Studies Of Charged Particle Beam Dynamics On The Paul Trap Simulator .

Supported by Office of Science Studies of Charged Particle Beam Dynamics on the Paul Trap Simulator Experiment (PTSX) Moses Chung In collaboration with Erik Gilson, Ron Davidson, Phil Efthimion, Dick Majeski, Ed Startsev, Mikhail Dorf , and Andy Carpe Graduate Seminars in Plasma Physics, Princeton University December 4th , 2006 1

What is a Charged Particle Beam? A collection of particles of same charge species all traveling in the nearly same direction with the nearly same speed x x' dx p θ dz p x z z Snapshot of beam in time (t) and space (z) Distribution of particles in phase space (x, x’) X’ Emittance Effective phase space area occupied by particles x When mutual interaction becomes significant, a charged particle beam behaves like a nonneutral plasma 2

Why Charged Particle Beam? Industry Medicine Ion implantation Radio Isotope Production Treatment of foodstuff Radiotherapy Sterilization of medical devices Precision surgery Beam lithography Medical Diagnostic Charged Particle Beam Basic Sciences High energy and nuclear physics Neutron production for biological and material research Energy Nuclear waste transmutation Heavy ion fusion Generation of coherent radiation 3

Modern Accelerators for Charged Particle Beams Spallation Neutron Source Heavy Ion Fusion Linac Coherent Light Source High current and intensity are required for various advanced applications Self-field effects are important Intense beams Need to accelerate intense beam for a long distance ( 1 km) 4

How to Focus Intense Beams ? Periodic focusing quadrupole magnetic field Alternating Gradient (AG) transport system FODO lattice 5

An Intense Beam is a Nonneutral Plasma in the Beam Frame s (space) t (time) Intense Beam Propagating in Periodic Focusing Quadrupole Magnetic Field Nonneutral Plasma Trapped in Time Varying Quadrupole Electric Field H ( x, y, x′, y ′, s) H ( x, y, x&, y& , t ) 1 1 ( x′ 2 y ′ 2 ) κ q (s)( x 2 y 2 ) ψ ( x, y, s) 2 2 1 1 mb ( x& 2 y& 2 ) mbκ q (t )( x 2 y 2 ) ebφ s ( x, y, t ) 2 2 Self-field potential Self-field potential 6

How Paul Trap Works? Radial direction Axial direction 7

Paul Trap Simulator Experiment (PTSX) Apparatus Pressure 10-10 10-8 Torr Trap Time 1 100 ms Density End Electrodes (DC) 105 106 cm-3 36 150 V Central Electrodes (AC) f 100 kHz , V0max 400 V 0.1 m 8

Smooth Focusing Frequency, Vacuum Phase Advance, and Normalized Intensity Parameter Characterize the System Smooth focusing period, 2π/ωq 1/f 0/f 5/f 15/f 10/f The smooth trajectory’s phase advance during 1 applied focusing period ω σ σ f sf v 20/f to avoid instabilities. q v max ω p2 1 to confine the space-charge. Normalized intensity parameter s 2ω q2 s 0.2 for Spallation Neutron Source. 9

Cesium Ion Source Has Been Used for the Initial Phase of PTSX Aluminosilicate cesium source Pierce electrode Acceleration/Deceleration grid 0.6 in 10 A 1000 oC 0.1 eV 67.5o opening angle 85% transparent electroformed copper mesh Good enough for low energy beam Contact ionization of cesium at hot porous tungsten Triode system having possibility to change the extraction field strength without changing the beam energy 1.25 in 10

Many Interesting Results Have Been Obtained by a Faraday Cup Charge Collector Pierce electrode 5 mm Radial scan along the potential null of the quadrupole field Data truncated at r 2.286 cm with 0.620 fC offset 1 0.1 Charge (pC) Charge (pC) Low level charge measurement ( 1 fC) Raw data of run1.txt (Fri Nov 17 18:30:51 2006 1 0.01 0.001 0.0001 2 4 6 8 0.1 0.001 10 0 2 A. U. 0 2 4 6 Radius (cm) 4 6 8 10 q Radius 2 (cm 2) Q(0) 0.513 0.002 pC, Q b 1.027 0.005 pC cm 2 8 10 R b 0.840 0.010 cm, h 1.167 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 0 Nq mω R 2kT 4πε 2 Radius (cm) 0.6 0.5 0.4 0.3 0.2 0.1 0 Rb, Nb 0.01 0.0001 0 Charge (pC) Because of low beam energy, there is no secondary electron emission 2 4 6 Radius (cm) 8 10 2 2 b b o T emittance 11

PTSX Has Simulated Several Important Scientific Issues in Accelerator Community 1. Beam Mismatch 2. Transverse Compression 3. Random Noise Effect Conditions for minimization of halo particle production during transverse compression of intense ion charge bunches in the Paul trap simulator experiment (PTSX), E. P. Gilson and M. Chung et. al. Nuclear Instruments and Methods in Physics Research A, submitted (2006). Experimental Simulations of Beam Propagation Over Large Distances in a Compact Linear Paul Trap, E. P. Gilson, and M. Chung et. al. Physics of Plasmas 13, 056705 (2006). 12

