- Email: [email protected]
0.3-nm SASE-FEL at PAL
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 528 (2004) 582–585
0.3-nm SASE-FEL at PAL J.S. Oh*, D.E. Kim, E.S. Kim, S.J. Park, H.S. Kang, T.Y. Lee, T.Y. Koo, S.S. Chang, C.W. Chung, S.H. Nam, W. Namkung Pohang Accelerator Laboratory, Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang 790-784, Republic of Korea
Abstract Recent success in SASE-FEL experiments provides high confidence in achieving FEL radiation wavelengths as short as 0.1 nm.The SASE-XFEL requires multi-GeV electron beams with extremely low-emittance, short bunches, and long undulator systems. PAL is operating a 2.5-GeV electron linac as a full-energy injector to the PLS storage ring. With a proposed energy upgrade to 3.0 GeV and an in-vacuum undulator, PAL will be able to produce coherent X-ray radiation at wavelengths as short as 0.3 nm.This paper presents the preliminary design details for the proposed PALXFEL. The required undulator period is 12.5 mm with a 3-mm gap. The third harmonic enhancement technique can be used to obtain radiation wavelengths of 0.1 nm.The technical parameters related to these goals are reviewed. r 2004 Elsevier B.V. All rights reserved. PACS: 41.60.Cr Keywords: PAL; X-ray SASE; In-vacuum undulator; 0.3 nm; Third-harmonic enhancement
1. Introduction The last two decades have ushered in rapid progress in basic and applied science research using synchrotron radiation and technological advancements in extremely intense electron beams for high-energy physics research. These result in both strong demands for, as well as the possibilities of, fully coherent radiation with high brilliance, called fourth-generation light sources. LCLS [1] at SLAC and TESLA-XFEL [2] at DESY are in the detailed design stages with *Corresponding author. E-mail address: [email protected] (J.S. Oh).
government funding approval. These SASE-XFEL facilities are expected to be operational by 2008 and 2012, respectively. Those projects require large-scale accelerators with 14–20-GeV electron beams and very long undulator systems with 113– 175-m lengths. We propose a compact X-ray Free Electron Laser Program at the Pohang Accelerator Laboratory, PAL-XFEL. PAL operates an electron linac, the third largest in the world, 2.5 GeV at present, as a full-energy injector to the PLS storage ring [3]. The linac is regularly injecting these beams to a storage ring twice a day for up to 5 min per injection. In its design stage, PAL was designed to use multi-application beams concurrently. With
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.04.106
ARTICLE IN PRESS J.S. Oh et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 582–585
2. PAL X-FEL The fundamental radiation wavelength lx of an undulator is given by lx ¼
lu ð1 þ K 2 =2Þ 2g2
where g ¼ E0 =0:511; K ¼ 0:934Bu lu ; E0 is the beam energy in MeV, Bu is the peak magnetic field of the undulator in Tesla, and lu is the undulator period in cm. Either a short-period undulator or a high-energy beam can provide short-wave radiation. However, the value of K should be reasonably large to obtain a short saturation length. An in-vacuum mini-gap undulator can meet this requirement. This concept was introduced by the SCSS project at SPring-8 [4]. We will use a 45 magnetized undulator with H ¼ lu =2: The peak magnetic field on axis is calculated by pffiffiffi N 4 2Br X 1 peak ð1 e2npH=lu Þenpg=lu By ¼ p n¼1;5;9 n where Br is assumed to be 1.19 T provided by Nd2Fe14B magnets, H is the block height, g is fullgap length as shown in Fig. 1 [5].
Nominal beam parameters for the PAL X-FEL linac are summarized in Table 1. The emittance can be further optimized by reducing the bunch charge and peak current, which provides the same saturation length with a moderate power reduction. Fig. 2 shows the saturation lengths and beam energies for 0.3-nm SASE as a function of undulator period and gap size, which are calculated by the use of equations given by Xie [6]. This figure clearly shows that the undulator must have a period of less than 1.3 cm and a gap size of less than 3 mm to limit the saturation length within 50 m for a 3-GeV beam energy. Table 2 summarizes key parameters of the undulator for a 0.3-nm PAL X-FEL. The undulator beta value is optimized to obtain as short a saturation length as possible. The result shows that we need 13 undulators, each 4.5-m long. Table 3 lists the X-ray radiation parameters. Due to the Table 1 Beam parameters for PAL X-FEL Beam energy (GeV) Normalized emittance (mm-rad) Peak current (kA) Bunch charge (nC) FWHM bunch length (fs) Energy spread (%)
3.0 1.5 4.0 1.0 235 0.02
1.0
2.5 GeV 3 GeV
0.8 Undulator Gap [cm]
the proposed upgrade modification for the beam energy of 3.0 GeV and an in-vacuum undulator system, it will be possible to produce coherent Xray radiation as short as 0.3 nm. To obtain radiation wavelengths of 0.1 nm, we propose to employ the third-harmonic enhancement technique that will utilize an additional undulator system with a shorter periodic length. The design goal is for the undulator to be less than 60 m in total length.
