# Presentation: 193757

## International Scoping Study Accelerator Working Group:Summary and Plans

**Michael S. Zisman**
**C****enter for ****B****eam ****P****hysics**
**Accelerator & Fusion Research Division**
**Lawrence Berkeley National Laboratory**
**ISS Plenary Meeting–Irvine**
**August 21-23, 2006**

## Introduction

**Meeting marks culmination of next step in ongoing development of a Neutrino Factory facility concept**
**completed a one-year exploration of an optimized Neutrino Factory design**
**carried out by international team with participants from all regions**
**Europe, Japan, U.S.**
**goal: study alternative configurations to arrive at baseline specifications for a system to pursue further**
**Work carried out at four ISS Plenary Meetings**
**CERN (September 2005); KEK (January 2006); RAL (April 2006); UC-Irvine (August 2006)**
** ****and four Accelerator Group Workshops**
**BNL (December 2005); KEK (January 2006); RAL (April 2006); UC-Irvine (August 2006)**
**Communications via ****NF-SB-ISS-ACCELERATOR**** e-mail list**

## History (1)

**There have been 41⁄2 previous NF “feasibility” studies**
**1 in Japan**
**1 in Europe**
**21⁄2 in the U.S.**
**studies I, II, IIa**

## References

**NuFact-J Study (2001)**
**http://www-prism.kek.jp/nufactj/nufactj.pdf**
**Study I (1999–2000) instigated by Fermilab**
**Study II (2000–2001) collaboration of ****NFMCC, BNL**
**http://www.cap.bnl.gov/mumu/studyii/final_draft/The-Report.pdf**
**European Study (2002) instigated by ****CERN**
**http://slap.web.cern.ch/slap/NuFact/NuFact/nf122.pdf**
**Study IIa (2004) ****APS**** Multidivisional Neutrino Study**
**http://www.aps.org/neutrino/loader.cfm?url=/commonspot/security/getfile.cfm&PageID=58766**

## History (2)

**Most studies focused on feasibility and performance**
**cost optimization was secondary, or ignored**
**U.S. Study IIa attempted to maintain performance while reducing costs**
**succeeded in keeping both sign muons and substantially lowering hardware cost estimate**
**simplified phase rotation**
**simplified cooling channel**
**improved acceleration scheme**

- NOTE: Hardware costs only. No ED&I, no escalation, no contingency.

## Why Another Study?

**Many different approaches have been considered**
**we wished to compare them to assess which features are optimal**
**in terms of ****performance**
**(ultimately) in terms of ****cost**
**we must include the detector in such optimizations**
**and the latest understanding of the (evolving) physics requirements**
**beam energy, baseline(s)**
**To select best approaches, must study and understand what the different regions have done**
**partly a team-building exercise**
**number of Neutrino Factory facilities likely to be built worldwide ******** 1**
**voluntarily working together toward a single design increases odds of *****some***** facility being built**
**Prepares the way for IDS (and hopefully WDS in 2009)**

## Neutrino Factory Ingredients

**Proton Driver**
**primary beam on production target**
**Target, Capture, Decay**
**create ********, decay into ******
**Bunching, Phase Rotation**
**reduce *********E *****of bunch**
**Cooling**
**reduce transverse emittance**
**Acceleration**
**130 MeV ******** 20–40 GeV**
**Decay Ring**
**store for ~500 turns; long straight section**

- “Front End”

- ISS Baseline (preliminary)

## FFAG-Based Neutrino Factory

**Alternative design concept based solely on ****scaling FFAG**** rings has been studied**
**the approach was evaluated and compared with other designs as part of our task**
**implications of keeping both sign muons need evaluation**
**as does performance of high-gradient, low-frequency RF system**

## NF Design: Driving Issues

**Constructing a muon-based NF is challenging**
**muons have short lifetime (2.2 ********s at rest)**
**puts premium on rapid beam manipulations**
**requires high-gradient NCRF for cooling (in B field)**
**requires presently untested ionization cooling technique**
**requires fast, large acceptance acceleration system**
**muons are created as a tertiary beam (p********)**
**low production rate ******** **
**target that can handle multi-MW proton beam**
**large muon beam transverse phase space and large energy spread ******** **
**high acceptance acceleration system and storage ring**
**neutrinos themselves are a quaternary beam**
**even less intensity and “a mind of their own”**

## Challenges

**Challenges go well beyond those of standard beams**
**developing solutions requires substantial R&D effort **
**R&D should aim to specify: **
**expected performance, technical feasibility/risk, cost (****matters!****)**

- We must do experiments and build components. Paper studies are not enough!

