Muons, Inc. October, Chuck Ankenbrandt, Muons, Inc. Muon Cooling for Conversion Experiments Chuck Ankenbrandt Muons, Inc. and Fermilab Guest Scientist, Retired October 26, 2011 Project X Collaboration Meeting Working Group 4

Muons, Inc. October 26, 20112Chuck Ankenbrandt, Muons, Inc. Outline  Review CRFI/MInX idea as described in white paper.  Update the idea based on recent developments.  Describe other promising cooling concepts.  Concluding remarks  Discuss next steps.

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Overview on Cooled RF and Ionization (CRFI) Option** or Muon Beams with Ionization Cooling at Project X (MInX)* Chuck Ankenbrandt Muons, Inc. November 8, 2010 The Project-X Muon Workshop *(my preferred title) **(the given title)

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Acknowledgments  Before proceeding, I want to thank many colleagues who contributed in various ways to the development of the ideas presented here, especially  Cary Yoshikawa  Rol Johnson  Dave Neuffer  Mary Anne Cummings  Katsuya Yonehara  Sergei Nagaitsev  Eric Prebys  Jim Miller  Anybody I forgot  They are of course responsible for any errors.

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Diverse Muon Beam Requirements for various intensity-frontier muon experiments  Beam intensity: high, higher, highest?  Polarization: good, bad, or indifferent?  Cycle time: 0.1, 1, 10, or times muon lifetime?  Beam purity?  Energy?  Emittances?  Time structure?  Duty factor: high*, medium, or low?  Etc. etc. * The Project-X CW linac is explicitly designed to provide high duty factor beams to the intensity-frontier experiments.

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop The Basic Idea of MInX  Use the Project X 3-GeV CW linac to make muon beams.  Intensity-frontier muon experiments have diverse requirements.  The linac can deliver flexible bunch patterns at high intensity.  So, let’s use that flexibility directly to help provide the diversity.  Provide added flexibility via the pion/muon beam processing.  Use ideas from muon collider/neutrino factory front end.  But there are differences between the two situations.  Most differences make it easier; one makes it harder.  It’s necessary and advantageous to adapt to the differences.

MCTF Neutrino Factory/Muon Collider Schematic Chuck Ankenbrandt, Muons, The Project-X Muon Workshop NEUTRINO FACTORY MUON COLLIDER In present MC baseline design, Front End looks same as for NF

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Major Subsystems of MC Front End  4 MW proton beam in short bunches at ~ 15 Hz  Mercury-jet target  Pion collection/focusing for both signs of charge  Decay channel plus long drift  Formation of multiple muon bunches  Rotate bunch train to reduce energy spread  4-d ionization cooling  6-d ionization cooling  Acceleration

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Major Subsystems for P-X Muon Beam  1 MW proton beam in shorter bunches at ~ 10 6 Hz  Solid target?  Pion collection/focusing for one charge sign  Decay channel  Maintain pion/muon beam in a single bunch  4-d ionization cooling  6-d ionization cooling  Deceleration by RF  Rotate bunch to reduce energy spread

Muons, Inc. ComparisonMuon colliderP-X Muon beam Protons Beam energy8 GeV3 GeV Beam power4 MW1 MW Bunches/second Duty factorlowhigh rms bunch length3 nsec20 psec Muons muon/proton ratio0.1~0.001 required coolingextrememoderate vive la différences November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Most of these differences make things easier. The main challenge is providing the necessary CW RF voltage in the presence of intense radiation and strong magnetic fields.

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Some details about these concepts  Deceleration by RF avoids longitudinal heating in a degrader.  Ionization cooling can discriminate against non-muons because the +dE from the RF is set to match the -dE from ionization only for the muons.  Pion collection/focusing for one charge sign => We may not need a target solenoid: might use a focusing coil instead. Target solenoids are difficult to shield.  Muon polarization can be adjusted by varying the phasing of RF cavities to provide different ratios of p  /p .

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Rate considerations for a  -e conv. exp’t  The Mu2e experiment expects a sensitivity of ~ for 25 kW of Booster beam. A 1 MW beam from Project X provides a factor of 40. That means we still need good collection and transmission to reach ~  So the  /p ratio is an important figure of merit for various designs. Also detection efficiencies, etc.  Mu2e has a  /p ratio of ~ at 8 GeV. (Compare MC  /p ~ 0.1 and  /p ~ 1 at production for the muon collider front end at 8 GeV.) Relative production (normalized to beam power) is expected to be similar at 3 GeV and 8 GeV. So we’d like  /p greater than ~10 -3 at 3 GeV.  Cf. pion production data; decide to work near the peak.  Cooling also works best for p ~ MeV/c.

