AVS2014 Session VT-WeM: Accelerator and Large Vacuum Systems I

The Vacuum Science group at the STFC Daresbury Laboratory has a unique position in that it has the capability to operate and design the vacuum systems for new accelerators whilst maintaining a very active research laboratory looking at many new facets of vacuum design for accelerators. This gives the group the opportunity to develop ideas in the laboratory before implementing them on the accelerator. This paper will present some of the latest accelerator ideas and machines at Daresbury and provide an insight into how some of our laboratory developments are helping improve the vacuum design.

A range of topics will be covered such as:

1) Machine developments – VELA, CLARA and ALICE

2) NEG coatings – a new quaternary alloy with a reduced activation temperature

3) Photocathode research – metal and semiconductor cathode developments

4) Bakeout – a new permanent thin film heater coating for in-situ bakeout

5) XHV – optimising the process to routinely achieve 10^-12 mbar

6) Thin films – SRF coating developments

National Synchrotron Light Source II is a new synchrotron radiation facility, consisting of a 200-MeV Linac, a 3-GeV Booster and a 3-GeV storage ring. The Linac and the Booster were completed and commissioned in 2012 and 2013, respectively. The 792m storage ring was completed in January. Commissioning with electron beam is underway in the last few months. The performance of these ultrahigh vacuum systems with intense electron and X-ray beams will be described. The reliability and usefulness of over 1500 vacuum pumps and instruments will be summarized. Experience with NEG coated narrow gap chambers, in-vacuum undulators and superconducting cavity will also be presented.

*Work performed under the auspices of U.S. Department of Energy, under contract DE-AC02-98CH10886.

A conceptual design is being developed for a storage ring vacuum system at the Advanced Photon Source (APS) which is compatible with a seven‐bend achromat lattice under consideration by the APS Upgrade (APS‐U) project. The design features a hybrid vacuum system to address outgassing and thermal loads which will combine discrete pumping, NEG-coated copper chambers, and NEG strip pumping in conventional extruded aluminum chambers. A preliminary 3D vacuum pressure analysis is described which uses the SynRad/MolFlow+ 3D vacuum analysis package developed at CERN to determine if the system can meet pressure requirements. The analysis uses the software package to predict photon stimulated desorption loads and then determine the resulting vacuum system pressure.

From 1980's to 2000's in Japan, electron storage rings had some key issues of their vacuum systems. To overcome two key issues especially, we observed dust trapping phenomena as a key issue, using lead-glass counters at first.^1,2 Dust particles collected in beam ducts were analyzed ³ and simulation experiments to trap dust particles were carried out using these collected dust particles^.2,4,5 As the results, the mechanism of the phenomena was found clearly and we knew how to prevent these phenomena occurring.^6,7 We review and discuss the phenomena using published and unpublished data.

As the other key issue, it was that ionization gauges misread due to radiation-induced currents. ⁸ A hot-cathode-ionization gauge with correcting electrode was developed and tested in simulation experiments ^9,10,11 and in actual radiation environments.^12,13 The pressure-measurement error of the developed vacuum gauge was about 20%. We also review and discuss the vacuum gauge and other devices ¹⁴ to overcome other issues using latest data.

References

¹Hiroshi Saeki, Takashi Momose, and Hajime Ishimaru, Rev. Sci. Instrum. 62(4), 874 (1991).

²Hiroshi Saeki, Takashi Momose, and Hajime Ishimaru, Rev. Sci. Instrum. 62(11), 2558 (1991).

³TAKASHI MOMOSE, HIROSHI SAEKI, and HAJIME ISHIMARU, VACUUM 43(3), 189 (1992).

⁴Hiroshi Saeki, Takashi Momose, and Hajime Ishimaru, Rev. Sci. Instrum. 62(11), 2568 (1991).

⁵Hiroshi Saeki, Takashi Momose, and Hajime Ishimaru, Rev. Sci. Instrum. 65(11), 3479 (1994).

⁶Hiroshi Saeki, Takashi Momose, and Hajime Ishimaru, Rev. Sci. Instrum. 67(4), 1475 (1996).

⁷Hiroshi Saeki, Takashi Momose, J. Vac. Sci. Technol. A 18(2), 492 (2000).

⁸Hiroshi saeki, Takashi Momose, J. Vac. Sci. Technol. A 18(1), 244 (2000).

⁹Hiroshi Saeki, Tamotsu Magome, and Tsuyoshi Aoki, Nobuaki Gotoh, Takashi Momose, Rev. Sci. Instrum. 75(12), 5152 (2004).

¹⁰Hiroshi Saeki, and Tamotsu Magome, Rev. Sci. Instrum. 79(5), 055102-1 (2008).

¹¹Hiroshi Saeki, and Tamotsu Magome, J. Vac. Sci. Technol. A 29(6), 061601-1 (2011).

¹²Tamotsu Magome, and Hiroshi Saeki, J. Vac. Sci. Technol. A 23(4), 725 (2005).

¹³Hiroshi Saeki, and Tamotsu Magome, Yoshihiko Shoji, J. Vac. Sci. Technol. A 24(4), 1148 (2006).

¹⁴For example, Hiroshi Saeki, Hiroyasu Ego, Takahiro Watanabe, Katsuya Ishibashi, Takafumi Satoh, Kazuo Miyamoto, Vacuum 85(10), 975 (2011).

Bulk Nb has so far been the material of choice for Superconducting RF (SRF) applications. With RF cavity performance approaching the theoretical limit for bulk niobium, alternative routes for the future of superconducting structures used in accelerators are explored. Over the years, Nb/Cu technology has positioned itself as an alternative route for the future of superconducting structures used in accelerators, but has suffered shortcomings due to the commonly used magnetron sputtering. The recent developments in ionized PVD coating techniques (i.e. vacuum deposition techniques using energetic ions) such as Electron Cyclotron Resonance (ECR) and High Power Impulse Magnetron Sputtering (HiPIMS) are opening avenues for the production of thin films tailored for SRF applications based on Nb and alternative materials.

This contribution reports the on-going efforts pursued at Jefferson Lab and in different institutions to exploit the potential of novel film technologies to produce bulk-like Nb films and go beyond Nb performance with the development of film systems, based on other superconducting materials and multilayer structures.