## Accelerator WG Organization

**Accelerator Working Group program managed by “Accelerator Council”**
**R. Fernow, R. Garoby, Y. Mori, R. Palmer, C. Prior, M. Zisman**
**met mainly by phone conference**
**Aided by Task Coordinators**
**Proton Driver: R. Garoby, H. Kirk, Y. Mori, C. Prior**
**Target/Capture: J. Lettry, K. McDonald**
**Front End: R. Fernow**
**Acceleration: S. Berg, Y. Mori, C. Prior**
**Decay Ring: C. Johnstone, G. Rees**

## Accelerator Study

**Study alternative configurations; arrive at baseline specifications for a system to pursue**
**examine both cooling and no-cooling options**
**Develop and validate tools for end-to-end simulations of alternative facility concepts**
**correlations in beam and details of distributions have significant effect on transmission at interfaces (****muons have “memory”****)**
**simulation effort ties all aspects together**
**Develop R&D list as we proceed**
**identify activities that must be accomplished to develop confidence in the community that we have arrived at a design that is:**
**credible**
**cost-effective**
**until construction starts, R&D is what keeps the effort alive**

## Accelerator Study Approach

**To ensure common understanding of, and buy-in for, the results**
**trade-off studies must include designs from all regions**
**also scientists from all regions (but uncorrelated)**
**Examine possibilities to choose the best ones**
**not easily done if each group “defends its own choices”**
**Study leadership fostered this “regional mixing”**
**this will equally be true in the IDS phase**

## Proton Driver Questions

**Optimum beam energy ****√**
**depends on choice of target**
**consider C, Ta, Hg**
**Optimum repetition rate ****√**** **
**depends on target and downstream RF systems**
**find that 50 Hz is reasonable compromise for cases studied**
**Bunch length trade-offs ****√**
**need (and approaches) for bunch compression**
**performance implications for downstream systems**
**Hardware options  ****(in progress)**
**FFAG, linac, synchrotron**
**compare performance**

## Proton Driver

**Examined candidate machine types for 4 MW operation**
**FFAG (scaling and/or non-scaling)**
**Linac (SPL and/or Fermilab approach)**
**Synchrotron (J-PARC and/or AGS approach)**
**consider **
**beam current limitations (injection, acceleration, activation)**
**bunch length limitations and schemes to provide 1-3 ns bunches**
**repetition rate limitations (power, vacuum chamber,...)**
**tolerances (field errors, alignment, RF stability,...)**
**optimization of beam energy**

## Optimum Energy

**Optimum energy for high-*****Z***** targets is broad, but drops at low-energy**

- –: 6 – 11 GeV

- +: 9 – 19 GeV

- We adopted 10 ± 5 GeV as representative range

## Bunch Length Dependence

**Investigated by Gallardo *****et al.***** using Study 2a channel**
**decrease starts from zero bunch length**
**1 ns is preferred, but 2-3 ns is acceptable**
**such short bunches harder to achieve at low beam energy**
**stronger sensitivity to bunch length than seen in Study 2**
**not yet understood in detail (different phase rotation and bunching)**

## Bunch Train Patterns

**.**

*Accel. of trains of 80 **μ**±** **bunches *
*                                                                            *
*NFFAG ejection delays:*
*(p + m/n) T**d**  for m = 1 to n (=3,5)*
*Pulse < 50 **μ**s for liquid target                                                                      *
*Pulse > 60 **μ**s for solid targets** **                                            *

*Decay rings, T**d *
*   **h = 2**3**3**3**5*

*μ**±*  *bunch rotation           P  target    *

*1 **          RCS (R**b** )                      NFFAG (2 R**b** )         **1 *

*(h=3, n=3)                            (h=24, n=3)      (h=5, n=5)                            (h=40, n=5) *

*3*

*2*

*2*

*3*

*  **Period*
*T**p** = T**d **/2*

*1*

*2*

*3*

*80 **μ**ˉ or** **μ**+** **bunches*

- Rees

## FFAG Proton Driver

## Layout of 3 GeV, RCS Booster

**.**

## J-PARC Scheme

**Comprises linac, 3 GeV RCS and 50 GeV synchrotron**
**under construction now!**

## SPL Scheme

**This scheme does not presently provide the bunch train parameters specified in baseline**

## Target/Capture/Decay

**Optimum target material**
**study production rates as *****f(E)***** for C, Hg, Ta ****√**
**still need reality check with HARP data eventually**
**Target limitations for 4 MW operation**
**consider bunch intensity, spacing, repetition rate ****√**
**limits could come from target...or from beam dump**
**Superbeam vs. Neutrino Factory trade-offs **
**horn vs. solenoid capture ****√**
**can one solution serve both needs?**
**is a single choice of target material adequate for both? ****√**

