CCD Thermal Control System

Table of Contents:

System Overview

The two CCDs within the main spectrometer are maintained at -100C to minimize thermal noise. Liquid nitrogen (LN2) is used to cool the CCDs to this temperature. Within KPF the temperature stability of the CCDs is of great importance, as any movements of the detector from thermal transients will appear as a movement of the spectrum. Within the science data this movement will mimic the Doppler shifts that KPF is designed to measure.

As shown in the overview diagram just below, CCD thermal control is achieved with a multi-stage system, starting with the coarsest control being at the Instec cold head (Stage 1) and progressing though finer and finer control to the CCD (Stage 4). Stage 1 provides cooling and heating control, whereas Stages 2 to 4 are heating control only. Each stage has a PID loop control for fine-tuning its characteristics.

In addition, there is a heater on the cyrostat body. Although this is not directly in-line with the CCD thermal path (Instec Cold Head → Cold Finger → CCD), it is important as it maintains the cryostat body at a consistent temperature and hence controls the radiative environment surrounding the CCD. The cryostat body heater also has a PID loop for controlling its characteristics.

Sensor Details (and KTL Keywords)

Cryostat Thermal Sensor Locations

Sensor locations and KTL keywords are shown below.

Lakeshore Channel Mapping (Cryostat Sensors Only)

See Thermal Sensor Locations (Spectrometer and Hallway) for the entire list of Lakeshore sensors.

The connectors on the various Lakeshore cable harnesses are labelled 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

This diagram indicates how they connect to the Lakeshore rear panel:

Green Lakeshore (cryostat sensors only)

Red Lakeshore (cryostat sensors only)

Heater Details (and KTL Keywords)

Cable Details