# Presentation: 539367

## 20-50 GeV Muon Storage Rings

- C. Johnstone and G. Rees
- NFMCC Meeting
- UCLA
- Jan 29-Feb 1, 2007

## Introduction:  Muon Storage Rings for a Neutrino Factory

- Neutrino beam/ Storage Ring energies	20 and 50 (_max_) GeV
- Production Straight
**Muon beam divergence***			**0.1/ ******** ******** 0.2/ ******
**Muon beam normalized emittance*****	****	****30,000******** mm-mrad (95%)**
**Momentum acceptance****	****	****	********1    4% (RF    no RF)**
**Note these two parameters dictate beam size in production straight**
**Peak magnetic field (assume NBTi SC)****	****~7T****	**
**Declination angle: 3 and 7x10****3**** km detector****	****~10******** and 36******** **
**Bunch train length****	****	****	****400 nsec (120 m)**
**Bunch train spacing****	****	****	****100 nsec****	****	**
**Overiding design Goal:**** **
**maximize muon decays in production straight or ratio of production straight(s)/circumference**
**	**
- *small compared to neutrino beam divergence, rms ~1/
- *assumes minimal, mainly transverse cooling

## Muon Decay and Storage Ring

*A triangular and bowtie shape with two production straights and two baseline experiments*
*Racetrack shape has single production straight, uncoupled straight*

## Storage Ring Designs

- Racetrack
- 2 rings (2 tunnels): 2 detector sites*
- 1 long production straight/ring     1 detector site
- Each ring supports both charge species of muons circulating in opposite directions (if opposing straights are identical)
- Alternate injection batches between rings
- Isosceles Triangle Ring
- 2 rings (in 1 tunnel): 2 detector sites
- 2 production straights/ring     2 detector sites
- Each ring supports only one charge species
- Interleave and separate +/- batches by 100 ns (requires RF)
- Bowtie  Ring – new
- Properties similar to triangle ring
- *of course 1 ring/1 detector is also an option for the racetrack

## 20, 40, 50 GeV Current Design Overview

- 20, 40, and 50 GeV lattice ring designs complete
- Arc: FODO cells with ~6T dipole fields:
- 72 arc cells, combined-function magnets (triangle, for now)
- 90 arc cells, separated-function, tunable magnets (racetrack design, for now)
- Combined dispersion suppressor and matching sections
- Designed for MW intensities - warm bores of SC
- Clad with Pb (absorbs 80% of e beam power)
- 1 cm of W @50 GeV will also sufficiently protect SC coils
- Production straight design:
- SC solenoids - minimize beam size
- NC, 30 cm -bore quadrupoles - confines cryogenics to arcs
- Permanent magnet ~30 cm bore quads appear feasible
- Background sweep dipoles at ends of production straights

## 20  50 GeV upgrade; present status

- Isosceles:
- modify lattice + some magnet changes required; _realignment_
- Muon/neutrino beam divergence fixed to 1/  at both energies
- Racetrack:
- no changes: 40 /50 GeV ring installed and can be operated @20 GeV;
- bores accommodate 20 GeV beam and shielding
- Muon beam rms divergence increases from 0.1/ @20 GeV to 0.14/ @40 GeV and 0.19/  @50 GeV
- These approaches are not specific to storage ring shape

## Racetrack Storage Ring 

- Ring operates at 20 and 50 GeV – Arc dipoles powered at 2.5 and 6.3 T

*Neutrinos*

*Neutrinos*

********* ****±**  injections*

- Background sweep dipoles at end of each straight

## Potential dual far/near detector locations

- C. Prior, 1/25/06     ISS scoping study

- # detector locations

- Apex angle of storage ring triangle

## Triangular Muon Storage Ring

- Designs for 20 and 50 GeV to fit in same tunnel

- C.Prior UKNF talk

*now 50**° to** 60**°*

## 20/50 GeV Lattice for Racetrack Ring

**20/50 GeV Lattice for Racetrack Ring**

- Production Straight

## 20 GeV Lattice Functions for Triangular Ring (Excluding Production Straights)

**20 GeV Lattice Functions for Triangular Ring (Excluding Production Straights)**

## n Determines Minimum Ring Circumference:

**n Determines Minimum Ring Circumference:**

- Triangular ring:
- +- interleaving – maintains 100 ns spacing between batches*

- Kicker gaps  600 ns

- *no interleaving required in dual racetrack scheme

## Site concerns for 7 & 3 x103 km detectors

- Vertical depth (arcs << straights):
- Racetrack:
- Isosceles triangle:
- Conclusion: relative depths of two similar circumference -triangular or racetrack - storage rings are very close

