March 29, 2007IDS: CERN - Zisman International Scoping Study Accelerator Working Group Summary Report Michael S. Zisman Center for Beam Physics Accelerator & Fusion Research Division Lawrence Berkeley National Laboratory International Design Study Meeting–CERN March 29, 2007

IDS: CERN - Zisman2 Introduction NuFact06 marked formal culmination of the ISS —completed a one-year exploration of an optimized Neutrino Factory design o carried out by international team (participants from Europe, Japan, U.S.) —goal: study alternative configurations to arrive at baseline specifications for a system to pursue further Work was quite successful —but, we have not done everything o final report not yet completed, but “abridged version” is now available Communications via NF-SB-ISS-ACCELERATOR list —worked well and should be continued for IDS

March 29, 2007IDS: CERN - Zisman3 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

March 29, 2007IDS: CERN - Zisman4 NF Design: Driving Issues Constructing a muon-based NF is challenging —muons have short lifetime (2.2  s at rest) o 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  ) o low production rate  –target that can handle multi-MW proton beam o large muon beam transverse phase space and large energy spread  –high acceptance acceleration system and decay ring —neutrinos themselves are a quaternary beam o even less intensity and “a mind of their own”

March 29, 2007IDS: CERN - Zisman5 Challenges Challenges go well beyond those of standard beams —developing solutions requires substantial R&D effort o 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!

March 29, 2007IDS: CERN - Zisman6 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

March 29, 2007IDS: CERN - Zisman7 Accelerator Study Aims 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 (not completed) —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: o credible o cost-effective —until construction starts, R&D is what keeps the effort alive

March 29, 2007IDS: CERN - Zisman8 Accelerator Study Approach Did trade-off studies including designs from all regions —also scientists from all regions (but uncorrelated) o ensured common understanding of, and buy-in for, the results —examined possibilities to choose the best ones This “regional mixing” was actively fostered —recommend this approach continue during IDS phase ISS was partly a team-building exercise —number of Neutrino Factory facilities likely built worldwide  1 –voluntarily working together toward a single design increases odds of some facility being built —for AWG, this worked pretty well

March 29, 2007IDS: CERN - Zisman9 Proton Driver Questions Optimum beam energy √ —depends on choice of target —fairly broad Optimum repetition rate √ —depends on target and downstream RF systems o find that 50 Hz is reasonable compromise for cases studied Bunch length trade-offs √ Hardware options √ —examined candidate machine types for 4 MW operation o FFAG (scaling and/or non-scaling) o Linac (SPL and/or Fermilab approach) o Synchrotron (J-PARC and/or AGS approach) —ultimately decided to specify only parameters, not hardware

March 29, 2007IDS: CERN - Zisman10 Optimum Energy Optimum (calculated) 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

March 29, 2007IDS: CERN - Zisman11 Bunch Length Dependence Investigated by Gallardo et al. using Study 2a channel —decrease starts beyond 1 ns bunch length o 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 o not yet understood in detail (different phase rotation and bunching)

March 29, 2007IDS: CERN - Zisman FFAG Proton Driver 180 MeV H ˉ linac Achromatic Hˉ collimation line 3 GeV RCS booster mean radius = m n=5, h=5 10 GeV non-scaling FFAG n = 5, h = 40, radius = twice booster radius = m Bunch compression for 5 bunches: Longitudinal bunch area = 0.66 eV-s 1.18 MV/turn compresses to 2.1 ns rms Add h = 200, 3.77 MV/turn for 1.1 ns rms Rees, Prior Works for n = 3 also

March 29, 2007IDS: CERN - Zisman13 SPL Scheme Proposed scheme increases energy to 5 GeV —requires accumulator and compressor rings to deliver baseline bunch parameters o delivery system for 2 ns bunches has been worked out

March 29, 2007IDS: CERN - Zisman14 Target/Capture/Decay Optimum target material √ —studied by Fernow, Gallardo, Brooks, Kirk o targets examined: C (5, 24 GeV); Hg (10, 24 GeV) –re-interactions included o Hg (24 GeV) is nominal Study 2/2a “benchmark” case 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 √ o can one solution serve both needs?

March 29, 2007IDS: CERN - Zisman15 Target Material Comparisons (1) Results from H. Kirk

March 29, 2007IDS: CERN - Zisman16 Target Material Comparisons (2) Results —Hg at 10 GeV looks best thus far Power handling capability of solid target materials is still an issue —R&D on solid target options is in progress (Bennett) —C at 4 MW still looks hard o 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

March 29, 2007IDS: CERN - Zisman17 Baseline Target System Neutrino Factory solenoid capture system Tapers from 20 T, 15 cm to 1.75 T, 60 cm over 20 m

March 29, 2007IDS: CERN - Zisman18 Front End Compare performance of existing schemes (KEK, CERN, U.S.-FS 2a) —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 √ —take V max = 0.75 V des and 0.5 V des Evaluated trade-offs between cooling and downstream acceptance √ Look at polarization issues √ —still some issues left if bow-tie ring option considered

March 29, 2007IDS: CERN - Zisman19 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 —only FS2a (with both signs) meets NuFact99 goal of useful decays per year

March 29, 2007IDS: CERN - Zisman20 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 o at 45  mm-rad, no cooling needed At present, A  30  mm-rad seems practical limit

March 29, 2007IDS: CERN - Zisman21 Acceleration Compared different schemes on an even footing —RLA, scaling FFAG, non-scaling FFAG o considered implications of keeping both sign muons o must consider not only performance but relative costs —brought scaling FFAG design to same level as non-scaling design Look at implications of increasing acceptance —transverse and longitudinal o acceptance issues have arisen in non-scaling case –leading to exploration of a revised acceleration scenario

