Vibration measurement and mount design for cryocoolers on GMT and large telescopes
Vibration measurement and mount design for cryocoolers on GMT and large telescopes
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DOI：
10.1117/12.2539923
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发表时间：
2020-01
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影响因子：
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通讯作者：
D. Adams;A. Vaccarella;W. Schofield;R. Sharp;J. Gilbert;G. Gausachs
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作者：
D. Adams;A. Vaccarella;W. Schofield;R. Sharp;J. Gilbert;G. Gausachs
长期以来，低温冷却器被证明是振动的主要来源，导致大型望远镜上的AO系统出现重大问题。现有的大型望远镜已经对仪器提出了严格的振动要求，以应对现有的问题，并且往往难以实现这些要求。随着该领域进入下一代望远镜GMT，TMT和eELT，振动要求继续变得越来越严格。仪器团队必须通过仔细选择低温冷却器和精心设计与望远镜的特定要求紧密匹配的低温冷却器支架来满足这些更苛刻的要求。正如我们将在本文中证明的那样，对于每种仪器和每台望远镜，没有一个通用的解决方案。在本文中，我们展示了一个通用的方法，推导出所需的性能的抗振动安装的制冷机。首先，我们描述了线性斯特林型制冷机作为振动源，并确定什么样的兼容安装将需要使他们可以接受的VLT，GMT和TMT上使用。对Cryotel GT线性斯特林冷却器（启用主动振动消除）的振动进行测量。通过将测得的振动与每个望远镜的要求进行比较，我们能够确定所需的传递函数，从而确定柔性支架所需的弹簧刚度。结果表明，虽然一些简单的橡胶支座可能足以与VLT和TMT一起使用，但GMT必须使用固有频率低于14 Hz的柔顺支座。
Cryocoolers have long been demonstrated to be a dominant source of vibration that have caused significant problems with AO systems on large telescopes. Existing large telescopes have already imposed strict vibration requirements on instruments in response to existing problems, and have often struggled to achieve them. As the field moves into the next generation telescopes with GMT, TMT and eELT, vibration requirements continue to get ever tighter. Instrument teams must respond to these more demanding requirements by careful selection of cryocoolers and thoughtful design of cryocooler mounts that are matched closely with the specific requirements of the telescope. As we will demonstrate in this paper there is not a one-size-fits-all solution for every instrument and every telescope. In this paper we demonstrate a general method of deriving the required performance for an anti-vibration mounts for cryocoolers. First we characterize a linear Stirling-type cryocooler as a source of vibration, and determine what compliant mounts would be required to make them acceptable for use on the VLT, GMT and TMT. Measurements are taken of vibration from a Cryotel GT linear Stirling cooler (with active vibration cancellation enabled). By comparing the measured vibration against the requirements of each telescope, we are able to determine the required transfer function and therefore the required spring rate for compliant mounts. The results indicate that while some simple rubber mounts may be sufficient for use with the VLT and TMT, but a compliant mount with natural frequency below 14 Hz must be used for GMT.