The DAFNE Linac during installation in Frascati.
The heart of the DAFNE injection system is a ~60 m long Linac built on the basis of a turn-keycontract. It is an S-band accelerator (2.865 GHz) driven by four 45 MWklystrons each followed by a SLED peak power doubling system. It delivers10 ns pulses at a repetition rate of 50 Hz. A quadrupole FODO focusingsystem is distributed along the entire structure.
A triode gun delivers up to 10 A electrons at 120 KV. The beam is thenaccelerated at 250 MeV by five 3 m long accelerating sections up to a removabletarget, where it is focused by a quadrupole system to a 1 mm radius spotto produce positrons with an efficiency of ~0.9%. The positrons are collectedby a high field pulsed magnetic lens, separated from the electrons by meansof a “chicane” of dipoles, and then accelerated up to a maximumenergy of 550 MeV by 10 accelerating sections. The expected positron currentduring the pulse is 36 mA within ±1% energy spread and 5 mm.mrademittance.
In the electron mode the converter is removed from the beam and theelectrons are accelerated through the whole structure up to a maximum energyof 800 MeV. The pulse current is 150 mA within ±0.5% energy spreadand 1 mm.mrad emittance.
The DAFNE Linac spectrometer magnet.
The average energy of the accelerated particles and the width of its distribution is measured by a spectrometer system consisting of a pulsed magnet, which deviates the beam from the Transfer Line, and a 60 degrees bending magnet, which focuses the beam on a hodoscope of secondary emission metallic strips.
The beam from the Linac can also be directed towards a Test Beam area BTF , mainly conceived for detector calibration purposes.
The design parameters, achieved with both electrons and positrons, are listed below.
LINAC PARAMETERS
GENERAL
| RF frequency | 2856 MHz |
| Klystron power | 45 MW |
| Number of klystrons | 4 |
| Number of SLED peak power doublers | 4 |
| Number of accelerating sections | 15 |
| Repetition rate | 50 Hz |
| Beam pulse width | 10 ns |
HIGH CURRENT ELECTRON LINAC
| Number of accelerating sections | 5 |
| Input current from gun | < 10 A |
| Input energy from gun | 120 KV |
| Harmonic prebuncher | |
| Output current | > 4 A |
| Output energy | 250 MeV |
| Output emittance | < 1 mm.mrad |
| Energy spread | 10% fwhm |
| Beam spot radius | 1 mm r.m.s. |
POSITRON LINAC MODE
| Number of accelerating sections | 10 |
| Output energy | 550 MeV |
| Input energy | 2 < E < 14 MeV |
| Output current | 36 mA |
| Output emittance | < 5 mm.mrad |
| Energy spread | 2% fwhm |
HIGH ENERGY ELECTRON LINAC MODE
| Output energy | 800 MeV |
| Output current | 150 mA |
| Output emittance | < 1mm.mrad |
| Energy spread | 1% fwhm |