Table of Contents

Temperature Control

To maintain stability ad sub-150K temperatures within the cryostaic volume, a mixed refrigerant Joule Thompson cooler combination with a PID driven heater / temperature sensor system is used.

ORCA Cryo-Cooler

The cryo-coller is an ORCA system, manufactured by Advanced Research Systems. The system is designed around a cooling cycle optimized to maintain temperatures of 90 K (-183.15 C) without the use of liquid cryogens. By exploiting the Joule-Thomson effect, the use of no moving parts within the cryo-head is achieved, resulting in a low vibration, orientation independent, operation with an air-cooled compressor. The system consists of two components: the air-cooled mixed refrigerant compressor (MRCM-150-2) with a 10.000 h maintenance cycle, and the ORCA-MR mylar wrapped cryo-head (MRCH-1).

The non-toxic MRSG-110 refrigerant is used in the system, allowing for minimum temperatures around 110K. Lower values may be achieved by transitioning to a different refrigerant which most possibly will require modifications to the compressor. The thermal capacity of different available refrigerants can be seen in the following plot:

The cryogenic system features no power or thermostatic control. Temperature regulation is achieved with a mixture of programmable power control and heater elements implemented at the attachment interface of the cryo-head.

Compressor Specifications Cryo-Cooller Specifications
Power Usage Frequency 50 / 60 Hz Model MR-90 MR-110 MR-125
Voltage 220 - 240 V Base Temperature < 90 K < 110 K < 125 K
Power 750 VA Maximum Cylinder Temperature 355 K
Dimentions Length 356 mm Cooldown Time ~3 hrs (to base temperature)
Width 483 mm Weight 7.1 kg (Expander)
Height 394 mm
Weight 36.3 kg
Typical Maintenance Cycle 10.000 h

Lakeshore Temperature Controller

Since the cryocooler has no thermostat, we use a heater with sensors to keep our samples at the desired temperature. We use the LakeShore 335 Temperature Controller as the heater, which has a heating capacity of 75 W and works in a temperature range from 300 mK to 1505 K. It comes with two sensor outputs: one is used to measure the CCD temperature, and the other is used to measure the temperature of the cryohead. It is mounted to a rack next to the Keithley 2470 SourceMeter. We use a LabVIEW script to control the LakeShore remotely via the server. To control the cryocooler, we use a PDU, which itself is controlled via a LabVIEW script. The LakeShore 335 has two outputs with different output settings (for more Information Datasheet, Manual):

Outpout 1
Type Variable DC current source
Control Modes Closed loop digital PID with manual output or open loop
D/A resolution 16-bit
25 Ω setting 50 Ω setting
Max Power 75 W* 50 W 50 W
Max current 1.73 A 1.41 A 1 A
Voltage compliance (min) 43.3 V 35.4 V 50 V
Heater load for max Power 25 Ω 25 Ω 50 Ω
Heater load range 10 Ω - 100 Ω
Ranges 3 (decade steps in power)
Heater noise 0.12 µA RMS (dominated by line frequency and its harmonics)
Grounding Output referenced to chassis ground
Safety limits Curve temperature, power up heater off, short circuit protection

* 75 W only available if Output 2 is in voltage mode.

Outpout 2
Type Variable DC current source or voltage source
Current mode Voltage mode
Control Modes Closed loop digital PID with manual output, zone, open loop Closed loop digital PID with manual output, zone, open loop, warm up, monitor out
D/A resolution 15-bit 16-bit (bipolar)/15-bit (unipolar)
25 Ω setting 50 Ω setting N/A
Max Power 25 W 25 W 1 W
Max current 1 A 0.71 A 100 mA
Voltage compliance (min) 25 V 35.4 V ±10 V
Heater load for max Power 25 Ω 50 Ω 100 Ω
Heater load range 10 Ω - 100 Ω 100 Ω min (short circuit protected)
Ranges 3 (decade steps in power) N/A
Heater noise 0.12 µA RMS 0.3 mV RMS
Grounding Dual banana Detachable terminal block
Safety limits Curve temperature, power up heater off, short circuit protection

Connection Layouts

The connection protocoll between the AlpineCube outside and the LakeShore 335:

DB 50, Alpine Cube - Lakeshore
Alpine Cube Side Lakeshore 335 Side
Function Pin Pin Function
Bottom Row 1 x
2 x
3 x
4 x
5 x
6 x
7 x
8 x
9 x
10 x
11 x
Heater 1 12 Lakeshore Heater Output 1
13
Temperature sensor 2 14 Lakeshore Sensor Input A
15
Temperatrue sensor 1 16 Lakeshore Sensor Input B
17
Middle Row 18 x
19 x
20 x
21 x
22 x
23 x
24 x
25 x
26 x
27 x
28 x
29 x
30 x
Temperature Sensor 2 31 Lakeshore Sensor Input A
32 x
Temperature Sensor 1 33 Lakeshore Sensor Input B
Top Row 34 x
35 x
36 x
37 x
38 x
39 x
40 x
41 x
42 x
43 x
44 x
Heater 2 45 Lakeshore Heater Output 2
46
Temperature sensor 2 47 Lakeshore Sensor Input A
48
Temperature sensor 1 49 Lakeshore Sensor Input B
50

The AlpineCube uses a passage connector, which inverts the pin numbers, because it goes from a male to male connector. In the pictures below the schematics for each sides are made.

Take note that pin 1 is only connected to pin 34 and not directly connected to the sensor (analog for the pins 2,3 and 4).

Take note that the on this side each sensor uses 5 pins (Sensor 1 uses: 16,17,33,49,50), while on the inside of the AlpineCube they only use 4.

System output configuration

In this system we go with a Resistor 50 Ω 1% 60W to 220. Which sets the max power setting to 50 W and max current to 1 A.