# Presentation: 037878

## -Factory Front EndPhase Rotation Gas-filled rf

- David Neuffer
**Fermilab**
**Muons, Inc.**

## 0utline

**Neutrino Factory Front End Optimization**
**Performance, cost, **
**Study 2A Front End **
**Variations on Study 2A**
**Shorter rotator – less adiabatic**
**Gas-filled rf cavities**
**Global optimizations **
**Different Approaches**
**Shorter bunch trains**
**Rotate, then bunch ?**

## Neutrino Factory - Study 2A

- Proton driver
- Produces proton bunches
- 8 or 24 GeV,  ~1015p/s, ~20Hz bunches
- Target and drift
-   (> 0.2 /p)
**Buncher, bunch rotation, cool**
- Accelerate  to 20 GeV
- Linac, RLA and FFAGs
- Store at 20 GeV (0.4ms)
-  e ++ e*
- Long baseline  Detector
- >1020 /year

## Study2A scenario details

**Target**- Hg-jet within 20T solenoid
- Drift –110.7m – within 1.75T solenoid
- Seems long ...
**Bunch** -51m **(110MV total)**
- 12 rf freq., 330 MHz  230MHz
- Quasi-adiabatic
******-E Rotate** – **54m –**** ****(416MV total)**
- 15 rf freq. 230 202 MHz
- Longer than needed – adiabatic
- Must work at B= ~1.75T or more
**Match and cool** (80m)
- 0.75 m cells, 0.02m LiH
- H2 would be better
- Do we need cooling??
- Captures both **μ****+ ****and ****μ****-**

## Features/Flaws of Study 2A Front End

- Fairly **long** section – ~350m long
- Study 2 was induction linac 1MV/m
- Produces long bunch trains of ~**200 MHz** bunches
- ~80m long (~50 bunches)
- Matches to downstream acceleration rf ??
- Transverse cooling is only factor of ~21⁄2 in x and y
- No cooling  or more cooling may be “better”
- Method works better than it should ...
- Vary Study 2A baseline or try very different scenario

## Reduce Rotator length

- Rotator reduced by factor of 2
- 54m 27m
- Acceptance only slightly degraded
- ~0.204 μ/p at ref. emittance
- ~0.094 μ/p at 1/2 emittance
- (in simplified ICOOL model)
- Would reduce cost by 42M$
- Palmer-Zisman estimate...

## rf in Rotation/Cooling Channels:

- Can cavities hold rf gradient in magnetic fields??
- MUCOOL result :
- V' goes from 45MV/m to 12MV/m (as B -> 4T)
- 800MHz rf
- Vacuum rf cavity
- Worse at 200MHz ??

## Use gas-filled rf cavities? 

- Muons, Inc. tests:
- Higher gas density permits higher gradient
- Magnetic field does **not** decrease maximum allowable gradient
- Gas filled cavities may be needed for cooling with focusing magnetic fields
- Density  > ~60 atm H2 (7.5% liq.)
- Energy loss for μ’s is >~ 2MV/m
- Can use energy loss for cooling

- Mo electrode, B=3T, E=66 MV/m
- Mo B=0 E=64MV/m
- Cu E=52MV/m
- Be E= 50MV/m 800 MHz rf tests

## Gas-filled rf cavites (Muons, Inc.)

**Cool here**

**Add gas** + higher gradient to obtain **cooling within rotator**
- ~300MeV energy loss in cooling region
- Rotator is 54m;
- Need ~4.5MeV/m H2 Energy
- 133atm equivalent 295oK gas
- ~250 MeV energy loss
- Alternating Solenoid lattice in rotator
- 20MV/m rf cavities
- Gas-filled cavities may enable higher gradient (Muons, inc.)

