Ultra-Low Current Beams in UMER to Model Space Charge Effects of High-Energy Proton and Ion Machines Santiago Bernal on behalf of UMER group, IREAP, University of Maryland, College Park, MD IREAP AAC16, National Harbor, MD, August 3rd, 2016 Work Supported by the U.S. Department of Energy

OUTLINE MOTIVATION SCALING OF INCOHERENT SPACE CHARGE TUNE SHIFT: –UMER, Large Proton and Ion Rings –Single-Turn Injection vs. Accumulation PRODUCING ULTRA-LOW CURRENT BEAMS IN UMER: –DC Electron Gun –Photoemission –Apertures + Solenoid Focusing, Pulsed Inj. Dipole SUMMARY

MOTIVATION Research in UMER has pioneered several areas in the physics of space-charge (SC) dominated beams: beam tomography and halo, beam stability, matching and betatron resonances, debunching and longitudinal confinement, soliton trains, etc. Initial motivation (e.g. intense beams for HIF drivers) has been expanded recently to include non-linear dynamics (IOTA-inspired lattices), but SC effects must be reduced significantly. See talk by Kiersten Ruisard in WG7 today. Furthermore, SC effects are increasingly important for new and upgraded large storage and accumulator proton and ion rings (e.g. SNS, SIS-18,100), but some of these are user facilities with limited time for beam physics experiments.

UMER, PROTON AND HEAVY-ION RINGS UMER SNS Acc. Ring SIS-18

SCALING OF INCOHERENT SPACE-CHARGE TUNE SHIFT. “BEAM INTENSITY”  SC INTENSITY SPACE-CHARGE INTENSITY: For small tune shift, insensitive to bare tunes  x,y. Typically,  x,y = 3 – 6. “Intensity” loosely defined as with “space-charge limited” meaning In UMER, typically,We intend to operate UMER in For small SC,  independent of . beam perveance or SC parameter

BEAM DEBUNCHING IN UMER GREATLY REDUCED AT LOW CURRENT Beam Current, I b “Sound” Speed C S (m/s) Approx. No.Turns to Debunch Approx. No.Turns with Long. Focusing 60 μA μA3  , mA8  mA mA2  FLUID MODEL: WITHOUT LONGITUDINAL CONTAINMENT, COASTING BEAMS IN UMER DEBUNCH AFTER A NUMBER OF TURNS

MACHINECIRC.KINETIC ENERGY Peak Curr. RMS ε x,y (norm.) TUNE  x  y βK, and/or ppp  ,   UMER e m 10 keV, 6 mA 1.3 μm × × , 2.4 UMER e - 10 keV, 40  A 5 μm6.0× × , UMER e - 10 keV, 60  A 0.13 μm9.0× × HIF Driver Xe m10 GeV, 1 kA 35.7 μm × , 2.0 ALS (LBNL) e m1.2 GeV, 400 mA 3.5 nm × , 0.00 SNS p Acc. Ring (ORNL) 248 m1.0 GeV, 52 A 120 μm × × , 0.15 SIS-18 U 28+ (FAIR-GSI) 216 m200 MeV/u, 15.1 mA (inj.) 150,50 μm 4.17, × , 0.45 ELECTRON, PROTON & ION RINGS Missing: beam transv. aspect ratio, bunch structure, injection type, and energy spread.

PRODUCING ULTRA-LOW CURRENT BEAMS IN UMER METHODBEAM CURRENT, PULSE IND. CURRENT / EMITT. CONTROL? EXPERIMENT? DC Electron Gun + Low Grid Bias + PD + timing 10 –100  A, 100 ns No. 40  A, Photoemission (355 nm, dispenser K) 10  A – 20mA, 5ns Yes. 1.6mA, min. power Apertures + Solenoid 60  A – 1mA, 100 ns Limited. Design in progress IDEALLY: INDEPENDENT CONTROL OF CURRENT AND INTRINSIC TRANSVERSE EMITTANCE

PRODUCING ULTRA-LOW CURRENT IN UMER: DC E-GUN APERTURE PLATE UMER Electron Gun PD QR70 Q5 Q6 QR1 YQ 10 cm QR71 Red: DC Blue: Quasi-DC PD: Pulsed UMER Injection Section

DC ELECTRON GUN: RESULTS FOR 40  A BEAM DC E-Gun V Grid Bias Ultra-low Current Beam at RC3 10 mm , QR11 = −1.75A Fast fluorescent screen diagnostics + Pimax fast camera

PRODUCING ULTRA-LOW CURRENT IN UMER: PHOTOEMISSION Minilite-II Nd:Yag, Q-Switched Laser: 355 nm, 4 mJ, 5 ns, 20 Hz P pk = 0.8 MW, P av = 80 mW First photoemission-only multi- turn beam (1.6mA) in UMER. Pulse stretcher based on fiber optics delay lines designed, but using the right laser may be simpler, safer and more cost-effective. PROFILE OF ATTENUATED LASER AT 4 MM (RAD.) CATHODE

Solenoid E-Gun IC1 AP1 Window Actuator iQ1 iQ2 Bergoz Transf. Z=0 10 cm PRODUCING ULTRA-LOW CURRENT IN UMER: APERTURES + SOLENOID FOCUSING AP2 6 mA Beam Sol Curr. = 5.5ASol Curr. = 0.0A 10 mm

SUMMARY The original regime of strong transverse space-charge (SC) intensities in UMER is being extended to include the regime of small (perturbation) SC in large proton and ion circular machines. The new regime requires operation at “ultra-low” beam currents, around 60  A. This regime is also appropriate for the non-linear dynamics studies already underway in IOTA-inspired lattices. The beams also eliminate the need for longitudinal focusing to prevent debunching. Three methods to achieve low beam currents are discussed: DC E-gun, photoemission, and a combination of apertures and solenoid focusing. Issues related to beam detection S/N and control are pending.