# Presentation: 073009

## Decay Pipe Extension:

-   It’s so – like – Wow.
-  Whatever.

## -4 possibilities-potential flux gains-trade-offs for future flexibility     narrow band beams     off-axis beams-comments on technical difficulty

*B**eam **Sp**ecifications **A**dvisory **G**roup*
*BSpAG*

- Decay Pipe Modifications

## Possible Modifications to Decay Pipe

- Window, air in chase present 37% *X*0 scattering for pions
- Smaller diameter of pion cloud at z = 15 m  thin window.
- Could do thin window at z = 45 m, but not as thin.
- Extension requires raising ceiling of shielding

- Existing
- Decay Pipe

**Option I**

**Option II**

*z*=0m

*z*=15m

*z*=25m

*z*=45m

**Option III**

- Extension

- 2m

- 1.12m

**Chase Shielding**

## The Gain:  Flux in LE Beam

- Both Extensions 0.030” thick window, Nominal DP = 0.186”
- Flux gain is 7% (ME Ext.) and 10% (LE Ext.) for *E*** < 6 GeV

- Nominal DP
- ME Extension
- LE Extension

- ME Extension
- LE Extension

## Option III:   Just a Thin Window

- z=15m

- z=45m

- For extension, 5% of the gain was thin central window 24”
- Option III:  simply put thin central window on existing decay pipe.
- Has to be 1m diameter to   contain 98% of pion cloud     (soft **’s diverge)
- Slightly thicker central window than extension (.045”)
- Net gain: 4.5% in events<6GeV

## Option IV:  Do Nothing

- Decide that all this effort is not worth 10% (or less) neutrino gain
- Decide that effort is distraction from more critical activity
- Live with .187” thick vacuum window
- Leave open possible future uses of target hall
- Narrow band beam
- Fully optimized off-axis beam

## Trade-Off:  Only Semi-beams in Future

- Moving just the Target

- Fully-Optimized Beam

## Trade-Off III:  Off-axis

- Off-axis beams perhaps best performed in ME position (peak 2 GeV).
- If build LE Extension, would have to do a semi-ME beam off-axis as a compromise.
- No loss of future off-axis if do Options II - IV

## Other things We Looked At:

- The extension is identically equivalent to moving the horns and the target *en masse* downstream to the decay pipe
- Causes groundwater problems (MARS studies).
- The extension requires raising ceiling of chase by ~ 1ft.
- No change in ground water from this
- Could we just put the extension off beam axis?
- Wouldn’t have to raise ceiling
- But doesn’t help flux (walls in the way of the beam)

## Summary:

| Option | Flux Gain
0-6 GeV (%) | Technical Difficulty | Future Flexibility Lost |
| --- | --- | --- | --- |
| I (LE Extension) | 10 | Raise chase ceiling, air cooling of target hall | NBB, Off-axis beam |
| II (ME Extension) | 7 | “ | NBB |
| III (Nominal Pipe, thin window) | 4.5 | Design of double thickness window | None |
| IV (Nothing) | 0 | None
 | None
 |

## Back-Up slides

## Slight Complication: Window Curvature

- Recall windows have 2:1 curvature.
- Large solid angle of extension window makes effective window thickness larger than 0.030”
- Less of effect at nominal window.

## Asymmetric Extension

## Comment on Window

- Our window was too thin for 44” diameter pipe
- Pion cloud after horn 2 is actually even narrower (broadens by 40m)
- Could make composite window with ‘thin spot’ in center