Synchrotron Based Proton Drivers

Transcription

1 Synchrotron Based Pron Drivers Weiren Chou Fermi National Accelerar Laborary P.O. Box 500, Batavia, IL 60510, USA Abstract. Pron drivers are pron sources that produce intense short pron bunches. They have a wide range of applications. This paper discusses pron drivers based on high-intensity pron synchrotrons. It gives a review of high-intensity pron sources over

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3 FIGURE The The layout layout of of Fermilab Fermilab 8-GeV 8-GeV Pron Pron Driver FIGURE Driver ( ( ring ring of of racetrack racetrack shape). shape). which is which is basically basically aa singlet singlet 3-cell 3-cell modular modular structure structure 6,7,8 with aa missing missing (or with (or short) short) dipole dipole in in mid-cell. mid-cell.6'7'8 (b) (b) with aa missing (or aa doublet doublet 3-cell 3-cell modular modular structure structure with missing (or 9 short) short) dipole dipole in in mid-cell. mid-cell.9 Figure Figure 22 is is an an example example of (b), of (b), which which is is designed designed for for Fermilab Fermilab 8-GeV 8-GeV Pron Driver. Pron Driver. The choice The choice of of phase phase advance advance per per module module is is of of critical importance in this type of lattice. There are critical importance in this type of lattice. There are two two reasons. (i) reasons, (i) The The chromaticity chromaticity sextupoles sextupoles are are placed placed in in mid-cell, where beta-function peaks mid-cell, where beta-function peaks and and available space available space exists. exists. In In order order cancel cancel higher higher order effects of se sextupoles, y need order effects of se sextupoles, y need be be paired properly, properly. (ii) paired (ii) The The phase phase advance advance per per arc arc in in horizontal plane plane must horizontal must be be multiple multiple of of 2π 2n in in order order get get zero dispersion zero dispersion in in straights straights without without using using dispersion suppressors dispersion suppressors (which (which are are space space consuming). consuming). Or requirements in Or requirements in lattice lattice design design include: include: ample space for correcrs (steering ample space for correcrs (steering magnets, magnets, trim trim quadrupoles, chromaticity quadrupoles, chromaticity and and harmonic harmonic sextupoles, sextupoles, etc.), ample etc.), ample space space for for diagnostics, diagnostics, low low beta beta and and 1. Lattice Lattice Design Design 1. Lattice isis foundation foundation of of aa synchrotron. synchrotron. It It is Lattice is worth every effort design best lattice as one can. worth every effort design best lattice as one can. would be be aa mistake mistake pick pick aa lattice lattice in in hurry hurry due due ItIt would or facrs (e.g., pressed by project schedule, or facrs (e.g., pressed by project schedule, which did did happen happen in in past). past). A A poorly poorly chosen chosen lattice lattice which will have have adverse adverse effects effects for for life life of of machine. machine. A A will pron driver driver has hastwo two basic basic requirements requirements on on lattice: lattice: pron (1) transition transition free, free, (2) (2) zero-dispersion zero-dispersion in in rf rf straight straight (1) sections. The former is avoid particle loss and sections. The former is avoid particle loss and emittance dilution during transition crossing; latter emittance dilution during transition crossing; latter avoid avoid synchro-betatron synchro-betatron coupling coupling resonance. resonance. For aa medium-energy medium-energy synchrotron synchrotron (above (above 6 6 GeV), GeV), For regular FODO lattice (in which γ R, t regular FODO lattice (in which yt oc V#, RR machine radius) is ruled out because it would use o machine radius) is ruled out because it would use o many bending bending magnets magnets in in order order achieve achieve (1). (1). There There many are several lattices that have been investigated are several lattices that have been investigated obtain eir a high or an imaginary γ. For example, t obtain eir a high or an imaginary yt. For example, (a) aa flexible flexible momentum momentum compaction compaction (FMC) (FMC) lattice, lattice, (a) 31

4 dispersion functions ( make beam size small), large dynamic aperture

5 remarkably similar value (about 0.2 ± 0.1 x 10 8 /mm 3 ) when reaching ECE threshold. 10 This is called critical mass phenomenon. It is believed that ECE is mainly due secondary electron yield from wall. Reducing primary electrons (which come from beam loss and stripping foil in pron machines) does not seem be helpful.

6 Fermilab-KEK design, which places chopper in front

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8 space

9 when beam intensity of a synchrotron is limited by