1. Beam Mismatch When initial injected beam radius is not equal to the final equilibrium radius in the focusing channel, there are oscillations in beam envelope shoulder In the PTSX 1 0 .1 Streaming current (A.U.) In the real accelerator 0 .0 1 1 E -3 1 E -4 1 E -5 -1 0 -8 -6 -4 -2 0 2 4 6 8 10 R a d iu s ( c m ) 13

2. Transverse Compression Application of present-generation accelerators require transverse compression of charge bunch to a small spot What about radial profiles ? How slow is slow ? 14

3. Random Noise Effect Limit on error MEBT 1.732 % DTL 0.5 % CCDTL & CCL 0.25 % 0.55 2.8 0.50 2.6 0.45 2.4 0.40 Amplitude of uniform noise 1.5 % 1.0 % 0.5 % 2.2 0.35 2.0 0.30 εf / εi Average on-axis charge (pC) In real accelerators, there are always unavoidable errors on components. Components 0.25 0.0 % uniform noise 0.5 % uniform noise 1.0 % uniform noise 1.5 % uniform noise 2.0 % uniform noise 0.20 0.15 0.10 0.05 1.8 1.6 1.4 1.2 1.0 0.8 0.00 0 5 10 15 20 Duration of noise (msec) 25 30 0 5 10 15 20 25 30 Duration of noise (msec) 15

More Advanced Diagnostic ? Can we do that in the PTSX too ? Maybe, by using the Laser-Induced Fluorescence (LIF) diagnostic 16

Barium Ion’s Atomic Structure is Amenable to LIF Barium ions are heavy enough (137 amu) to be confined in the PTSX Barium ions are produced primarily in the ground state (6 2S1/2 ), but some in the metastable states (5 2D3/2 ,5 2D5/2) Because PTSX does not utilize external magnetic field, there is no Zeeman split Because time average electric field vanishes in the PTSX, there is no first order Stark effect 17

Possible LIF Schemes for Barium Ion 493.4077 nm 649.6898 nm 649.6899 nm 493.4077 nm Plan A: 5 2D3/2 Plan B: WVU’s Dye laser 6 2S1/2 5 2D3/2 6 2S1/2 A23 33.2 x 106 s-1 A23 95.5 x 106 s-1 Quantum efficiency 40% Quantum efficiency 15% Filter efficiency 50% Filter efficiency 45% Small stray light Small stray light Dye : C102 (unstable) Dye : DCM (stable) Laser power 450 mW Laser power 800 mW Density of initial state : Density of initial state : 105 106 cm-3 0.8 % x 105 106 cm-3 Nova Photonics’ Dye laser with DCM Plan C: Nova Photonics’ Dye laser with C102 18

New Compact Barium Ion Source Has Been Developed Currents about 100 200 nA are required to fill up the PTSX Ionizer (Pt mesh) will be maintained near 1000 oC Reservoir (Ta tube) will be maintained above 400 oC, so that barium oxide can decompose Ionizer-reservoir assembly 0.5 in 4 in Length of the tube is determined so that heat conduction and radiation processes sustain proper temperature distribution along the tube Stainless steel can reduces visible radiation from the hot source and prevents neutral barium from contaminating electrodes Radius of the source is determined so that beam can be RMS-matched to external focusing field for nominal operating condition of PTSX 19

Schematic Diagram of LIF Diagnostic Setup (Aquadag Coated) (A/R Coated) Custom-made Reentrant Flange 20

Laser Injection System Coherent 899-21 ring dye laser used for MSE-LIF diagnostic – Optically pumped by an argon ion laser – Dye : Exciton DCM dye for 649.6898 nm transition – Laser linewidth : 2 GHz 0.0025 nm for broadband operation using a three plate birefringent filter ( mode-hopping ?) – Laser power : up to 1000 mW for broadband operation Assembly of the optical fiber, line generator, beam shutter, and x-y translation stage, which is enclosed by a light-tight aluminum box A line generator, which uses a Powell lens, transforms the collimated laser beam into a line with a uniform output intensity 21

Collection Optics Aquadag coating 70 % 500 nm 4” 40 nm Only 1” OD viewport (to minimize distortion in quadrupole field) Overall efficiency of collection optics 5.4 % Bandpass filter Lens Requirements f 11 mm , FOV 41o , MOD 135 mm PULNiX TM-1010 high resolution camera 1” (9.1 mm x 9.2 mm) CCD imager 1008 x 1018 resolution Up to 10 sec integration time FS9901 inverting image intensifier 22

Initial Background Light Measurements A glowing red-hot ion source can be a source of background light Scattered laser light from windows and electrodes can be a source of background light W/O Laser W/ Laser 23

Conclusions A laser-induced fluorescence diagnostic system has been developed for the nondestructive measurement of the transverse ion density profile in the PTSX device The accompanying barium ion source has been developed with the goal of maximizing the metastable ion fraction and minimizing the visible radiation Since the density of the metastable ions is very low, technical issues such as suppressing background light and data acquisition with long integration times must be resolved to obtain meaningful data for the study of beam mismatch and halo particle production Initial experiments will begin in January, 2007. 24

I like to thank my colleagues 25

What is a Charged Particle Beam? 2 A collection of particles of same charge species all traveling in the nearly same direction with the nearly same speed z x θ z x p p dz dx x' Snapshot of beam in time (t) and space (z) Distribution of particles in phase space (x, x') Emittance Effective phase space area occupied by particles x X'