126 research outputs found
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Measurements of the helium propagation at 4.4 K in a 480 m long stainless steel pipe
The Relativistic Heavy Ion Collider (RHIC), with two concentric rings 3.8 km in circumference, uses superconducting magnets to focus the high energy beams. Each sextant of RHIC will have continuous cryostats up to 480 m in length housing the magnets and the cold beam pipes. For an acceptable lifetime of the stored beam, the pressure in the cold beam pipe will be < 10{sup {minus}11} Torr. The characteristics of He pressure front propagation due to He leaks will be of importance for beam lifetimes and for vacuum monitoring due to the high vapor pressure of He at 4.4 K, even with small surface coverage. The travel of the He pressure fronts along a 480 m long, 6.9 cm I.D. stainless steel beam pipe cooled to 4.4 K has recently been measured during the RHIC first sextant test. The experiment was carried out over a 12-day period by bleeding in a calibrated He leak of 3 {times} 10{sup {minus}5} Torr{center_dot}l/s (20 C) while measuring the He pressures along this 480 m cold tube at {approximately} 30 m intervals. The measured speed of the pressure fronts and the pressure profiles are summarized and compared with the calculated ones
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Outgassing rate of the copper-plated beam tube for ISABELLE
The ultrahigh vacuum system of the intersecting storage accelerator, ISABELLE, will consist of two interlaced rings of stainless steel beam tubes with a circumference 2-1/2 miles each. To obtain a good heat conduction during bakeout and to reduce the resistive wall instability during beam operation, a lmm thick copper coating will be electroplated to the outer surface of this 1.5 mm thick beam tube. To minimize the beam loss due to beam-gas collision, the pressure inside the beam tube is required to be 1 x 10/sup -11/ Torr (N/sub 2/ equivalent) or less. To achieve this ultrahigh vacuum, the outgassing rate of the 304 LN stainless steel tubes has been reduced to approx. 1 x 10/sup -13/ Torr. l/cm/sup 2/. sec by vacuum firing at 950/sup 0/C for one hour. However, during acid-bath electroplating of copper, significant amount of hydrogen will be reintroduced and trapped in stainless steel which will substantially increase the outgassing rate (to approx. 2 x 10/sup -12/ Torr . l/cm/sup 2/ sec). The outgassing characteristics of these copper-plated beam tubes are studied and discussed within the scope of diffusion and energy of activation. Methods to reduce the outgassing rate to an acceptable level (approx. 1 x 10/sup -13/ Torr . l/cm/sup 2/ . sec) are also given
Low secondary electron yield engineered surface for electron cloud mitigation
Secondary electron yield (SEY or δ) limits the performance of a number of devices. Particularly, in high-energy charged particle accelerators, the beam-induced electron multipacting is one of the main sources of electron cloud (e-cloud) build up on the beam path; in radio frequency wave guides, the electron multipacting limits their lifetime and causes power loss; and in detectors, the secondary electrons define the signal background and reduce the sensitivity. The best solution would be a material with a low SEY coating and for many applications δ < 1 would be sufficient. We report on an alternative surface preparation to the ones that are currently advocated. Three commonly used materials in accelerator vacuum chambers (stainless steel, copper, and aluminium) were laser processed to create a highly regular surface topography. It is shown that this treatment reduces the SEY of the copper, aluminium, and stainless steel from δmax of 1.90, 2.55, and 2.25 to 1.12, 1.45, and 1.12, respectively. The δmax further reduced to 0.76-0.78 for all three treated metals after bombardment with 500 eV electrons to a dose between 3.5 × 10-3 and 2.0 × 10-2 C·mm-2
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Electron Cloud Observations and Cures in Rhic
Since 2001 RHIC has experienced electron cloud effects, which have limited the beam intensity. These include dynamic pressure rises - including pressure instabilities, tune shifts, a reduction of the stability threshold for bunches crossing the transition energy, and possibly incoherent emittance growth. We summarize the main observations in operation and dedicated experiments, as well as countermeasures including baking, NEG coated warm beam pipes, solenoids, bunch patterns, anti-grazing rings, pre-pumped cold beam pipes, scrubbing, and operation with long bunches
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AN OVERVIEW OF THE SNS ACCELERATOR MECHANICAL ENGINEERING.
The Spallation Neutron Source (SNS*) is an accelerator-based neutron source currently nearing completion at Oak Ridge National Laboratory. When completed in 2006, the SNS will provide a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron production. SNS is a collaborative effort between six U.S. Department of Energy national laboratories and offered a unique opportunity for the mechanical engineers to work with their peers from across the country. This paper presents an overview of the overall success of the collaboration concentrating on the accelerator ring mechanical engineering along with some discussion regarding the relative merits of such a collaborative approach. Also presented are a status of the mechanical engineering installation and a review of the associated installation costs
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Vacuum Chamber Design of NSLS-II Storage Ring
National Synchrotron Light Source II (NSLS II) will be a 3-GeV, 792-meter circumference, 3rd generation synchrotron radiation facility, with ultra low emittance and extremely high brightness. the storage ring has 30 Double-Bend-Achromatic (DBA) cells. in each cell, there are five magnets and chamber girders, and one straight section for insertion devices or Radio Frequency (RF) cavities or injection. Most vacuum chambers are made from extruded aluminum with two different cross sections: one fitted in the dipole magnets, and the other surrounded by multipole magnets. They discuss the layout of the DBA cells, the detailed design of the cell's vacuum chambers, the mounting of the Beam-Position-Monitor (BPM) buttons, discrete absorbers, lumped pumps and the distributed Non-Evaporable Getter (NEG) strips, and describe the fabrication and testing of these prototype cell chambers. The account also details the development of the chamber bakeout process, the NEG stri's supports, and the RF shielded bellows
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Hydrogen Outgassing and Surface Properties of Tin Coated Stainless Steel Chambers.
The stainless steel vacuum chambers of the 248m accumulator ring of Spallation Neutron Source (SNS) are coated with {approx} 100 nm of titanium nitride (TiN) to reduce the secondary electron yield. The coating is produced by DC magnetron sputtering using a long cathode imbedded with permanent magnets. The outgassing rates of several SNS half-cell chambers were measured with and without TiN coating, and before and after in-situ bake. One potential benefit of a TiN coating is to serve as hydrogen permeation barrier that reduces the ultimate outgassing rate. By varying the coating parameters, films of different surface roughness were produced and analyzed by Auger electron spectroscopy, scanning electron microscopy and atomic force microscopy to illustrate the dependence of the outgassing on the film structure
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