The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 1 Lionel Prost, F. M. Bieniosek, C. M. Celata, A. Faltens, P. A. Seidl, W.L. Waldron, R. Cohen, A. Friedman, M. Kireeff Covo, S. M. Lund, A.W. Molvik, I. Haber LBNL, LLNL, UMD HIF 2004 Symposium Princeton, NJ June 9, 2004 Experimental study of the transport limits of intense heavy ion beams in the High Current Transport Experiment

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 2 Talk outline Experiment objectives, layout Matching, transport through electrostatic quadrupoles Transverse phase space Longitudinal phase space Transport through magnetic quadrupoles

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 3 IBEAM results: (fixed number of beams, initial pulse length, and quadrupole field strength) Robust Point Design (2.8 B$) Beam pipe R pipe Beam a avg a max Fill factor = a max /R pipe Clearance range being explored ~$1B Heavy ion fusion system studies show that driver cost is very sensitive to fill factor W. Meier, LLNL

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 4 HCX explores two driver options for low energy transport Electrostatic quadrupoles provide clearing fields which sweep out unwanted electrons (clarifies study of other beam dynamics issues without electrons). –Vary fill factor (emittance growth, halo, beam loss: sensitivity to mismatch, alignment, focusing & image nonlinearities). –Simulations predict beam fill factors of 0.8 of the aperture radius (R=23 mm) may be possible, with negligible beam degradation. Magnetic quadrupole experiments at high beam current – first with four pulsed magnets; later with superconducting magnets. –Explore secondary e -, A o, A - production from beam scraping and collisions with background gas. This gives information on needed clear aperture and on surface conditioning.

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 5 HCX is exploring driver-scale dynamics Transverse phase space evolution, fill factor, halo,… Longitudinal bunch control, space charge waves,… ≈11 m D-end, Energy Analyzer, GESD QD1 K + source & triode I = A 4 RT pulsed magnetic quadrupoles Bunch control module MeV ESQ injector Matching section (6 quadrupoles) 10 electrostatic transport quadrupoles Current monitor D2 TOF pulser 15 diagnostic systems, + halo pickups on each electrostatic quadrupole

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 6 Electrostatic transport section 1 QD (Diagnostic)ESQ Removable from beam axis to allow insertion of intercepting slit-scanner diagnostics. 2 QS ESQ’s Translatable in x and y to allow centroid steering Six-strut Mounting System and Kinematic Support Structure For rail alignment decoupled from vacuum tank 4 QI ESQ’s Independent voltages to allow beam envelope manipulations 1 Azimuthally rotatable ESQ Allows variable skew coupling (  =  4 o Max)

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 7 Magnetic transport section (4 room temperature pulsed magnets with elliptical bore) Capacitive probe Electron suppressor Support rail

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 8 Talk outline Experiment objectives, layout Matching, transport through electrostatic quadrupoles Transverse phase space Longitudinal phase space Transport through magnetic quadrupoles

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 9 The matching section compresses the beam transversely and prepares it for periodic transport. F(x,y), crossed slit time slice 41 (28 mm  30 mm) Kapton exposed to injector exit x(mm) y(mm) Envelope based on QD1 data vertical horizontal QD1 R electrode  n = 0.44  mm mrad Vertical phase space Vertical profile Horizontal  n = 0.48  mm mrad

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 10 BEAM LOSSES THROUGH THE 10 QUAD TRANSPORT SECTION FOR 60% & 80% FILLING FACTOR ≤1% Measured two ways:  Total beam current measurements (Faraday cups) at entrance and exit.  e - current collected on quad electrodes throughout the HCX channel (Electrode capacitive monitors). Beam loss: 0.5% (  V (capacitive mon.) ) to 1% (Faraday cups), Expect ≈ 0.05% loss from beam- background gas collisions assuming a stripping cross-section (on N 2 and/or O 2 ) of 3.5 x cm 2 and a pressure of 2 x Torr. N ≈ 6x10 12 K + /pulse (1 MeV)

