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Design study of a 10 GeV electron accumulator ring for the PEARL project at RCNP
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ELSEVIER
Nuclear Physics A663&664 (2000) 1087c-1090c www.elsevier.nl/locate/npe
Design study of a 10 GeV electron accumulator ring for the PEARL project at RCNP K. Hatanaka, S. Ninomiya, M. Nomachi and H. Ejiri& &Research Center for Nuclear Physics, Osaka University, Mihogaoka 10-1, Ibaraki, Osaka 567-0047, Japan Results of design studies are presented for an electron accumulator ring proposed for the PEARL project. Maximum energy of electrons is 10 GeV. Electrons are polarized and the luminosity for internal target experiment reaches 1033 to 1034 nucleons cm- 2 S - 1 • High energy real photons are produced with Compton backscattering technique. The maximum photon energy is expected be 5 GeVat the intensity of 5x 105 photons GeV- l A- IW- I S - I • 1. Introduction
The Research Center for Nuclear Physics(RCNP), Osaka University, is a laboratory complex. The main facility is the cyclotron laboratory located in Suita-campus. It consists of coupled cyclotrons, K140 AVF and K400 ring cyclotrons, and unique experimental apparatuses including dual magnetic spectrometers and a neutron TOF facility. Others are Laser Electron Photon Laboratory at the SPring-8 site, and the underground laboratory at Oto Cosmo Observatory. Recently, on the basis of the review on the present RCNP activities and important physics subjects to be studied by RCNP, medium range plans were discussed. RCNP will contribute to the progress of nuclear physics in those current subjects in nuclear physics. 1. Standard theory and beyond 2. Neutrinos and weak interactions 3. Hadrons and non-perturbative QCD Flavor nuclear Physics 4. Quark confinement A conceptual design of an electron-nucleus collider was performed according to the suggestion. [lJ In the design, beam energy is 5 GeV for both electrons and protons. With this combination of energies, the luminosity was found to be limited to 1031 cm- 2s- 1 • The limitation comes from the space charge effect in the proton accelerator. An asymmetric collider geometry can provide the luminosity of 1033 cm- 2 8 - 1 for the collision of a few GeV electrons and and a few tens GeV(fu) protons(ions). Such kind of collider is proposed at IUCF as discussed by Prof. J. Cameron in this Conference. [2] As the first stage to extend the present RCNP activities to quark nuclear physics, an action program was started to design an electron accumulator ring at 8-10 GeV proposed as the Photon Electron Accumulator Ring Laboratory (PEARL). The non-perturbative regime of QCD is a current challenging task on the border line between nuclear and particle physics. Outstanding questions are the quark-gluon structure of baryons and 0375-9474/00/$ - see front matter © 2000 Elsevier Science B.Y. All rights reserved. PH S0375-9474(99)00783-6
1088c
K. Hatanaka et al./Nuclear Physics A 663&664 (2000) 1087c-1090c
mesons, the existence or non-existence of glueballs which are predicted by QCD and the origin of the confinement which prevents colored objects propagating freely in space. The PEARL project will give the opportunity to investigate these subjects. The results of the design and feasibility studies of the 10 GeV electron accumulator ring are presented in the following sections.
