High Gradient Quadrupole Magnets Research Articles

Monte Carlo evaluation of high-gradient magnetically focused planar proton minibeams in a passive nozzle

Objective. To investigate the potential of using a single quadrupole magnet with a high magnetic field gradient to create planar minibeams suitable for clinical applications of proton minibeam radiation therapy. Approach. We performed Monte Carlo simulations involving single quadrupole Halbach cylinders in a passively scattered nozzle in clinical use for proton therapy. Pencil beams produced by the nozzle of 10–15 mm initial diameters and particle range of ∼10–20 cm in water were focused by magnets with field gradients of 225–350 T m−1 and cylinder lengths of 80–110 mm to produce very narrow elongated (planar) beamlets. The corresponding dose distributions were scored in a water phantom. Composite minibeam dose distributions composed from three beamlets were created by laterally shifting copies of the single beamlet distribution to either side of a central beamlet. Modulated beamlets (with 18–30 mm nominal central SOBP) and corresponding composite dose distributions were created in a similar manner. Collimated minibeams were also compared with beams focused using one magnet/particle range combination. Main results. The focusing magnets produced planar beamlets with minimum lateral FWHM of ∼1.1–1.6 mm. Dose distributions composed from three unmodulated beamlets showed a high degree of proximal spatial fractionation and a homogeneous target dose. Maximal peak-to-valley dose ratios (PVDR) for the unmodulated beams ranged from 32 to 324, and composite modulated beam showed maximal PVDR ranging from 32 to 102 and SOBPs with good target dose coverage. Significance. Advantages of the high-gradient magnets include the ability to focus beams with phase space parameters that reflect beams in operation today, and post-waist particle divergence allowing larger beamlet separations and thus larger PVDR. Our results suggest that high gradient quadrupole magnets could be useful to focus beams of moderate emittance in clinical proton therapy.

Development of a novel high gradient quadrupole magnet

High gradient quadrupoles are key components for advanced synchrotron radiation light sources. This paper presents the magnet design, the mechanical structure and the magnetic field measurements of a novel high gradient quadrupole magnet. This high gradient quadrupole magnet with a gradient greater than 100 T/m uses permanent magnets (PMs) on the poles to improve the excitation efficiency. The magnetic field measurement results show the feasibility of this magnetic design.

Superconducting quadrupole magnet R&D in the interaction region of CEPC

To obtain high luminosity, compact high gradient quadrupole magnets QD0 and QF1 are required on both sides of the interaction points of the proposed Circular Electron Positron Collider (CEPC). QD0 is a double aperture superconducting quadrupole closest to the interaction point with a crossing angle between two aperture centerlines of 33 mrad. Magnetic field crosstalk between two apertures of QD0 is negligible using iron yoke, and the 3D coil end is optimized by ROXIE. In the design study, both NbTi conductor and HTS conductor are taken into account. The first step of the R&D is to design and manufacture a QD0 short model magnet with a magnetic length of 0.5 m. In this paper, the R&D status of QD0 short model magnet is described, and the design study of quadrupole magnet including NbTi technology and HTS Bi-2212 technology is presented.

Test Results of the First Pre-Series Quadrupole Magnets for the LHC Hi-Lumi Upgrade

The future high luminosity (Hi-Lumi) upgrade of the Large Hadron Collider (LHC) at CERN will include eight (plus two spares) 10.2 m-long Cryo-assemblies which will be components of the triplets for two LHC insertion regions. Each cold mass in the Cryo-assemblies will consist of two 4.2 m-long Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn high gradient quadrupole magnets, designated MQXFA, with aperture 150 mm and operating gradient 132.2 T/m, for a total of twenty magnets. Before assembling and testing the final cold masses at Fermilab, the component quadrupoles are being tested first at the vertical superconducting magnet test facility of the Superconducting Magnet Division (SMD) at Brookhaven National Laboratory (BNL), in superfluid He at 1.9 K and up to 18.0 kA, in accordance with operational requirements of the LHC. The tests of the first two full-length prototype quadrupole magnets MQXFAP1 and MQXFAP2 at BNL have been reported previously. The first two pre-series magnets, the first two that will be used in the LHC, have also now been tested. This paper reports on the quench test and training results of these two magnets. The test results of these magnets will be important for validating the final MQXFA design for operational magnets.

