Following the significant impedance related issues that occurred during the LHC Run 1, all involv... more Following the significant impedance related issues that occurred during the LHC Run 1, all involved equipment groups made an impressive effort to assess and reduce the impedance of their near-beam components. Concerning beam induced RF heating, many problems in Run 1 were linked to unexpected non-conformities. Mitigations were put in place but new non-conformities are likely to appear in Run 2, and this is why efficient monitoring and alarms are currently put in place. Besides, known limitations that led to increase the bunch length from 1 ns to 1.25 ns were removed, which would open the possibility to try and reduce the target bunch length at top energy. Regardless of the target bunch length, many components will need careful follow up in 2015 (e.g. TDI, BSRT, Roman pots, MKI, BGV). Concerning the LHC impedance, announced hardware changes are expected to be transparent, but the new TCTP and TCSP collimators with BPMs and ferrites should be monitored closely, as well as the modified...
We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is ... more We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is part of the CERN Axion Solar Telescope (CAST), searching for axion dark matter in the 34.67 μeV mass range. A radio frequency cavity consisting of 5 sub-cavities coupled by inductive irises took physics data inside the CAST dipole magnet for the first time using this filter-like haloscope geometry. An exclusion limit with a 95% credibility level on the axion-photon coupling constant of gaγ ≳ 4 × 10−13 GeV−1 over a mass range of 34.6738 μeV < ma< 34.6771 μeV is set. This constitutes a significant improvement over the current strongest limit set by CAST at this mass and is at the same time one of the most sensitive direct searches for an axion dark matter candidate above the mass of 25 μeV. The results also demonstrate the feasibility of exploring a wider mass range around the value probed by CAST-RADES in this work using similar coherent resonant cavities.
We report the results of impedance measurements, per-formed by the triaxial wire method, on a 2 m... more We report the results of impedance measurements, per-formed by the triaxial wire method, on a 2 m long model of the LHC vacuum chamber. The model consists of an inner screen (liner) with pumping holes and of the outer vacuum chamber. The transmission coefficient for differ-ent numbers of holes with various radii confirms the role played by TEM modes, propagating at the same speed of the beam particles in the coaxial structure formed by the liner and the outer vacuum chamber. We also compare the results of these measurements to analytical estimates of the coupling impedance.
Proceedings of International Conference on Particle Accelerators
Beam current bench tests and simulations, c.g. with beam monitors, arc of interest for diagnostic... more Beam current bench tests and simulations, c.g. with beam monitors, arc of interest for diagnostic purposes. For highlyrelativistic tests, the common coaxial wire method may bc used. In contrast, a configuration for non-relativistic beams was devised for transverse impedance measurements. We have combined the two approaches to permit both frequency and time domain low-beta bench tests of the line charge, and of the longitudinal beam impedance. The basic structure is of coaxial 50 R gcomctry, whcrc the outer diamctcr matches the bean-pipe diameter of COSY, while the inner conductor carrics, both around the azimuth and along ~hc axis, suitable pinand-loop arrays for imposing electric and magnetic fields, rcspcctivcly. The arrays ensure nearly azimuthal (coaxial) symmctry, and are wired via delay lines such that axially varying field patterns may bc gcncratcd, permitting the simulation of a broad beta range. We use standard mcasurcmcnt techniques with a network analyzer at a frequency range from 500 kHz up to 100 MHz. A calibration procedure, measuring field pickup via coupling loops and pins installed in the outer beam pipe wall, cnsurcs the correct IEI/IBI ratio.
Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He This article has bee... more Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He This article has been downloaded from IOPscience. Please scroll down to see the full text article.
Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He This article has bee... more Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He This article has been downloaded from IOPscience. Please scroll down to see the full text article.
