Characterization of a low frequency magnetic noise from a two-stage pulse tube cryocooler

M. J. Eshraghi, I. Sasada, J. M. Kim, Y. H. Lee

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Magnetic noise of a two-stage pulse tube cryocooler (PT) was measured by a fundamental mode orthogonal fluxgate magnetometer and by a LTS Double Relaxation Oscillation SQUID (DROS) first-order planar gradiometer. The magnetometer was installed in a dewar made of aluminum at 12 cm distance from a section containing magnetic regenerative materials of the second pulse tube. The magnetic noise spectrum showed a clear peak at 1.8 Hz, which is the fundamental frequency of the He gas pumping rate. The 1.8 Hz magnetic noise registered a peak, during the cooling down process, when the second cold-stage temperature was around 12 K, which is well correlated with the 1.8 Hz variation of the temperature of the second cold stage. Hence, we attributed the main source of this magnetic noise to the temperature variation of the magnetic moments resulting from magnetic regenerative materials, Er3Ni and HoCu2, in the presence of background static magnetic fields. We have also pointed out that the superconducting magnetic shield of lead sheets reduced the low frequency magnetic noise generated from the magnetic regenerative materials. With this arrangement, the magnetic noise amplitude measured with the LTS DROS gradiometer, mounted at 7 cm horizontal distance from the magnetic regenerative materials, in the optimum condition, was lower than 500 pT peak-to-peak, whereas the noise level without lead shielding was higher than the dynamic range of DROS instrumentations which was around ± 10 nT.

Original languageEnglish
Pages (from-to)334-339
Number of pages6
JournalCryogenics
Volume49
Issue number7
DOIs
Publication statusPublished - Jul 1 2009

Fingerprint

SQUIDs
tubes
low frequencies
Magnetometers
pulses
gradiometers
Lead
Dewars
magnetometers
oscillations
Magnetic moments
Aluminum
Shielding
Temperature
Gases
noise spectra
Magnetic fields
Cooling
dynamic range
temperature

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Physics and Astronomy(all)

Cite this

Characterization of a low frequency magnetic noise from a two-stage pulse tube cryocooler. / Eshraghi, M. J.; Sasada, I.; Kim, J. M.; Lee, Y. H.

In: Cryogenics, Vol. 49, No. 7, 01.07.2009, p. 334-339.

Research output: Contribution to journalArticle

Eshraghi, M. J. ; Sasada, I. ; Kim, J. M. ; Lee, Y. H. / Characterization of a low frequency magnetic noise from a two-stage pulse tube cryocooler. In: Cryogenics. 2009 ; Vol. 49, No. 7. pp. 334-339.
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