Status of the SNS Superconducting Linac and Future Plan

Kim, Sang-ho

doi:10.3938/jkps.52.714

Cited by 8 publications

(9 citation statements)

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“…The availability is the accumulated up time divided by the planned neutron production time. The availability of the SRF cavities, cryomodules and CHL system has been 99.5% which corresponds to 25 hours of down time per year [27]. Each neutron production run has issues with various equipment that affect the machine availability.…”

Section: Insert Figure 10 52 Scl Downtime Statisticsmentioning

confidence: 99%

Overview of ten-year operation of the superconducting linear accelerator at the Spallation Neutron Source

Kim

Afanador

Barnhart

et al. 2017

Nuclear Instruments and Methods in Physics Research Section A:

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The Spallation Neutron Source (SNS) has acquired extensive operational experience of a pulsed proton superconducting linear accelerator (SCL) as a user facility. Numerous lessons have been learned in its first 10 years operation to achieve a stable and reliable operation of the SCL. In this paper, an overview of the SNS SCL design, qualification of superconducting radio frequency (SRF) cavities and ancillary subsystems, an overview of the SNS cryogenic system, the SCL operation including SCL output energy history and downtime statistics, performance stability of the SRF cavities, efforts for SRF cavity performance recovery and improvement at the SNS, and maintenance activities for cryomodules are introduced.

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Section: Insert Figure 10 52 Scl Downtime Statisticsmentioning

confidence: 99%

Overview of ten-year operation of the superconducting linear accelerator at the Spallation Neutron Source

Kim

Afanador

Barnhart

et al. 2017

Nuclear Instruments and Methods in Physics Research Section A:

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“…Equation (4) and (5) are based on the Fowler-Nordheim equation for field emission in DC fields given in Equation (1). But, using the equation for field emission in RF fields from [8] yields the exact same result to first order.…”

Section: =0mentioning

confidence: 99%

“…Multiple campaigns of RF conditioning of SNS cavities at cryogenic temperature were conducted at the SNS over the first few years of operation and the accelerating gradient for each cavity was determined empirically for highest energy gain and stable operation [4,5]. The gradients haven't varied significantly since then but extensive progress in the understanding and use of sub-systems such as cold-cathode gauges and beam loss detectors have contributed to make the overall SCL operation remarkably reliable for a machine of its complexity.…”

Section: In-situ Plasma Processing To Improve Accelerating Gradientsmentioning

confidence: 99%

“…extremities of the accelerating cavities, are particularly prone to thermal instabilities since they are not actively cooled by liquid Helium but rather by conduction from the adjacent end-cells [4]. Experimental evidence has shown that field emission at the SNS is the main limiting factor for reaching higher accelerating gradients in operated cavities [5]. Figure 1 shows the accelerating gradient and peak surface electric field of all 81 cavities (33 mediumbeta cavities and 48 high-beta cavities) at 60 Hz operation in the SNS linac.…”

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confidence: 99%

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In-situ plasma processing to increase the accelerating gradients of superconducting radio-frequency cavities

Doléans

Tyagi

Afanador

et al. 2016

Nuclear Instruments and Methods in Physics Research Section A:

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A new in-situ plasma processing technique is being developed at the Spallation Neutron Source (SNS) to improve the performance of the cavities in operation. The technique utilizes a low-density reactive oxygen plasma at room-temperature to remove top-surface hydrocarbons. The plasma processing technique increases the work function of the cavity surface and reduces the overall amount of vacuum and electron activity during cavity operation; in particular it increases the field-emission onset, which enables cavity operation at higher accelerating gradients. Experimental evidence also suggests that the SEY of the Nb surface decreases after plasma processing which helps mitigating multipacting issues. In this article, the main developments and results from the plasma processing R&D are presented and experimental results for in-situ plasma processing of dressed cavities in the SNS horizontal test apparatus are discussed. 2. FIELD EMISSION AND END-GROUP THERMAL INSTABILITY LIMITING THE ACCELERATING GRADIENTS IN THE SNS LINAC Field emission in superconducting radio-frequency (SRF) cavities is a well-known limiting factor for operation at high accelerating gradients [1-3]. Beyond certain electric field thresholds, the electrons from the metal surface of the cavity have a non-negligible probability of tunneling out. The field emitted electrons are accelerated by the stored electromagnetic fields in the cavity and subsequently deposit their energy by collision with the cavity radio-frequency (RF) surface leading to vacuum activity, increase of the surface temperature and Bremsstrahlung radiation. If the deposited energy-density is larger than the cooling capacity it can also lead to thermal breakdown of the superconductivity.

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“…Field emission is one of the critical issues in high gradient superconducting radio frequency (SRF) cavities that limits the cavity performance [1] [2] [3]. Previous studies on field emission in SRF cavities have concentrated on protrusions and particulate contaminations at the RF surface [4][5] [6].…”

Section: Introductionmentioning

confidence: 99%

Improving the work function of the niobium surface of SRF cavities by plasma processing

Tyagi

Doléans

Hannah

et al. 2016

Applied Surface Science

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An in-situ plasma processing technique using chemically reactive oxygen plasma to remove hydrocarbons from superconducting radio frequency cavity surfaces at room temperature has been developed at the spallation neutron source, at Oak Ridge national laboratory. To understand better the interaction between the plasma and niobium surface, surface studies on small samples were performed. In this article, we report the results from those surface studies. The results show that plasma processing removes hydrocarbons from top surface and improves the surface work function by 0.5 to 1.0 eV. Improving the work function of RF surface of cavities can help to improve their operational performance.

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Status of the SNS Superconducting Linac and Future Plan

Cited by 8 publications

References 0 publications

Overview of ten-year operation of the superconducting linear accelerator at the Spallation Neutron Source

Overview of ten-year operation of the superconducting linear accelerator at the Spallation Neutron Source

In-situ plasma processing to increase the accelerating gradients of superconducting radio-frequency cavities

Improving the work function of the niobium surface of SRF cavities by plasma processing

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