2. Electron Accumulator Ring 2.1. General Description of the Ring General features of the electron accumulator ring are summarized below. 1. Maximum electron energy is 10 GeV. 2. Expected beam current is 0.5 A and will be increased to 1 A in future. 3. Polarized photons are produced by the Compton backscattering of Laser lights. 4. Electrons are polarized and internal gas targets are 20 used. 't 5. Circumference is around 600 m in order to accom'.~G modate the ring in an available area. Figure 1 shows kinematic regions of the electron energy ....> .. loss, 11, and the squared electron four momentum trans... ~IO fer, Q2, accessible with 10 GeV beam. It enables C3 1. the access to high momentum transfers, implying fine spatial resolution, 2. the broad access to the deep inelastic scattering (DIS) regime, and ~IG9V) 3. the access to baryons up to 4 GeV mass, and (;12 _ 4E1E _~)Stn2[9/2) mesons up to 3 GeV mass. For both baryons and mesons, a large fraction of the spectrum is missing as discussed by M. Takayama in this Conference. [31 Figure 1: Kinematic regions of the 10 GeV accumulator ring. 2.2. Lattice Parameters The general parameters of the accumulator ring are listed in Table 1 and the optical functions for the arc section are shown in Fig.2. The injection energy is 8 GeV, and the maximum energy 10 GeV. Arcs are composed of simple FODO arrays and bending radius is 27.5 m. Dispersion suppressors ensure the transition between arcs and the straight sections where the dispersion is zero. Length of a long and a short straight section is 100 m and 40 m, respectivelly. The RF paramerters of the ring are listed in Tabe 1, too. Radio frequency is 508.58 MHz, which is same as that of SPring-8 storage ring. Shunt impedance of a cavity is assumed 6 Mn. There are 4 stations in the ring, and 6 units per station. 4 cavities are installed at each unit. In total, 96 cavities are used to supply 42 MV and 16 MW continuously to a beam of 0.5 A. Power dissipated in the cavities is 3.4 MW assuming 10 % shunt impedance drop. Total power is 21 MW assuming 10 % loss in transmission lines. Input power per cavity is 200 kW, and power dissipated per cavity is 35 kW. There is a limit of 300 kW for the power that can be carried by each input coupler.
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K. Hatanaka et al. /Nuclear Physics A663&664 (2000) 1087c-l090c
1089c
Table 1 Parameters of a 10 GeV Accumulator Ring. Circumference Injection energy Maximum energy Lattice type Bending radius Number of dipole magnets Number of normal cells Number of dispersion suppression cells Super periodicity Momentum spread Nominal tune (lIx/lly ) Natural chromaticity Dispersion in straight cells (Dx ) Long straight section (100 m) Short straight section (40 m) Radiation loss Harmonic number Damping time Tx Ty T.
Radio frequency Maximum RF voltage Number of RF stations Number of units/station Number of cavities/unit Total number of cavities Power transferred to the beam at 0.5 A Power Dissipated in the cavities* Total Power** Shunt impedance of a cavity Input power per cavity Power dissipated per cavity
586 8 10
m GeV GeV
FODO 27.52 48 20 8 2 1.5 x 10- 3 17.9/12.7 -26.3/-18.5 0.0 2 2 32 994 2.0 2.0 1.0 508.58 42 4 6
m
MeV/turn ms ms ms MHz MV
4 96 16 3.4
21 6 200 35
MW MW MW MQ kW kW
3. Internal Target Luminosities The luminosity that can be obtained with internal targets depends strongly on the atomic number Z. The beam lifetime is reduced by atomic bremsstrahlung of electrons in the target, In the absence of other beam-loss mechanisms, the lifetime is given by [4]
I'target
183 n -1 ~ To[Z(Z + l)(ln Zl/3)(8 x 1025atoms/cm2)] ,
where n is the target thickness and To = 2p,s is the revolution time in the accumulator ring. The maximum thickness for internal targets are obtained for gaseous elements corresponding to T'target = 1hour. Figure 3 shows the corresponding luminosity LA for a beam current of 0.5 A as a function of the target mass. It is found the luminosity for internal target experiment can reach 1033 to 1034 nucleons cm- 2s- 1 •
K. Hatanaka et al. /Nuclear Physics A663&664 (2000) 1087c-1090c
l090c
Optlc~l
.,
Functions
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... .. 0 <:
9 CD 0.
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102
,0'
. ..
Z
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CD
Unpclerized
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s
. ... .
1.·
10-1
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Polar-ized
,.
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SoFt X-ray -
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502 eV
·······136 eV
CD
co co co
2.
