HEAVY ION FUSION SCIENCE VIRTUAL NATIONAL LABORATORY 1ST QUARTER 2010 MILESTONE REPORT: Simulations of fast correction of chromatic aberrations to establish physics specifications for implementation on NDCX-1 and NDCX-2

LIDIA, S.M. ; LUND, S.M. ; SEIDL, P.A.

关键词: 70;    BEAM DYNAMICS;    CHROMATIC ABERRATIONS;    COMPRESSION;    FOCUSING;    HEAVY IONS;    IMPLEMENTATION;    INDUCTION;    ION BEAMS;    LENSES;    PHYSICS;    SIMULATION;    SPACE CHARGE;    SPECIFICATIONS;    TARGETS;    TRANSPORT;    VELOCITY;    WAVE FORMS;   

DOI  :  10.2172/981728
RP-ID  :  LBNL-3040E
PID  :  OSTI ID: 981728
Others  :  TRN: US1004102

美国|英语

来源: SciTech Connect

【 摘 要 】

This milestone has been accomplished. The Heavy Ion Fusion Science Virtual National Laboratory has completed simulations of a fast correction scheme to compensate for chromatic and time-dependent defocusing effects in the transport of ion beams to the target plane in the NDCX-1 facility. Physics specifications for implementation in NDCX-1 and NDCX-2 have been established. This milestone has been accomplished. The Heavy Ion Fusion Science Virtual National Laboratory has completed simulations of a fast correction scheme to compensate for chromatic and time-dependent defocusing effects in the transport of ion beams to the target plane in the NDCX-1 facility. Physics specifications for implementation in NDCX-1 and NDCX-2 have been established. Focal spot differences at the target plane between the compressed and uncompressed regions of the beam pulse have been modeled and measured on NDCX-1. Time-dependent focusing and energy sweep from the induction bunching module are seen to increase the compressed pulse spot size at the target plane by factors of two or more, with corresponding scaled reduction in the peak intensity and fluence on target. A time-varying beam envelope correction lens has been suggested to remove the time-varying aberration. An Einzel (axisymmetric electric) lens system has been analyzed and optimized for general transport lines, and as a candidate correction element for NDCX-1. Attainable high-voltage holdoff and temporal variations of the lens driving waveform are seen to effect significant changes on the beam envelope angle over the duration of interest, thus confirming the utility of such an element on NDCX-1. Modeling of the beam dynamics in NDCX-1 was performed using a time-dependent (slice) envelope code and with the 3-D, self-consistent, particle-in-cell code WARP. Proof of concept was established with the slice envelope model such that the spread in beam waist positions relative to the target plane can be minimized with a carefully designed Einzel lens waveform and transport line. WARP simulations have verified the efficacy of the Einzel lens while including more detailed beam physics. WARP simulations have also indicated some unpredicted transittime effects, and methods are currently being explored to compensate and reduce this complication. We have explored the use of an Einzel lens, or system of Einzel lenses, to compensate for chromatic aberrations in the beam focal spot in the NDCX-2 target plane. The final beam manipulations in NDCX-2 (linear velocity ramp, charge neutralization, high field final focus solenoid) are similar to NDCX-1 though the NDCX-2 beam has much higher energy and current. The most relevant distinctions are that the pulse duration at the entrance to the drift compression section is tenfold shorter, and that the beam energy tenfold higher, than in NDCX-1. Placing a time-dependent, envelope angle correcting element at the neutralized drift region entrance presents a very significant challenge to voltage holdoff and voltage swing V(t) in a single Einzel lens. Placing the Einzel lens(es) further upstream reduces the required voltage risetime V'(t) to effect the necessary envelope correction, while increasing the duration over which the timedependent voltage must vary. While this simplifies the technological challenge of designing and operating a Einzel lens in NDCX-2, it does require much finer control of the correcting waveform and measurements of its effect on space-charge dominated beams over a much longer axial path length to target than in the NDCX-1.