiN-coated chamber was clearly smaller than those of the NEG-coated and the non-coated copper chambers by a factor of 2 for all beam currents. Using the previous results of the NEG-coated and the non-coated copper chambers as well as the TiN-coated one here, the maximum SEY (δmax) and the PEY (ηe) of the TiN coating, the NEG coating and the copper were again estimated based on a simulation. The evaluated δmax values for these three surfaces were 0.8–1.0, 0.9–1.1 and 1.1–1.3, and the ηe values were 0.13–0.15, 0.22–0.27 and 0.28–0.31, respectively. It was found that the TiN coating had an SEY (δmax∼0.9) as low as the NEG coating (δmax∼1.0), but the electron current was clearly smaller than that of the NEG coating, due to its lower photoelectron yield (ηe∼0.14). This study again indicated that the suppression of photoelectrons is required to make effective use of a surface with a low SEY, such as a TiN or a NEG coating. As an application of the simulation code, the electron current of a beam duct with an antechamber was calculated for the case of a NEG coating or a TiN coating ( δ max = 0.9 – 1.0 ). The calculated electron current for a copper duct with an antechamber was about 1/4 of that of a simple circular copper duct ( δ max = 1.2 for both cases) at a high current (∼1700 mA, 1284 bunches), which was in good agreement with the measurement. By combining with a surface with a low SEY ( δ max = 1.0 – 0.9 ), that is, a TiN coating or a NEG coating, a further reduction of the electron current by a factor of about 2 was obtained.
43 citations
01 Dec 2005-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a beam duct coated with NEG materials (Ti, Zr, V) was studied for the first time under intense photon irradiation using a positron beam at the KEK B-Factory (KEKB) to investigate a way to suppress the electron cloud instability.
Abstract: A beam duct coated with NEG materials (Ti, Zr, V), which had been known to have a low secondary electron yield (SEY), was studied for the first time under intense photon irradiation using a positron beam at the KEK B-Factory (KEKB) to investigate a way to suppress the electron cloud instability (ECI). A 2.56 m test copper chamber was coated with the NEG materials (we call it NEG coating here) by magnetron sputtering. It was installed at an arc section of the KEKB positron ring, where the chamber was irradiated by direct photons with a line density of 6.5×10 14 photons m −1 s −1 mA −1 . The vacuum pressure around the test chamber during a usual beam operation was lower than the case of non-coated copper chambers by a factor of 4–5. The number of electrons around positron bunches was measured by a special electron monitor up to a stored beam current of 1600 mA. The measured electron current, however, was almost the same as a non-coated copper chamber, especially at low-beam currents, and the effect of the NEG coating was smaller than expected. A simulation explained the result that abundant photoelectrons in the positron ring reduce the effect of the low SEY. The maximum SEYs of the NEG coating and non-coated copper were evaluated using a simulation as about 0.9–1.0 and 1.1–1.3, respectively, which were consistent with the values after a sufficient electron bombardment. Their photoelectron yields were also estimated as 0.22–0.28 and 0.26–0.34, respectively, and were in good agreement with the previous experimental results. The study indicates that the suppression of photoelectrons, by a beam duct with an antechamber, for example, is indispensable to make effective use of a surface with a low SEY, such as the NEG coating.
32 citations
11 Feb 2005-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a beam duct with an antechamber scheme for high-current accelerators was designed and the test chambers were studied experimentally, which showed a good static vacuum property, i.e., gas desorption rates with less than 3.5 × 10 - 9 Pa m 3 s - 1 m - 2 after baking.
Abstract: A beam duct with an antechamber scheme for high-current accelerators was designed and the test chambers were studied experimentally. The duct consists of two channels, i.e., a beam channel where a beam circulates and a Synchrotron Radiation (SR) channel (antechamber) aside where the SR passes through. By using the antechamber scheme, the maximum power density of SR can be diluted at the side wall. The impedance is small owing to the pumping ports not being at the beam channel, but at the SR channel. Photoelectrons inside the beam channel are also expected to be reduced, which would be a big merit for a positron ring to suppress the electron cloud effect since the photoelectron is a major source of electrons composing the cloud. Two copper test chambers were manufactured with different methods, by pressing and by drawing. These chambers showed a good static vacuum property, i.e., gas desorption rates with less than 3.5 × 10 - 9 Pa m 3 s - 1 m - 2 after baking. After the installation to the positron ring of the KEK B-factory (KEKB), electron numbers in the beam channel, temperatures and pressures were measured during beam operation. The electrons in the beam channel were found to be reduced by a factor of 4 at 1.5 A compared to the case of the usual circular chamber. The reduction, however, was much larger, about 1/300, at a beam current of about 20 mA where the photoelectrons were dominant and the multiplication of electrons by the multipactoring was small. The temperatures were almost in agreement with the expectation. Vacuum scrubbing by photons proceeded almost smoothly, although pressure bursts were sometimes observed, especially for one test chamber, which was possibly due to discharges at the transverse joints in the beam chamber. Various instructive information had been obtained for future practical beam ducts for high-intensity accelerators.
24 citations
KEK1
11 Nov 2003-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The KEK B-factory (KEKB), an electron-positron collider serving an unprecedented high luminosity, has a movable mask (or collimator) system to reduce the background noise of BELLE detector coming from spent particles as mentioned in this paper.
Abstract: The KEK B-factory (KEKB), an electron–positron collider serving an unprecedented high luminosity, has a movable mask (or collimator) system to reduce the background noise of BELLE detector coming from spent particles. The movable masks have been developed employing RF technologies in dealing with intense higher order modes (HOM) resulted from high beam currents. The mask system is now working as expected at the stored beam current up to 1 A. The design and performance of the latest movable mask system for the KEKB are presented.
