1. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 1 Strategic Planning Exercise CEBAF as a High Energy Fixed Target Machine: An Alternate Possibility for Nuclear Physics Beyond the 12 GeV Upgrade

2. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 2 Strategic Planning Exercise Talks so far have discussed: 12 GeV (extremely well understood, exciting, and happily well underway) A possible EIC as a follow-on (a growing science program and developing machine and experimental equipment designs; preliminary case made to the larger community) This talk will raise the possibility of an alternate future based on a higher energy, fixed target accelerator

3. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 3 Strategic Planning Exercise CEBAF as a High Energy Fixed Target Machine: An Alternate Possibility for Nuclear Physics Beyond the 12 GeV Upgrade Bottom Line Question: Will a higher energy fixed target machine deliver better physics for comparable (or lower) cost? With thanks to: G. A. Krafft, Y. Roblin, and Y. Zhang, who have done much of the speculating and all of the performance estimates

4. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 4 Strategic Planning Exercise Possible Future Cases Explored 24 GeV Recirculated Linac (push present tunnel to limit) —Average current de-scoped by a factor of 2 (to 40 µA/hall max) due to 1 MW dump limit (get to 100 µA with new, higher power dump?) —Magnet layout and types roughly the same as 12 GeV, but 24 GeV requires stronger focusing and a completely new set of magnets! —Need 20 "C150s" and 10 C100s, and 20 C50s, yielding just over 2.5 GeV per linac pass (better than 50 total C100s) 50 GeV “Blue Sky Site Filler” —Same dumps w/ 1 MW limit imply 20 µA/hall maximum; for 100 µA either develop 5 MW dump or full (or partial) energy recovery (interesting to explore possibility) —Arcs are Theoretical Minimum Emittance (TME), Normal Conducting —Optimize shape, pass #, and cryomodule energy gain (C200s?) for lowest cost, as done for CEBAF

5. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 5 Strategic Planning Exercise A Possible “Phase II”: 12  24 GeV

6. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 6 Strategic Planning Exercise 22 x C150 or 17 x C200 400 m long 400 m radius CEBAF @ 50 GeV: Five Passes through Three 3.33 GeV Linacs

7. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 7 Strategic Planning Exercise What Beam Performance Appears to be Feasible? The CASA folk have looked broadly at the question of technical feasibility and provided rough estimates of achievable beam properties If we are seriously interested in either of these possibilities, further work is highly desirable

8. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 8 Strategic Planning Exercise Expected Beam Parameters Units6 GeV12 GeV24 GeV50 GeV @ 24 GeV 50 GeV Energy @ A, B, CGeV61124 50 Energy @ DGeVn/a1227n/a ModeCW Total CurrentµAµA2008540 (80  A with 2 MW Dump) 20 100  A with 5 MW Dump (& ERL?) 20 100  A with 5 MW Dump (& ERL?) Beam Power/DumpMW11111 Emittance (unnormalized,rms) nm- rad <12.786140 Relative Energy Spread (rms) 10 -3 0.0250.21.10.42.2 %0.52.42610110 Spot Size (rms)mm0.2 0.70.20.6

9. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 9 Strategic Planning Exercise 22 x C150 or 17 x C200 400 m long 400 m radius CEBAF @ 50 GeV: Five Passes through Three 3.33 GeV Linacs Spin Rotator Fix Spin Dilution Problem by injecting w/ orientation vertical (along arc magnetic fields) and rotating to longitudinal on the way to the halls

10. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 10 Strategic Planning Exercise Physics Example – Pion Form Factor 24 GeV fixed target 12 GeV Upgrade 50 GeV fixed target Garth Huber (private communication) EIC

11. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 11 Strategic Planning Exercise Physics Example: DIS/DES Reach Harut Avakian (private communication) 12 GeV Upgrade CEBAF @ 50 GeV

12. ep→e’   X Kinematic coverage For a given luminosity (30min of runtime with L=10 35 cm -2 s -1 ) and given bin in hadron z and P T, higher energy provides higher counting rates and wider coverage in x and Q 2 24 GeV 50 GeV Harut Avakian (private communication)

13. ep→e’   X Kinematic coverage For a given luminosity (30 min of runtime with L=10 35 cm -2 s -1 ) and given bin in hadron z and P T, higher energy provides higher counting rates and wider coverage in x and P T to allow studies of correlations between longitudinal and transverse degrees of freedom Wider x range allow studies of transverse distributions of sea quarks and gluons Wider P T range will be important in extraction of k T -dependences of PDFs Harut Avakian (private communication)

14. ep→e’   X Kinematic coverage For a given luminosity (30min of runtime with L=10 35 cm -2 s -1 ) ) and given bin in hadron z and P T, higher energy provides higher counting rates and wider coverage in Q 2, allowing studies of Q 2 evolution of 3D partonic distributions in a wide Q 2 range. Harut Avakian (private communication)

15. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 15 Strategic Planning Exercise Physics Issues Is it worth investigating possible external beam upgrades more seriously? Much has been done to develop the physics that can be done with an Electron Ion Collider, but what can be done with a fixed target machine, and which machine can do the physics we consider essential better??? The issue should be discussed, and pursued if we consider the effort waranted

