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Thin film studies toward improving the performance of accelerator electron sources.

机译：薄膜研究旨在改善加速器电子源的性能。

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摘要

Future electron accelerators require DC high voltage photoguns to operate beyond the present state of the art to conduct new experiments that require ultra-bright electron beams with high average current and higher bunch charge. To meet these demands, the accelerators must demonstrate improvements in a number of photogun areas including vacuum, field emission elimination in high voltage electrodes, and photocathodes. This dissertation illustrates how these improvements can be achieved by the application of suitable thin-films to the photogun structure for producing ultra-bright electron beams.;This work is composed of three complementary studies. First, the outgassing rates of three nominally identical 304L stainless steel vacuum chambers were studied to determine the effects of chamber coatings (silicon and titanium nitride) and heat treatments. For an uncoated stainless steel chamber, the diffusion limited outgassing was taken over by the recombination limited process as soon as a low outgassing rate of ~1.79(+/-0.05) x 10--13 Torr L s--1 cm--2 was achieved. An amorphous silicon coating on the stainless steel chambers exhibited recombination limited behavior and any heat treatment became ineffective in reducing the outgassing rate. A TiN coated chamber yielded the smallest apparent outgassing rate of all the chambers: 6.44(+/-0.05) x 10--13 Torr L s--1 cm--2 following an initial 90 °C bake and 2(+/-20) x 10--16 Torr L s --1 cm--2 following the final bake in the series. This perceived low outgassing rate was attributed to the small pumping nature of TiN coating itself.;Second, the high voltage performance of three TiN-coated aluminum electrodes, before and after gas conditioning with helium, were compared to that of bare aluminum electrodes and electrodes manufactured from titanium alloy (Ti-6Al-4V). This study suggests that aluminum electrodes, coated with TiN, could simplify the task of implementing photocathode cooling, which is required for future high current electron beam applications. The best performing TiN-coated aluminum electrode demonstrated less than 15 pA of field emission current at --175 kV for a 10 mm cathode/anode gap, which corresponds to a field strength of 22.5 MV/m.;Third, the effect of antimony thickness on the performance of bialkali-antimonide photocathodes was studied. The high-capacity effusion source enabled us to successfully manufacture photocathodes having a maximum QE around 10% and extended low voltage 1/e lifetime (> 90 days) at 532 nm via the co-deposition method, with relatively thick layers of antimony (≥ 300 nm). We speculate that alkali co-deposition provides optimized stoichiometry for photocathodes manufactured using thick Sb layers, which could serve as a reservoir for the alkali.;In summary, this research examined the effectiveness of thin films applied on photogun chamber components to achieve an extremely high vacuum, to eliminate high voltage induced field emission from electrodes, and to generate photocurrent with high quantum yield with an extended operational lifetime. Simultaneous implementation of these findings can meet the challenges of future ultra-bright photoguns.
机译：未来的电子加速器需要直流高压光枪在现有技术水平之外运行，以进行新的实验，这些实验需要具有高平均电流和较高束电荷的超亮电子束。为了满足这些需求，加速器必须在许多光枪领域展示出改进之处，包括真空，消除高压电极中的场发射以及光阴极。本文阐述了如何通过在光枪结构上应用合适的薄膜来产生超亮电子束，来实现这些改进。这项工作由三个互补研究组成。首先，研究了三个名义上相同的304L不锈钢真空室的脱气率，以确定室涂层（硅和氮化钛）和热处理的效果。对于未镀膜的不锈钢腔室，一旦低脱气速率为〜1.79（+/- 0.05）x 10--13 Torr L s--1 cm--2，则通过限制复合工艺来控制扩散受限的脱气。已实现。不锈钢腔室上的非晶硅涂层表现出复合受限的行为，任何热处理都无法有效降低脱气率。经过TiN涂层的腔室在所有腔室中的表观除气率最低：在初始90°C烘烤后，腔室的放气速率为6.44（+/- 0.05）x 10--13 Torr L s--1 cm--2和2（+/- 20）x 10--16 Tors L s -1 cm--2（在系列的最后烘烤之后）。这种低脱气率归因于TiN涂层本身的小的泵送特性。其次，比较了三个用TiN涂层的铝电极在用氦气气化之前和之后的高压性能与裸露的铝电极和高铝电极的性能。由钛合金（Ti-6Al-4V）制造。这项研究表明，涂有TiN的铝电极可以简化实现光电阴极冷却的任务，这是未来大电流电子束应用所必需的。性能最佳的TiN涂层铝电极在--175 kV的阴极/阳极间隙为10 mm时显示小于15 pA的场发射电流，这对应于22.5 MV / m的场强;第三，锑的作用研究了厚度对碱金属-锑化物光电阴极性能的影响。大容量的发射源使我们能够通过共沉积方法成功地制造出具有最大QE约10％且在532 nm下扩展了低电压1 / e寿命（> 90天）且具有相对较厚的锑层的光电阴极（≥ 300 nm）。我们推测，碱共沉积为使用厚Sb层制造的光电阴极提供了优化的化学计量，该阴极可以用作碱的储库。综上所述，本研究检查了应用于光枪腔室组件的薄膜的有效性，以实现极高的化学计量。真空，以消除电极上的高压感应场发射，并以高量子产率产生光电流，并延长使用寿命。这些发现的同时实施可以应对未来的超亮照相枪的挑战。

著录项

  • 作者

    Mamun, Md Abdullah Al.;

  • 作者单位

    Old Dominion University.;

  • 授予单位 Old Dominion University.;
  • 学科 Materials science.;Energy.;Mechanical engineering.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 154 p.
  • 总页数 154
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 古生物学;
  • 关键词

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