L. Walckiers

An improved limit on the axion–photon coupling from the CAST experiment

We have searched for solar axions or similar particles that couple to two photons by using the CERN Axion Solar Telescope (CAST) setup with improved conditions in all detectors. From the absence of excess X-rays when the magnet was pointing to the Sun, we set an upper limit on the axion-photon coupling of 8.8 x 10^{-11} GeV^{-1} at 95% CL for m_a<~ 0.02 eV. This result is the best experimental limit over a broad range of axion masses and for m_a<~ 0.02 eV also supersedes the previous limit derived from energy-loss arguments on globular-cluster stars.

Towards a new generation axion helioscope

We study the feasibility of a new generation axion helioscope, the most ambitious and promising detector of solar axions to date. We show that large improvements in magnetic field volume, x-ray focusing optics and detector backgrounds are possible beyond those achieved in the CERN Axion Solar Telescope (CAST). For hadronic models, a sensitivity to the axion-photon coupling of gaγ few × 10−12 GeV−1 is conceivable, 1–1.5 orders of magnitude beyond the CAST sensitivity. If axions also couple to electrons, the Sun produces a larger flux for the same value of the Peccei-Quinn scale, allowing one to probe a broader class of models. Except for the axion dark matter searches, this experiment will be the most sensitive axion search ever, reaching or surpassing the stringent bounds from SN1987A and possibly testing the axion interpretation of anomalous white-dwarf cooling that predicts ma of a few meV. Beyond axions, this new instrument will probe entirely unexplored ranges of parameters for a large variety of axion-like particles (ALPs) and other novel excitations at the low-energy frontier of elementary particle physics.

A decommissioned LHC model magnet as an axion telescope

The 8.4 T, 10 m long transverse magnetic field of a twin aperture LHC bending magnet can be utilized as a macroscopic coherent solar axion-to-photon converter. Numerical calculations show that the integrated time of alignment with the Sun would be 33 days/yr with the magnet on a tracking table capable of

Conceptual design of the International Axion Observatory (IAXO)

5i in the vertical direction and

Twin rotating coils for cold magnetic measurements of 15 m long LHC dipoles

40i in the horizontal direction. The existing lower bound on the axion-to-photon coupling constant can be improved by a factor between 30 and 100 in 3 yr, i.e., g !cc [9]10~11 GeV~1 for axion masses [ 1 eV. This value falls within the existing open axion mass window. The same set-up can simultaneously search for low- and high-energy celestial axions, or axion-like particles, scanning the sky as the Earth rotates and orbits the Sun. ( 1999 Elsevier Science B.V. All rights reserved.

Measurement of AC loss and magnetic field during ramps in the LHC model dipoles

The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO will look for axions or axion-like particles (ALPs) originating in the Sun via the Primakoff conversion of the solar plasma photons. In terms of signal-to-noise ratio, IAXO will be about 4–5 orders of magnitude more sensitive than CAST, currently the most powerful axion helioscope, reaching sensitivity to axion-photon couplings down to a few × 10−12 GeV−1 and thus probing a large fraction of the currently unexplored axion and ALP parameter space. IAXO will also be sensitive to solar axions produced by mechanisms mediated by the axion-electron coupling gae with sensitivity — for the first time — to values of gae not previously excluded by astrophysics. With several other possible physics cases, IAXO has the potential to serve as a multi-purpose facility for generic axion and ALP research in the next decade. In this paper we present the conceptual design of IAXO, which follows the layout of an enhanced axion helioscope, based on a purpose-built 20 m-long 8-coils toroidal superconducting magnet. All the eight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able to focus the signal photons into ~ 0.2 cm2 spots that are imaged by ultra-low-background Micromegas x-ray detectors. The magnet is built into a structure with elevation and azimuth drives that will allow for solar tracking for ~ 12 h each day.

Quench observation in LHC superconducting one meter long dipole models by field perturbation measurements

We describe here a new harmonic coil system for the field measurement of the superconducting, twin aperture LHC dipoles and the associated corrector magnets. Besides field measurements the system can be used as an antenna to localize the quench origin. The main component is a 16 m long rotating shaft, made up of 13 ceramic segments, each carrying two tangential coils plus a central radial coil, all working in parallel. The segments are connected with flexible Ti-alloy bellows, allowing the piecewise straight shaft to follow the curvature of the dipole while maintaining high torsional rigidity. At each interconnection the structure is supported by rollers and ball bearings, necessary for the axial movement for installation and for the rotation of the coil during measurement. Two such shafts are simultaneously driven by a twin-rotating unit, thus measuring both apertures of a dipole at the same time. This arrangement allows very short measurement times (typically 10 s) and is essential to perform cold magnetic measurements of all dipoles. The coil surface and direction are calibrated using a reference dipole. In this paper we describe the twin rotating coil system and its calibration facility, and we give the typical resolution and accuracy achieved with the first commissioned unit.

Field errors decay and "snap-back" in LHC model dipoles

We describe the systems for AC loss and magnetic field measurements developed for the LHC superconducting magnets. AC loss measurements are performed using an electric method, while field measurements are performed using either fixed pick-ups or rotating coils. We present results obtained on 1-m long model dipoles, and compare the results of the different methods in terms of average interstrand resistance.

Quench location in the superconducting model magnets for the LHC by means of pick-up coils

A novel method to localize and characterize the origin of a quench in a superconducting dipole has been developed during the tests of the Large Hadron Collider (LHC) 1-m-long superconducting dipole models. It consists of an extended analysis of the voltage signals generated at the onset of a quench in pickup coils distributed along the inside of the magnet bore in conjunction with the pole voltage signals. The authors discuss the measurement method and the main results obtained during the training of these magnets, reaching a bore field of 10 T.<<ETX>>

Dynamic magnetic measurements of superconducting magnets for the LHC

The magnetic field in accelerator magnets decays when the current is kept constant during the particles injection phase, and returns quickly (snaps back) to the original values as soon as ramping is restarted. Here we show results of measurements of the decay of the field errors in 10 m long LHC model dipole magnets. In accordance with previous findings, precycles and stops at intermediate current levels influence the decay. We discuss a possible mechanism causing the decay and snap-back, based on the internal field change in the cable.