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 11  n  0.48  mm mrad In both fill-factor cases measured so far, no evidence of emittance growth, within diagnostic sensitivity. Expect ~±10% fluctuations in  z) due to non-equilibrated distribution.  QD1  10 quads downstream 60% fill factor (  o = 64 o,  =12 o space charge tune depression  /  o = 0.2) 80% fill factor (  o = 44 o,  =7 o,  /  o = 0.2)  n  0.40  mm mrad

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 12 Envelope calculation, initialized with QD1 data for 80% fill factor Mismatch ≈ 1 mm Improvements to envelope modeling include: 1.Realistic fringe field model based on 3D field calculations. 2.Quadrupole E z and corresponding radial focusing force. 3.Corrections for the grounded slit plates of the intercepting diagnostics that short out the self- field of the beam near the diagnostic. 4.More thorough crosschecks on the beam current and energy.  o = 44 o,  =7 o tune depression  /  o = 0.2

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 13 Experimental envelope parameters compared to envelope model predictions at the exit of the electrostatic section Experimental uncertainties: standard deviation from 5 repeated measurements Envelope model uncertainties: standard deviation of a Monte Carlo distribution of envelope predictions, representing measurements uncertainties and equipment accuracies (e.g.: stability of the quadrupole voltages)

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 14 Talk outline Experiment objectives, layout Matching, transport through electrostatic quadrupoles Transverse phase space Longitudinal phase space Transport through magnetic quadrupoles

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 15 Beam energy determination from fitting cold fluid model to data The wave (beam current perturbation) observed 5.5 m downstream, is compared to a cold fluid model of the beam. The beam energy is the ‘free’ parameter that is adjusted. 1  s  I b (t) Beam velocity: v b = 220 cm/  s Space charge wave velocity: c s = 6 cm/  s Standard g-factor model: g = ln(b/a) / 2  ε 0 assumes beam is incompressible

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 16 calibrated absolute E via detection of K ++ & biasing stripping grid. 1 MeV Electrostatic energy analyzer for independent measurement of the beam energy

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 17 Beam energy calibration valuable for envelope control & input to PIC simulations (preliminary) Electrostatic energy analyzer (EA) measures longitudinal phase space  (E)/E ≈ 0.5% relative accuracy ±0.2% E is constant to within 0.5 % for 3.1  s. TOF and EA diagnostics determine absolute E beam to ±1.5%, with both measurements agreeing within these uncertainties.

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 18 Talk outline Experiment objectives, layout Matching, transport through electrostatic quadrupoles Transverse phase space Longitudinal phase space Transport through magnetic quadrupoles

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 19 Next: measurement of the evolution of desorbed neutrals and secondary e - ’s in magnetic quadrupoles (Molvik et al. Th.I.01) WARP simulations with mocked-up electron distributions (200 quads): 0 % 2  2% 10%  10% Ion Beam Electron Fraction R. Cohen, LLNL 52 cm 5 cm

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 20 Optical data from early transport experiments showed very distorted beam distributions due to the diagnostics intercepting the beam in a field free region Sum of images Single slit image Installation of an electron suppressor between the last magnet and the diagnosing slits Upstream beam images for reference Sum of images Single slit image

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 21 Addition of clearing electrodes between magnets influences the beam distribution Single pulse images Clearing electrodes grounded Clearing +9 kV 2 different magnet gradient solutions 

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 22 Good transport of the apertured beam (I = 32 mA) – Negligible emittance growth  n  0.09  mm mrad  n  0.13  mm mrad Horizontal direction (upstream of magnets) Horizontal direction (downstream of magnets)

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 23 Apertured beam 2-D PIC simulation initialized with measured a, a′, b, b′,,,, I = 32 mA 53% fill factor Clearing electrodes Magnet aperture PIC statistical edge Z (m) Expt data Magnet aperture Good agreement between measurements and simulations