One way to proof or exclude the existence of axion like particles is a microwave light shining th... more One way to proof or exclude the existence of axion like particles is a microwave light shining through the wall experiment. In this publication we will emphasize on the engineering aspects of such a setup, currently under development at CERN. One critical point, to achieve meaningful results, is the electromagnetic shielding between axion-emitter and receiver cavity, which needs to be in the order of 300 dB to improve over existing experimental bounds. The RF leakage or electromagnetic crosstalk between both cavities must be well controlled and quantified during the complete duration of the experiment. A very narrow band (in the µHz range) homodyne detection method is used to reveal the axion signal from background thermal noise. The current status of the experiment is presented.
One way to proof or exclude the existence of axion like particles is a microwave light shining th... more One way to proof or exclude the existence of axion like particles is a microwave light shining through the wall experiment. In this publication we will emphasize on the engineering aspects of such a setup, currently under development at CERN. One critical point, to achieve meaningful results, is the electromagnetic shielding between axion-emitter and receiver cavity, which needs to be in the order of 300 dB to improve over existing experimental bounds. The RF leakage or electromagnetic crosstalk between both cavities must be well controlled and quantified during the complete duration of the experiment. A very narrow band (in the µHz range) homodyne detection method is used to reveal the axion signal from background thermal noise. The current status of the experiment is presented.
For the microwave equivalent of “light shining through the wall” (LSW) experiments, a sensitive m... more For the microwave equivalent of “light shining through the wall” (LSW) experiments, a sensitive microwave detector and very high electromagnetic shielding is required. The screening attenuation between the axion generating cavity and the nearby detection cavity should be greater than 300 dB, in order to improve over presently existing exclusion limits. To achieve these goals in practice, a “box in a box” concept was utilized for shielding the detection cavity, while a vector signal analyzer was used as a microwave receiver with a very narrow resolution bandwidth in the order of a few micro-Hz. This contribution will present the experimental layout and the results to date. MOTIVATION The axion is a hypothetical elementary particle, which emerged originally from a proposal by Peccei and Quinn, intended to solve the strong CP problem [1] in theoretical physics. The axion is neutral, only interacts weakly with matter, has a low mass (≈ 10 −4 eV /c 2 ), spin zero, and a natural decay con...
The LHC Schottky System has been under commissioning since summer 2010. This non destructive obse... more The LHC Schottky System has been under commissioning since summer 2010. This non destructive observation relies on a slotted wave-guide structure resonating at 4.8 GHz. Four monitors, one for each plane of the two counter-rotating LHC beams, are used to measure the transverse Schottky side-bands. Electronic gating allows selective bunch-by-bunch measurements, while a triple down-mixing scheme combined with heavy filtering gives an instantaneous dynamic range over 100 dB within a 20 kHz bandwidth. Observations of both proton and lead ions Schottky spectra will be discussed along with a comparison of predicted and measured performance.
<p><strong>Figure 5.</strong> The change of the microwave power over the measur... more <p><strong>Figure 5.</strong> The change of the microwave power over the measured frequency range for the (a) 11.125 GHz and the (b) 11.157 GHz transition.</p> <p><strong>Abstract</strong></p> <p>In this work, we describe the latest results for the measurements of the hyperfine structure of antiprotonic <sup>3</sup>He. Two out of four measurable super–super-hyperfine (SSHF) transition lines of the (<em>n</em>, <em>L</em>) = (36, 34) state of antiprotonic <sup>3</sup>He were observed. The measured frequencies of the individual transitions are 11.125 48(08) GHz and 11.157 93(13) GHz, with the increased precisions of about 43% and 25%, respectively, compared to our first measurements with antiprotonic <sup>3</sup>He (Friedreich <em>et al</em> 2011 <em>Phys. Lett.</em> B <strong>700</strong> 1–6). They are less than 0.5 MHz higher with respect to the most recent theoretical values, still within their estimated errors. Although the experimental uncertainty for the difference of 0.032 45(15) GHz between these frequencies is large as compared to that of theory, its measured value also agrees with theoretical calculations. The rates for collisions between antiprotonic helium and helium atoms have been assessed through comparison with simulations, resulting in an elastic collision rate of γ<sub><em>e</em></sub> = 3.41 ± 0.62 MHz and an inelastic collision rate of γ<sub><em>i</em></sub> = 0.51 ± 0.07 MHz.</p
A 1.7 GHz waveguide Schottky detector system was recently built and installed in the SPS accelera... more A 1.7 GHz waveguide Schottky detector system was recently built and installed in the SPS accelerator following the design of the detectors of the Fermilab Tevatron and Recycler accelerators. The waveguide detector is designed to measure the transverse and longitudinal Schottky signals of the accelerator at a frequency high enough to avoid coherent effects. This paper describes the first tests carried out with the Schottky detector using LHC type beams. The principal goal of these tests was to check whether such a detector can be used for transverse Schottky diagnostics in LHC.
