Injection of the beam is done axially, through the lower yoke and pole. Two different geometries are used depending on the harmonic number (table 3).
Table 3: injection elements
|Harmonic number ||Inflector type ||Magnetic radius (mm) ||Max. source voltage (kV)|
|2, 3, (4) ||Hyperboloïd (Mueller) ||34 ||34|
|4, 5 ||SPIRAL (Belmont-Pabot) ||45 ||34|
The geometry of the central region was studied with special care. The electromagnetic fields were calculated in the whole injection space and multi-particle programs allowed to simulate the behavior of bunches of particles. The injection line allows to perfectly match the injected beam to the cyclotron acceptance. An injection efficiency higher than 50% (with buncher) has been measured.
The beam is extracted at a mean radius of 1500 mm. Extraction is complete in less than half a turn. It is performed by one electrostatic deflector (splitted into two parts) and two magneto-static channels. Position and electric field of the electrostatic channel can be adjusted while only the positions of the magnetic channels are adjustable. The table 4 gives some details on these elements.
Table 4: Extraction elements
| ||Electrostatic ||Magneto static|
|Azimuthal extension ||2 x 17° ||2 x 16°|
|Maximum field/gradient ||70 kV/mm ||5.5 and 13.3 T/m|
|Free aperture ||14 mm ||32 mm|
The magneto static channels were designed in order to minimize the perturbation of the field in the acceleration region. Nevertheless, in addition, image channels were added at 180° to suppress any possible first harmonic.
Acceleration, the RF Cavities
The beam is accelerated by two l/4, cantilever dees with a maximum peak voltage of 80/100 kV. The main characteristics of the CIME RF system are given in table 4.
|Dee number ||2|
|Dee angle (°) ||40|
|Frequency range (Mhz) ||9.6-14.5|
|Accelerating gap (mm) ||15 to 30|
|Vertical dee aperture (mm) ||30|
|Max. peak voltage (kV) ||100|
|Max. sur-tension coefficient Q ||9130|
|Coupling system ||Adjustable loop|
Table 5: RF characteristics
The dee tips were carefully studied for injection. The angle is 60° for the first turns and 40° further. Posts help to get a better definition of the electric field in the first gaps.
Due to the very large intensity range of the beams which can be accelerated by CIME (10 3 to 10 12 pps), two type of diagnostics are used :
- Classical diagnostics including :
- A main radial, intercepting probe, with several fingers, covering the whole radial range.
- A set of central non intercepting phase probes.
- A retractable plate in front of each magnetic channel.
- « Nuclear » type diagnostics :
- A plastic scintillator, followed by a photo multiplier is supported by the radial probe. It can be retracted behind the probe when the intensity is large.
- A silicon detector, installed in an other radial probe at 45° from the main one.
These detectors are sensitive to very low intensities (down to a few pps). They give a precise measurement of the phase and also, possibly of the energy. On the other hand, the life-time of these diagnostics is limited, they are easily destroyed by an excess of beam and their useful range is limited as they do not deliver signal if the energy is too low.