0
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10"
Tarqrt mass
Figure 2: Optical functions for the arc section.
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Figure 3: Maximum obtainable luminosity in nucleons / cm2 / s for gaseous elements assuming a beam life time of 1 hour and a beam current of 0.5 A.
'1.:.
0..
.
... .
E,CGeVl
10.0
Figure 4: Energy spectrum of I-rays for incoming electron beam energy 10 GeV.
4. Photon Beams In 1963 it was pointed out for the first time that the backward scattering of Laser light against high energy electrons could produce polarized I-rays ('9). [5] There are several working facilities based on the Compton backscattering technique and the RCNP LEPS facility will be in opration in 1999. [6] With the electron energy of 10 GeV, the maximum photon energy is expected be 5 GeVat the intensity of 5x10 5 photons GeV- 1A-1W-1s-l using a Laser light of 200 nm wavelength. If X-rays or soft X-rays from SPring-8 are available in stead of a Laser light, Compton backscatterd I-rays have almost monochromatic energy. Figure 4 shows energy spectrum of I-ray for incoming electron beam energy 10 GeV and Laser energy, 136 eV and 502 eV, respectively. 5. Conclusion
The results of the design and feasibility studies of the 10 GeVelectron accumulator ring for the PEARL project are discussed. The ring will give the opportunity to challenge the non-perturbative regime of QCD with polarized electrons and real photons. REFERENCES 1. 2. 3. 4. 5.
K. Hatanaka et al, RCNP Annual Report (1997) 312.
J. Cameron, to be published in these Proceedings.
M. Takayama et al., to be published in these Proceedings. M. Duren, DESY-HERMES 90-01 (1990). F.R. Arutyunyan and V.A. Tumanian, Phys. Lett. 4(1963)176. R.H. Milburn, Phys. Rev. Lett. 10(1963)75. 6. T. Nakano et al., T. Nakano et al., Nucl. Phys. A629(1998)559c.
~ ~.--
~
ELSEVIER
Nuclear Physics A663&664 (2000) 1087c-1090c www.elsevier.nl/locate/npe
Design study of a 10 GeV electron accumulator ring for the PEARL project at RCNP K. Hatanaka, S. Ninomiya, M. Nomachi and H. Ejiri& &Research Center for Nuclear Physics, Osaka University, Mihogaoka 10-1, Ibaraki, Osaka 567-0047, Japan Results of design studies are presented for an electron accumulator ring proposed for the PEARL project. Maximum energy of electrons is 10 GeV. Electrons are polarized and the luminosity for internal target experiment reaches 1033 to 1034 nucleons cm- 2 S - 1 • High energy real photons are produced with Compton backscattering technique. The maximum photon energy is expected be 5 GeVat the intensity of 5x 105 photons GeV- l A- IW- I S - I • 1. Introduction
The Research Center for Nuclear Physics(RCNP), Osaka University, is a laboratory complex. The main facility is the cyclotron laboratory located in Suita-campus. It consists of coupled cyclotrons, K140 AVF and K400 ring cyclotrons, and unique experimental apparatuses including dual magnetic spectrometers and a neutron TOF facility. Others are Laser Electron Photon Laboratory at the SPring-8 site, and the underground laboratory at Oto Cosmo Observatory. Recently, on the basis of the review on the present RCNP activities and important physics subjects to be studied by RCNP, medium range plans were discussed. RCNP will contribute to the progress of nuclear physics in those current subjects in nuclear physics. 1. Standard theory and beyond 2. Neutrinos and weak interactions 3. Hadrons and non-perturbative QCD Flavor nuclear Physics 4. Quark confinement A conceptual design of an electron-nucleus collider was performed according to the suggestion. [lJ In the design, beam energy is 5 GeV for both electrons and protons. With this combination of energies, the luminosity was found to be limited to 1031 cm- 2s- 1 • The limitation comes from the space charge effect in the proton accelerator. An asymmetric collider geometry can provide the luminosity of 1033 cm- 2 8 - 1 for the collision of a few GeV electrons and and a few tens GeV(fu) protons(ions). Such kind of collider is proposed at IUCF as discussed by Prof. J. Cameron in this Conference. [2] As the first stage to extend the present RCNP activities to quark nuclear physics, an action program was started to design an electron accumulator ring at 8-10 GeV proposed as the Photon Electron Accumulator Ring Laboratory (PEARL). The non-perturbative regime of QCD is a current challenging task on the border line between nuclear and particle physics. Outstanding questions are the quark-gluon structure of baryons and 0375-9474/00/$ - see front matter © 2000 Elsevier Science B.Y. All rights reserved. PH S0375-9474(99)00783-6
1088c
K. Hatanaka et al./Nuclear Physics A 663&664 (2000) 1087c-1090c
mesons, the existence or non-existence of glueballs which are predicted by QCD and the origin of the confinement which prevents colored objects propagating freely in space. The PEARL project will give the opportunity to investigate these subjects. The results of the design and feasibility studies of the 10 GeV electron accumulator ring are presented in the following sections.
