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Papers by Enrique Henestroza

In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from ... more In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from the exit of the final focus magnet system through the target chamber to hit millimeter spot sizes on the target. Effective plasma neutralization of intense ion beams through the target chamber is essential for the viability of an economically competitive heavy ion fusion power plant. The physics of neutralized drift has been studied extensively with PIC simulations. To provide quantitative comparisons of theoretical predictions with experiment, the Heavy Ion Fusion Virtual National Laboratory has completed the construction and has begun experimentation with the NTX (Neutralized Transport Experiment) as shown in . The experiment consists of 3 phases, each with physics issues of its own. Phase 1 is designed to generate a very high brightness potassium beam with variable perveance, using a beam aperturing technique. Phase 2 consists of magnetic transport through four pulsed quadrupoles. Here, beam tuning as well as the effects of phase space dilution through higher order nonlinear fields must be understood. In Phase 3, a converging ion beam at the exit of the magnetic section is transported through a drift section with plasma sources for beam neutralization, and the final spot size is measured under various conditions of neutralization. In this paper, we present first results from all 3 phases of the experiment.

Proceedings of the 17th …, Oct 26, 2008

Cross-lingual tasks are especially difficult due to the compounding effect of errors in language ... more Cross-lingual tasks are especially difficult due to the compounding effect of errors in language processing and errors in machine translation (MT). In this paper, we present an error analysis of a new cross-lingual task: the 5W task, a sentence-level understanding task which seeks to return the English 5W's (Who, What, When, Where and Why) corresponding to a Chinese sentence. We analyze systems that we developed, identifying specific problems in language processing and MT that cause errors. The best cross-lingual 5W system was still 19% worse than the best monolingual 5W system, which shows that MT significantly degrades sentence-level understanding. Neither source-language nor targetlanguage analysis was able to circumvent problems in MT, although each approach had advantages relative to the other. A detailed error analysis across multiple systems suggests directions for future research on the problem.

Accelerator designs intended to provide acceleration at a much lower cost per Joule than the ILSE... more Accelerator designs intended to provide acceleration at a much lower cost per Joule than the ILSE or ELISE designs are under study. For these designs, which typically have many beams, an injector of significantly lower cost is needed. A goal, which from our design appears to be achievable, is to reduce the transverse dimension to half that of the 2 MeV, 800 mA ILSE injector(E. Henestroza, ``Injectors for Heavy Ion Fusion", Proc. of the 11th International Wkshp. on Laser Interaction and Related Plasma Phenomena, 1993.) while generating about the same current. A single channel of a lower cost injector includes an 800 kV column, accelerating a 700 mA beam extracted from a potassium source of 4 cm radius by a 120 kV electrode. The beam passes into a superconducting 7 T solenoid of 15 cm aperture and 15 cm length. This high-field solenoid provides the focusing needed for a small beam without increasing the electric field gradient. The injector and its matching section, also designed, fit within a 12 cm radius, which is small enough to allow construction of attractive multi-beam injectors. We will present solutions for the generation and transport of 700 mA potassium beams of up to 1.6 MeV within the same transverse constraint.

A driver scale (2 MeV, 800 mA, K+) injector for the Heavy Ion Fusion Induction Linac Systems Expe... more A driver scale (2 MeV, 800 mA, K+) injector for the Heavy Ion Fusion Induction Linac Systems Experiments (ISLE) is under development at LBL. It consists of a 750 keV diode pre-injector followed by an electrostatic quadrupole accelerator (ESQ). One of the key issues for the ESQ centers on the control of beam aberrations due to the energy effect: in a strong electrostatic quadrupole field, ions at beam edge will have energies very different from those on the axis. The resulting kinematic distortions lead to S-shaped phase spaces, which, if not corrected, will lead eventually to emittance growth. These beam aberrations can be minimized by increasing the injection energy and/or strengthening the beam focusing. It may also be possible to compensate for the energy effect by proper shaping of the quadrupoles electrodes. We have chosen to control the energy effect by increasing the injection energy of the diode and strengthening the beam focusing of the ESQ within the voltage breakdown limits. To check the physics of the energy effect of the ESQ design a quarter-scale experiment was designed to accommodate the parameters of the source, as well as the voltage limitations, of the Single Beam Transport Experiment (SBTE) apparatus. The voltage breakdown limits were studied by running a cold test of a full scale ESQ quadrupole. Design of the experiments as well as the one-beam version of the ILSE ESQ Injector and corresponding 3D PIC simulations will be presented.

