Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU The Making and Using of Spin-Polarized H  and D  Beams

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU Talk Outline What does it mean to polarize a beam? How do we polarize beams at TUNL? What are polarized beams used for?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What Does it Mean to Polarize a Beam? Underlying Basic Physics Electrons and nucleons all have spin magnetic moments. –For electrons:  e  eħ/2m e –For protons:  p  eħ/2m p Note that since m e >  p.

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU Underlying Basic Physics Like for simple magnets, electrons and proton magnetic moments have orientations in magnetic fields which determine their energy. Energy = - . B = -  Bcos   NS  B-field What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What Does it Mean to Polarize a Beam? Polarize Atomic Electron Select atoms with electron spins aligned in one direction in an external B-field. ed MagneticField MagneticField Energy ep

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU TUNL Atomic Beam Polarized Ion Source Atomic Beam Systems Ionizer Systems Acceleration & Spin Precession Systems What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU TUNL Atomic Beam Polarized Ion Source Atomic Beam Systems Ionizer Systems Acceleration & Spin Precession Systems What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU Dissociate H 2 or D 2 to make H or D atoms Dissociate molecules to produce emerging jet of H (or D) atoms traveling at ~1 km/sec along the source axis. What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU Polarize atomic electrons by sextupole focusing Resulting beam is polarized in electron spin. Multiple sextupoles efficiently focus a beam with wide energy spread along the source axis. Electron spin-up atoms focused Electron spin-down atoms defocused What Does it Mean to Polarize a Beam?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU Energy B-Field Polarize atomic nuclei using RF transitions Populations of coupled states 2 and 4 are inverted. Carefully designed RF electric and magnetic fields cause precessing spins to invert their direction. How Do We Polarize Beams at TUNL?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU Ionize atoms by collisions with fast electrons Polarized atoms are ionized by the process H + e --> H + + 2e How Do We Polarize Beams at TUNL? Microwave discharge produces and accelerates electrons Polarized H atoms enter H + out Electron Cyclotron Resonance (ECR) Ionizer W of 3 GHz  -wave Power Solenoidal coils produce axial B-field

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU Produce H - /D - by Cesium Charge Exchange When needed to make H - or D - ions, the H + or D + beam passes through a curtain of cesium vapor. How Do We Polarize Beams at TUNL? Processes Used: H + + Cs  H o (2S) + Cs + H o (2S) + Cs  H - + Cs + Heated Cesium Reservoir ( deg.) H + inH - out

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU Accelerate Beam and Precess Spins Accelerate and transport beams to experimental target stations for use in experiments. Deflect beam to target with bending magnets. Nuclear spins precess when beam is deflected. Pre-orient spins at the polarized ion source to orient spin in desired direction at target after deflection. How Do We Polarize Beams at TUNL?

Triangle Universities Nuclear Laboratory July 26, 2001-TUNL REU What are polarized beams used for? Bread and butter measurements at a nuclear physics lab like TUNL are cross- section measurements Nscatt/sec = Ninc/sec t ds/dO dO