## Target Material Comparisons (1)

**Studied by ****Fernow, Gallardo, Brooks, Kirk**
**targets examined: C; Hg; Ta**
**target tilted with respect to solenoid axis**
**re-interactions included**
**accelerator normalized acceptance**
**transverse: 30 mm**
**longitudinal: 150 mm**
**momentum range: 100–300 MeV/c**
**compared: C (5, 24 GeV); Hg (10, 24 GeV)**
**Hg (24 GeV) is nominal Study 2/2a “benchmark” case**

## Target Material Comparisons (2)

- Results from H. Kirk

## Target Material Comparisons (3)

**Results**
**Hg at 10 GeV looks best thus far**
**Power handling capabilities of solid target materials is still an issue**
**C at 4 MW still looks hard**
**would require frequent target changes**
**Can required short bunches be produced at E ~ 5 GeV?**
**important for Neutrino Factory but not for Superbeam**
**Results all based on MARS predictions**
**need experimental data**** to validate**

## Solenoid vs. Horns (1)

**Looked at spectra produced with dual horn system compared with solenoid capture (not Neutrino Factory version)**
**still questions about normalizations to be resolved**

**Horn 1: Length =2.2 m**

**Horn 2: Length =1.6 m**

**Δ****L ****Horn 2-Horn 1 =10 m**

**J. Heim, M. Bishai, B. Viren   BNL**

## Solenoid vs. Horns (2)

**Neutrino Factory solenoid capture system**

- Tapers from 20 T, 15 cm to 1.75 T, 60 cm over 20 m

## Front End

**Compare performance of existing schemes (KEK, CERN, U.S.-FS 2b)**
**use common proton driver and target configuration(s) ****√**
**consider possibility of both signs simultaneously ****√**
**final conclusions require cost comparisons, which will come later**
**Evaluate implications of reduced *****V*****RF**** for each scheme**
**take *****V*****max**** = 0.75 *****V*****des**** and 0.5 *****V*****des**
**re-optimize system based on new *****V*****max****, changing lattice, absorber, no. of cavities, etc. ****√**
**Evaluated trade-offs between cooling and downstream acceptance ****√**
**Look at polarization issues ****√**

## Cooling Channel Comparisons (1)

**Palmer**** has looked at all current designs**
**  ****FS2, FS2a, CERN, KEK channels**
**Performance of FS2a channel is best**
**includes benefits of both sign muons**

## Cooling Channel Comparisons (2)

**Intensity predictions **
**only FS2a (with both signs) meets initial NuFact99 goal of 10****21**** useful decays per year**

## Effect of Reduced RF Gradient

**Explored effects of reduced RF gradient on throughput (****Gallardo****)**
**operating at reduced gradient lowers transmission without compensation**
**adjusting absorber thickness and RF phase would recover some of this**

## Cooling vs. Acceptance

**Evaluated trade-offs between cooling efficacy and downstream acceptance (****Palmer****)**
**increasing from 30 to 35 ******** mm-rad halves the required length of cooling channel**
**at 45 ******** mm-rad, no cooling needed**
**Not presently clear that A > 30 ******** mm-rad is practical**
**even 30 ******** mm-rad is not easy!**

## Muon Helicity

**Average muon helicity is small**
**average polarization about 8%**
**Correlation with position in bunch train is weak**

## Acceleration

**Compare different schemes *****on an even footing***
**RLA, scaling FFAG, non-scaling FFAG**
**consider implications of keeping both sign muons**
**consider not only performance but relative costs**
**bring scaling FFAG design to same level as non-scaling design**
**Look at implications of increasing acceptance **
**transverse and longitudinal**
**some acceptance issues have arisen in non-scaling case (Machida)**
**leading to exploration of a revised acceleration scenario**

## Non-scaling FFAGs (1)

**In attempting to increase the acceptance, discovered a dynamics problem due to the fact that the ****revolution time depends on transverse amplitude (****Machida, Berg****)**
**larger amplitudes and bigger angles give longer path length**
**different flight times for different amplitudes lead to acceleration problems in FFAG**
**large-amplitude particles slip out of phase with RF and are no longer accelerated**
**Possible fixes are under study**

## Non-scaling FFAGs (2)

**Present conclusions**
**30 ******** mm-rad probably possible, but is already a stretch**
**cascading FFAG rings is harder than anticipated**
**two in series probably possible, but three in series looks iffy**
**We are revisiting acceleration system design in consideration of this issue**

## Non-scaling FFAGs (3)

**Tracking with errors has begun**
**H, V misalignment of quadrupoles**
**gradient errors**
**use Gaussian errors with 2******** cutoff**
**Assumptions**
**constant *****E***** gain per turn (avoids TOF vs. amplitude effects)**
**30 ******** mm-rad emittance**
**nominal initial longitudinal emittance **
**tunes well away from half-integer to avoid large beta beating**
**particle amplitudes beyond 45 ******** mm-rad are taken as lost**