Final Focus Superconducting Magnets for CEPC

Final focus high gradient quadrupole magnets QD0 and QF1 are key devices of the Proposed Circular Electron Positron Collider (CEPC). They are both double aperture superconducting quadrupoles with held gradients of 136 T/m and 110 T/m, respectively. The angles between the two aperture centerlines are both 33 mrad. Though the two apertures of QD0 is in close proximity, the problem of multipole helds caused by held crosstalk is successfully solved by using cos2θ quadrupole coil with iron core. The quadrupol magnets are operated inside the magnetic held of the Detector solenoid magnet, so superconducting anti-solenoid is required to generate solenoid held that can cancel the Detector solenoid held. The hrst step of the R&D is to develop a QD0 short model magnet with a magnetic length of 0.5 m. In this paper, the layout and magnetic design of CEPC hnal focus superconducting magnets are described, and the detailed design of the QD0 short model magnet is presented.

Test Results of the First Two Full-Length Prototype Quadrupole Magnets for the LHC Hi-Lumi Upgrade

The future high luminosity (Hi-Lumi) upgrade of the Large Hadron Collider (LHC) at CERN will include eight (plus two spares) 8.4 m-long cryostatted cold masses which will be components of the triplets for two LHC insertion regions. Each cold mass will consist of two 4.2 m long Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn high gradient quadrupole magnets, designated MQXFA, with aperture 150 mm and operating gradient 132.6 T/m, for a total of twenty magnets. Before assembling and testing the final cold masses at Fermilab, the twenty component quadrupoles will be tested first at the vertical superconducting magnet test facility of the Superconducting Magnet Division at Brookhaven National Laboratory (BNL), in superfluid He at 1.9 K and to 18.0 kA, to meet LHC operational requirements. The first two full-length prototype quadrupole magnets, MQXFAP1 and MQXFAP2, have been tested at BNL. This paper reports on the quench test and training results of these magnets, and also the retest of the first prototype, rebuilt and designated as MQXFAP1b. The test results of these magnets will be important for validating the MQXFA design.

Design and Fabrication of the 1.9 K Magnet Test Facility at BNL, and Test of the First 4-m-Long MQXF Coil

The future high luminosity upgrade of the Large Hadron Collider (LHC) at CERN will include 20 4.2-m-long Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn high gradient quadrupole magnets, which will be components of the triplets for two LHC insertion regions. In order to test these and four preproduction models, the vertical superconducting magnet test facility of the Superconducting Magnet Division (SMD) at Brookhaven National Laboratory (BNL) has been upgraded to perform testing in superfluid He at 1.9 K and 1 bar, the operational condition at the LHC. This has involved extensive modification of the 4.5 K cryogenics plant, including piping, compressors, and other upgraded components; a new vertical test cryostat, which can accept larger diameter magnets; a modernized power supply system upgraded with IGBT switches and fast shutoff capability, and that can supply 24 kA to test high field Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnets; and completely new data acquisition, signal analysis, and control software and hardware, allowing for fast, high precision, large volume data collection. This paper reports on the design, assembly, and commissioning of this upgraded test facility, and presents results of the first magnet test performed.

Conceptual design of a compact high gradient quadrupole magnet of varying strength using permanent magnets

A concept is presented to design magnets using cylindrical-shaped permanent-magnet blocks, where various types of magnetic fields can be produced by either rotating or varying the size of the magnetic blocks within a given mechanical structure. A general method is introduced to calculate the 3D magnetic field produced by a set of permanent magnets. An analytical expression of the 2D field and the condition to generate various magnetic fields like dipole, quadrupole, and sextupole are derived. Using the 2D result as a starting point, a computer code is developed to get the optimum orientation of the magnets to obtain the user-specific target field profile over a given volume in 3D. Designs of two quadrupole magnets are presented, one using 12 and the other using 24 permanent-magnet blocks. Variation of the quadrupole strength is achieved using tuning coils of a suitable current density and specially designed end tubes. A new concept is introduced to reduce the integrated quadrupole field strength by inserting two hollow cylindrical tubes made of iron, one at each end. This will not affect the field gradient at the center but reduce the integrated field strength by shielding the magnetic field near the ends where the tubes are inserted. The advantages of this scheme are that it is easy to implement, the magnetic axis will not shift, and it will prevent interference with nearby devices. Around 40% integrated field variation is achieved using this method in the present example. To get a realistic estimation of the field quality, a complete 3D model using a nonlinear $B\text{\ensuremath{-}}H$ curve is also studied using a finite-element-based computer code. An example to generate around an $80\text{ }\text{ }\mathrm{T}/\mathrm{m}$ quadrupole field gradient is also presented.