16. Another Topic for Consideration: Positrons in CEBAF @ 12 GeV and Beyond The PEPPo experiment (below), which will use polarization transfer to convert an intense e - beam into a usable (nA level) e + beam, is in preparation for commissioning during the last 6 month run and then running at the start of the 12 month shutdown It aims to demonstrate that state-of-the-art mA e - beams could drive  A level e + sources, but will need continued encouragement to succeed Such a source could support research ranging from GPD and TPE physics (after acceleration to 12 GeV in CEBAF) to condensed matter studies (at 10- 100 keV energies) Polarization controls Variable energy 2-7.5 MeV Polarization measurement (1.5%) Energy measurement (10 -2 ) PEPPo Laser Intensity controls

17. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 17 Strategic Planning Exercise Parallel Positron Source Concept Should it be included as part of our long range planning, implying resource allocations over the next few years? Parallel to Injector: Duplicate Gun  100MeV portion of injector available for low energy positron operations (materials and/or NP research) in parallel with CEBAF in electron mode First CW polarized positron source: Beam currents up to ~microAmpere (10 13 e + /s) Polarization TBD, calculations suggest it will be as high as 70% Injection/Extraction energy tunable via RF.

18. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 18 Strategic Planning Exercise Conclusions Efforts on MEIC collider continue and progress is being made, but consideration should be given to alternatives: A 24 GeV CEBAF-like machine in the present tunnel It would require further upgrades to the beam acceleration system and a completely new (normal conducting) complement of magnets A 50 GeV fixed target machine The CEBAF site could support such a machine, but it would be a major construction effort (of the scale of MEIC). Polarization and emittance dilution imply a completely new layout is required, and even so, special optics (or transverse injection w/ rotation at 50 GeV) may be needed to retain the polarization For both of these machines there are tradeoffs between beam power, dump development, cost, etc. In addition, should we consider developing a positron source to add new physics capabilities at a relatively modest cost?

19. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 19 Strategic Planning Exercise

20. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 20 Strategic Planning Exercise From 6 GeV to 12 GeV has been studied in detail ARC1ARC2ARC3ARC4ARC5ARC6ARC7ARC8ARC9 ARCA HALLD

21. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 21 Strategic Planning Exercise Transverse Emittance* and Energy Spread † Area  p/p [x10 -3 ]  x [nm]  y [nm] Chicane0.54.00 Arc 10.050.41 Arc 20.030.260.23 Arc 30.0350.220.21 Arc 40.0440.210.24 Arc 50.0600.330.25 Arc 60.0900.580.31 Arc 70.1040.790.44 Arc 80.1331.210.57 Arc 90.1672.090.64 Arc 100.1942.970.95 Hall D0.182.701.03 * Emittances are geometric † Quantities are rms 12 GeV Beam Properties Double Bend Achromat Design Sync. Rad. Damping

22. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 22 Strategic Planning Exercise Emittance Growth By Scaling Beam emittance growth over a section of beam line due to synchrotron radiation (ODU Lectures) For a FODO lattice where α is the bending angle of the beam line, equals to π for a half circle, ϑ = l b /ρ is bending angle of a dipole, l b /l b0 is the packing factor of the FODO cell, [ /ρ ϑ 3 ] only depends on phase advance of the FODO cell In this case Comparing the 12 GeV case and a potential 50 GeV accelerator: E increased by a factor of 45/11=4.09 and ρ increased by a factor of 3, then emittance growth scales by a factor of 4.09 5 /3 4 ~ 14

23. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 23 Strategic Planning Exercise Energy Spread by Scaling Energy spread after passing a section of circular beam line with uniform 180 degree bend Thus, Comparing 12 GeV and 50 GeV CEBAF, after last arc E increased by a factor of 45/11=4.09, ρ increased by a factor of 3, then δE/E increased by a factor of 4.09 5/2 /3=11.3

24. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 24 Strategic Planning Exercise Polarization Loss Spin precession per 180 degree bend For 9 arcs Polarization angle spread yields dilution Fixed By Clever Longitudinal Optics?

25. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 25 Strategic Planning Exercise

26. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 26 Strategic Planning Exercise The 12 GeV Upgrade is Well Underway

27. It’s Science Case is Well Developed and Growing The Hadron spectra as probes of QCD (GluEx and heavy baryon and meson spectroscopy) The transverse structure of the hadrons (Elastic and transition Form Factors) The longitudinal structure of the hadrons (Unpolarized and polarized parton distribution functions) The 3D structure of the hadrons (Generalized Parton Distributions and Transverse Momentum Distributions) Hadrons and cold nuclear matter (Medium modification of the nucleons, quark hadronization, N-N correlations, hypernuclear spectroscopy, few-body experiments) Low-energy tests of the Standard Model and Fundamental Symmetries (Møller, PVDIS, PRIMEX, …..) And other science we can’t foresee

28. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 28 Strategic Planning Exercise The EIC is an Evolving Candidate to Follow 12 GeV With an evolving science case ELIC @ JLab: add figure-8 hadron & electron rings to CEBAF medium energy IP low energy IP Three compact rings: 3 to 11 GeV electron Up to 20 GeV/c proton (warm) Up to 100 GeV/c proton (cold)

29. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 29 Strategic Planning Exercise There is Still Work to be Done on the Science Case Bob McKeown at the JLab S&T “Visit” this year