A rotatable collimator is proposed for the LHC phase II collimation upgrade. When the beam crosse... more A rotatable collimator is proposed for the LHC phase II collimation upgrade. When the beam crosses the collimator, trapped modes will be excited that result in beam energy loss and collimator power dissipation. Some of the trapped modes can also generate transverse kick on the beam and affect the beam operation. In this paper the parallel eigensolver code Omega3P is used to search for all the trapped modes below 2GHz in the collimator, including longitudinal modes and transverse modes. The loss factors and kick factors of the trapped modes are calculated as function of the jaw positions. The amplitude ratio between transverse and longitudinal trapped mode intensity can be used as a direct measure of the position of the beam. We present simulation results and discuss the results.
The International Axion Observatory (IAXO) is a proposed 4 th-generation axion helioscope with th... more The International Axion Observatory (IAXO) is a proposed 4 th-generation axion helioscope with the primary physics research goal to search for solar axions via their Primakoff conversion into photons of 1 − 10 keV energies in a strong magnetic field. IAXO will achieve a sensitivity to the axion-photon coupling g aγ down to a few ×10 −12 GeV −1 for a wide range of axion masses up to ∼ 0.25 eV. This is an improvement over the currently best (3 rd generation) axion helioscope, the CERN Axion Solar Telescope (CAST), of about 5 orders of magnitude in signal strength, corresponding to a factor ∼ 20 in the axion photon coupling. IAXO's sensitivity relies on the construction of a large superconducting 8-coil toroidal magnet of 20 m length optimized for axion research. Each of the eight 60 cm diameter magnet bores is equipped with x-ray optics focusing the signal photons into ∼ 0.2 cm 2 spots that are imaged by very low background x-ray detectors. The magnet will be built into a structure with elevation and azimuth drives that will allow solar tracking for 12 hours each day. This contribution is a summary of our papers [1, 2, 3] and we refer to these for further details.
By analysing beam transfer functions, i.e. the beam response to an RF excitation signal at a harm... more By analysing beam transfer functions, i.e. the beam response to an RF excitation signal at a harmonic of the revolution frequency or at a betatron sideband, the low frequency ripple of the bending and focusing fields can be deduced. The underlying theory as well as experimental results of ripple measurements for two of CERN's machines (Booster, Antiproton Collector) are presented. In the Antiproton Collector ring for example, fluctuations smaller than 10 -6 have been observed using this technique. 1 PRINCIPLE
IEEE Transactions on Applied Superconductivity, 2012
In particle accelerators, "field markers" provide a digital trigger when the magnetic field cross... more In particle accelerators, "field markers" provide a digital trigger when the magnetic field crosses a given threshold. In this paper, the metrological characterization of a magnetic field marker, based on a ferrimagnetic resonance transducer referencing the flux sensed by a coil, is reported. The experimental results of a validation test campaign at the European Organization for Nuclear Research (CERN) to test the marker in static as well as fast ramping fields (up to 2.5 T/s) are illustrated. The repeatability of ±4 T attained in the range (60 to 100) mT is very promising to increase the performance of the Proton Synchrotron accelerator at CERN.