A review of conductor performance for the LARP high-gradient quadrupole magnets

We summarize critical current measurements and parameterizations of the data of 112 round wires and extracted strands that were reacted with the first 17 coils for the high-gradient quadrupole (HQ) magnets for the US LHC Accelerator Research Program (LARP). We standardize the strand parameterizations and coil ‘short sample’ calculations, and demonstrate that the entire critical current database can be captured in two scaling parameters per coil. These parameters summarize the short sample performance for each coil for either HQ magnet tests, or mirror tests of individual coils. We also demonstrate that for RRP® conductors, generic strain scaling parameters can be derived for at least four substantially different wire configurations, and standardize self-field corrections for LARP. The parameterized conductor performance is used to judge the performance of the HQ magnets and mirror tests. We find that although the HQ magnets reach around 86% of their short sample limitations, they are limited by factors other than the critical current of the conductor. Individual coils in mirror tests reach up to 98% of the expected performance, and do appear limited by the critical current of the conductor. Detailed analysis of short sample performance through accurate parameterizations simplifies the accessibility of short sample data, and enables accurate judgment of magnet performance as well as conductor and cable quality.

Cold Test Results of the LARP HQ $\hbox{Nb}_{3} \hbox{Sn}$ Quadrupole Magnet at 1.9 K

The high gradient quadrupole magnet is a 120-mm-aperture, 1-m-long Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupole developed by the LHC Accelerator Research Program collaboration in support of the High-Luminosity LHC project. Several tests were performed at Lawrence Berkeley National Laboratory in 2010-2011 achieving a maximum gradient of 170 T/m at 4.4 K. As a next step in the program, the latest model (HQ01e) was sent to CERN for testing at 1.9 K. As part of this test campaign, the magnet training has been done up to a maximum current of 16.2 kA corresponding to 85% of the short sample limit. The ramp rate dependence of the quench current is also identified. The efficiency of the quench heaters is then studied at 4.2 K and at 1.9 K. The analyses of the magnet resistance evolution during fast current discharge showed evidence of quench whereas high energy quenches have been successfully achieved and sustained with no dump resistor.

Compact Superconducting High Gradient Quadrupole Magnets for the Interaction Regions of High Luminosity Colliders

Recent developments in the high luminosity <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> colliders are based on a collision scheme with a large Piwinski angle, a vertical beta function β <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> much smaller than the bunch length, and a crab waist transformation. This scheme is being adopted in the SuperB asymmetric collider, to be built in Italy, with a design peak luminosity of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">36</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> sec <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . A crucial role is played by the quadrupole doublets QD0/QF1, which are placed close to the interaction point and generate gradients close to 100 T/m. The available space for the doublets is very small, causing the magnets to be operated with a high engineering current density (2000 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). Starting from the helical coil concept, an advanced design of the quadrupole has been developed. The paper discusses the basic design concepts and the development of a coil model aimed at assessing the design criteria and demonstrating the feasibility of the quadrupole. The successful test of the coil model opens the way to new compact superconducting high gradient quadrupole magnets for the interaction regions of high luminosity colliders.

Development of Wide-Aperture Quadrupole Magnets for Plasma Experiments in the FAIR Project

Heavy ion heating and expansion and laboratory planetary sciences experiments are designed by the high energy density matter generated by heavy ion beams collaboration to study matter under extreme conditions of temperature and pressure at the FAIR facility in Darmstadt, Germany. A special final focusing system has to be installed at the end of the high energy density matter generated by heavy ion beams beam line for strong transverse focusing. To provide a focal spot of the size of a millimeter or less, a large focal angle is needed and, consequently, large-aperture high-gradient quadrupole magnets have to be used in the final focusing system. The Institute for High Energy Physics has considered the basic principles of the development of these magnets. The main parameters of the quadrupole are: the central gradient is 33 T/m; the inner diameter of the coil is 240 mm; the effective length of the magnet is 2 m; and the operating mode is dc. Design features of these quadrupole magnets are detailed: the superconducting wire, 2- and 3-D optimization of the coil and yoke geometry, and mechanical analysis. Preliminary considerations are given on the parameters of the protection and cooling systems of the magnets.

Quench Antenna Studies of Mechanical and Quench Performance in Fermilab Interaction Region Quadrupoles for LHC

As part of the US-LHC collaboration, Fermilab has built and tested seventeen high gradient quadrupole magnets, assembled into nine cryostats, for installation at the Large Hadron Collider Interaction Regions. Most of these magnets have only quarter coil voltage taps for quench characterization, but the magnetic measurement warm bore is instrumented with a quench antenna for localization and characterization. We report on studies using the quench antenna for pre-production prototype (with extensive voltage taps) and 17 production magnets. These include a summary of quench localization and development characteristics, as well as general features of flux changes observed during training ramps

Thermal studies of a high gradient quadrupole magnet cooled with pressurized, stagnant superfluid