Muons, Inc.  A better muon-to-proton ratio than what the Mu2e system would obtain at the same proton energy;  Much smaller momentum spread for the muons headed for the stopping target, allowing the use of much thinner stopping foils;  A much tighter time distribution of the stopping muons, allowing the use of high-Z stoppers;  Very good hadron rejection, greatly reducing the flash that occurs when the muons stop. Obviously, simulations are necessary to verify these expectations. Concomitant design work may result in significant changes from these initial concepts. Expected advantages of this design November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop

Muons, Inc. Helical Cooling Channels October, Chuck Ankenbrandt, Muons, NuFact10

Muons, Inc. HCC Engineering Concept October, Chuck Ankenbrandt, Muons, NuFact10

z = 0, R inner = 7.5 cm B z = 10 T z = 2 m, R inner = 12 cm B z = 4 T P (3 GeV) π –π – μ –μ – νμνμ G4Beamline simulations by Cary Yoshikawa

z = 2 m z = 17 m 325 MHz 10 MV/m # particles in bunch per 100k POT at z = 17 m # particles in bunch per 100k POT at z = 32 m μ–μ– π–π– μ – & π – μ– & z = 17 m ε trans (mm-rad) of μ – ‘s ε long (mm-rad) of μ – ‘s z = 17 to 32 m1160 to 90 HCC2040 Pions are reddish, muons are blue, MInX is sweet and so are you…

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Tapering of RF Frequencies in Channel  Start by capturing pions and muons in stationary 650 MHz buckets  Transition to 325 MHz for Helical Cooling Channel: Katsuya Yonehara has an example HCC that works very well at that frequency. (Cf. e.g. next slide.)  Do final bunch rotation in a MHz bucket. This should provide about a factor of 4 (=650/162.5) reduction in muon momentum spread.  That implies that the initial proton bunch spacing (in the case of more than one bunch per cycle) should correspond to MHz.

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Helical Cooling Channel Performance K. Yonehara, HCC, Muon Collider Design Workshop, Dec. 2009

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Providing the needed CW RF Voltage  Use superconducting RF where it’s feasible.  Issue: SCRF doesn’t like intense radiation or strong B fields  Shielding (against radiation and B fields) may allow SCRF to be used in some parts of the system.  Use hyperconducting RF elsewhere.  Some pure metals, e.g. Al and Be, become very good (but not super-) conductors at very low temperatures.  This technology needs to be developed and demonstrated.

Muons, Inc. November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop Summary/Conclusions  There are promising new preliminary concepts for using the beam from the Project-X CW linac directly to provide high-duty-factor muon beams with a variety of useful characteristics.  The work has just gotten started.  Support (financial and collaborative) is needed in order to continue the development of these promising ideas.  The needed development includes  Design, simulation, and optimization of the whole channel;  RD&D on hyperconductive RF cavities—the enabling technology.

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Outline  Review CRFI/MInX idea as described in white paper.  Update the idea based on recent developments.  Describe other promising cooling concepts.  Concluding remarks  Discuss next steps.

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Recent developments  Anomalous skin effect in hyperconductive cavities  Affects their performance at RF frequencies  Project X specs have evolved  RFQ frequency for PX is now MHz, not 325 MHz –Affects details of plan  Plans for delivering beam to 8-GeV pulsed linac for MI and MC have been developed. –So a pulsed 3-GeV beam will eventually be available.  RF cavities filled with hydrogen gas perform as expected.  Encourages use of HCCs for cooling.  MInX SBIR/STTR proposal has been resubmitted with modifications for anomalous skin effect.

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Anomalous skin effect  The cold war may affect assertions about cold cavities:  “Warning! The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.”--Wikipedia  Google: when the electron mean free path becomes longer than the skin depth, the electrons can scatter away from the surface and then feel little E field. So the low-temp improvement in DC conductivity is reduced at high frequencies.  As a result, our RF experts decided to stop at LN2 temp.  See following excerpts from our SBIR/STTR proposal.

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Recent SBIR Proposal  Phase I-SBIR/STTR Fiscal Year 2012 (Release 1)  FIRM NAME: MuPlus Inc.  RESEARCH INSTITUTION:  Thomas Jefferson National Accelerator Facility  Dr. Robert Rimmer, subgrant PI  PRINCIPAL INVESTIGATOR: Dr. Frank Marhauser  PROJECT TITLE: Hyperconductive RF cavities for CW Muon Beams

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Resistivity for Beryllium

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Cold Be vs. Warm Cu Cavities

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. How to rescue the MInX concept 1) Use SCRF everywhere.  Keep B fields and SC cavities separate.  FRIB has a 9 Tesla solenoid near RF cavities.  Note “separated-function” HCC concept 2) Or, run at a duty factor of about 10% with pulsed RF.  100% may not be the optimal duty factor for a mu-to-e expt.  Cosmic-ray bkgds are a reason to prefer lower duty factor.