2. Electron Accumulator Ring 2.1. General Description of the Ring General features of the electron accumulator ring are summarized below. 1. Maximum electron energy is 10 GeV. 2. Expected beam current is 0.5 A and will be increased to 1 A in future. 3. Polarized photons are produced by the Compton backscattering of Laser lights. 4. Electrons are polarized and internal gas targets are 20 used. 't 5. Circumference is around 600 m in order to accom'.~G modate the ring in an available area. Figure 1 shows kinematic regions of the electron energy ....> .. loss, 11, and the squared electron four momentum trans... ~IO fer, Q2, accessible with 10 GeV beam. It enables C3 1. the access to high momentum transfers, implying fine spatial resolution, 2. the broad access to the deep inelastic scattering (DIS) regime, and ~IG9V) 3. the access to baryons up to 4 GeV mass, and (;12 _ 4E1E _~)Stn2[9/2) mesons up to 3 GeV mass. For both baryons and mesons, a large fraction of the spectrum is missing as discussed by M. Takayama in this Conference. [31 Figure 1: Kinematic regions of the 10 GeV accumulator ring. 2.2. Lattice Parameters The general parameters of the accumulator ring are listed in Table 1 and the optical functions for the arc section are shown in Fig.2. The injection energy is 8 GeV, and the maximum energy 10 GeV. Arcs are composed of simple FODO arrays and bending radius is 27.5 m. Dispersion suppressors ensure the transition between arcs and the straight sections where the dispersion is zero. Length of a long and a short straight section is 100 m and 40 m, respectivelly. The RF paramerters of the ring are listed in Tabe 1, too. Radio frequency is 508.58 MHz, which is same as that of SPring-8 storage ring. Shunt impedance of a cavity is assumed 6 Mn. There are 4 stations in the ring, and 6 units per station. 4 cavities are installed at each unit. In total, 96 cavities are used to supply 42 MV and 16 MW continuously to a beam of 0.5 A. Power dissipated in the cavities is 3.4 MW assuming 10 % shunt impedance drop. Total power is 21 MW assuming 10 % loss in transmission lines. Input power per cavity is 200 kW, and power dissipated per cavity is 35 kW. There is a limit of 300 kW for the power that can be carried by each input coupler.
..
"
..
"
K. Hatanaka et al. /Nuclear Physics A663&664 (2000) 1087c-l090c
1089c
Table 1 Parameters of a 10 GeV Accumulator Ring. Circumference Injection energy Maximum energy Lattice type Bending radius Number of dipole magnets Number of normal cells Number of dispersion suppression cells Super periodicity Momentum spread Nominal tune (lIx/lly ) Natural chromaticity Dispersion in straight cells (Dx ) Long straight section (100 m) Short straight section (40 m) Radiation loss Harmonic number Damping time Tx Ty T.
