System design and measurements of flux concentrator and its solid-state modulator for CEPC positron source

Positron sources are one of the most important components of the injector of a circular electron positron collector(CEPC).The CEPC is designed as an e^(+)e^(−)collider for a Higgs factory.Its accelerator system is composed of 100-km-long storage rings and an injector.The design goal of the positron source is to obtain positron beams with a bunch charge of 3 nC.The flux concentrator(FC)is one of the cores of the positron source.This paper reports the design,development,and measurements of an FC prototype system.The prototype includes an FC and an all-solid-state high-current pulse modulator.Preliminary tests show that the peak current on the FC can reach 15.5 kA,and the peak magnetic field can reach 6.2 T.The test results are consistent with the theoretical simulation.The FC system fulfills the requirements of the CEPC positron source as well as provides a reference for the development of similar devices both domestically and abroad.

A positron source using an axially oriented crystal associated to a granular amorphous converter

A non-conventional positron source using the intense y radiation from an axially oriented monocrys- tal which materializes into e^＋e^- pairs in a granular amorphous converter is described. The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its 〈111〉 axis is reported. The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream, is also re- ported. Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density. Substituting a granular target made of small spheres for the usual compact one, makes the energy dissipation easier. The deposited energy and correspond- ing heating are analyzed and solutions for cooling are proposed. The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC.

Conceptual design of an intense positron source based on an LIA

Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA （linear induction accelerator） is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source.

CEPC positron source design

Purpose Circular Electron Positron Collider(CEPC)is a 100-km-ring e+e−collider for a Higgs factory.The injector is composed of a 10-GeV Linac and a 120-GeV Booster.The CEPC Linac is a normal conducting S-band Linac with frequency of 2860 MHz providing electron and positron beams at an energy up to 10 GeV with 100 Hz repetition frequency.The positron source is the most important part of the CEPC Linac,and the bunch charge of positron beam within some cut-off condition should be larger than 3 nC.Methods The positron source of CEPC is composed of a target,a flux concentrator,a capture section,a pre-accelerating section and a beam separation system.Higher positron yield and capture efficiency are the design goal.Based on simulation,the design will be presented and discussed in detail.Result The positron yield at the PSPAS exit is larger than 0.55,and the normalized rms emittance is 2370 mm-mrad with a strict cut-off condition.The detailed simulation results will be presented.Conclusions The design of the positron source including positron production and capture will be presented and can meet the requirements.

Development and application of the intense slow positron beam at IHEP

This paper describes the development and application of an intense slow positron beam at IHEP with regard to its two main components. The Variable-Energy Positron Lifetime Spectroscopy （VEPLS） based on the pulsing system consisting of a chopper, a prebuncher and a buncher has been constructed in order to meet the needs of materials science development. At present, the time resolution of the VEPLS can easily reach about 386 ps with a peak-to-background ratio of about 600：1. A plugged-in ^22Na positron source section for adjusting the newly built experimental station and for increasing the beam operation efficiency has been constructed. A slow positron beam with an intensity of 2.5×10^5 e^＋/s and the beam profile whose diameter is 10 mm has been obtained; the moderation efficiency of the tungsten mesh moderator reaches 5.1×10^-4 as calculated with an original positron source activity of 52 mCi.