# Presentation: 712991

## Storage Ring: Status, Issues and Plans 

*C Johnstone, FNAL and G H Rees, RAL*
* *

## Current Storage Ring Designs

*Ring(s) T(GeV) Beam  Detcs  P.dr(Hz,N,MW) Circ(m)   Eff(%)*
*US2a(2)    20     ******, ****─**    1         3,    5, 1        358.2       35 (31)*
*J-Parc(1)   20       ******       1    0.66,    8, 4        820.0       35  (?)*
*Keil (1T)    50       ******       2      50, 140, 4     2074.8    2x28  (?)*
*                                                                                            *
*Racetrack                                                                   detector                                        *
*Triangle                                             detector*

*detector*

## Features of Designs

*1. Tilting of the rings relative to the horizontal plane.*
*2. Very different proton drivers (24, 50 and 2.2 GeV).*
*3. Muon injection fillings in each storage cycle (n= 1).*
*4. Merging of the ****** and ****─** beams in one of designs.*
*5. Long straights reduced if weak dipoles are added. *
*6. RF systems needed to retain bunch structures. *
*7. High reactive beam loading of the RF cavities.*
*8. Muon beam powers large (**≈** 0.25 and 1.25 MW).*

## Muon Storage Ring Issues

*1.  Design for 20 or for 50 GeV rings, or for both?*
*2.  Design Triangle & 2 detectors, or Racetrack &1?*
*3.  Possibility of  an Isosceles Triangle design?*
*4.  Merging of ****** and ****─** beams in straights or not?*
*5.  Cooling of warm bore of S/C magnets & straights.*
*6.  S/C magnet shielding, and the effects of e**** & e**─**.*
*7.  Protection from muon beam loss on the walls.*
*8.  Influence of n and length of the muon bunch train.*
*9.  Designs for lattice, RF, injection, diagnostics, etc.*
*10. Optimisation of the ring designs. *

## Beam Power Levels

*Proton driver (50 Hz?):           4 MW   (with potential of 8 MW)   *
*8-20 GeV Muon ring:          **≈** 1 MW    (combined ****** and ****─**)** *
*20 GeV Storage rings:     **≈** 0.5 MW    (separate ****** and ****─**)**       *
*20-50 GeV Muon ring:     **≈** 2.5 MW    (combined ****** and ****─**)** *
*50 GeV Storage rings:   **≈** 1.25 MW    (separate ****** and ****─**)** *
*Peak beam loading at the fundamental ring RF frequency: *
*8-20 GeV,16-turn, ring:    **≈** 50 MW (50 Hz, n = 5, C = 900 m)*
*(1 bunch train at a time)  **≈** 1000 MW (25 Hz, n = 1, C = 450 m)*
*Storage rings:  n (****** or ****─**) bunch trains injected per cycle. *
*Reactive loading of cavities (402 MHz?) scales as 1/(2CF). *

## Effect of Length of Muon Bunch Train

*CERN design: proton and muon bunch number = 140*
*                           **length of muon bunch train  **≈** 900 m*
*US bunch rotation scheme: muon bunch number = 90*
*                           **length of n bunch trains **≈** n x 180 m*
*Here, n is the number of bunches in the proton driver;*
*                           **length for five bunch trains **≈** 900 m*
* *
*A 4 MW driver with 1 ns rms bunches needs n > **≈** 4*
*So, minimum length for muon storage rings **≈** 900 m*
*(short length of US2a is for a 20 GeV, 1 MW driver)*

## Storage Ring Filling

*Repetition rate is that of the muon rings (50 Hz?)*
*The number of  muon fillings per pulse = n (> 4?)*
*Interval between each of the “n” fillings **≈** 50 ****s*
*(holding time in the proton driver (target shock) & *
*acceleration time in 16 turn, 8-20 GeV, muon ring)*
*Injection of ****** and ****─ ** beams into separate rings  *
*(to prevent extension of the bunch train length)*
*Rise and fall time for injection kickers **≈** 150 ns*
*Multiple (**x** n) pulsing of kickers at **≈** 50 ****s intervals*

## Lattice Design for the Arcs

*Allow 0.4 m for the ends of the S/C magnet cryostats.*
*Allow 1.4 m (0.4+0.6+0.4 m) in between arc magnets.*
*Minimize arc length by using combined function units.*
*Adopt a FODO type for the lattice cell (BF  O  BD  O).*
*Choose 6 T fields for the central orbits ( **≈** 5 to 7 T).*
*Circumference of 50 GeV rings of similar efficiencies:*
*Racetrack **≈** 0.9 km, **∆** **≈** 1.5 km, Isosceles **∆** **≈** 1 km.*
*cf 0.36/0.8 km (20GeV, 1MW), 2.1 km (50GeV, 4MW)  *

## Lattice Design for the Straights

*Use weak dipoles (1.8**°) at ends of production region.*
*Match with the **(1.8**°)** dipoles to have zero dispersion*
*and a reduced variation of **β** in the production region.*
*Length of the production region(s) is ≈ 230 to 360 m.       *
*RF, loss protection & cooling easier if separate rings.*
*Best to inject the ****** and ****─ **beams into separate rings.*
*Circumference larger & efficiency less if rings merge.*
*So, avoid merging the rings at the straight sections? *
* *

## Possibility of Isosceles Triangle Design

*Production straight*
*(1.8**° end dipoles)*

*Production straight             (1.8**° end dipoles)*

*Straight for loss protection, RF,  Q-control and 1.8**° end dipoles*

*97**° arc of 10 cells*

*97**° arc of 10 cells*

*(97 x 1.6)**° arc of 16,  **** =72**° cells,     (**ξ** correction over groups of 5 cells)*

*Injection*

## Beam Loss Protection

*Losses are from ****± **decay, ****± **and **e**±** interception and*
*synchrotron radiation on outer wall of magnet bores.*
*About **1⁄3** of the ****± **beam power appears in **e**±** beams.*
*Power loss in the arcs will be approximately uniform,*
*but the density may be high in regions of the straights.*
*Effect of high energy e**±** at inner walls of the magnets? *
*Loss protection proposed at downstream end of non-*
*production straight to limit ****±  **interceptions in the arcs.*
*Primary and secondary collectors over three cells , to*
*contain direct ****±  **losses**  **(up to approx 1⁄2 % level).*

## Cooling and Shielding

*Cooling is needed for average power losses of:*
*≈ **420 kW per ring for the 50 GeV ****** & ****─ **rings,*
*≈ **170 kW per ring for the 20 GeV ****** & ****─ **rings.*
*Average loss in 0.9km racetrack: 467,189 W/m.*
*Design for 5 x these levels after weak dipoles.*
*Design for 2 kW/m for the beam loss collectors.*
*Shielding is needed for S/C magnets in the arcs *
*High density material, eg tungsten, is proposed.*

## Plans (prior to feedback from talk)

*Liaise with proton driver & muon ring designs*
*Liaise with detector group on ring orientations*
*Design 20 and 20-50 GeV ****±** racetrack rings*
*Design 20 and 20-50 GeV ****±** triangular rings*
*Study possibility of an isosceles triangle ring*
*Study e**±** effects, ring shielding and cooling*
*Study injection, loss protection & tunnel safety *
*Study chromaticity correction and RF issues*
*Optimise and provide parameters for costing *