583
4 GeV 0.6
60 m 0.4
50 m 0.2
40 m
g 0.0
H
0
1
2
3
Undulator Period [cm]
λu Fig. 1. Undulator geometry with 45 magnetization.
Fig. 2. Undulator period vs. gap length for 0.3-nm SASE with saturation lengths of 40, 50, and 60 m and beam energies of 2.5, 3, and 4 GeV.
ARTICLE IN PRESS J.S. Oh et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 582–585
584
Table 2 Undulator parameters for 0.3-nm XFEL Period (mm) Gap (mm) Peak magnetic field (T) Undulator parameter, K Beta (m) Saturation length (m)
12.5 3.0 0.97 1.14 15 52
Table 3 X-ray radiation parameters FEL parameter 1D gain length (m), L1d 3D gain length correction, Z Gain length (m), Lg Peak power (GW) Peak brightness ( 1032)
0.00043 1.35 0.97 2.67 2.1 1.4
Table 4 Undulator parameters for 0.1-nm XFEL
1E+35 TESLA SASE FEL
1E+33 DESY TTF-FEL
1E+29
A
SPring-8 SCSS
1E+27 1E+25 1E+23
300
SPring-8 Undulator (4.5 m in-vacuum)
1E+21
SPring-8 Bending PLS Bending
1E+15 1.E+01
1.E+02
Lsat (energy spread) Lsat (beta) Lsat (emittance) Lsat (bunch length)
250
PLS U7
1E+19 1E+17
6.5 3.0 0.5 0.3 30 23
Spontaneous Spectrum PAL X-FEL
1.E+03
1.E+04
1.E+05
Energy [eV] Fig. 3. Peak brilliance for PAL X-FEL.
rather higher emittance, the 3D gain length is twice the 1D gain length. The solid line ‘B’ in Fig. 3 shows the expected peak brilliance for the 0.3-nm PAL X-FEL. The
Saturation Length [m]
2
Period (mm) Gap (mm) Peak magnetic field (T) Undulator parameter (K) Beta (m) Undulator length (m)
LCLS
B 1E+31
2
Peak Brilliance [Phot./(sec-mrad -mm -0.1% bandwidth)]
L ¼ ð1 þ ZÞL : g 1d Photons/s-mm2-mrad2 0.1%BW.
three circles on the line correspond to beam energies of 2.0, 2.5, and 3.0-GeV. ‘A’ denotes the 0.1-nm PAL X-FEL with the third-harmonic enhancement technique employing an additional undulator with a shorter periodic length, as shown in Table 4. Fig. 4 shows the sensitivity of saturation length on the system performance. The system parameters such as beam emittance, energy spread, bunch length, and undulator beta are normalized by the nominal values given in Table 1. The most sensitive parameter is the emittance of the electron beam for PAL X-FEL. Therefore, the prime effort has to be concentrated on the design of a low emittance gun. Fig. 5 shows a possible upgrade layout of the PAL linac including a new 0.5-GeV injector. The injector consists of a low-emittance laser-driven photocathode-gun, three S-band accelerating modules (X1, X2, X3), and a bunch compressor BC1.
200
150
100
50
0 0
1
2
3
4
Normalized System Performance
Fig. 4. Saturation length vs. system performance for beam emittance, energy spread, bunch length, and undulator beta.
ARTICLE IN PRESS J.S. Oh et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 582–585
10m
E-gun Accelerating Column Bending Magnet Bunch Compressor Undulator Beam Dump
30m
50m
100 m
Scale
K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12 X1 X2
585
X3
To 2.5 GeV Storage Ring To X-ray Beam Line
BC2 BC1
Fig. 5. PAL X-FEL compression and acceleration scheme.
