Bluefors-coaxial-wiring-2018

LD System

The LD is our most sold dilution refrigerator system. It has best-in-class heat exchangers with superior performance. The LD400 system typically provides more than 15 μW at 20 mK on the experimental flange with only 18 litres of helium-3. In addition, it has a high cooling power of ∼ 0.5 mW when operated at 100 mK. This well-engineered dilution refrigerator has a clean and open design with sensitive parts well protected and out of reach for the user – minimal risk of damage during installation of experimental equipment. A single push of a button initiates a fully automated cool-down sequence from room to base temperature.

In addition:

Nine LOS Access Ports

All line-of-sight ports reach from room temperature to mixing chamber.

  • 2 x KF63 slotted in all flanges
  • 5 x KF40 including central port
  • 2 x KF16
Large Experimental Space

MXC Flange Diameter: 290 mm | 11.42″
Off-center placed dilution unit maximizes useful space on all flanges. Open design permits easy experimental access without being obscured by heat exchangers or system support structure

Superior Performance
  • Base temperature well below 10 mK
  • Fast cool-down: < 24 hours to 10 mK
Low Total Cost of Ownership

Oil-free pumps and compressors in gas handling unit guarantee minimal maintenance requirements with service interval up to 3 years. The systems employ only high quality components such as Pfeiffer Vacuum pumps and pressure sensors, VAT vacuum valves and bellows.

Options

Vibration Isolation

We offer improved vibration isolation for experiments that are particularly sensitive to low frequency vibrations (< 1 kHz).

  • Basic vibration isolation frame
  • Active vibration damping
  • GHS isolation frame
  • Pulse tube pause system
Optical Ports

We offer direct optical access to the sample space. The optical ports can be equipped with different window materials and are available in different sizes and configurations. With four 0.5″ optical ports, equipped with our standard fused silica windows, our DR systems still reach a base temperature of < 15 mK.

Magnetic Shielding

We offer magnetic shielding that can be fitted directly to the system (e.g. a magnetic shielding metal cylinder with one end closed inside the lower section of the vacuum can). For magnetic shielding we work together with Amuneal Manufacturing Corp.

Additional Radiation Shields

We offer the possibility for additional EM shielding around the sample space. These shields can be attached to the mixing chamber plate (LD and XLD) and the cold plate (XLD). Standard shields are made from gold-plated copper. Other materials and platings are available upon request.

Long-Life Cold Trap

We have developed a unique long-life cold trap that allows for continuous operation of the system for up to three years. The trap is integrated with the system and does not need any cryogenic liquids to operate (care-free).

4K Heater Kit

Fully automated fast warm-up option, which allows overnight warm-up for our standard LD systems.

LN2 Pre-cooling Loop

Engaging LN2 pre-cooling loop with an external source of liquid nitrogen allows to reduce the cool-down time by ~ 40% in case of a basic system.

Helium battery

We have developed a solution which enables running experiments at dilution refrigerator temperatures for a limited time with the pulse tube cryo-cooler switched off. Helium gas is condensed into a container installed at the 4K flange. Once the container has been filled with liquid helium, the pulse tube can be switched off and by pumping on the reservoir the 4K flange is cooled sufficiently for the dilution circuit to continue operating. Since this mode of operation involves both a mechanical cryo-cooler as well as cryogenic liquids we call it hybrid cooling. The battery performance is characterized by the hold time i.e. how long the dilution unit can be operated while the pulse tube is switched off. For an empty LD cryostat the hold time is approximately 3.5 hours. Due to the increased heat load at the 4K flange the hybrid system is not compatible with a superconducting magnet and any experimental wiring that would increase the heat load to the 4K flange will also decrease the hold time. In practical cases the hold time is between 2 to 3 hours.

Service Packages and Extended Warranty are available upon request

Technical Specifications

Note: Cooling power is measured on the experimental flange outside MXC.

LD250GuaranteedExpected
Base temperature10 mK8 mK
Cooling power @ 20 mK12 μW14 μW
Cooling power @ 100 mK250 μW300 μW
Cooling power @ 120 mK360 μW400 μW
Cool-down time to base24 hrs22 hrs
LD400GuaranteedExpected
Base temperature10 mK8 mK
Cooling power @ 20 mK14 μW16 μW
Cooling power @ 100 mK400 μW450 μW
Cooling power @ 120 mK575 μW650 μW
Cool-down time to base24 hrs22 hrs

Performance Graphs

1
2
3
4
5
6
Bluefors-cool-down-profiles-for-three-LD-dilution-refrigerator-configurations-2018
1

Start cool-down

2

Start pulse pre-cooling

3

Stop pulse pre-cooling

4

Start mixture condensation

5

Stop mixture condensation

6

Normal circulation mode

Above are cool-down curves for three different configurations of LD systems measured with calibrated resistance thermometers.

System 1: basic LD with LN2 pre-cool
System 2: basic LD
System 3: LD with 100 mm extra sample space, MXC shield, additional sample mounting plate and large amount of DC and RF cabling.

Pulse pre-cooling sequence (see spots 2 and 3) is one of the key points in reducing the cool-down time. Because we do not use exchange gas some parts of the DR unit stay ‘hot’ on cool down, which prevents condensation of the mixture. By repeatedly admitting the mixture from the tanks through the low impedance still side of the DR and then pumping it out again, these hot spots are effectively cooled down.

Typical Layout

Each of our systems is designed to be installed to a specific location defined in advance. A separate layout drawing is made for each Bluefors system, which should always be referred to for exact dimensions.

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Bluefors dilution refrigerator LAYOUT LD STANDARD 2019
1

Oil-free pumps and compressors in Bluefors’ gas handling unit guarantee minimal maintenance requirements with service interval up to 3 years.

Technical Requirements

The basic requirements are 3-phase electricity, cooling water, compressed air. The full list of requirements and specification details can be found in the Pre-Installation Guide, please contact our sales team for a copy.

Contact our sales team for questions, requests and Pre-Installation Guide.

© Copyright 2019 — Bluefors Oy

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