High Energy Density Physics (HEDP) applications require high line charge density ion beams. An ef... more High Energy Density Physics (HEDP) applications require high line charge density ion beams. An efficient method to obtain this type of beams is to extract a long pulse, high current beam from a gun at high energy, and let the beam pass through a decelerating field to compress it. The low energy beam-bunch is loaded into a solenoid and matched to a Brillouin flow. The Brillouin equilibrium is independent of the energy if the relationship between the beam size (a), solenoid magnetic field strength (B) and line charge density is such that (Ba)^ 2 is proportional to the line charge density. Thus it is possible to accelerate a matched beam at constant line charge density. An experiment, NDCX-1c is being designed to test the feasibility of this type of injectors, where we will extract a 1 microsecond, 100 mA, potassium beam at 160 keV, decelerate it to 55 keV (density ∼ 0.2 μC/m), and load it into a 2.5 T solenoid where it will be accelerated to 100– 150 keV (head to tail) at constant line charge density. The head-to-tail velocity tilt can be used to increase bunch compression and to control longitudinal beam expansion. We will present the physics design and numerical simulations of the proposed experiment.

Accurate numerical simulations of ion driven Warm Dense Matter experiments requires accurate mode... more Accurate numerical simulations of ion driven Warm Dense Matter experiments requires accurate models of stopping powers for targets with temperatures up to a few eV. For finite temperature targets, energy loss of beam ions is comprised of contributions from nuclear stopping, bound electron stopping, and free electron stopping. We compare two different stopping power algorithms and the implications on target heating for two different beams corresponding to the current Neutralized Drift Compression Experiment (NDCX) and proposed NDCX II experiments. The NDCX I beam has a beam energy much lower than the Bragg peak while the NDCX II beam is designed to enter the target just above the Bragg peak, and exit just below. The first stopping power algorithm is based on the classical Bethe-Bloch formulation as is currently implemented in the HYDRA simulation code. The second algorithm is based on rescaling of experimental protonic stopping powers as developed by Brandt and Kitagawa for nuclear and bound electronic stopping, and free electron stopping following the model developed by Peter and Meyer-ter-Vehn.

In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from ... more In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from the exit of the final focus magnet system through the target chamber to hit millimeter spot sizes on the target. Effective plasma neutralization of intense ion beams through the target chamber is essential for the viability of an economically competitive heavy ion fusion power plant. The physics of neutralized drift has been studied extensively with PIC simulations. To provide quantitative comparisons of theoretical predictions with experiment, the Heavy Ion Fusion Virtual National Laboratory has completed the construction and has begun experimentation with the NTX (Neutralized Transport Experiment) as shown in . The experiment consists of 3 phases, each with physics issues of its own. Phase 1 is designed to generate a very high brightness potassium beam with variable perveance, using a beam aperturing technique. Phase 2 consists of magnetic transport through four pulsed quadrupoles. Here, beam tuning as well as the effects of phase space dilution through higher order nonlinear fields must be understood. In Phase 3, a converging ion beam at the exit of the magnetic section is transported through a drift section with plasma sources for beam neutralization, and the final spot size is measured under various conditions of neutralization. In this paper, we present first results from all 3 phases of the experiment.

Physical Review Special …, 2006

3--D particle--in--cell simulations of neutralized ballistic transport are performed to study fin... more 3--D particle--in--cell simulations of neutralized ballistic transport are performed to study final focus and neutralization of high perveance ion beams envisioned for inertial confinement fusion drivers. Pre--formed plasmas in the last meter before the target provide a source of electrons which neutralize the ion current and prevent the space--charge induced spreading of the beam spot. 4--D phase--space data of a 266 keV, 6 mA K^+ ion beam in the neutralization region has been acquired at the Neutralized Transport Experiment (NTX) at Lawrence Berkeley National Laboratory. This data is used to provide a more accurate beam distribution with which to initialize the simulation. Previous treatments have used various idealized beam distributions which lack the detailed features of the experimental ion beam images. Simulation results are compared with NTX experimental results with good agreement.

Physical Review Special Topics - Accelerators and Beams, 2005

The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performan... more The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performance of neutralized final focus systems for high perveance heavy ion beams. The NTX final focus system produces a converging beam at the entrance to the neutralized drift section where it focuses to a small spot. The final focus lattice consists of four pulsed quadrupole magnets. The main issues are the control of emittance growth due to high order fields from magnetic multipoles and image fields. We will present experimental results from NTX on beam envelope and phase space distributions, and compare these results with particle simulations using the particle-in-cell code WARP.

