The Decay Ring -First Design- A. Chancé, J.Payet CEA/DSM/DAPNIA/SACM

1. The Decay Ring -First Design-A. Chancé, J.PayetCEA/DSM/DAPNIA/SACM

2. Summary • General parameters • Optical functions • The injection system • Optical properties • Decay products losses

3. General parameters Decay ring Parameters of the radioactive ion beams 688 m 2385 m • Total length 6931 m, arc length 1080 m. • The injection is located in the arc. • Low contribution of the optic to the ν-beam angular divergence. • Free straight sections, at each arc entry, enable decay products extraction. injection

4. Optical functions Half ring optical functions Optical functions in the long straight sections keep the ν beam angle growth below 5%. The arc is a 2insertion. Optical functions in the arcs are smaller to reduce magnet apertures. At the injection point, dispersion is as high as possible (8.18 m) while the horizontal beta function is as low as possible (13.1 m). Free straight sections behind the first bend, used as a dispersion suppressor, are designed to enable extraction of the decay products coming from the long straight sections. Arc optical functions

5. Injection injected beam SEPTUM E/E D deviated beam kicker Dispersive area Injected beam Injected beam after one turn Deviated beam • Injection is located in a dispersive area • The stored beam is pushed near the septum blade with 4 “kickers”. At each injection, a part of the beam is lost in the septum • Fresh beam is injected off momentum on its chromatic orbit. “Kickers” are switched off before injected beam comes back • During the first turn, the injected beam stays on its chromatic orbit and passes near the septum blade • Injection energy depends on the distance between the deviated stored beam and the fresh beam axis Layout Horizontal envelopes at injection envelopes (cm) Septum blade s (m)

6. Beam losses and beam size (in rms number) • T : repetition rate (8 s)  : half-life of the ion at rest • NI : injected ions number at each injection • a : transmission coefficient of the stored beam through the septum blade • ais related to the number of rms,nm • 1D Gaussian beam distribution assumed Power lost by the stored beam on the septum blade Then, with 4.1 rms for the stored beam and 3.3 rms for the injected beam, the deposited power on the septum blade is below 20 W. Therelative injection energy is then about 0.5%. The “kicker” deviations are 1.1 mrad (0.5T) and 0.41 mrad (0.38 T)

7. Beam envelopes Stored beam envelopes In the long straight sections, the apertures (±5 cm in both planes) are defined by the stored beam sizes. In the arc, the horizontal aperture is defined by the injected beam and the vertical one by the stored beam sizes. By arc, there are 590 m of 5 T field bend with 4 cm radius aperture. The injection septum is 22.5 m long and its field is 1 T. Injected beam envelopes

8. 2nd order study Chromaticity corrected by 2 families of sextupoles. Arcs are 2Pi insertions. • The tunes are given by the straight sections phase advances. • It is quite easy to optimize the tunes. The working point is chosen according to : • the dynamic aperture • the momentum acceptance Best point Dynamic aperture at the injection point Physically, the momentum acceptance is limited by the septum position.

9. Decay products extraction Lithium extraction Two free straight sections after the first arc dipole enable the extraction of decay products coming from long straight sections. Lithium extraction can be made without a septum. Fluorine extraction needs an additional septum. In the Lithium extraction case, the first bend aperture has to be increased to 5 cm. The permanent septum for Fluorine extraction is 22.5 m long and its field is 0.6 T. Fluorine extraction

10. Decay products losses in the arcs Lithium deposit We have begun studying the repartition of the disintegrations in the arcs. Most of decay productsdeposits come into the dipoles. • Problem of radioprotection in the arc • Problem of dipole cooling • This design is not valuable due to this deposit level Fluorine deposit

11. Decay products losses in the arcs (2) Helium decay Most of Lithium is deposited at the middle of dipoles • we have divided the dipoles in two 6T bends and separated them with a drift. The chamber sizes between the two dipoles are small to maximize the deposition here. • Problem of radioprotection • Fewer problems in the dipoles The injection section must still be studied. We have to compare with the TRIUMF results. Neon decay

12. Conclusions Some positive remarks can be made : • The injection system and the bending magnet seem realistic. • The contribution of the optic to the ν-beam angular divergence is low. • The decay ring length, 6930 m, is what was expected. • Free straight sections, at each arc entry enable the extraction of a part of decay products. More studies are yet needed : • The acceptable beam losses on the septum blade have to be defined according to the radio-protection. • This can modify the beam sizes and then the injection energy, the apertures and the fields of the magnetic elements. • A new design could focus most of losses outside the bends. Recently, we are working on this.