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Outline  Review CRFI/MInX idea as described in white paper.  Update the idea based on recent developments.  Describe other promising cooling concepts.  Concluding remarks  Discuss next steps.

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Decisions, decisions…  Does cooling help? If not, then we’re done…  but we need a viable concept for the experiment.  We must compare options with/without cooling  Do we need more than one stage of cooling?  If not, then we might just decelerate using dE/dx –Properly arranged absorber can cool the beam  If so, then we need to reaccelerate— need RF cavities –Then also need to capture the beam in RF buckets –Might as well use RF to decelerate, too.  RF cavities are expensive—affordability issue  Perhaps develop a multi-purpose, high-performance beam

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc.  Retreat, hell, we’re just advancing in another direction!*  *Major General Oliver Smith, USMC, Korea, December 1950  The choice of a cooling strategy is not an isolated decision; it depends on a number of other choices:  Choices about the rest of the system –The pion/muon collection/capture strategy –The muon deceleration/stopping strategy  Choices about muon beam requirements –The desired duty factor –The desired muon flux –Beam purity –Beam phase space distributions –Beam formatting –Budget, etc. Other possibilities

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Other promising cooling concepts  Dipole plus wedge idea  Cf. Stopping Muons Project  Energy-dependent HCC  Cf. MANX proposal  “separated function” HCC

Muons, Inc. AAC Feb M. A. C. Cummings 33 Intense Stopping Muon Beams 180° dipole bend removes large neutral backgrounds. Muons with a narrow time and momentum spreads will enable the use of higher Z target, and maintain the necessary “extinction” factor. Dipole and Wedge Into HCC Wedge narrows P distribution Matching into the HCC which degrades muons to stop in target +

Muons, Inc. AAC Feb M. A. C. Cummings 34 MANX channel Use Liquid He absorber No RF cavity Length of cooling channel: 3.2 m Length of matching section: 2.4 m Helical pitch k: 1.0 Helical orbit radius: 25 cm Helical period: 1.6 m Transverse cooling: ~1.3 Longitudinal cooling: ~1.3 6D cooling: ~2 Innovative superconducting Helical Solenoidal (HS) magnet is the major component of a momentum-dependent Helical Cooling Channel (HCC) G4BL Simulatio n

Muons, Inc. AAC Feb M. A. C. Cummings 35 Possible MANX configurations 35 Increase gap between coils from 20 mm to 100 mm HCC Matching Without matching – requires transverse displacement of downstream spectrometer (with MICE spectrometers) Helix period = 1.2 m Coil length = 0.05 m Gap between coils = 0.01m Matching sections

Muons, Inc. PAC09 Paper November 8, Chuck Ankenbrandt, Muons, The Project-X Muon Workshop This paper described another concept: pion collection by a dipole plus a wedge, followed by a single stage of ionization cooling w/o RF.

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Concluding remarks  It would be premature to down-select among the proposed muon beam-delivery concpets.  The requirements for a next-generation mu-to-e conversion experiment may depend on the results from Mu2e. E.g. whether it has seen a signal with an Al target.  But we can’t wait that long to make decisions=> need flexibility.  The proposed techniques for capture, cooling, and deceleration all require further R&D.  Development of these techniques is synergistic with the R&D necessary to enable neutrino factories and muon colliders.

Muons, Inc. October, 2010 Chuck Ankenbrandt, Muons, NuFact10 38 From V.Lebedev’s Presentation

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Outline  Introductory remarks  Review CRFI/MInX idea as described in white paper.  Update the idea based on recent developments.  Describe other promising cooling concepts.  Concluding remarks  Discuss next steps.

Muons, Inc. October 26, Chuck Ankenbrandt, Muons, Inc. Discuss next steps.  What is the nature of the necessary R&D for muon beam-delivery systems?  Design and simulation work to advance the development of proposed systems and optimize their performance.  Comparisons of performance of resulting system designs.  Development and testing of prototypes, e.g. low-temp RF, helical cooling channels. –Design and simulation are not enough if there are questions of technical feasibility.  What is the nature of the necessary R&D for designing the next-generation experiment?  Refine the experimental requirement specs.  Other activities specified by experiment experts.