March 29, 2007IDS: CERN - Zisman22 Non-scaling FFAGs (1) Discovered dynamics problem related to dependence of revolution time on transverse amplitude (Machida, Berg) —larger amplitudes and bigger angles give longer path length o different flight times for different amplitudes lead to acceleration problems in FFAG –large-amplitude particles slip out of phase with RF and are not fully accelerated Present conclusions —30  mm-rad probably possible, but is already a stretch —cascading FFAG rings is harder than anticipated o two in series probably possible, but three in series looks iffy

March 29, 2007IDS: CERN - Zisman23 Decay Ring Design implications of final energy (20 vs. 40 GeV) √ —25 and 50 GeV? Optics requirements vs. beam emittance √ —arcs, injection and decay straight sections Implications of keeping both sign muons √ Implications of two simultaneous baselines √ Both triangle and racetrack rings have been examined —recently started to re-examine “bow-tie” configuration

March 29, 2007IDS: CERN - Zisman24 Decay Ring Geometry (1) Triangle rings would be stacked side by side in tunnel —one ring stores  + and one ring stores  – o permits illuminating two detectors with (interleaved) neutrinos and antineutrinos simultaneously Rees

March 29, 2007IDS: CERN - Zisman25 Decay Ring Geometry (2) Racetrack rings have two long straight sections that can be aimed at a single detector site —could alternate storing  + and  – in one ring, or store both together —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 Johnstone

March 29, 2007IDS: CERN - Zisman26 Decay Ring Geometry (3) Triangle ring more efficient than racetrack ring for two suitable detector sites —for a single site, or sites in same direction from ring, racetrack is better Depth may be an issue for some sites, especially for racetrack with long baseline

March 29, 2007IDS: CERN - Zisman27 R&D Program Neutrino Factory R&D programs under way in —Europe under the auspices of BENE and UKNF —Japan, NuFact-J supported by university, and some U.S.-Japan, funds o substantial scaling-FFAG results have come from this source —U.S. under the auspices of the NFMCC (DOE + NSF supported) Several international experiments in progress —MERIT —MICE —EMMA (UK), electron model to study non-scaling FFAG performance Proposals in preparation for new international efforts —high-power target test facility (CERN), to provide dedicated test-bed for next generation of high-power targets

March 29, 2007IDS: CERN - Zisman28 Decisions on Baseline (1) Proton Driver —specified parameters, not design o implicitly assumes liquid-metal target ParameterValue Energy (GeV)10 ± 5 Beam power (MW)4 Repetition rate (Hz)  50 No. of bunch trains3,5 a) Bunch length, rms (ns)2 ± 1 Beam duration b) (  s)  40 a) Values ranging from 1–5 possibly acceptable. b) Maximum spill duration for liquid-metal target.

March 29, 2007IDS: CERN - Zisman29 Decisions on Baseline (2) Target —assume Hg target; look at Pb-Bi also Front End —bunching and phase rotation o use U.S. Study 2a configuration —cooling o include in baseline; use U.S. Study 2a configuration —keep both signs of muons o “waste not, want not” Acceleration —used mixed system o linac, dog-bone RLA(s), FFAGs

March 29, 2007IDS: CERN - Zisman30 Decisions on Baseline (3) Decay Ring —adopt racetrack o keep alive triangle as alternative –depends on choice of source and baselines o energy 20 to 50 GeV

March 29, 2007IDS: CERN - Zisman31 Summary Made good progress toward consensus on a single optimized Neutrino Factory scheme Must continue to articulate need for an adequately- funded accelerator R&D program —being encouraged to do this in an international framework o IDS is one ingredient —synergy with Muon Collider R&D is an advantage (in U.S.) It was a privilege to work on the ISS with such a talented and dedicated group —my thanks to: o Program Committee (Dornan, Blondel, Nagashima/Long) o Accelerator Council and task leaders (slide 6) o all members of Accelerator Group (see NF-SB-ISS-ACCELERATOR list)

March 29, 2007IDS: CERN - Zisman32 History (1) There have been 4½ previous NF “feasibility” studies —1 in Japan —1 in Europe —2½ in the U.S. o studies I, II, IIa

March 29, 2007IDS: CERN - Zisman33 References NuFact-J Study (2001) — Study I (1999–2000) instigated by Fermilab — /muon_collider/nu/study/report/machine_report/ Study II (2000–2001) collaboration of NFMCC, BNL — European Study (2002) instigated by CERN — Study IIa (2004) APS Multidivisional Neutrino Study —

March 29, 2007IDS: CERN - Zisman34 J-PARC Scheme Comprises linac, 3 GeV RCS and 50 GeV synchrotron —under construction now! Not clear J-PARC can reach 4 MW

March 29, 2007IDS: CERN - Zisman35 RLA Design Considerable progress made on RLA design (Bogacz) —optics compatible with simultaneous acceleration of  + and  – developed —possible layouts for multi-stage RLA acceleration worked out 0.9 GeV 0.2 GeV 0.6 GeV/pass 3 GeV 2 GeV/pass 10 GeV

March 29, 2007IDS: CERN - Zisman36 Non-scaling FFAGs (2) Tracking with errors has begun (Machida) —rms alignment errors in the range of 20–50  m are okay —rms gradient errors of 2–5 x 10 –4 are okay o both specifications are tight 0  m (rms)10  m (rms) 20  m (rms)50  m (rms)

March 29, 2007IDS: CERN - Zisman37 MERIT MERIT experiment will test Hg jet in 15-T solenoid —24 GeV proton beam from CERN PS o scheduled July T solenoid during tests at MIT Integration tests completed at MIT. Equipment shipped to CERN. MERIT experiment will test Hg jet in 15-T solenoid —24 GeV proton beam from CERN PS o scheduled July 2007

March 29, 2007IDS: CERN - Zisman38 MICE