Damping of Intrinsic Temperature Oscillations in a 4 K Pulse Tube Cooler by Means of Rare Earth Plates

Materials for damping the PTC-induced thermal fluctuations of the cold-head

“…The observed discrepancy on thermal conductivity may also be due to the fact that the manufacturing process of the discs did not exactly match the same protocol as the materials reported in ref [5]: a heat treatment was missing, which should lead to a grain increase and consequent conductance increase [11]. The related work on ErNi [2] also reported a significant reduction on the experimental effective thermal conductance, suggesting the existence of more than one single phase of the material apart from contact resistance added.…”

“…Keeping the system simple is also desirable. A vibration isolation and thermal damper for a 4 K GM cooler was reported in ref [1], although without details of its composition, showing to be able to reduce the 200 mK at 3.5 K oscillation down to 1 mK at 4.1 K. A report on the addition of 3.6 mm plates of ErNi in a 4 K PTC have shown a reduction from 275 mK to 14.5 mK [2] on the temperature oscillations. The ErNi material exhibits a ferromagnetic transition at about 10.5 K, hence not reflecting its high heat capacity peak on the 4 K temperature range.…”

1 K cryostat with sub-millikelvin stability based on a pulse-tube cryocooler

“…Closed-cycle cryocoolers have some disadvantages compared with traditional liquid-helium systems. First, the cyclic nature of a pulse-tube cryocooler leads to rather large temperature oscillations, on the order of 0.2 K, at the ∼1 Hz frequency of the cooler's operation [1]. Second, while base temperatures have continued to improve over the years, they are still above the ∼1 K temperature reachable with pumped helium systems.…”

Sub-millikelvin stabilization of a closed cycle cryocooler

“…Prior attempts to stabilize GM cryocoolers were based on added thermal resistance, 2 rare earth alloys, 3 pressurized helium vessel, [4][5][6] or long conduction paths. 7,8 Of these concepts, only the last one has matured to a commercial product.…”

“…The need of a second radiation shield also adds complexity and reduces usable sample space. Allweins et al 3 used an Erbium-Nickel alloy plate, reaching 14 mK fluctuations at 4.2 K. However, this rare-earth alloy is not commonly available and the fluca) Also at École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland. b) G. Dubuis and X.…”