19 citations
KEK1
11 Aug 2007-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the effect of the SEY spectrum on the estimation of δmax values is briefly discussed, as well as the application of the simulation, the effective η e, ηe−eff (which included the geometrical effect of antechamber) and δ max values were also estimated for copper chambers with one or two antechambers.
Abstract: In order to obtain a method to suppress electron-cloud instability (ECI), the photoelectron and the secondary electron yields (PEY and SEY) of a TiN coating and an NEG (Ti–Zr–V) coating on copper have been studied so far by using the KEK B-factory (KEKB) positron ring. Recently, test chambers with these coatings were installed at a straight section of the ring where the irradiated photon density was considerably smaller than that at the arc section of a previous experiment. The number of electrons around beams was measured by an electron current monitor; this measurement was performed up to a stored beam current of approximately 1700 mA (1389 bunches). For the entire range of the beam current, the electron currents of the NEG-coated and the TiN-coated chambers were clearly smaller as compared to those of the uncoated copper chamber by the factors of 2–3 and 3–4, respectively. The small photon density, that is, the weak effect of photoelectrons, elucidated the differences in the SEYs of these coatings when compared to the measurements at the arc section. By assuming almost the same PEY (ηe) values obtained in the previous study, the maximum SEY (δmax) for the TiN and NEG coatings and the copper chamber was again estimated based on a previously developed simulation. The evaluated δmax values for these three surfaces were in the ranges of 0.8–1.0, 1.0–1.15, and 1.1–1.25, respectively. These values were consistent with the values obtained so far. As an application of the simulation, the effective ηe, ηe−eff (which included the geometrical effect of the antechamber) and δmax values were also estimated for copper chambers with one or two antechambers. These chambers were installed in an arc section and a wiggler section, respectively. The evaluated ηe−eff and δmax values were approximately 0.008 and 1.2, and 0.04 and 1.2, respectively, where ηe=0.28 was assumed on the side wall. As expected, the ηe−eff values were considerably smaller than those obtained in the case of a simple circular chamber (ηe=0.28–0.3). Further, the δmax values were consistent with those obtained so far. With regard to the uncertainty in the simulation, the effect of the SEY spectrum on the estimation of δmax values is briefly discussed. As the next step in our study, we plan to combine beam ducts with antechambers and TiN coatings; this combination is the most promising solution to ECI at present.
16 citations
References
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Book•
01 Oct 1993
TL;DR: In this paper, the Hamiltonian Resonance Theory and Hamiltonian Nonlinear Beam Dynamics (HNDD) are used to model the dynamics of coupled motion in a single particle.
Abstract: Tools We Need.- Of Fields and Forces.- Particle Dynamics in Electromagnetic Fields.- Electromagnetic Fields.- Beam Dynamics.- Single Particle Dynamics.- Particle Beams and Phase Space.- Longitudinal Beam Dynamics.- Periodic Focusing Systems.- Beam Parameters.- Particle Beam Parameters.- Vlasov and Fokker-Planck Equations.- Equilibrium Particle Distribution.- Beam Emittance and Lattice Design.- Perturbations.- Perturbations in Beam Dynamics.- Hamiltonian Resonance Theory.- Hamiltonian Nonlinear Beam Dynamics.- Acceleration.- Charged Particle Acceleration.- Beam-Cavity Interaction.- Coupled Motion.- Dynamics of Coupled Motion.- Intense Beams.- Statistical and Collective Effects.- Wake Fields and Instabilities.- Synchrotron Radiation.- Fundamental Processes.- Overview of Synchrotron Radiation.- Theory of Synchrotron Radiation.- Insertion Device Radiation.- Free Electron Lasers.
2,577 citations
TL;DR: In this article, a radio frequency (RF) shield was designed and developed for the KEK B factory (KEKB), which is the usual finger type but has a special spring finger to press contact fingers onto the beam tube.
Abstract: A bellows assembly with a radio frequency (rf) shield has been designed and developed for the KEK B factory (KEKB). The rf shield is the usual finger type but has a special spring finger to press contact fingers onto the beam tube. A test of the mechanical performance using a trial model shows good results. Further experimental studies are focused on the two key points of the finger‐type rf shield, that is, the contact force of fingers and the length of slits between adjacent fingers. First, to reduce the excess abrasion at contact points, the necessary contact force is studied experimentally utilizing microwaves. Abnormal heating is checked by transmitting a 508 MHz cw microwave through a trial model in a coaxial line. Arcing at the contact point in vacuum is observed by transmitting a 2856 MHz pulse microwave in a rectangular waveguide equipped with a model piece of the rf shield. A contact force of 50 g/finger is found to be necessary. Second, the optimum slit length is studied with a strategy to minimize the higher order mode (HOM) power leaked from the beam tube into the inside of the bellows while keeping a sufficient sliding stroke. The coupling coefficient, β, of the rf shield is measured experimentally from the Q value of a TE mode resonance in a cylindrical cavity connected to the bellows assembly. Using the measured dependence of β on the slit length, a rough estimation of leaked HOM power is tried for the KEKB. The expected leaked power is about 6–18 W for a slit length of 20 mm, which is in the allowable range. The results obtained through these experiments are reflected to the design for the KEKB: the contact force of 80–100 g/finger will be adopted finally considering the manufacturing error of typically ±10 g/finger in our test and leaving a margin for higher frequencies. The nominal slit length will be set to be 20 mm, keeping the expansion/contraction of ±10 mm.
25 citations
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TL;DR: In this article, two rings with a circumference of 3016m, mainly made of copper, were constructed at the KEK B-factory to store a positron beam with the energy at 3.5
22 citations
01 Jan 2001
15 citations
"The vacuum system of KEKB" refers background in this paper
...This is understood as electron multipactoring, [11]; their dependence on the bunch pattern is well explained by this model [12]....
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