In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from ... more In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from the exit of the final focus magnet system through the target chamber to hit millimeter spot sizes on the target. Effective plasma neutralization of intense ion beams through the target chamber is essential for the viability of an economically competitive heavy ion fusion power plant. The physics of neutralized drift has been studied extensively with PIC simulations. To provide quantitative comparisons of theoretical predictions with experiment, the Heavy Ion Fusion Virtual National Laboratory has completed the construction and has begun experimentation with the NTX (Neutralized Transport Experiment) as shown in . The experiment consists of 3 phases, each with physics issues of its own. Phase 1 is designed to generate a very high brightness potassium beam with variable perveance, using a beam aperturing technique. Phase 2 consists of magnetic transport through four pulsed quadrupoles. Here, beam tuning as well as the effects of phase space dilution through higher order nonlinear fields must be understood. In Phase 3, a converging ion beam at the exit of the magnetic section is transported through a drift section with plasma sources for beam neutralization, and the final spot size is measured under various conditions of neutralization. In this paper, we present first results from all 3 phases of the experiment.

Proceedings of the 17th …, Oct 26, 2008

Cross-lingual tasks are especially difficult due to the compounding effect of errors in language ... more Cross-lingual tasks are especially difficult due to the compounding effect of errors in language processing and errors in machine translation (MT). In this paper, we present an error analysis of a new cross-lingual task: the 5W task, a sentence-level understanding task which seeks to return the English 5W's (Who, What, When, Where and Why) corresponding to a Chinese sentence. We analyze systems that we developed, identifying specific problems in language processing and MT that cause errors. The best cross-lingual 5W system was still 19% worse than the best monolingual 5W system, which shows that MT significantly degrades sentence-level understanding. Neither source-language nor targetlanguage analysis was able to circumvent problems in MT, although each approach had advantages relative to the other. A detailed error analysis across multiple systems suggests directions for future research on the problem.

Accelerator designs intended to provide acceleration at a much lower cost per Joule than the ILSE... more Accelerator designs intended to provide acceleration at a much lower cost per Joule than the ILSE or ELISE designs are under study. For these designs, which typically have many beams, an injector of significantly lower cost is needed. A goal, which from our design appears to be achievable, is to reduce the transverse dimension to half that of the 2 MeV, 800 mA ILSE injector(E. Henestroza, ``Injectors for Heavy Ion Fusion", Proc. of the 11th International Wkshp. on Laser Interaction and Related Plasma Phenomena, 1993.) while generating about the same current. A single channel of a lower cost injector includes an 800 kV column, accelerating a 700 mA beam extracted from a potassium source of 4 cm radius by a 120 kV electrode. The beam passes into a superconducting 7 T solenoid of 15 cm aperture and 15 cm length. This high-field solenoid provides the focusing needed for a small beam without increasing the electric field gradient. The injector and its matching section, also designed, fit within a 12 cm radius, which is small enough to allow construction of attractive multi-beam injectors. We will present solutions for the generation and transport of 700 mA potassium beams of up to 1.6 MeV within the same transverse constraint.

A driver scale (2 MeV, 800 mA, K+) injector for the Heavy Ion Fusion Induction Linac Systems Expe... more A driver scale (2 MeV, 800 mA, K+) injector for the Heavy Ion Fusion Induction Linac Systems Experiments (ISLE) is under development at LBL. It consists of a 750 keV diode pre-injector followed by an electrostatic quadrupole accelerator (ESQ). One of the key issues for the ESQ centers on the control of beam aberrations due to the energy effect: in a strong electrostatic quadrupole field, ions at beam edge will have energies very different from those on the axis. The resulting kinematic distortions lead to S-shaped phase spaces, which, if not corrected, will lead eventually to emittance growth. These beam aberrations can be minimized by increasing the injection energy and/or strengthening the beam focusing. It may also be possible to compensate for the energy effect by proper shaping of the quadrupoles electrodes. We have chosen to control the energy effect by increasing the injection energy of the diode and strengthening the beam focusing of the ESQ within the voltage breakdown limits. To check the physics of the energy effect of the ESQ design a quarter-scale experiment was designed to accommodate the parameters of the source, as well as the voltage limitations, of the Single Beam Transport Experiment (SBTE) apparatus. The voltage breakdown limits were studied by running a cold test of a full scale ESQ quadrupole. Design of the experiments as well as the one-beam version of the ILSE ESQ Injector and corresponding 3D PIC simulations will be presented.