Radio frequency Maximum RF voltage Number of RF stations Number of units/station Number of cavities/unit Total number of cavities Power transferred to the beam at 0.5 A Power Dissipated in the cavities* Total Power** Shunt impedance of a cavity Input power per cavity Power dissipated per cavity
586 8 10
m GeV GeV
FODO 27.52 48 20 8 2 1.5 x 10- 3 17.9/12.7 -26.3/-18.5 0.0 2 2 32 994 2.0 2.0 1.0 508.58 42 4 6
m
MeV/turn ms ms ms MHz MV
4 96 16 3.4
21 6 200 35
MW MW MW MQ kW kW
3. Internal Target Luminosities The luminosity that can be obtained with internal targets depends strongly on the atomic number Z. The beam lifetime is reduced by atomic bremsstrahlung of electrons in the target, In the absence of other beam-loss mechanisms, the lifetime is given by [4]
I'target
183 n -1 ~ To[Z(Z + l)(ln Zl/3)(8 x 1025atoms/cm2)] ,
where n is the target thickness and To = 2p,s is the revolution time in the accumulator ring. The maximum thickness for internal targets are obtained for gaseous elements corresponding to T'target = 1hour. Figure 3 shows the corresponding luminosity LA for a beam current of 0.5 A as a function of the target mass. It is found the luminosity for internal target experiment can reach 1033 to 1034 nucleons cm- 2s- 1 •
K. Hatanaka et al. /Nuclear Physics A663&664 (2000) 1087c-1090c
l090c
Optlc~l
.,
Functions
:§
... .. 0 <:
9 CD 0.
'"0E
102
,0'
. ..
Z
~ -'
CD
Unpclerized
"-
M C'I
s
. ... .
1.·
10-1
. '0·
Polar-ized
,.
c0
;:; 0
1IO
SoFt X-ray -
••
502 eV
·······136 eV
CD
co co co
2.
0
c: U
10"
Tarqrt mass
Figure 2: Optical functions for the arc section.
CJ
"-" E
Figure 3: Maximum obtainable luminosity in nucleons / cm2 / s for gaseous elements assuming a beam life time of 1 hour and a beam current of 0.5 A.
'1.:.
0..
.
... .
E,CGeVl
10.0
Figure 4: Energy spectrum of I-rays for incoming electron beam energy 10 GeV.
4. Photon Beams In 1963 it was pointed out for the first time that the backward scattering of Laser light against high energy electrons could produce polarized I-rays ('9). [5] There are several working facilities based on the Compton backscattering technique and the RCNP LEPS facility will be in opration in 1999. [6] With the electron energy of 10 GeV, the maximum photon energy is expected be 5 GeVat the intensity of 5x10 5 photons GeV- 1A-1W-1s-l using a Laser light of 200 nm wavelength. If X-rays or soft X-rays from SPring-8 are available in stead of a Laser light, Compton backscatterd I-rays have almost monochromatic energy. Figure 4 shows energy spectrum of I-ray for incoming electron beam energy 10 GeV and Laser energy, 136 eV and 502 eV, respectively. 5. Conclusion
The results of the design and feasibility studies of the 10 GeVelectron accumulator ring for the PEARL project are discussed. The ring will give the opportunity to challenge the non-perturbative regime of QCD with polarized electrons and real photons. REFERENCES 1. 2. 3. 4. 5.
K. Hatanaka et al, RCNP Annual Report (1997) 312.
J. Cameron, to be published in these Proceedings.
M. Takayama et al., to be published in these Proceedings. M. Duren, DESY-HERMES 90-01 (1990). F.R. Arutyunyan and V.A. Tumanian, Phys. Lett. 4(1963)176. R.H. Milburn, Phys. Rev. Lett. 10(1963)75. 6. T. Nakano et al., T. Nakano et al., Nucl. Phys. A629(1998)559c.