- 6000 km

- 7000 km

- 36

- to 3 km site

- 10

- surface

- 36

- 46

- to 7 km site

## n=5 Storage Ring Parameters - updated

-      PARAMETER		     TRIANGLE		RACETRACK
-                                                        20 : 50 GEV		 20 : 50 GEV
- Circumference   		        1573 m		   1573 m
- Production straight	 	2x~378 m  (2x~24%) 	635 m (40%)
- Depth				       ~_340 m_		    ~_430 m_
- acceptance (beam emittance)          4.8 cm   (30)	      same normalized, 95%
- Momentum acceptance		    1-2% (RF determined)	      4%
- rms prod divergence 	               0.10/ : 0.12/ 	            0.12/ : 0.19/ 
- Global Tune, x / y	   10.79 / 11.15 : 10.44 / 10.64   10.23 / 9.24
- xmax/ymax	                           117 m : 184 m             155 m / 167 m
- Peak Field arcs 		                     6.4T 		     6.3T
- Peak Field prod straight	                 4.3T : 6.4T*		     0.2T**
- * solenoids     ** quadrupoles

##  Magnetic components:

- Racetrack:
- Magnets, in particular SC arc magnets, will resemble design in feasibility I study – see figures below
- Triangle
- Vertical mounting of SC elements in vertical return arc looks difficult
- Should look at this aspect asap

- Dipole (left) and cryostat design (right) for racetrack, Feasibility I Study

## Site Considerations

- Detector sites
- Coupled near/far detector sites in triangular ring (apex angles>~60, triangle production efficiency rapidly declines)
- Uncoupled in dual-racetrack case
- Depth
- Water tables
- Geological constraints for tunnel construction
- Civil engineering for tunnels “hundreds of meters” deep

## Example: Fermilab Site-specific constraints:  from Feas. I Study for a U.S. Neutrino Factory

- 50 GeV Fermilab Storage Ring:  racetrack
- 13 declination angle
- circumference, C = 1753 m
- 39% ratio (1 prod str./C)
- Design predicated on ~6T SC arc dipoles

| 600 | Feet | Ring Vertical Drop |
| --- | --- | --- |
| 10 | Feet | Tunnel ceiling to floor |
| 10  | Feet | Shielding above ring |
| 50  | Feet | Undisturbed bottom layer of Galena Platteville |
| 10 | Feet | For uncertainties in the above three numbers |
| 680 | Feet | Total  from Surface to Bottom of Galena Platteville |

## Example: BNL site specific constraints:from Feas. II study for a U.S. Neutrino Factory

- 20 GeV BNL Storage Ring: racetrack
- 10 declination angle
- C = 358 m
- 35% ratio
- Design predicated on ~7T SC arc dipoles- (hence the short circumference achieved at 20 GeV)

## General concerns

- Site depth and civil engineering:
- Fermilab and BNL have depth constraints, for example; the larger of the two, restricted to <200m down.
- The NUMI project at Fermilab entailed considerable civil engineering for an ~1 km long tunnel only 100 m deep – (won the 2005 civil engineering award)
- Maintenance, water leaks are a problem even with the NUMI depth (muons are much nicer, however, from an activation standpoint)
- # of batches, assuming separate rings for , determines ring size
- ~300 m / batch (400 ns for batch, 600 ns for kicker window)
- interleave  batches in two different rings (otherwise only 1/2   # of batches for one ring)
- Number of batches + 7000 km detector site determines depth

## Proposal: n=3 batches each sign muonin two racetrack rings

- Derived from 200 m depth constraint and two-ring, interleaving scheme for  batches for the 7,000 and 3,000 detector sites.

## Proposal: n=3 batches different sign muons in two triangular rings

- Derived from 200 m depth constraint and two-ring, interleaving scheme for  batches.

## Circumference and efficiency comparisons:  Triangle vs Racetrack

| Circumference | Triangle
52.8 apex  | racetrack |
| --- | --- | --- |
| 1609 | 49.6% | 38.2% |
| 1258 | 42.8% | 34.9% |
| 944 | 33.2% | 29.9% |
| 804 | 27.6% | 26.3% |
| 629 | 4.7% | 19.7% |

## Time Structures

- Racetrack rings:  3 batch scenario
- Ring 1:  3 batches of either + or -
- 788 – 3x120 = 428/3 m  or 475 ns for kicker window
- Ring 2:  3 batches of either + or -
- For 3 batches: 2412 – 3x120 = 2052/3 m or 2280ns for kicker window.
- This ring can handle 8 batches with 600 ns for kicker gaps
- Racetrack rings:  5 batch scenario
- Ring 1:  1 batch of +  and 1 batch - counter-rotating
- Ring 2:  4 batches of +  and 4 batches - counter-rotating
- Operate racetrack rings at different energies?
- Triangular ring: 3 batch scenario
- Ring 1:  3 batches of +  or -
- Ring 2:  3 batches of +  or -

## General concerns:

-  Site constraints
- Depth
- Detector sites/ different for triangle vs racetrack
- Emittance measurements:
- Injection
- Vertical orientation and mounting of SC magnets in triangular ring mechanically challenging?
- Tracking
- Chromatic correction and other high-order correctors
- Fringe fields

## Recommendations for Future Work

- Further survey of potential detector sites with angular ranges covered by triangular and now bowtie storage rings – preliminary survey done
- Matching to FFAG accelerators
- Mechanical design for vertical mounting of SC magnets
- Design and comparison of injection
- In production straight
- In arcs
- Emittance measurement design and accuracy
- Tracking with fringe fields