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(Color) Photon spectrum per period (solid) and circular polarization rate (dashed) from PM ring undulator (top) and SC undulator (bottom) for 150 GeV (black) and 250 GeV (red) energy electrons. Calculated using the measured magnetic flux density data.
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A comparison of possible undulator designs for the International Linear Collider positron source has resulted in a superconducting bifilar wire design being selected. After a comprehensive paper study and fabrication of the two preeminent designs, the superconducting undulator was chosen instead of the permanent magnet alternative. This was because...
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... block sorting was to be performed, no spare blocks were purchased on which further tests could be performed. The undulator was mounted vertically in a liquid helium bath. The level of liquid helium in the cryostat was monitored with discrete level sensors to ensure that liquid helium covered both the undulator coil and the superconducting current leads. The temperature of the undulator was monitored during cool-down and operation. Voltage taps were used to measure the resistive voltage across the undulator coil with a nanovoltmeter when the undulator was powered. In the cold test, the undulator reached the maximum current of the power supply at 225 A without quenching. The voltage across the complete undulator coil was at the level of 10 ÿ 6 V . This indicates that the wire interconnections have a total resistance < 10 ÿ 8 . The undulator field profile, measured at a current of 220 A, is shown in Fig. 15 and has the expected peak field. It was measured using a Hall probe similar to the pure PM undulator measurements that was calibrated for 4 K operation by the manufacturers. The first and second field integrals, K parameters and mean on-axis peak field are given in Table II. For a 150 GeV electron beam the final angles at the end of the undulator are 14 and 762 prad in the x and the y direction, respectively. The final displacements off axis are 30.9 and 54.9 nm in the x and y directions, respectively. (Although these numbers sound incredibly small it must remembered that the electron beam is ex- tremely rigid and the total length of undulator is only 0 : 3 m .) The trajectory is shown in Fig. 16. From the measured magnetic field of the undulators, the radiation spectrum and polarization can be calculated. This was done using the numeric code SPECTRA [21] and is shown in Fig. 17 for an ILC beam with parameters as given in Table III for the two different models. Two different beam energies have been considered to show the difference between the TESLA and ILC designs. Table IV gives the peak flux and circular polarization rate. Because of interference effects, characteristic of all undulator radiation, there will be some spectral broadening in the photon spectrum due to the finite length of the undulators. The FWHM of the ten period PM undulator device is approximately a factor of 2 larger than the FWHM of the 20 period superconducting device for each harmonic peak, as can be seen in the widths of the first harmonics in Fig. 17. For the real ILC undulator, this would not be a significant factor as both devices would have many thousands of periods. The difference between the total number of photons for the two undulators is explained by the differing K parameters. The total photon flux scales line- arly with the undulator length and determines the maximum positron intensity in the ILC positron source. As the PM undulator produces less photons per unit length, it would consequently have to be longer to produce the same positron intensity as the SC undulator. The circular polarization rates are between 0.78 and 0.93 and although there is no specification for the ILC it is assumed that these rates, being close to the ideal value of 1, are acceptable. The polarization rates for the SC undulator results are higher than those for the PM undulator because the magnetic field quality in the SC undulator is ...
