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.
|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|
|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|