# Presentation: 109583

## Comparison of Solenoid and Horn Focusing Systems

- Steve Kahn
- Muons Inc.
- 27 July 2006

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Introduction

- We have been using a solenoid capture system for capturing pions off the target since we started looking at neutrino factories.
- The neutrino physicists (that we were talking to) seemed more  enamored with *Superbeams.*
- We had looked at using a solenoid in the place of horns for a superbeam, since we had thought that we could build a neutrino factory as a later stage of an existing superbeam facility.
- At the right is a PAC paper showing one of the early studies.

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## First Phase Super Neutrino Beam

- Upgrade AGS to 1MW Proton Driver:
- Both BNL and JParc have eventual plans for their proton drivers to be upgraded to 4 MW.
- Build Solenoid Capture System:
- 20 T Magnet surrounding target.  Solenoid field falls off to 1.6 T in 20 m.
- This magnet focuses both +  and .  Beam will have both  and 
- A solenoid is more robust than a horn magnet in a high radiation.
- A horn may not function in the 4 MW environment.
- A solenoid will have a longer lifetime since it is not pulsed.

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Types of Capture/Focus Systems Considered

- Traditional Horn Focus System
- Uses *toroidal *magnetic field.
- Focuses efficiently
- B  pz
- Conductor necessary along access.
- Concern for radiation damage.
- Cannot be superconducting.
- Pulsed horn may have trouble surviving ~109 cycles that a 1-4 MW system might require.
- Solenoid Capture System similar to that used by Neutrino Factory
- Solenoid Horn System

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

##  Simulations to Calculate Fluxes

- Model Solenoid/Horn Magnet in GEANT. (Geant 3.21)
- Use Geant/Fluka option for the particle production model.
- Use 30 cm Hg target ( 2 interaction lengths.)
- No target inclination.
- We want the high momentum component of the pions.
- Re-absorption of the pions is not a problem.
- Solenoid Field profile on axis is B(z)=Bmax/(1+a z)
- Independent parameters are Bmax, Bmin and the solenoid length, L.
- Horn Field is assumed to be a toroid.
- Pions and Kaons are tracked through the field and allowed to decay.
- Fluxes are tallied at detector positions.
- The following plots show  flux and e / flux ratios.

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Solenoid Capture

- Sketch of solenoid arrangement for Neutrino Factory

- If only  and not  is desired, then a dipole magnet could be inserted between adjacent solenoids above.

- Inserting a dipole also gives control over the mean energy  of the neutrino beam.

- Since  and  events can be separated with a modest magnetic field in the detector, it will be desirable to collect both signs of  at the same time.

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Captured Pion Distributions

- PT distribution of 

- PT  =225 MeV/c corresponding to 7.5 cm radius of solenoid

- 66% of  are lost since they have PT>225 MeV/c

- PT, GeV/c

- Decay Length of Pions

- <L>=7 m

- L, cm

- P > 2 GeV/c

-  = 50 m

- A 15 cm radius of the solenoid would capture 67% of the +

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Rate and e/ as a function of Decay Tunnel Length

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Comparison of Horn and Solenoid Focused Beams

- The Figure shows the spectra at 0o at     1 km from the target.
- Solenoid Focused Beam.
- Two Horned Focused Beam designed for E889.
- So-called *Perfect Focused* beam where every particle leaving the target goes in the forward direction.
- The perfect beam is not attainable.  It is used to evaluate efficiencies.
- A solenoid focused beam selects a lower energy neutrino spectrum than the horn beam.
- This may be preferable for CP violation physics

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Horn and Solenoid Comparison (cont.)

- This figure shows a similar comparison of the 1 km spectra at 1.25o off axis.
- The off axis beam is narrower and lower energy.
- Also a curve with the  flux plus 1/3 the anti- flux is shown in red.
- Both signs of  are focused by a solenoid capture magnet.
- A detector with a magnetic field will be able to separate the charge current  and anti-.

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

##  Flux Seen at Off-Axis Angles 

- We desire to have *Low Energy * beam.

- We also desire to have a narrow band beam.

- I have chosen 1.5o off-axis for the calculations.

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## e/ Ratio

- The figure shows the e flux spectrum for the solenoid focused and horn beams.
- The horn focused beam has a higher energy e spectrum that is dominated by Koee
- The solenoid channel is effective in capturing and holding  and .
- The e spectrum from the solenoid system has a large contribution at low energy from ee.
- The allowed decay path can be varied to reduce the e/ ratio at the cost of reducing the  rate.
- We expect the e/ ratio to be ~1%

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Running the AGS with 12 GeV Protons

- We could run the AGS with a lower energy proton beam.
- If we keep the same machine power level we would run at a  5 Hz repetition rate.
- This would work for a conventional beam since we are not concerned with merging bunches.
- Figure shows *Perfect Beam *for 12 and 24 GeV incident protons.
- 12 GeV profile is multiplied by 2 for the higher repetition rate.

- 24 GeV protons

- 12 GeV Protons

- Perfect Beam

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## 12 GeV Protons (cont.)

- On Axis

- 1.25 degrees off axis

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006

## Conclusions

- Most of this work had been done on and off between 1999 and 2001.
- We had appreciated that making long solenoid channels would be an effective way to hold pions until they decayed.
- We were concerned about the cost of these long solenoid channels since horns were relatively cheap.
- We were not successful keeping the beam focused after we left the solenoid.
- Horns were reasonably efficient in capturing pions particularly the high part of the spectrum.
- There was not much room for enormous gain.
- This talk should provide an introduction into Harold Kirk’s talk which discusses more recent work that has been done on this subject.

- S. Kahn -- Comparison of Solenoid and Horn

- July 27, 2006