12.5 mm with a 3-mm gap. To obtain the 0.1-nm radiation wavelength, we propose to employ the third harmonic enhancement technique utilizing an additional undulator system with a shorter periodic length of 6.5 mm.
1E+10 1E+09 1E+08
Power [W]
1E+07 1E+06 1E+05 1E+04 Genesis Simplex
1E+03 1E+02
Acknowledgements
1E+01 1E+00
0
10
20
30 40 50 60 Undulator Length [m]
70
80
This work is supported by POSCO and the Ministry of Science and Technology (MOST) of Korea.
Fig. 6. Saturation curves of X-ray SASE at PAL linac.
The analytic design is confirmed by simulation codes. The FODO layout with a focusing strength of 18 T/m (F) and 12.5 T/m (D) is assumed in the simulation. Fig. 6 shows the saturation curves for the 0.3-nm PAL X-FEL by SIMPLEX [7] and GENESIS [8].
3. Summary With an upgrade modification for the beam energy of 3.0 GeV and an in-vacuum undulator system, the PAL linac will be able to produce coherent X-ray radiation down to 0.3 nm.The undulator period required to obtain this is
References [1] LCLS Conceptual Design Report, SLAC-R-593, 2002. [2] TESLA-XFEL Technical Design Report, Supplement, DESY 2002-167, TESLA-FEL 2002-09, 2002. [3] http://pal.postech.ac.kr/. [4] T. Shintake, et al., SPring-8 compact SASE source (SCSS), in: Proceedings of the SPIE2001, San Diego, USA, 2001: http://www-xfel.spring8.or.jp. [5] X. Mar!echal, J. Chavanne, P. Elleaume, On 2D periodic magnetic field, ESRF-SR/ID 90-38, 1990. [6] M. Xie, Design Optimization for an X-ray Free Electron Laser Driven by SLAC Linac, LBL Preprint No-36038, 1995. [7] http://radiant.harima.riken.go.jp/simplex/; Takashi Tanaka, The Institute of Physical and Chemical Research. [8] S. Reiche, Nucl. Instr. and Meth. A 429 (1999) 243.
Nuclear Instruments and Methods in Physics Research A 528 (2004) 582–585
0.3-nm SASE-FEL at PAL J.S. Oh*, D.E. Kim, E.S. Kim, S.J. Park, H.S. Kang, T.Y. Lee, T.Y. Koo, S.S. Chang, C.W. Chung, S.H. Nam, W. Namkung Pohang Accelerator Laboratory, Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang 790-784, Republic of Korea
Abstract Recent success in SASE-FEL experiments provides high confidence in achieving FEL radiation wavelengths as short as 0.1 nm.The SASE-XFEL requires multi-GeV electron beams with extremely low-emittance, short bunches, and long undulator systems. PAL is operating a 2.5-GeV electron linac as a full-energy injector to the PLS storage ring. With a proposed energy upgrade to 3.0 GeV and an in-vacuum undulator, PAL will be able to produce coherent X-ray radiation at wavelengths as short as 0.3 nm.This paper presents the preliminary design details for the proposed PALXFEL. The required undulator period is 12.5 mm with a 3-mm gap. The third harmonic enhancement technique can be used to obtain radiation wavelengths of 0.1 nm.The technical parameters related to these goals are reviewed. r 2004 Elsevier B.V. All rights reserved. PACS: 41.60.Cr Keywords: PAL; X-ray SASE; In-vacuum undulator; 0.3 nm; Third-harmonic enhancement
1. Introduction The last two decades have ushered in rapid progress in basic and applied science research using synchrotron radiation and technological advancements in extremely intense electron beams for high-energy physics research. These result in both strong demands for, as well as the possibilities of, fully coherent radiation with high brilliance, called fourth-generation light sources. LCLS [1] at SLAC and TESLA-XFEL [2] at DESY are in the detailed design stages with *Corresponding author. E-mail address: [email protected] (J.S. Oh).
