High Oradient Superconducting Cavities for Storage Rings

Sundelin, R.

doi:10.1109/tns.1985.4334430

Cited by 29 publications

(11 citation statements)

References 8 publications

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“…The cavity used for this experimental study has the same shape as the one used in the CEBAF accelerator [8]. The resonant frequency of the TM 010 mode is at 1.47 GHz for a center cell with beam pipe and the ratios of peak surface electric and magnetic fields to the accelerating field are E p =E acc 1:78, B p =E acc 4:43 mT=MV=m as calculated with the SUPERFISH code [9].…”

Section: Methodsmentioning

confidence: 99%

Measurement of the high-fieldQdrop in a high-purity large-grain niobium cavity for different oxidation processes

Ciovati

Kneisel

Gurevich

2007

Phys. Rev. ST Accel. Beams

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The most challenging issue for understanding the performance of superconducting radio-frequency (rf) cavities made of high-purity (residual resistivity ratio >200) niobium is due to a sharp degradation (''Q-drop'') of the cavity quality factor Q 0 B p as the peak surface magnetic field (B p) exceeds about 90 mT, in the absence of field emission. In addition, a low-temperature (100-140 C) in situ baking of the cavity was found to be beneficial in reducing the Q-drop. In this contribution, we present the results from a series of rf tests at 1.7 and 2.0 K on a single-cell cavity made of high-purity large (with area of the order of few cm 2) grain niobium which underwent various oxidation processes, after initial buffered chemical polishing, such as anodization, baking in pure oxygen atmosphere, and baking in air up to 180 C, with the objective of clearly identifying the role of oxygen and the oxide layer on the Q-drop. During each rf test a temperature mapping system allows measuring the local temperature rise of the cavity outer surface due to rf losses, which gives information about the losses location, their field dependence, and space distribution. The results confirmed that the depth affected by baking is about 20-30 nm from the surface and showed that the Q-drop did not reappear in a previously baked cavity by further baking at 120 C in pure oxygen atmosphere or in air up to 180 C. These treatments increased the oxide thickness and oxygen concentration, measured on niobium samples which were processed with the cavity and were analyzed with transmission electron microscope and secondary ion mass spectroscopy. Nevertheless, the performance of the cavity after air baking at 180 C degraded significantly and the temperature maps showed high losses, uniformly distributed on the surface, which could be completely recovered only by a postpurification treatment at 1250 C. A statistic of the position of the ''hot spots'' on the cavity surface showed that grain boundaries are not the preferred location. An interesting correlation was found between the Q-drop onset, the quench field, and the low-field energy gap, which supports the hypothesis of thermomagnetic instability governing the Q-drop and the baking effect.

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Section: Methodsmentioning

confidence: 99%

Measurement of the high-fieldQdrop in a high-purity large-grain niobium cavity for different oxidation processes

Ciovati

Kneisel

Gurevich

2007

Phys. Rev. ST Accel. Beams

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“…It was judged that recent international progress with the technology provided adequate basis for the change. In addition, the availability of a 1947 MHz SRF cavity solution, only just successfully demonstrated in a test with stored beam in CESR at Cornell University in 1984, [6] for direct adoption as the building block for an SRF-based CEBAF was essential for the project to maintain its timeline and its tenuous Congressional budgetary support.…”

Section: Influences On the Launch Of Cebafmentioning

confidence: 99%

“…These were mechanically tuned as necessary to support the very successful beam test at 1499.2845 MHz in 1984. [6,15,16] Each cavity also incorporated a reducedheight waveguide input coupler and two smaller waveguide couplers to extract beyond cut-off higherorder-mode (HOM) power. Sundelin was strongly attracted to the inherent broadband coupling provided by waveguide couplers in contrast to coaxial style RF couplers.…”

Section: Influences On the Launch Of Cebafmentioning

confidence: 99%

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Continuous wave superconducting radio frequency electron linac for nuclear physics research

Reece

2016

Phys. Rev. Accel. Beams

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CEBAF, the Continuous Electron Beam Accelerator Facility, has been actively serving the nuclear physics research community as a unique forefront international resource since 1995. This CW electron linear accelerator (linac) at the U.S. Department of Energy's Thomas Jefferson National AcceleratorFacility (Jefferson Lab) has continued to evolve as a precision tool for discerning the structure and dynamics within nuclei. Superconducting RF (SRF) technology has been the essential foundation for CEBAF, first as a 4 GeV machine, then 6 GeV, and currently capable of 12 GeV. We review the development, implementation, and performance of SRF systems for CEBAF from its early beginnings to the commissioning of the 12 GeV era.

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“…The cavity used for this experimental study has the same shape as the one used in the CEBAF accelerator [5]. The main electromagnetic parameters of the TM 010 and TE 011 mode are shown in Table I as calculated with SUPERFISH [6].…”

Section: A Experimental Setupmentioning

confidence: 99%

Measurement of the high-fieldQdrop in theTM010andTE011modes in a niobium cavity

Ciovati

Kneisel

2006

Phys. Rev. ST Accel. Beams

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In the last few years superconducting radio-frequency (rf) cavities made of high-purity (residual resistivity ratio > 200) niobium achieved accelerating gradients close to the theoretical limits. An obstacle towards achieving reproducibly higher fields is represented by ''anomalous'' losses causing a sharp degradation of the cavity quality factor when the peak surface magnetic field (B p ) is above about 90 mT, in the absence of field emission. This effect, called ''Q drop'' has been measured in many laboratories with single-and multicell cavities mainly in the gigahertz range. In addition, a lowtemperature (100 -140 C) ''in situ'' baking of the cavity was found to be beneficial in reducing the Q drop. In order to gain some understanding of the nature of these losses, a single-cell cavity has been tested in the TM 010 and TE 011 modes at 2 K. The feature of the TE 011 mode is to have zero electric field on the cavity surface, so that electric field effects can be excluded as a source for the Q drop. This article will present some of the experimental results for different cavity treatments and will compare them with existing models.

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High Oradient Superconducting Cavities for Storage Rings

Cited by 29 publications

References 8 publications

Measurement of the high-fieldQdrop in a high-purity large-grain niobium cavity for different oxidation processes

Measurement of the high-fieldQdrop in a high-purity large-grain niobium cavity for different oxidation processes

Continuous wave superconducting radio frequency electron linac for nuclear physics research

Measurement of the high-fieldQdrop in theTM010andTE011modes in a niobium cavity

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