HARP: Mixer Bias Performance Investigation and Mixer Spares Production

“HARP”是一个16单元350 GHz焦平面阵列接收器，于2005年底交付给JCMT。HARP最初主要由STFC以其对JCMT仪器开发计划的贡献的形式提供资金，其中包括资本要素，加上支付工作人员的努力，卡文迪什天体物理学作为主要承包商（提出此申请的集团）的研究赠款以及UK-ATC的一些分包合同开发工作的资金。HARP是世界上唯一一个在亚毫米波长上运行的同类阵列，其性能是最先进的，可以以前所未有的速度对天空进行大规模测绘。它已被联合委员会正式接受为一种设施仪器，目前正在为许多不同的观测方案定期提供数据。在仪器安装、试运行和验收（从而结束最初的卡文迪什天体物理学赠款）以来的这段时间里，在JCMT上仪器的持续运行和维护方面出现了一些需要注意的相对较小的问题。本申请书提出了一项工作方案，以适当的费用解决这些问题。申请的大部分资金用于支付建造四个新的HARP混合器块作为“备件”的费用，以及修理三个在试运行过程中损坏或出现故障的原始混合器块的费用。还要求提供资金，使研究人员能够对HARP混频器在某些直流偏置条件下出现的寄生振荡的性质和原因进行研究。这将通过在天体物理组实验室中建立一个与HARP几乎相同的实验混频器/LO/IF系统来完成。我们的目标是试图理解这些问题，并因此建议对HARP偏置电子系统进行改进，使超导结能够在目前不可行的直流水平上偏置。据信，这些将允许实现较低的接收机噪声温度，从而实现更高的灵敏度。

'HARP' is a 16-element 350 GHz focal plane array receiver that was delivered to the JCMT in late 2005. HARP was originally funded largely by STFC in the form of its contribution to the JCMT instrument development programme, which covered the capital elements, plus, to cover the staff effort, research grants to Cavendish Astrophysics as main contractor (the Group making this application) and the funding of some sub-contract development work at the UK-ATC. HARP is the only array of its kind operating in the world at sub-millimetre wavelengths and has a performance that is state of the art, allowing large scale mapping of the sky at hitherto unheard of rates. It has been formally accepted as a facility instrument by the JCMT and is now routinely producing data for many diverse observational programmes. In the period since installation, commissioning and acceptance of the instrument (and hence closure of the original Cavendish Astrophysics grant) a number of relatively minor issues have arisen in relation to the ongoing operation and maintenance of the instrument on the JCMT that require attention. This application proposes a programme of work to address these at a modest cost. The bulk of the funding requested is to cover the costs of building four new HARP mixer blocks to act as 'spares' and repairing three original mixer blocks that were damaged or have become faulty during the commissioning process. Funding is also requested to enable the investigators to undertake a study into the nature and cause of spurious oscillations that have been found to occur at some d.c. bias conditions of the HARP mixers. This would be done by setting up a near identical experiment mixer/LO/IF system to that of HARP in the Astrophysics Group laboratories. The goal would be to attempt to understand the issues and hence suggest improvements to the HARP bias electronics system that would allow the superconducting junctions to be biased at d.c. levels that are currently not viable. It is believed that these will allow lower receiver noise temperatures to be achieved and hence greater sensitivity.