Context 2
... block sorting was to be performed, no spare blocks were purchased on which further tests could be performed. The undulator was mounted vertically in a liquid helium bath. The level of liquid helium in the cryostat was monitored with discrete level sensors to ensure that liquid helium covered both the undulator coil and the superconducting current leads. The temperature of the undulator was monitored during cool-down and operation. Voltage taps were used to measure the resistive voltage across the undulator coil with a nanovoltmeter when the undulator was powered. In the cold test, the undulator reached the maximum current of the power supply at 225 A without quenching. The voltage across the complete undulator coil was at the level of 10 ÿ 6 V . This indicates that the wire interconnections have a total resistance < 10 ÿ 8 . The undulator field profile, measured at a current of 220 A, is shown in Fig. 15 and has the expected peak field. It was measured using a Hall probe similar to the pure PM undulator measurements that was calibrated for 4 K operation by the manufacturers. The first and second field integrals, K parameters and mean on-axis peak field are given in Table II. For a 150 GeV electron beam the final angles at the end of the undulator are 14 and 762 prad in the x and the y direction, respectively. The final displacements off axis are 30.9 and 54.9 nm in the x and y directions, respectively. (Although these numbers sound incredibly small it must remembered that the electron beam is ex- tremely rigid and the total length of undulator is only 0 : 3 m .) The trajectory is shown in Fig. 16. From the measured magnetic field of the undulators, the radiation spectrum and polarization can be calculated. This was done using the numeric code SPECTRA [21] and is shown in Fig. 17 for an ILC beam with parameters as given in Table III for the two different models. Two different beam energies have been considered to show the difference between the TESLA and ILC designs. Table IV gives the peak flux and circular polarization rate. Because of interference effects, characteristic of all undulator radiation, there will be some spectral broadening in the photon spectrum due to the finite length of the undulators. The FWHM of the ten period PM undulator device is approximately a factor of 2 larger than the FWHM of the 20 period superconducting device for each harmonic peak, as can be seen in the widths of the first harmonics in Fig. 17. For the real ILC undulator, this would not be a significant factor as both devices would have many thousands of periods. The difference between the total number of photons for the two undulators is explained by the differing K parameters. The total photon flux scales line- arly with the undulator length and determines the maximum positron intensity in the ILC positron source. As the PM undulator produces less photons per unit length, it would consequently have to be longer to produce the same positron intensity as the SC undulator. The circular polarization rates are between 0.78 and 0.93 and although there is no specification for the ILC it is assumed that these rates, being close to the ideal value of 1, are acceptable. The polarization rates for the SC undulator results are higher than those for the PM undulator because the magnetic field quality in the SC undulator is ...
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Citations
... In 1984, an HSCU was installed in a straight section of the VEPP-2M storage ring in Novosibirsk to measure the polarization of the electron-positron colliding beams [3]. And in the early 2000s, several HSCU prototypes for the International Linear Collider were fabricated and measured in a liquid helium bath cryostat [4]. The effects of the magnetic fields on an electron beam at the entrance and exit of a helical undulator have been analyzed and various geometries of a coil have been proposed [5,6]. ...
... A second feature of the concept is that pins used to transition the conductor between adjacent helical grooves do not extend beyond the diameter of the winding mandrel. This approach differs from previous winding techniques that used ribbon cable, like in [4], which required mechanical junctions and transition pins located on a flange that extended beyond the diameter of the undulator winding groove. ...
Development of superconducting undulators (SCUs) continues at the Advanced Photon Source (APS). Several planar SCUs were designed and built, and two of them are currently in operation at the APS. In January 2018 a new helical SCU (HSCU) was installed on the storage ring at the APS. It has a 1.2 m-long magnet with bifilar winding that generates on its axis a single harmonic of about 6 keV x-rays. The magnet is housed in the newly designed compact cryostat equipped with four cryocoolers. The HSCU was extensively tested prior to its installation on the APS storage ring, and it demonstrated cryogenic and magnetic performance in accordance with the design specifications. The HSCU was rapidly and successfully commissioned, and in February 2018 it was transferred to user operations. Its performance as an x-ray radiation source has been studied and spectral characteristics confirmed. The HSCU is currently used to support unique scientific program at the APS.
In this paper, we make a review of the International Linear Collider design with regard to its positron source. The properties of the intense gamma ray undulator radiation of the dedicated free electron laser is reviewed. We review the discussions about the proposed undulator parameters to obtain an efficient operation of the positron source. The proposals and experimental results about the optimization of the positron beam yield, undulator properties, the injected electron beam energy, polarisation qualities of the produced gamma rays and the positron beam, are discussed. Alternative ideas and suggestions about the use of excess gamma rays in other nuclear energy experiments or the use of positrons in the undulator instead of electrons are also mentioned.
