Vacuum
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Abstract: Two complementary vacuum system simulation programs, “MCTPVac” and “Pressure Profile”, have been developed and tested at Diamond and used to model sections of the Diamond storage ring. The MCTPVac program implements the Monte Carlo Test Particle (MCTP) method in 3 dimensions. The Pressure Profile program uses a 1-dimensional method based on a steady-state diffusion equation. The validity of the MCTPVac program is confirmed by comparison with previously-published results and formulae for simple geometries. The pressure predictions made by the two methods for the Diamond storage ring injection straight are then compared with each other and to actual observed pressures.
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Apr 2009
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Vacuum
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Abstract: Diamond Light Source (Diamond) utilises a large number of Inverted Magnetron Gauges (IMGs) for both monitoring the vacuum and as a source of interlocks for protection of the machine. During storage ring operation it has been found that, in the presence of the stored electron beam, charged particles, assumed to be electrons, impinging on some of the gauges cause the pressures indicated by the gauges to drop to zero which causes problems with the operation of the storage ring. Diamond has designed and fitted a magnetic filter at the neck of each affected gauge port to eliminate this problem. This paper reports on and discusses experiments and proposed experiments with an electron flood gun and IMGs from two different manufacturers (MKS Instruments and Pfeiffer Vacuum) aimed at obtaining a better understanding of the effect. Externally-generated electrons from the flood gun can cause serious errors in the pressures indicated by the gauges; the error can be positive or negative depending on the gauge current-measuring circuit. Methods aimed at eliminating these spurious pressure readings, such as magnetic filters, bias voltages within the gauges and the use of earth meshes and baffles are also discussed.
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Apr 2009
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Vacuum
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Abstract: The Diamond storage ring has been operating with a 3 GeV electron beam since September 2006 and 190 A.h of beam dose have been accumulated. The pressure in the storage ring is 4.2 10(-10) mbar without beam, rising to 7.9 10(-10) mbar with 125 mA of stored beam. Data on the storage ring vacuum performance and experience from commissioning and beam conditioning are presented.
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Sep 2008
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Vacuum
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Abstract: The ion to neutral ratio of the sputtered material have been studied for high power pulsed magnetron sputtering and compared with a continuous direct, current (dc) discharge using the same experimental setup except for the power source. Optical emission spectroscopy (OES) was used to study the optical emission from the plasma through a side window. The emission was shown to be dominated by emission from metal ions. The distribution of metal ionized states clearly differed from the distribution of excited states, and we suggest the presence of a hot dense plasma surrounded by a cooler plasma. Sputtered material was ionized close to the target and transported into a cooler plasma region where the emission was also recorded. Assuming a Maxwell-Boltzmann distribution of excited states the emission from the plasma was quantified. This showed that the ionic contribution to the recorded spectrum was over 90% for high pulse. powers. Even at relatively low applied pulse powers, the recorded spectra were dominated by emission from ions. OES analysis of the discharge in a continuous dc magnetron discharge was also made, which demonstrated much lower ionization. (C) 2005 American Vacuum Society.
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Nov 2004
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Vacuum
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Abstract: Commissioning of the ultra-high vacuum systems for the 3 GeV Diamond Light Source is in progress. All the machine vacuum systems are installed, under vacuum and performing well. The vacuum control system and machine protection systems are also operational. The measured static pressure in the storage ring is 5 x 10-10 mbar. Pressure rises up to the 10-8 mbar region have been observed during initial beam tests at 700 MeV 2 mA. The effective initial photon stimulated desorption (PSD) yield is estimated to be of order 10-3 molecules per incident photon which is in agreement with expectations.
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Jun 2006
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Vacuum
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Abstract: A one-dimensional diffusion model of the Diamond Light Source storage ring vacuum system is described and its predictions are compared with actual measured static (without beam) and dynamic (with beam) pressures over more than 2000 A h of beam conditioning at 3 GeV. An average specific thermal outgassing yield of 1.10(-11) mbar l/(s cm(2)) during initial beam circulation is obtained, which reduces to 2.10(-12) mbar l/(s cm(2)) after an accumulated beam dose of 1000 A h and an elapsed time of 769 days. In the presence of stored electron beam, the pressure rises as expected due to photon stimulated desorption (PSD). The PSD yield reduces with beam dose according to a (-2/3) power law as was applied in the model. Predicted and measured dynamic pressures generally agree within a factor of 2 over the whole range of beam conditioning dose studied. (c) 2012 Elsevier Ltd. All rights reserved.
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May 2012
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Vacuum
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Stefan
Gerstl
,
Tilo
Baumbach
,
Sara
Casalbuoni
,
Andreas
Grau
,
Michae
Hagelstein
,
David
Saez De Jauregui
,
Tomas
Holubek
,
Cristian
Boffo
,
Guenther
Sikler
,
Vincent
Baglin
,
Matthew
Cox
,
Jos
Schouten
,
Roberto
Cimino
,
Mario
Commisso
,
Bruno
Spataro
,
Andrea
Mostacci
,
Eric
Wallen
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Ralf
Weigel
,
Jim
Clarke
,
Duncan
Scott
,
Tom
Bradshaw
,
Roger
Jones
,
Ian
Shinton
Abstract: Superconductive insertion devices (IDs) have higher fields for a given gap and period length compared with the state of the art technology of permanent magnet IDs. This technological solution is very interesting for synchrotron light sources since it permits to increase the brilliance and/or the photon energy at moderate costs. One of the key issues for the development of superconducting IDs is the understanding of the beam heat load to the cold vacuum chamber. Therefore a cold vacuum chamber for diagnostic was built. Here we report about the design, planned measurements and the factory acceptance test of COLDDIAG.
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Apr 2011
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Vacuum
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Abstract: Diamond Light Source has currently 15 in-vacuum insertion
devices (ID) installed, mostly built in-house. Their
measured impact on multi-bunch mode damping as a result
of varying magnet gap was shown before, now we augment
these with measurements of broadband frequency spectra
with stored beam obtained using an antenna placed in the
ID vacuum. Finally, we present off-line measurements of
resonances in the ID vessel acquired using a vector network
analyser and two antennae installed in-vacuum.
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May 2017
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Vacuum
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Open Access
Abstract: One cell of the Diamond Light Source (Diamond) storage ring was upgraded in late 2016 to a Double Double Bend Achromat (DDBA) configuration to provide an additional mid-achromat insertion device straight. For practical reasons it was decided to use discrete non-evaporable getter (NEG) pumps rather than NEG coatings. This paper outlines the vacuum design of the up-grade, the reasons for the choices made and the vacuum simulation tools used as well as describing the vacuum system engineering, assembly, installation and commissioning. The measured vacuum performance is found to be in close agreement with the simulations and a simple expression is derived for the beam gas lifetime.
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May 2017
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Vacuum
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Open Access
Abstract: The conceptual design of the vacuum system for the Diamond-II storage ring upgrade is described. Due to the small vessel cross section, typically 20 mm inside diameter (ID), and the consequent conductance limitation, distributed pumping is provided by non-evaporable getter (NEG) coating supplemented by ion pumps at high gas load locations. In-situ bakeout is incorporated to allow rapid recovery from both planned vacuum interventions and unplanned vacuum events. The vacuum vessels are constructed mainly from copper alloy while stainless steel is used in regions of AC magnets requiring low electrical conductivity. The proposed layout, engineering and build sequence of the vacuum system are described along with gas flow simulations confirming the vacuum performance advantages of NEG-coated vessels compared with uncoated vessels.
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Jun 2019
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