A 2-m long superconducting model of an LHC Interaction Region quadrupole magnet was wound with stabrite coated cable. The resulting low interstrand resistance and high AC losses presented the opportunity to measure magnet quench performance in superfluid as a function of helium temperature and heat deposition in the coil. Our motivation was to duplicate the high radiation heat loads predicted for the inner triplet quadrupoles at LHC and study the coil cooling conditions in the magnet. At the Magnet Test Facility in Fermilab's Technical Division, the magnet quench performance was tested as a function of bulk helium temperature and current ramp rate near the planned high luminosity interaction region field gradient of 205 T/m. AC loss measurements provided a correlation between current ramp rate and heat deposition in the coil. Analysis indicates that the results are consistent with there being little participation of superfluid helium in the small channels inside the inner layer in the heat removal from the coil. However magnet performance will be limited by the outer coil pole turn in LHC at a current level well above the operating current.

Field quality in Fermilab-built models of high gradient quadrupole magnets for the LHC interaction regions

Superconducting quadrupole magnets for the interaction regions of the Large Hadron Collider are being developed by the US-LHC Accelerator Project. These 70 mm bore quadrupole magnets are intended to operate in superfluid helium at 1.9 K with a nominal field gradient of 215 T/m. A series of 2 m model magnets are being built and tested at Fermilab to optimize design and construction parameters. Measurements of the field quality of the model magnets tested to date and comparisons with the required field quality are reported in this paper.

Mechanical design and analysis of LHC inner triplet quadrupole magnets at Fermilab

A series of model magnets is being constructed and tested at Fermilab in order to verify the design of high gradient quadrupole magnets for the LHC interaction region inner triplets. The 2 m models are being built in order to refine the mechanical and magnetic design, optimize fabrication and assembly tooling, and ensure adequate quench performance. This has been carried out using a complementary combination of analytical and FEA modeling, empirical tests on 0.4 m mechanical assemblies and testing of model magnets during fabrication and under cryogenic conditions. The results of these tests and studies have led to improvements in the design of the magnet end restraints, to a preferred choice in coil end part material, and to a better understanding of factors affecting coil stress throughout the fabrication and operational stages.

Influence of mechanical vibrations on the field quality measurements of LHC interaction region quadrupole magnets

The high gradient quadrupole magnets being developed by the US-LHC Accelerator Project for the LHC Interaction Regions have stringent field quality requirements. The field quality of these magnets will be measured using a rotating coil system presently under development. Mechanical vibrations of the coil during field quality measurements are of concern because such vibrations can introduce systematic errors in measurement results. This paper presents calculations of the expected influence of vibrations on field quality measurements and a technique to measure vibrations present in data acquired with standard "tangential-style" probes. Measured vibrations are reported and compared to simulations. Limits on systematic errors in multipole measurements are discussed along with implications for probe and measurement system design.

Mechanical studies of the Fermilab low beta quadrupole collared coils

Finite element results of Low Beta Quadrupole magnets are compared to measurements from three mechanical models. Stress, as measured with internal strain gauges, and radial deflections, as measured with a precision measuring device, are compared to the finite element analysis. The results indicate that measured internal pressures are in agreement with calculations but measured deflections are approximately lower than predicted. The findings will help develop better analyzing and manufacturing techniques to be used on developing the High Gradient Quadrupole magnet.

Design and fabrication of a high aspect ratio cable for a high gradient quadrupole magnet

The Large Hadron Collider interaction regions require quadrupoles with a 70 mm diameter bore, a gradient of 250 T/m, and good cooling so that the magnets can operate in a high radiation background without quenching. In order to meet these stringent requirements, a two-layer magnet with a high aspect ratio cable has been designed. This cable utilizes the SSC inner and outer layer strands, which have been optimized and are available in large quantities. The initial design parameters for both cables are 15.2 mm width; the inner cable has 38 strands of 0.8 mm diam wire and a keystone angle of 0.99 deg. The outer cable has 46 strands of 0.65 mm diam wire and a keystone angle of 0.69 deg. These cables have been fabricated and then subjected to a number of tests to insure their performance in the quadrupole. These test results, including model coil winding studies, electrical property measurements, and mechanical property measurements will be presented.

A high gradient quadrupole magnet for a polarized beam facility

A prototype quadrupole magnet with 2.8 m effective length is under design and construction for use in a polarized beam transport system at Fermi National Accelerator Laboratory. The operating gradient required is 50 T/m and the higher multipole error fields must not exceed a few parts in one thousand over a 10 cm diameter bore. For cryogenic efficiency the magnet will operate at 1000 amperes and a cold iron yoke will provide complete field shielding.