Skew Quadrupole Research Articles

Detector solenoid compensation in the EIC electron storage ring

The Electron-Ion Collider (EIC) uses crab cavities to restore the geometrical luminosity loss associated with the large crossing angle. Due to space limitations, the detector solenoid cannot be compensated locally. This paper presents the lattice design to compensate the detector solenoid effects without interfering with the crab cavities. Skew quadrupoles are employed to avoid additional crab cavities. The correction scheme is checked by beam-beam simulation.

Design and Field Performance of Octupole Magnet With Skew Quadrupole Component in HEPS

The High Energy Photo Source (HEPS) is being built in China and the magnets are in batch production. The octupole magnets with skew quadrupole component used in the storage ring have been designed and manufactured. The octupole has an aperture of 30 mm, a field gradient of 735000 T/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and a length of 0.26 m. In this paper, detailed magnetic design of HEPS octupole magnets is presented. Different design schemes of the skew quadrupole coils are compared, and the temperature effect on magnetic center and the integral field in the first batch of octupole magnets are also given. In addition, the influence of the combined power-on mode on the magnetic field is studied.

Construction and Power Test of the Superferric Skew Quadrupole for HL-LHC

INFN is developing at LASA laboratory (Milano, Italy) the prototypes of five high order corrector magnets, from skew quadrupole to dodecapole, which will equip the high-luminosity interaction regions of the High Luminosity-LHC (HL-LHC). These magnets are based on a superferric design, which allows a relatively simple, modular and easy to construct magnet. This activity takes place within the framework of a collaboration agreement between CERN and INFN. Four prototypes, from sextupole to dodecapole, have been built and tested starting in 2016. We present here the last prototype of the high order correctors, to be installed in LHC, the skew quadrupole: magnetic and mechanical design are discussed together with quench protection. We report also on the overall experience gained during construction aiming toward the series production. The power test of the quadrupole, including the training, the qualification and the quench behavior in operational conditions are also described.

Rotating coil field measurement of superconducting magnet for BEPCII interaction region

Two multifunction superconducting magnets in the interaction region (IR) for Beijing electron positron collider upgrade project (BEPCII) have been measured in BESIII detector hall in 2007. Each superconducting magnet package contains multiple concentric layers with several function magnets called as a vertical focusing quadrupole (SCQ), a horizontal corrector (HDC/SCB), a vertical corrector (VDC), a skew quadrupole (SKQ) and three anti-solenoids (AS1, AS2 and AS3) to compensate the experimental detector solenoid field. All these function magnets SCQs, SCB/HDCs, VDCs and SKQs have been measured using two rotating coils. Their integral fields, their high order harmonics contents and the local fields along the beam line are obtained in detail with the rotating coil probe system. Comparing the results to the stretched wire, the differences for the integral fields are less than 0.2%. As a result, the method presented in this paper can be used as an absolute field measurement in our lab.

Shift Dependent Skew Quadrupole in Advanced Light Source Elliptically Polarizing Undulators, Cause and Corrections

Three elliptically polarizing undulators (EPU) are installed and operational at the Advanced Light Source (ALS); the most recent was installed in April '05. Operational experience has shown a variation in electron beam size which correlates with the EPU's magnetic quadrant shifts used to vary polarization. Storage ring electron dynamics studies pointed to the existence of a shift dependent skew quadrupole (SQ) component generated within the EPU's. Detailed magnetic and mechanical measurements demonstrated that the field errors were the result of systematic individual magnetic block displacements which vary with quadrant shift. This paper will discuss the results of electron dynamics studies, magnetic and mechanical measurements, design modifications planned for future EPU's to eliminate the SQ source, and the design and implementation of SQ compensation coils

Skew quadrupole in RHIC dipole magnets at high fields

In the RHIC are dipoles, the center of the cold mass lies above the center of the cryostat. At the maximum design field, the magnetic flux lines leak through the yoke to the asymmetrically located cryostat, which provides an additional return path. This introduces a systematic top-bottom asymmetry leading to a skew quadrupole term at high fields. A similar asymmetry is also created by any difference in weights of the upper and the lower yoke halves. Data from measurements of several RHIC dipoles are presented to study this effect. In the current production series of the RHIC dipoles, an attempt is made to compensate the effect of the cryostat by an asymmetry in the iron yoke. Seven dipoles with this type of yoke have been cold tested, and show a reduced saturation in the skew quadrupole term, as expected.

Antiproton Losses at Large Transverse Amplitudes in the CERN Antiproton Accumulator and Corrective Measures Using Skew Quadrupoles and Sextupoles

The CERN Antiproton Accumulator captures 3.5 GeV/c antiprotons with a nominal transverse acceptance of 100? mm. mrad in each plane. The transverse phase space population has been predicted by tracking antiprotons, created in the production target, through the transport line into the Accumulator. The predicted betatron amplitude distributions have been compared to those measured using internal scrapers in a zero momentum dispersion region. It is found that the antiproton population fits the predictions at low amplitudes, but for amplitudes beyond about half of the maximum values there is a progressive depopulation resulting in an overall shortfall in integrated antiproton yield by a factor of about two. This is attributed to the effects of linear and non-linear transverse coupling. After correction by skew quadrupoles and sextupoles the shortfall is reduced significantly but not entirely eliminated due to the practical difficulties in achieving complete compensation of the coupling forces.

The Revised Skew Quadrupole System for Coupling Compensation in the CERN Intersecting Storage Rings (ISR)

With the existing and proposed installations of solenoid detector magnets and low-ß schemes, the original coupling compensation scheme in the ISR was no longer sufficiently versatile to provide adequate compensation under all conditions. A brief description of the new scheme, which was installed early in 1978, is given. This scheme can excite coupling vectors at any phase so that it is able to compensate solenoids and large localized quadrupole errors in low-ß schemes as well as random magnet tilts. The design of the scheme is also strongly influenced by the fact that there are no regions with zero horizontal dispersion in the ISR and the skew quadrupoles have to be specially arranged so as to avoid exciting vertical dispersion. The experience gained with this scheme and the methods used for measurement and correction of the machine are illustrated by practical examples.

A Method for Increasing the Multiturn Injection Efficiency in AG Proton Synchrotrons by Means of Skew Quadrupoles

An increase of the injection efficiency due to linear coupling [already known at the Cosmotron in 1953 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> )] is shown to work in AG Proton Synchrotrons for Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> - Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> = P. The system is in operational use at the CERN Proton Synchrotron Booster (PSB) to reach intensities above 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> ppp. An intensity increase of 20% is achieved at the expense of a slight vertical blow-up, which is however not noticeable for high-intensity beams as their emittance is already increased because of an integer stop-band. In this paper a comprehensive model is presented, which describes the efficiency as a function of several parameters, such as the coupling strength, injection geometry and Q-values. Provided enough vertical acceptance is available, the same scheme may be profitable for other accelerators using betatron stacking for |Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> - Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> - P| < 0.1; ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> >> ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> .