High Energy Density Physics (HEDP) applications require high line charge density ion beams. An ef... more High Energy Density Physics (HEDP) applications require high line charge density ion beams. An efficient method to obtain this type of beams is to extract a long pulse, high current beam from a gun at high energy, and let the beam pass through a decelerating field to compress it. The low energy beam-bunch is loaded into a solenoid and matched to a Brillouin flow. The Brillouin equilibrium is independent of the energy if the relationship between the beam size (a), solenoid magnetic field strength (B) and line charge density is such that (Ba)^ 2 is proportional to the line charge density. Thus it is possible to accelerate a matched beam at constant line charge density. An experiment, NDCX-1c is being designed to test the feasibility of this type of injectors, where we will extract a 1 microsecond, 100 mA, potassium beam at 160 keV, decelerate it to 55 keV (density ∼ 0.2 μC/m), and load it into a 2.5 T solenoid where it will be accelerated to 100– 150 keV (head to tail) at constant line charge density. The head-to-tail velocity tilt can be used to increase bunch compression and to control longitudinal beam expansion. We will present the physics design and numerical simulations of the proposed experiment.

Accurate numerical simulations of ion driven Warm Dense Matter experiments requires accurate mode... more Accurate numerical simulations of ion driven Warm Dense Matter experiments requires accurate models of stopping powers for targets with temperatures up to a few eV. For finite temperature targets, energy loss of beam ions is comprised of contributions from nuclear stopping, bound electron stopping, and free electron stopping. We compare two different stopping power algorithms and the implications on target heating for two different beams corresponding to the current Neutralized Drift Compression Experiment (NDCX) and proposed NDCX II experiments. The NDCX I beam has a beam energy much lower than the Bragg peak while the NDCX II beam is designed to enter the target just above the Bragg peak, and exit just below. The first stopping power algorithm is based on the classical Bethe-Bloch formulation as is currently implemented in the HYDRA simulation code. The second algorithm is based on rescaling of experimental protonic stopping powers as developed by Brandt and Kitagawa for nuclear and bound electronic stopping, and free electron stopping following the model developed by Peter and Meyer-ter-Vehn.

In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from ... more In heavy ion inertial confinement fusion systems, intense beams of ions must be transported from the exit of the final focus magnet system through the target chamber to hit millimeter spot sizes on the target. Effective plasma neutralization of intense ion beams through the target chamber is essential for the viability of an economically competitive heavy ion fusion power plant. The physics of neutralized drift has been studied extensively with PIC simulations. To provide quantitative comparisons of theoretical predictions with experiment, the Heavy Ion Fusion Virtual National Laboratory has completed the construction and has begun experimentation with the NTX (Neutralized Transport Experiment) as shown in . The experiment consists of 3 phases, each with physics issues of its own. Phase 1 is designed to generate a very high brightness potassium beam with variable perveance, using a beam aperturing technique. Phase 2 consists of magnetic transport through four pulsed quadrupoles. Here, beam tuning as well as the effects of phase space dilution through higher order nonlinear fields must be understood. In Phase 3, a converging ion beam at the exit of the magnetic section is transported through a drift section with plasma sources for beam neutralization, and the final spot size is measured under various conditions of neutralization. In this paper, we present first results from all 3 phases of the experiment.

Physical Review Special …, 2006

3--D particle--in--cell simulations of neutralized ballistic transport are performed to study fin... more 3--D particle--in--cell simulations of neutralized ballistic transport are performed to study final focus and neutralization of high perveance ion beams envisioned for inertial confinement fusion drivers. Pre--formed plasmas in the last meter before the target provide a source of electrons which neutralize the ion current and prevent the space--charge induced spreading of the beam spot. 4--D phase--space data of a 266 keV, 6 mA K^+ ion beam in the neutralization region has been acquired at the Neutralized Transport Experiment (NTX) at Lawrence Berkeley National Laboratory. This data is used to provide a more accurate beam distribution with which to initialize the simulation. Previous treatments have used various idealized beam distributions which lack the detailed features of the experimental ion beam images. Simulation results are compared with NTX experimental results with good agreement.

Physical Review Special Topics - Accelerators and Beams, 2005

The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performan... more The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performance of neutralized final focus systems for high perveance heavy ion beams. The NTX final focus system produces a converging beam at the entrance to the neutralized drift section where it focuses to a small spot. The final focus lattice consists of four pulsed quadrupole magnets. The main issues are the control of emittance growth due to high order fields from magnetic multipoles and image fields. We will present experimental results from NTX on beam envelope and phase space distributions, and compare these results with particle simulations using the particle-in-cell code WARP.