Following the significant impedance related issues that occurred during the LHC Run 1, all involv... more Following the significant impedance related issues that occurred during the LHC Run 1, all involved equipment groups made an impressive effort to assess and reduce the impedance of their near-beam components. Concerning beam induced RF heating, many problems in Run 1 were linked to unexpected non-conformities. Mitigations were put in place but new non-conformities are likely to appear in Run 2, and this is why efficient monitoring and alarms are currently put in place. Besides, known limitations that led to increase the bunch length from 1 ns to 1.25 ns were removed, which would open the possibility to try and reduce the target bunch length at top energy. Regardless of the target bunch length, many components will need careful follow up in 2015 (e.g. TDI, BSRT, Roman pots, MKI, BGV). Concerning the LHC impedance, announced hardware changes are expected to be transparent, but the new TCTP and TCSP collimators with BPMs and ferrites should be monitored closely, as well as the modified...
We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is ... more We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is part of the CERN Axion Solar Telescope (CAST), searching for axion dark matter in the 34.67 μeV mass range. A radio frequency cavity consisting of 5 sub-cavities coupled by inductive irises took physics data inside the CAST dipole magnet for the first time using this filter-like haloscope geometry. An exclusion limit with a 95% credibility level on the axion-photon coupling constant of gaγ ≳ 4 × 10−13 GeV−1 over a mass range of 34.6738 μeV < ma< 34.6771 μeV is set. This constitutes a significant improvement over the current strongest limit set by CAST at this mass and is at the same time one of the most sensitive direct searches for an axion dark matter candidate above the mass of 25 μeV. The results also demonstrate the feasibility of exploring a wider mass range around the value probed by CAST-RADES in this work using similar coherent resonant cavities.
We report the results of impedance measurements, per-formed by the triaxial wire method, on a 2 m... more We report the results of impedance measurements, per-formed by the triaxial wire method, on a 2 m long model of the LHC vacuum chamber. The model consists of an inner screen (liner) with pumping holes and of the outer vacuum chamber. The transmission coefficient for differ-ent numbers of holes with various radii confirms the role played by TEM modes, propagating at the same speed of the beam particles in the coaxial structure formed by the liner and the outer vacuum chamber. We also compare the results of these measurements to analytical estimates of the coupling impedance.
Proceedings of International Conference on Particle Accelerators
Beam current bench tests and simulations, c.g. with beam monitors, arc of interest for diagnostic... more Beam current bench tests and simulations, c.g. with beam monitors, arc of interest for diagnostic purposes. For highlyrelativistic tests, the common coaxial wire method may bc used. In contrast, a configuration for non-relativistic beams was devised for transverse impedance measurements. We have combined the two approaches to permit both frequency and time domain low-beta bench tests of the line charge, and of the longitudinal beam impedance. The basic structure is of coaxial 50 R gcomctry, whcrc the outer diamctcr matches the bean-pipe diameter of COSY, while the inner conductor carrics, both around the azimuth and along ~hc axis, suitable pinand-loop arrays for imposing electric and magnetic fields, rcspcctivcly. The arrays ensure nearly azimuthal (coaxial) symmctry, and are wired via delay lines such that axially varying field patterns may bc gcncratcd, permitting the simulation of a broad beta range. We use standard mcasurcmcnt techniques with a network analyzer at a frequency range from 500 kHz up to 100 MHz. A calibration procedure, measuring field pickup via coupling loops and pins installed in the outer beam pipe wall, cnsurcs the correct IEI/IBI ratio.
Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He This article has bee... more Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He This article has been downloaded from IOPscience. Please scroll down to see the full text article.
Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He This article has bee... more Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He This article has been downloaded from IOPscience. Please scroll down to see the full text article.
