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Low Energy Positron Source

#0767-3


RIKEN/Budker INP Low Energy Positron Source: Target-moderator System

Tech Area / Field

  • PHY-OTH/Other/Physics

Status
8 Project completed

Registration date
06.08.1998

Completion date
30.10.2000

Senior Project Manager
Malakhov Yu I

Leading Institute
Budker Institute of Nuclear Physics, Russia, Novosibirsk reg., Akademgorodok

Supporting institutes

  • VNIITF, Russia, Chelyabinsk reg., Snezhinsk

Collaborators

  • Institute of Physical and Chemical Research (RIKEN) / SPring-8, Japan, Hyogo

Project summary

The proposed Project is a logical prolongation of the work which was carried out within the previous two years in frame of ISTC Project №767, during which the key element of a slow positron source - 8-10 Tesla superconducting wiggler was designed, fabricated and tested in situ at Budker INP, Novosibirsk.

The main objective of this Project is to create a slow positron source of high brightness on the basis of pair photoproduction in a system target - moderator from hard gamma-quanta of synchrotron radiation (SR). The roll of a powerful SR source it supposed to be played by the unique high- field superconducting wiggler, fabricated at Budker INP, after its installation on the electron storage ring SPring-8 of 8 GeV energy. The later was made and started to operation in Japan as a SR source and by its parameters also unique nowadays.

The main prospective tasks for next 12 months are


- Magnetic measurements of the key element of the project -the superconducting wiggler in the own cryostat of Budker INP which include calibration of Hall probes at high fields, mapping at different field levels in the wiggler and alignment of field integrals with the help of the current wire method.
- Test of the cryogenic system and various operation modes of the superconducting wiggler, detailed measurement of heat in-leaks and selection of operation modes of cooling machines for steady work of the wiggler.
- Eexperimental study of moderator prototypes with the use of isotope sources at RFNC-VNIITF.
- Custom clearance of the equipment before sending to Japan.
- Transportation of the superconducting wiggler and other equipment to Japan to the storage ring SPring-8.
- Assembly of the equipment on the storage ring SPring-8 with participation of the Budker INP team and representatives of SPring-8, which provide necessary materials and mechanisms for assembly of the equipment, training and instructing for realization of safe work in the specially planned temporary frameworks.
- Conduction in collaboration with the SPring-8 team of wiggler tests for the maximal field and carrying out of measurements on conformity of parameters to the requirements placed from the point of view of reliability and stability of work.

Preparation of the joint agreement on transfer of the equipment to the joint usage as a powerful synchrotron radiation source in the field of hard X-ray and as slow positron source of high brightness.

-Development of the Russia-Japan long - term program of joint research with participation of laboratories of other countries with the use of the Slow Positron Source based on the superconducting wiggler and SPring-8 storage ring.

In the technical plan the slow positron source consists of two basic systems: the superconducting wiggler and the target- moderator system.

For the wiggler to correspond to the requirements placed for such a magnetic and to provide motion stability of electrons in the storage ring SPring-8, it is necessary to carry out reliable magnetic measurements for magnetic field mapping and alignment of field integrals along a trajectory with the help of the specially developed method of measurement of field integral using a tensed wire with a current. For field mapping it is required to carry out special calibration of Hall probes to account for non-linearity of the probes in large magnetic fields, using the specially developed NMR (Nuclear Magnetic Resonance) probe. For improvement of various modes of wiggler operations in conditions of the closed current through a persistent current key and current supply through the connected power supplies it is proposed to conduct series of measurements for adjustment of operation modes of coolers at Budker INP.

Brightness of a slow positron source to a large measure depends on the target -moderator system. Thus computer simulation of positron production and moderation is conducted for different geometries of this system with account of experience of other laboratories of the world. For purpose of experimental confirmation of correctness of calculations manufacture the prospective systems, experimental measurement of moderation efficiency and selection of optimum parameters and operation modes of the target- moderator system with the use of isotope sources received on the neutron generator NG-12 are planned.

The considered slow positron source is unique because in it direct conversion of a hard part of synchrotron radiation to positrons for the first time in the world will be realized. As the photon flux of synchrotron radiation in this case falls down exponentially for energies above 1 MeV, the activity induced on the system target - moderator and other parts of installation at a flux of useful positron within of 1010 e+ /sec will be negligibly small. That considerably simplifies realization of experiments and makes cheaper necessary protection for safe work.

At deenergizing beam in the storage ring or switch off wiggler magnetic field practically at this moment the equipment is accessible to replacement of samples or other works. That is impossible in case of sources on the basis of the linear accelerator or isotope radioactive source.

The significance of the project is that as a result of works there will be a unique opportunity of creation of the slow positron source of high brightness for the international scientific public on the basis of unique, well technically equipped center of science SPring-8 for realization of joint experiments and researches in the field of solid state physics, nuclear physics, medical and technical applications etc. Besides alongside with slow positrons a synchrotron radiation beam from the wiggler also of high brightness in a wide energy spectrum from soft X-ray up to gamma-quanta of some MeVs simultaneously can be accessible.

RIKEN, SPring-8 was as foreign collaborator under the project № 767 together with which the numerous discussions and working meetings on the project were carried out, the joint works were published and the presentations at conferences during realization of the project were made. During the examined project the cooperation with the Japanese party will become closer, when the team SPring-8 will become the direct participant of works during mounting, installation and commissioning of the equipment on the storage ring SPring-8.


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