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 24  n  0.38  mm mrad  n  0.42  mm mrad Full beam (I = 175 mA) transported with minimal loss but emittance increases ~4x in the horizontal direction  Upstream of the magnets  Downstream of the magnets Horizontal directionVertical direction  n  1.67  mm mrad  n  0.43  mm mrad

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 25 2-D PIC simulations helped getting enough clearance for diagnostics insertion diagnostics Extreme particle edge 67% fill factor Magnet aperture PIC statistical edge I = 175 mA Inconsistencies remain between data and simulations, which cannot explain the observed emittance growth + + Expt data

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 26 Summary – upcoming plan Transport results through ten electrostatic quadrupoles show good beam control. 80% beam filling factors at the front end of a heavy-ion induction linac might be possible with acceptable emittance growth and beam loss. Details of the measured phase space distribution are being used to initialize particle-in-cell simulations for comparison of data with theoretical models. New optical diagnostics will provide previously unmeasured correlations and accelerate data acquisition time. Transport through four magnetic quadrupoles for studying secondary electron and gas effects: Beam dynamics for highest beam current not yet fully understood. New diagnostics providing interesting results. (A. Molvik et al., Th.I-01)

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 27 Summary – upcoming plan (con’t) Induction cores will be installed between magnets to study the effect of accelerating fields on the secondary electrons distribution. Bunch control induction module will be installed this fall to study longitudinal space-charge field chromatic effects. Other fill factors will be measured. Results will have a direct impact on future heavy ion induction accelerators.

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 28 EXTRAS

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 29 What must we understand? Intense Beam Physics Stability, waves, phase space changes, nonlinear dynamics Beam Manipulations Beam production, acceleration, longitudinal compression, bending, focusing, chamber transport Multiple-Beam Interactions Pulse-length Limits Emittance growth Beam loss

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 30 Matching section quadrupole electrode monitors show little scraping during the flat-top of the beam Good agreement between the capacitive signal derived from the current transformer and the electrode monitor signal collected in the matching section  minimal beam loss (except at the beam tail) R Monitor I Beam (t)

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 31 simulated x,y Simulation distributions, initialized with upstream data, are in coarse agreement with data at end of electrostatic lattice simulated x,x crossed-slit Spatial hollowing is a common feature Other correlations, e.g. (y,p x ), influence dynamics; to be resolved with new optical diagnostics (Bieniosek et al., this conference, Th.I-10) Phase space scan x,x line is mean x´(x=0) vs. y; note the correlation Scintillator imaged after beam passes thru slit

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 32 TOF pulser diagnostic calibrates beam energy. Space charge waves puts a precise time mark on beam. A short-pulse perturbation in the beam energy within the matching section launches forward and backward traveling space charge waves in the beam frame, providing an accurate time-of- flight measurement to determine the beam energy. This also has allowed the study of longitudinal dynamics. Generated by a thyratron pulsed capacitive discharge 0.3  s V(t) Initial  V

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 33 calibrated absolute E via detection of K ++ & biasing stripping grid. 1 MeV Time (  s) E beam (MeV) head/tail spread -> longitudinal space charge Electrostatic energy analyzer shows longitudinal distribution 3D WARP simulations (preliminary) : uses experimental injector extraction voltage waveform (shortened) simulation ran to the end of the matching section; measurements were made at the HCX exit WARP3d simulation (scaled voltage) measurement 3/20/2003

The Heavy Ion Fusion Virtual National Laboratory Prost, HIF-04, HCX, 34 Bunch control induction module will be tested on HCX, and will be needed in next-step transport & acceleration experiments induction module Matching section Electrostatic transport K + beam –Apply agile control of the acceleration waveforms to correct for space charge field effects on the head/tail of the beam. Deliverables: Complete system of induction cores and modulators for installation in the HCX lattice between matching section and 1st HCX ESQ tank: Regulate 20kV variations during the flattop (±0.1%V Marx ) to study consequences of pulse energy variations. ± 200kV “ear” waveforms, actively regulated (±3%) to allow analysis and control of the bunch ends. “200kV ears”