One way to proof or exclude the existence of axion like particles is a microwave light shining th... more One way to proof or exclude the existence of axion like particles is a microwave light shining through the wall experiment. In this publication we will emphasize on the engineering aspects of such a setup, currently under development at CERN. One critical point, to achieve meaningful results, is the electromagnetic shielding between axion-emitter and receiver cavity, which needs to be in the order of 300 dB to improve over existing experimental bounds. The RF leakage or electromagnetic crosstalk between both cavities must be well controlled and quantified during the complete duration of the experiment. A very narrow band (in the µHz range) homodyne detection method is used to reveal the axion signal from background thermal noise. The current status of the experiment is presented.
One way to proof or exclude the existence of axion like particles is a microwave light shining th... more One way to proof or exclude the existence of axion like particles is a microwave light shining through the wall experiment. In this publication we will emphasize on the engineering aspects of such a setup, currently under development at CERN. One critical point, to achieve meaningful results, is the electromagnetic shielding between axion-emitter and receiver cavity, which needs to be in the order of 300 dB to improve over existing experimental bounds. The RF leakage or electromagnetic crosstalk between both cavities must be well controlled and quantified during the complete duration of the experiment. A very narrow band (in the µHz range) homodyne detection method is used to reveal the axion signal from background thermal noise. The current status of the experiment is presented.
For the microwave equivalent of “light shining through the wall” (LSW) experiments, a sensitive m... more For the microwave equivalent of “light shining through the wall” (LSW) experiments, a sensitive microwave detector and very high electromagnetic shielding is required. The screening attenuation between the axion generating cavity and the nearby detection cavity should be greater than 300 dB, in order to improve over presently existing exclusion limits. To achieve these goals in practice, a “box in a box” concept was utilized for shielding the detection cavity, while a vector signal analyzer was used as a microwave receiver with a very narrow resolution bandwidth in the order of a few micro-Hz. This contribution will present the experimental layout and the results to date. MOTIVATION The axion is a hypothetical elementary particle, which emerged originally from a proposal by Peccei and Quinn, intended to solve the strong CP problem [1] in theoretical physics. The axion is neutral, only interacts weakly with matter, has a low mass (≈ 10 −4 eV /c 2 ), spin zero, and a natural decay con...
The LHC Schottky System has been under commissioning since summer 2010. This non destructive obse... more The LHC Schottky System has been under commissioning since summer 2010. This non destructive observation relies on a slotted wave-guide structure resonating at 4.8 GHz. Four monitors, one for each plane of the two counter-rotating LHC beams, are used to measure the transverse Schottky side-bands. Electronic gating allows selective bunch-by-bunch measurements, while a triple down-mixing scheme combined with heavy filtering gives an instantaneous dynamic range over 100 dB within a 20 kHz bandwidth. Observations of both proton and lead ions Schottky spectra will be discussed along with a comparison of predicted and measured performance.
<p><strong>Figure 5.</strong> The change of the microwave power over the measur... more <p><strong>Figure 5.</strong> The change of the microwave power over the measured frequency range for the (a) 11.125 GHz and the (b) 11.157 GHz transition.</p> <p><strong>Abstract</strong></p> <p>In this work, we describe the latest results for the measurements of the hyperfine structure of antiprotonic <sup>3</sup>He. Two out of four measurable super–super-hyperfine (SSHF) transition lines of the (<em>n</em>, <em>L</em>) = (36, 34) state of antiprotonic <sup>3</sup>He were observed. The measured frequencies of the individual transitions are 11.125 48(08) GHz and 11.157 93(13) GHz, with the increased precisions of about 43% and 25%, respectively, compared to our first measurements with antiprotonic <sup>3</sup>He (Friedreich <em>et al</em> 2011 <em>Phys. Lett.</em> B <strong>700</strong> 1–6). They are less than 0.5 MHz higher with respect to the most recent theoretical values, still within their estimated errors. Although the experimental uncertainty for the difference of 0.032 45(15) GHz between these frequencies is large as compared to that of theory, its measured value also agrees with theoretical calculations. The rates for collisions between antiprotonic helium and helium atoms have been assessed through comparison with simulations, resulting in an elastic collision rate of γ<sub><em>e</em></sub> = 3.41 ± 0.62 MHz and an inelastic collision rate of γ<sub><em>i</em></sub> = 0.51 ± 0.07 MHz.</p
A 1.7 GHz waveguide Schottky detector system was recently built and installed in the SPS accelera... more A 1.7 GHz waveguide Schottky detector system was recently built and installed in the SPS accelerator following the design of the detectors of the Fermilab Tevatron and Recycler accelerators. The waveguide detector is designed to measure the transverse and longitudinal Schottky signals of the accelerator at a frequency high enough to avoid coherent effects. This paper describes the first tests carried out with the Schottky detector using LHC type beams. The principal goal of these tests was to check whether such a detector can be used for transverse Schottky diagnostics in LHC.
