Coupling of APT Transported Ion beam to Hybrid Target D. R. Welch and D. V. Rose Mission Research Corporation C. L. Olson Sandia National Laboratories S. S. Yu Lawrence Berkeley National Laboratory July 1-2, 2002 Presented at the ARIES Project Meeting at GA, San Diego, CA Research supported by the DOE through PPPL and the HIF VNL

5 Torr Xe kA Assisted Pinched Transport can reduce chamber focus requirements and reduce driver costs - Back up to NBT Laser Hybrid Target IPROP simulation starts

Channel current I c BB Potential well increases as I c (r/r c ) 2 Minimum I c =43 kA to capture beam, where here I A  18 MA –For slow changes (conserving beam emittance), as r c decreases the beam radius will decrease as r c 1/2 43 kA net current required to capture beam at 1/2 cm radius R L rsrs r cf Nominal parameters: r s =1 cm, r ci =2 cm, r cf = r b =.5 cm  M =.03 rad r ci Adiabatic section rbrb MM

IPROP is used to model beam/plasma interaction with initial discharge conditions IPROP is a quasi 3D EM hybrid code 2 T fluid model for the plasma, PIC beam ions Ohm’s Law, J e =  (  p e /n e -v i m + E + v  B) Spitzer, e-neutral resistivity Ionization X-section falls as 1/Z 2 Moliere scattering, Bethe slowing down 50-kA discharge 5-Torr, 3 eV ambient Xe 0.5 torr reduced density within discharge Initial Discharge Conditions

87% energy transport calculated for APT with 50 kA discharge - main pulse only 10 m ballistic transport Pb cm 4-GeV, 6 MA Pb +72 ions, 1-mrad divergence 10-m ballistic transport to discharge Calculated  m = 5  s limits net current growth to 30 kA over 8-ns pulse halo grows from self-field interaction Discharge radius halo Previous IPROP APT calculation

APT Coupling of foot and main pulses to D. Callahan’s Hybrid Target –125-ns long IPROP simulation –Discharge parameters 5-Torr ambient, 0.5-Torr channel Xe kA discharge –Beam parameters (1 side) MJ 3.0-GeV, 12.5-kA, 25-ns Pb foot pulse 4.5-GeV, 66.5-kA, 8-ns Pb main pulse Xe beam was also simulated 1-2 milliradian divergence –Hybrid Target has 5-mm radiator

New simulations have 2 distinct beams - halo is weaker Peak electrical current is lower than previous sims 4.8 vs. 6 MA, energy is 4.5 vs. 4 GeV Foot and Main pulses well focused Nose of main pulse must “catch” tail of foot pulse

Self fields of order those of 50- kA discharge Self fields reach 45 kG, highly rippled by 80 ns Some enhanced confinement? Beam interacts with ripple and a halo forms 26.7 ns 80 ns

Self Fields Degrade Transport 50-kA Discharge Full sim main Full sim foot No fields foot No fields main

85% energy efficiency within 5 mm for nominal beam/discharge Energy transport within given Radius Ideal case (no self fields) yields 94% efficiency 6% collisional loss 4% inductive loss

Efficiency falls for currents below 50 kA 75 kA discharge yields best transport within.5 cm Efficiency falls from 87 to 80%

Comparison of 25 vs. 50 kA Discharge Both pulses have larger halos for lower discharge current 25 kA foot 50 kA main 50 kA foot 25 kA main

Efficiency falls slowly with beam divergence < 1.5 milliradian is adequate for 50 kA discharge defines minimum beam emittance

Comparison of 1 vs. 2 mr beams Main pulse is clearly larger for larger divergence beam Head to tail improvement suggests self-fields help for 2-mr sim 2-mr foot 1-mr main 1-mr foot 2-mr main

Transport insensitive to beam ion Xe +44 beam scaled to deliver same energy on target –1.8-GeV foot and 2.4-GeV main pulse –Similar stripped electrical current and charge to mass ratio Roughly 85% transport for both within 5 mm radius 50-kA discharge

Xe vs. Pb transport in 50-kA channel Differences are minor - Xe has slightly larger halo but loses less energy Xe +44 main Pb +72 main Xe +44 foot Pb +72 foot

Conclusions APT scheme efficiently couples HIF beam to the Hybrid Target with no cliff edges – 85% coupling efficiency for nominal case Efficiency falls slowly as discharge current decreases Transport degrades for beam divergence (< 1.5 milliradians) Scheme is insensitive to ion species