The Siam Photon Source (SPS) is an electron accelerator complex consisting of a 40 MeV linear accelerator (LINAC), a 1 GeV booster synchrotron (SYN) and a 1.2 GeV electron storage ring (STR). The elctrons are produced by a thermionic electron gun then accelerated by 2856 MHz high power microwave in the linear accelerator. The 40 MeV electrons are transported by the low energy beam transport line (LBT) to the booster synchrotron and accelerated to 1 GeV by 118 MHz Radio Frequency wave in the RF cavity of the booster synchrotron. The 1 GeV electrons are transported by the high energy beam transport line (HBT) to the storage ring and further accelerated to 1.2 GeV.

Components of Siam Photon Source

1. Electron gun

Electron beam is produced by the electron gun via thermionic process, that is, the gun filament is heated by the applied electric current causing electrons to be released. These electrons are then ‘pulled’ toward the linear accelerator by an applied electric field.

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2. Linear accelerators

Electron beam from the electron gun is then accelerated by two 20 MeV (20 million electron volts) linear accelerators, or linacs for short. After passing through the two accelerating structures, the 40 MeV electrons then enter the booster synchrotron via the low-energy beam transport line (LBT) for further acceleration.

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3. Booster synchrotron

The booster synchrotron accelerates 40 MeV low energy electrons to 1.0 GeV (1 billion electron volts). Each round an electron circulates in the booster ring it gains incremental energy through applied radio wave inside the radio-frequency (RF) cavity. To attain 1.0 GeV energy electrons must circulate approximately 4 million turns in the booster, although the whole process lasts merely 0.6 seconds.

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4. Storage ring

The 1.0 GeV electrons are then sent to the storage ring to be further accelerated up to 1.2 GeV. After this energy ramping process the electrons are stored in the ring to produce synchrotron radiation. Each time electron passes through a bending magnet or an insertion device, i.e. a magnet specially designed for the production of higher-energy and/or higher-brilliance or specifically polarized synchrotron light, it loses a small portion of its energy in the form of electromagnetic radiation, i.e. synchrotron radiation. This portion of energy is then recovered when the electron passes through the RF cavity in the ring.

5. Photon beamlines

Synchrotron light is carried to the experimental stations via photon beamlines. Two most important components of a photon beamline are the monochromator and focusing elements. Mirrors are used to focus the photon beam to a small area of interest while retaining the available photon fluxes. Monochromator is used to select the photon energy suitable for a particular experiment. Each beamline has different components and setups depending on the photon energy range to be used and type of experiment to be carried out.

6. Experimental stations

Experimental station is where the sample to be studied is located. A great number of measurements and experiments can be set up to utilize the generated synchrotron radiation. Data from the interaction processes between light and matter is then collected for subsequent analyses. Measurement techniques utilizing synchrotron radiation have been proven to be invaluable in researches in a wide variety of disciplines, including physical science, biological science, materials science, agriculture, archaeology, environmental science, among others.

SPS operation

The Siam Photon Source electron beam energy is 1.2 GeV, and the electron current injected for each operation cycle (filling) is 150 mA. At present the beam emittance is 41 nm-rad, and the beam lifetime is approximately 12 hours at 100 mA. Since the energy of the SPS booster is only 1.0 GeV, the energy of the beam needs to be ramped up to 1.2 GeV in the storage ring at each injection. The development activities to upgrade the SPS booster energy to 1.2 GeV are currently ongoing. Currently there is only one insertion device (ID), the U60 permanent magnet planar undulator, installed in the ring. Two more IDs, a 2.4 Tesla permanent magnet wiggler (PMW) and a 6.5 Tesla superconducting magnet wavelength shifter (WLS), will soon be installed to produce higher energy x-rays for SLRI users.

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