## ICOOL results- gas cavities

- End of Rotator

**~0.20 ****μ/p** within reference acceptance at end of φ-E Rotator
**~0.10 μ/p** within restricted acceptance (ε⊥<0.015m)
- Rms emittance cooled from ε⊥ = 0.019 to                ε⊥ = ~0.009
- Longitudinal rms emittance ≅0.075
- Continuing  ~ Study 2A cooling can improve to
**~0.22 ****μ/p, **ε⊥ = ~0.008
- ~30m, V’ = 18MV/m

## Modify initial solution

- Transverse emittance

- Acceptance (per 24GeV p)

- Change pressure to **150Atm**
- Rf voltage to **24 MV/m**
- Transverse rms emittance cools 0.019 to ~0.008m
- Acceptance **~0.22********/p** at        εT < 0.03m
- ~0.12/p at εT < 0.015m
**About equal to Study 2B**

## Cooling simulation results

- 0

- 0.4m

- -0.4m

- 0.4m

- 0.5GeV

- -50m

- 50m

## Same geometry – Be or LiH Windows

- Replace 150A H2 with 0.65cm thick Be windows or 1.2 cm LiH windows
- Similar dynamics as H2 but
**Much worse** than Study 2B performance (?)
- Transverse emittance cooling : 0.019→ 0.0115 (Be)
-  → 0.0102m LiH
-  Muons within Study 2B acceptance:
**0.134 ****μ/p** (εt < 0.03) Be
- 0.056 μ/p (εt < 0.015)
**0.160 ****μ/p** (εt < 0.03) LiH
- 0.075μ/p (εt < 0.015)

- Worse than expected;
- Needs reoptimization?

## Cost impact of Gas cavities

- Removes 80m cooling section  **(-185 M$)**
- Increase Vrf' from 12.5 to 20 or 24  MV/m
- Power supply cost  V'2 (?)
- 44 M$  107M$ or 155M$
- Magnets: 2T  2.5T Alternating Solenoids
- 23 M$  26.2 M$
- Costs due to vacuum  gas-filled cavities  (??)
- Total change:
**Cost decreases by 110 M$ to 62 M$**  (???)

## Summary

- Buncher and E Rotator (ν-Factory) Variations
**Gas-filled rf cavities can be used in Buncher-Rotator**
- Gas cavities can have high gradient in large B (3T or more?)
- Variations that meet Study 2A performance can be found
**Shorter systems – possibly much cheaper??**
**Gas-filled rf cavities**
**To do:****	**
- Optimizations, Best Scenario, cost/performance ...
- More realistic systems

## Short Front-end option

- Drift (20m), Bunch–20m **(100 MV)**
-  Vrf = 0 to 15 MV/m ( 2/3)
- Rotate – 20m (200MV)
- Vrf = 15 MV/m ( 2/3)
- Cooler up to 100m
- Study 2B Cooler
- ICOOL results
**0.12 ********/p **within 0.3 cm
- Only ~10 bunches (15m train)
- Reduces  base cost by ~100 MP$

**60m**

**40m**

**95m**

- -20m

- 30m

- 0

- 0.4GeV

## Front-end variant (K. Paul)

- Low frequency capture and phase rotation
- SuperInvar target, 8GeV protons
- Solenoid capture (20T5T)
- Rf: Start at 75MHz
- Reduce frequency as bunch lengthens
- 75→50→25 MHz : phase-energy rotation
- Rebunch at 325MHz (~8 bunches)
- ~0.14 μ/8 GeV proton
- 5 to 10 bunches
- Cool with gas-filled
- 	rf cavities

## Phase/energy rotation

- 75MHz – 4MV/m
- 50MHz – 2MV/m
- 25MHz – 1MV/m
- 325MHz – 5+ MV/m

## Cost estimates:

- Costs of a neutrino factory (MuCOOL-322, Palmer and Zisman):

**Study 2 **

**Study 2B**** **

- “Study 2B  front end  reduces cost by ~ 350MP$

## Advantages of high-pressure cavities 

-  **high gradient rf**
- In magnetic fields B=3T, or more ...
- With beam
- Can Integrate cooling with capture
- Capture and phase-energy rotation + cooling
- Can get high-gradient at low frequencies (30, 50, 100 MHz ???)
- Beam manipulations

**Research can be funded...**