The baseline design of the positron
source for the International Linear Collider (ILC) incorporates a helical undulator and pair‐production target in order to generate the unprecedented quantities of positrons required to sustain the intended ILC physics programme. This configuration is challenging but readily achievable by using novel adaptations of existing technologies to avoid problems inherent in conventional positron
sources in which the stresses in the target(s) and activation of the target station are both serious problems. In addition, a highly polarized positron beam, essential for realizing the full potential of the ILC, can be produced by a simple upgrade to the baseline design.
A major contribution to the international design effort is being led by the UK‐based HeLiCal collaboration. The collaboration is responsible for the design and prototyping of the helical undulator itself, which is a short period device with a small aperture, and also leads development of the start to end simulations of the polarised particles to ensure that high levels of polarization are maintained from the sources, through the beam transport systems and up to the interaction point(s). Members of the collaboration are also involved in the EUROTeV‐funded research programme to produce a design for a pair‐production target which can operate reliably in the high photon flux of the undulator. This paper will provide an update on the work of the collaboration, focusing on the design, construction and testing of components of the polarized positron
source, and will also discuss future plans.
The first demonstration of a full-scale working undulator module suitable for future TeV-scale positron-electron linear collider positron sources is presented. Generating sufficient positrons is an important challenge for these colliders, and using polarized e(+) would enhance the machine's capabilities. In an undulator-based source polarized positrons are generated in a metallic target via pair production initiated by circularly polarized photons produced in a helical undulator. We show how the undulator design is developed by considering impedance effects on the electron beam, modeling and constructing short prototypes before the successful fabrication, and testing of a final module.
The positron source for the International Linear Collider (ILC) is dependent upon a ~200 m long helical undulator to generate a high flux of multi-MeV photons. The undulator system is broken down into a series of 4 m cryomodules, which each contain two superconducting helical undulators. Following a dedicated R&D phase and the construction and measurement of a number of short prototypes a full scale cryomodule has now been manufactured for the first time. This paper reports on the design, manufacture, and test results of this cryomodule.
The high luminosity requirements and the option of a polarized positron beam present a great challenge for the positron source of a future linear collider. This paper provides a comprehensive overview of the latest proposed design for the baseline positron source of the International Linear Collider (ILC). We report on recent progress and results concerning the main components of the source: including the undulator, capture optics, and target.
Polarised positrons have a range of applications in modern physics: from surface science measurements requiring energies as low as a few eV, to studies of the proton structure function and of the fundamental interactions of elementary particles at energies approaching the TeV scale. The common challenge for all of these studies is to generate sufficient numbers of positrons. A discussion of this topic is pertinent to these proceedings as it has been suggested that anti-protons can be efficiently polarised through a hyperfine spin-flip interaction with polarised positrons. In this paper I review the current state of high-intensity sources of polarised positrons. Emphasis is placed on those sources being developed to meet the requirements of future electron-positron colliders.
The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.
The international linear collider has about 80 km of beamlines which require over 13,000 magnets for focusing and steering the beams. Approximately 18% are superconducting magnets and the rest "conventional" warm iron-dominated magnets with copper coils, totaling about 135 styles. Superconducting technology is primarily used for the magnets located in the linacs' RF cryomodules, but it is also required for the spin rotation solenoids, damping ring wigglers, positron source undulator and beam delivery octupoles, sextupoles and final doublet quadrupoles. A major criterion for ILC magnet design is to achieve very high availability in spite of the very large number of magnets. The "availability" goal of the ILC is 85% (or better) and the magnets have been budgeted to cause no more than 0.75% down time. Alignment and mechanical stability requirements in many areas are very challenging. In the Beam delivery system, beam positions must be maintained at sub-micron levels to collide the beams at the interaction point. The ILC has 11 styles of kicker, pulsed or septum magnets. Some kickers need rise and fall times of a few ns and will require very powerful pulsers. Strategies for dealing with the major challenges confronting the ILC magnets will be described.
The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of about 31 km and is designed for a peak luminosity of 2x10^34 cm^-2 s^-1. The complex includes a polarized electron source, an undulator-based positron source, two 6.7 km circumference damping rings, two-stage bunch compressors, two 11 km long main linacs and a 4.5 km long beam delivery system. This report is Volume III (Accelerator) of the four volume Reference Design Report, which describes the design and cost of the ILC.