## Non-scaling FFAGs (4)

**Tracking with errors has begun**
**rms alignment errors in the range of 20–50 ********m are okay**
**rms gradient errors of 2–5 x 10****–4**** are okay**
**both are tight**

- 0 m (rms)

- 10 m (rms)

- 20 m (rms)

- 50 m (rms)

## Decay Ring

**Design implications of final energy (20 vs. 40 GeV) ****√**
**Optics requirements vs. beam emittance ****√**
**arcs, injection and decay straight sections**
**Implications of keeping both sign muons ****√**
**need both injection and decay optics in same straight section**
**Implications of two simultaneous baselines ****√**
**Both triangle and racetrack rings have been examined**
**recently started to re-examine “bow-tie” configuration**

## Decay Ring Geometry (1)

**Triangle rings would be stacked side by side in tunnel**
**one ring stores ********+**** and one ring stores ********–**** **
**permits illuminating two detectors with (interleaved) neutrinos and antineutrinos simultaneously**

## Decay Ring Geometry (2)

**Racetrack rings have two long straight sections that can be aimed at a single detector site**
**store both ********+**** and ********– ****in one ring**
**second ring, with both particles, would be used for another detector site**
**More flexibility than triangle case, but probably more expensive**
**can stage the rings if one detector is ready first**
**can point to two sites without constraints**

## Decay Ring Geometry (3)

**Comparison at similar circumference indicates that, for two suitable detector sites, a triangle ring is more efficient than a racetrack ring**
**for a single site, racetrack is better**

- Depth may be an issue for some sites, especially for racetrack with long baseline

## R&D Program

**Two international experiments in progress**
**MERIT and MICE**
**Neutrino Factory R&D programs under way in **
**Europe under the auspices of BENE and UKNF**
**Japan, supported by university, and some U.S.-Japan, funds**
**substantial scaling-FFAG results have come from this source**
**U.S. under the auspices of the NFMCC (DOE + NSF supported)**
**Proposals in preparation for new international efforts**
**EMMA (UK), electron model to study non-scaling FFAG performance**
**several U.S. firms getting SBIR grants similar FFAG studies **
**high-power target test facility (CERN), to provide dedicated test-bed for next generation of high-power targets**
**R&D list prepared during ISS effort ****to be in our report**

## MERIT

**MERIT experiment will test Hg jet in 15-T solenoid**
**24 GeV proton beam from CERN PS**
**scheduled Spring 2007**

- 15-T solenoid during tests at MIT

- Hg delivery and containment system under construction at ORNL. Integration tests scheduled this Fall at MIT.

## MICE (1)

## MICE (2)

**MICE channel at RAL will be built in steps to ensure complete understanding and control of systematic errors**

## MICE (3)

## Decisions on Baseline (1)

**Proton Driver**
**specify parameters, not design**
**implicitly assumes liquid-metal target**

| Parameter | Value |
| --- | --- |
| Energy (GeV) | 10 ± 5 |
| Beam power (MW) | 4 |
| Repetition rate (Hz) | 50 |
| No. of bunch trains | 3,5a) |
| Bunch length, rms (ns) | 2 ± 1 |
| Beam durationb) (s) | 40 |

- a)Values ranging from 1–5 possibly acceptable.
- b)Maximum spill duration for liquid-metal target.

## Decisions on Baseline (2)

**Target**
**assume Hg target; look at Pb-Bi also**
**Front End**
**bunching and phase rotation**
**use U.S. Study IIa configuration**
**cooling**
**include in baseline**
**keep both signs of muons**
**“****waste not, want not”**
**Acceleration**
**used mixed system**
**linac, dog-bone RLA(s), FFAGs**
**transition energies between subsystems still being debated**

## Decisions on Baseline (3)

**Decay Ring**
**adopt racetrack**
**keep alive triangle as alternative**
**depends on choice of source and baselines**
**energy 20 to 40 GeV**
**50 GeV okay for ring, but implies more acceleration than presently planned**

## Accelerator Study Next Phase

**Focus on selected option(s)**
**as part of upcoming International Design Study**
**IDS will eventually have more of an engineering aspect than the ISS**
**Making final choices requires (“top-down”) cost evaluation**
**requires engineering resources knowledgeable in accelerator and detector design**
**Internationally organize R&D efforts in support of facility design**

## Summary

**Making progress toward consensus on a single optimized Neutrino Factory scheme **
**comparison of competing schemes is complete**
**report to be completed by end of 2006**
**Must continue to articulate need for an adequately-funded accelerator R&D program**
**and define its ingredients**
**being encouraged to do this in an international framework**
**It has been a privilege to work on the ISS with such a talented and dedicated group**
**my thanks to: **
**Program Committee (Dornan, Blondel, Nagashima)**
**Accelerator Council and task leaders (slide 11)**
**all members of Accelerator Group (see ****NF-SB-ISS-ACCELERATOR ****list)**