<p>A super-radiant terahertz free-electron laser (THz-FEL) light source was developed for the first time in Thailand and Southeast Asia at the PBP-CMU Electron Linac Laboratory (PCELL) of Chiang Mai University. This radiation source requires relatively ultrashort electron bunches to produce intense coherent THz pulses. Three electron bunch compression processes are utilized in the PCELL accelerator system comprising pre-bunch compression in an alpha magnet, velocity bunching in a radio-frequency (RF) linear accelerator (linac), and magnetic bunch compression in a 180° acromat system. Electron bunch compression in the magnetic compressor system poses considerable challenges, which are addressed through the use of three quadrupole doublets. The strengths of the quadrupole fields significantly influence the rotation of the beam line longitudinal phase space distribution along the bunch compressor. Start-to-end beam dynamics simulations using the ASTRA code were performed to optimize the electron beam properties for generating super-radiant THz-FEL radiation. The operational parameters considered in the simulations comprise the alpha magnet gradient, linac RF phase, and quadrupole field strengths. The optimization results show that <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1729_Article_IEq1.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="82" /> </InlineMediaObject> <EquationSource Format="TEX">$10{-}{16\,\textrm{MeV}}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>10</mn> <mo>-</mo> <mrow> <mn>16</mn> <mspace width="0.166667em" /> <mtext>MeV</mtext> </mrow> </mrow> </math></EquationSource> </InlineEquation> femtosecond electron bunches with a low energy spread (<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1729_Article_IEq2.gif" Format="GIF" Height="6" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">$\sim$</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>0.2<InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1729_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">$\%$</EquationSource> <EquationSource Format="MATHML"><math> <mo>%</mo> </math></EquationSource> </InlineEquation>), small normalized emittance (<InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1729_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="131" /> </InlineMediaObject> <EquationSource Format="TEX">$\sim {15}\,{\pi \hbox {mm}\,\cdot \, \hbox {mrad}}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>∼</mo> <mn>15</mn> <mspace width="0.166667em" /> <mrow> <mi>π</mi> <mtext>mm</mtext> <mspace width="0.166667em" /> <mo>·</mo> <mspace width="0.166667em" /> <mtext>mrad</mtext> </mrow> </mrow> </math></EquationSource> </InlineEquation>), and high peak current (<InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1729_Article_IEq5.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="77" /> </InlineMediaObject> <EquationSource Format="TEX">$165{-}{247\,\textrm{A}}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>165</mn> <mo>-</mo> <mrow> <mn>247</mn> <mspace width="0.166667em" /> <mtext>A</mtext> </mrow> </mrow> </math></EquationSource> </InlineEquation>) can be produced by the PCELL accelerator system at the optimal parameters. A THz-FEL with sub-microjoule pulse energies can thus be obtained at the optimized electron beam parameters. The physical and conceptual design of the THz-FEL beamline were completed based on the beam dynamics simulation results. The construction and installation of this beamline are currently underway and expected to be completed by mid-2024. The commissioning of the beamline will then commence.</p>

Design and start-to-end beam dynamics simulation of the first super-radiant THz free-electron laser source in Thailand

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发表日期：

2025年5月27日

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Natthawut Chaisueb,
Sakhorn Rimjaem

摘要

A super-radiant terahertz free-electron laser (THz-FEL) light source was developed for the first time in Thailand and Southeast Asia at the PBP-CMU Electron Linac Laboratory (PCELL) of Chiang Mai University. This radiation source requires relatively ultrashort electron bunches to produce intense coherent THz pulses. Three electron bunch compression processes are utilized in the PCELL accelerator system comprising pre-bunch compression in an alpha magnet, velocity bunching in a radio-frequency (RF) linear accelerator (linac), and magnetic bunch compression in a 180° acromat system. Electron bunch compression in the magnetic compressor system poses considerable challenges, which are addressed through the use of three quadrupole doublets. The strengths of the quadrupole fields significantly influence the rotation of the beam line longitudinal phase space distribution along the bunch compressor. Start-to-end beam dynamics simulations using the ASTRA code were performed to optimize the electron beam properties for generating super-radiant THz-FEL radiation. The operational parameters considered in the simulations comprise the alpha magnet gradient, linac RF phase, and quadrupole field strengths. The optimization results show that $10{-}{16\,\textrm{MeV}}$ $10 - 16 MeV$ femtosecond electron bunches with a low energy spread ( $\sim$ $\sim$ 0.2 $\%$ $%$ ), small normalized emittance ( $\sim {15}\,{\pi \hbox {mm}\,\cdot \, \hbox {mrad}}$ $\sim 15 π mm \cdot mrad$ ), and high peak current ( $165{-}{247\,\textrm{A}}$ $165 - 247 A$ ) can be produced by the PCELL accelerator system at the optimal parameters. A THz-FEL with sub-microjoule pulse energies can thus be obtained at the optimized electron beam parameters. The physical and conceptual design of the THz-FEL beamline were completed based on the beam dynamics simulation results. The construction and installation of this beamline are currently underway and expected to be completed by mid-2024. The commissioning of the beamline will then commence.