government funding approval. These SASE-XFEL facilities are expected to be operational by 2008 and 2012, respectively. Those projects require large-scale accelerators with 14–20-GeV electron beams and very long undulator systems with 113– 175-m lengths. We propose a compact X-ray Free Electron Laser Program at the Pohang Accelerator Laboratory, PAL-XFEL. PAL operates an electron linac, the third largest in the world, 2.5 GeV at present, as a full-energy injector to the PLS storage ring [3]. The linac is regularly injecting these beams to a storage ring twice a day for up to 5 min per injection. In its design stage, PAL was designed to use multi-application beams concurrently. With
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.04.106
ARTICLE IN PRESS J.S. Oh et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 582–585
2. PAL X-FEL The fundamental radiation wavelength lx of an undulator is given by lx ¼
lu ð1 þ K 2 =2Þ 2g2
where g ¼ E0 =0:511; K ¼ 0:934Bu lu ; E0 is the beam energy in MeV, Bu is the peak magnetic field of the undulator in Tesla, and lu is the undulator period in cm. Either a short-period undulator or a high-energy beam can provide short-wave radiation. However, the value of K should be reasonably large to obtain a short saturation length. An in-vacuum mini-gap undulator can meet this requirement. This concept was introduced by the SCSS project at SPring-8 [4]. We will use a 45 magnetized undulator with H ¼ lu =2: The peak magnetic field on axis is calculated by pffiffiffi N 4 2Br X 1 peak ð1 e2npH=lu Þenpg=lu By ¼ p n¼1;5;9 n where Br is assumed to be 1.19 T provided by Nd2Fe14B magnets, H is the block height, g is fullgap length as shown in Fig. 1 [5].
Nominal beam parameters for the PAL X-FEL linac are summarized in Table 1. The emittance can be further optimized by reducing the bunch charge and peak current, which provides the same saturation length with a moderate power reduction. Fig. 2 shows the saturation lengths and beam energies for 0.3-nm SASE as a function of undulator period and gap size, which are calculated by the use of equations given by Xie [6]. This figure clearly shows that the undulator must have a period of less than 1.3 cm and a gap size of less than 3 mm to limit the saturation length within 50 m for a 3-GeV beam energy. Table 2 summarizes key parameters of the undulator for a 0.3-nm PAL X-FEL. The undulator beta value is optimized to obtain as short a saturation length as possible. The result shows that we need 13 undulators, each 4.5-m long. Table 3 lists the X-ray radiation parameters. Due to the Table 1 Beam parameters for PAL X-FEL Beam energy (GeV) Normalized emittance (mm-rad) Peak current (kA) Bunch charge (nC) FWHM bunch length (fs) Energy spread (%)
3.0 1.5 4.0 1.0 235 0.02
1.0
2.5 GeV 3 GeV
0.8 Undulator Gap [cm]
the proposed upgrade modification for the beam energy of 3.0 GeV and an in-vacuum undulator system, it will be possible to produce coherent Xray radiation as short as 0.3 nm. To obtain radiation wavelengths of 0.1 nm, we propose to employ the third-harmonic enhancement technique that will utilize an additional undulator system with a shorter periodic length. The design goal is for the undulator to be less than 60 m in total length.
583
4 GeV 0.6
60 m 0.4
50 m 0.2
40 m
g 0.0
H
0
1
2
3
Undulator Period [cm]
λu Fig. 1. Undulator geometry with 45 magnetization.
Fig. 2. Undulator period vs. gap length for 0.3-nm SASE with saturation lengths of 40, 50, and 60 m and beam energies of 2.5, 3, and 4 GeV.
ARTICLE IN PRESS J.S. Oh et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 582–585
584
Table 2 Undulator parameters for 0.3-nm XFEL Period (mm) Gap (mm) Peak magnetic field (T) Undulator parameter, K Beta (m) Saturation length (m)
12.5 3.0 0.97 1.14 15 52
Table 3 X-ray radiation parameters FEL parameter 1D gain length (m), L1d 3D gain length correction, Z Gain length (m), Lg Peak power (GW) Peak brightness ( 1032)
0.00043 1.35 0.97 2.67 2.1 1.4
Table 4 Undulator parameters for 0.1-nm XFEL
1E+35 TESLA SASE FEL
1E+33 DESY TTF-FEL
1E+29
A
SPring-8 SCSS
1E+27 1E+25 1E+23
300
SPring-8 Undulator (4.5 m in-vacuum)
1E+21
SPring-8 Bending PLS Bending
1E+15 1.E+01
1.E+02
Lsat (energy spread) Lsat (beta) Lsat (emittance) Lsat (bunch length)
250
PLS U7
1E+19 1E+17
6.5 3.0 0.5 0.3 30 23
Spontaneous Spectrum PAL X-FEL
1.E+03
1.E+04
1.E+05
Energy [eV] Fig. 3. Peak brilliance for PAL X-FEL.