A rotatable collimator is proposed for the LHC phase II collimation upgrade. When the beam crosse... more A rotatable collimator is proposed for the LHC phase II collimation upgrade. When the beam crosses the collimator, trapped modes will be excited that result in beam energy loss and collimator power dissipation. Some of the trapped modes can also generate transverse kick on the beam and affect the beam operation. In this paper the parallel eigensolver code Omega3P is used to search for all the trapped modes below 2GHz in the collimator, including longitudinal modes and transverse modes. The loss factors and kick factors of the trapped modes are calculated as function of the jaw positions. The amplitude ratio between transverse and longitudinal trapped mode intensity can be used as a direct measure of the position of the beam. We present simulation results and discuss the results.
The International Axion Observatory (IAXO) is a proposed 4 th-generation axion helioscope with th... more The International Axion Observatory (IAXO) is a proposed 4 th-generation axion helioscope with the primary physics research goal to search for solar axions via their Primakoff conversion into photons of 1 − 10 keV energies in a strong magnetic field. IAXO will achieve a sensitivity to the axion-photon coupling g aγ down to a few ×10 −12 GeV −1 for a wide range of axion masses up to ∼ 0.25 eV. This is an improvement over the currently best (3 rd generation) axion helioscope, the CERN Axion Solar Telescope (CAST), of about 5 orders of magnitude in signal strength, corresponding to a factor ∼ 20 in the axion photon coupling. IAXO's sensitivity relies on the construction of a large superconducting 8-coil toroidal magnet of 20 m length optimized for axion research. Each of the eight 60 cm diameter magnet bores is equipped with x-ray optics focusing the signal photons into ∼ 0.2 cm 2 spots that are imaged by very low background x-ray detectors. The magnet will be built into a structure with elevation and azimuth drives that will allow solar tracking for 12 hours each day. This contribution is a summary of our papers [1, 2, 3] and we refer to these for further details.
By analysing beam transfer functions, i.e. the beam response to an RF excitation signal at a harm... more By analysing beam transfer functions, i.e. the beam response to an RF excitation signal at a harmonic of the revolution frequency or at a betatron sideband, the low frequency ripple of the bending and focusing fields can be deduced. The underlying theory as well as experimental results of ripple measurements for two of CERN's machines (Booster, Antiproton Collector) are presented. In the Antiproton Collector ring for example, fluctuations smaller than 10 -6 have been observed using this technique. 1 PRINCIPLE
IEEE Transactions on Applied Superconductivity, 2012
In particle accelerators, "field markers" provide a digital trigger when the magnetic field cross... more In particle accelerators, "field markers" provide a digital trigger when the magnetic field crosses a given threshold. In this paper, the metrological characterization of a magnetic field marker, based on a ferrimagnetic resonance transducer referencing the flux sensed by a coil, is reported. The experimental results of a validation test campaign at the European Organization for Nuclear Research (CERN) to test the marker in static as well as fast ramping fields (up to 2.5 T/s) are illustrated. The repeatability of ±4 T attained in the range (60 to 100) mT is very promising to increase the performance of the Proton Synchrotron accelerator at CERN.
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Papers by F. Caspers