rather higher emittance, the 3D gain length is twice the 1D gain length. The solid line ‘B’ in Fig. 3 shows the expected peak brilliance for the 0.3-nm PAL X-FEL. The
Saturation Length [m]
2
Period (mm) Gap (mm) Peak magnetic field (T) Undulator parameter (K) Beta (m) Undulator length (m)
LCLS
B 1E+31
2
Peak Brilliance [Phot./(sec-mrad -mm -0.1% bandwidth)]
L ¼ ð1 þ ZÞL : g 1d Photons/s-mm2-mrad2 0.1%BW.
three circles on the line correspond to beam energies of 2.0, 2.5, and 3.0-GeV. ‘A’ denotes the 0.1-nm PAL X-FEL with the third-harmonic enhancement technique employing an additional undulator with a shorter periodic length, as shown in Table 4. Fig. 4 shows the sensitivity of saturation length on the system performance. The system parameters such as beam emittance, energy spread, bunch length, and undulator beta are normalized by the nominal values given in Table 1. The most sensitive parameter is the emittance of the electron beam for PAL X-FEL. Therefore, the prime effort has to be concentrated on the design of a low emittance gun. Fig. 5 shows a possible upgrade layout of the PAL linac including a new 0.5-GeV injector. The injector consists of a low-emittance laser-driven photocathode-gun, three S-band accelerating modules (X1, X2, X3), and a bunch compressor BC1.
200
150
100
50
0 0
1
2
3
4
Normalized System Performance
Fig. 4. Saturation length vs. system performance for beam emittance, energy spread, bunch length, and undulator beta.
ARTICLE IN PRESS J.S. Oh et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 582–585
10m
E-gun Accelerating Column Bending Magnet Bunch Compressor Undulator Beam Dump
30m
50m
100 m
Scale
K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12 X1 X2
585
X3
To 2.5 GeV Storage Ring To X-ray Beam Line
BC2 BC1
Fig. 5. PAL X-FEL compression and acceleration scheme.
12.5 mm with a 3-mm gap. To obtain the 0.1-nm radiation wavelength, we propose to employ the third harmonic enhancement technique utilizing an additional undulator system with a shorter periodic length of 6.5 mm.
1E+10 1E+09 1E+08
Power [W]
1E+07 1E+06 1E+05 1E+04 Genesis Simplex
1E+03 1E+02
Acknowledgements
1E+01 1E+00
0
10
20
30 40 50 60 Undulator Length [m]
70
80
This work is supported by POSCO and the Ministry of Science and Technology (MOST) of Korea.
Fig. 6. Saturation curves of X-ray SASE at PAL linac.
The analytic design is confirmed by simulation codes. The FODO layout with a focusing strength of 18 T/m (F) and 12.5 T/m (D) is assumed in the simulation. Fig. 6 shows the saturation curves for the 0.3-nm PAL X-FEL by SIMPLEX [7] and GENESIS [8].
3. Summary With an upgrade modification for the beam energy of 3.0 GeV and an in-vacuum undulator system, the PAL linac will be able to produce coherent X-ray radiation down to 0.3 nm.The undulator period required to obtain this is
References [1] LCLS Conceptual Design Report, SLAC-R-593, 2002. [2] TESLA-XFEL Technical Design Report, Supplement, DESY 2002-167, TESLA-FEL 2002-09, 2002. [3] http://pal.postech.ac.kr/. [4] T. Shintake, et al., SPring-8 compact SASE source (SCSS), in: Proceedings of the SPIE2001, San Diego, USA, 2001: http://www-xfel.spring8.or.jp. [5] X. Mar!echal, J. Chavanne, P. Elleaume, On 2D periodic magnetic field, ESRF-SR/ID 90-38, 1990. [6] M. Xie, Design Optimization for an X-ray Free Electron Laser Driven by SLAC Linac, LBL Preprint No-36038, 1995. [7] http://radiant.harima.riken.go.jp/simplex/; Takashi Tanaka, The Institute of Physical and Chemical Research. [8] S. Reiche, Nucl. Instr. and Meth. A 429 (1999) 243.