Cryoelectronics Mr. SQUID® User's Guide Version 6.1.1 STAR Cryoelectronics, LLC 862 Estates Drive Los Alamos, NM 87544 U. S. A. Mr. SQUID® User's Guide Manual written by Randy W. Simon, Michael J. Burns, Mark S. Colclough, Greg Zaharchuk, and Robin Cantor Advanced Experiments written by Michael J. Burns (Exp. 1-5 and 7) and Greg Zaharchuk (Exp. 6) Mr. SQUID® is a registered trademark of STAR Cryoelectronics, LLC Copyright © 1996 – 2000 STAR Cryoelectronics, LLC ii Mr. SQUID User’s Guide TABLE OF CONTENTS Technical Support ........................................................................................................................... v Warranty ........................................................................................................................................ vi Safety Precautions.......................................................................................................................... vi 1 Introduction............................................................................................................................. 1 2 Setting Up Mr. SQUID® ......................................................................................................... 5 2.1 What You'll Need............................................................................................................5 2.2 Assembling the Mr. SQUID® System............................................................................. 6 3 Getting Started with Mr. SQUID® (New Users)................................................................... 10 3.1 Setting Up the Output Device....................................................................................... 10 3.2 Varying the Current Bias .............................................................................................. 11 3.3 Varying the Amplitude of the Current Sweep .............................................................. 11 3.4 Calculating the Current................................................................................................. 12 3.5 The V-I Curve ............................................................................................................... 12 3.6 Observing V-Φ Characteristics using Mr. SQUID® ..................................................... 15 3.7 Modulating the Critical Current of the SQUID ............................................................ 15 3.8 Additional SQUID Measurements................................................................................ 18 3.9 Summary of Basic Experiments.................................................................................... 21 4 Getting Started with Mr. SQUID® (Advanced Users).......................................................... 23 4.1 Electronics Box Front Panel ......................................................................................... 23 4.2 Electronics Box Rear Panel .......................................................................................... 24 4.3 Basic Operation............................................................................................................. 25 4.4 V-Φ Characteristics....................................................................................................... 26 5 An Introduction to Superconductivity and SQUIDs............................................................. 27 5.1 A Capsule History of Superconductivity ...................................................................... 27 5.2 Superconductivity: A Quantum Mechanical Phenomenon.......................................... 27 5.3 The Superconducting State ........................................................................................... 27 5.4 The Quantum of Flux.................................................................................................... 28 5.5 Superconducting Rings ................................................................................................. 29 5.6 Josephson Junctions...................................................................................................... 30 5.7 The dc SQUID .............................................................................................................. 31 5.8 Details of dc SQUID operation..................................................................................... 32 STAR Cryoelectronics, LLC iii Mr. SQUID User’s Guide 5.9 SQUID Parameters........................................................................................................ 36 5.10 SQUID Operation ......................................................................................................... 38 5.11 Practical SQUID Magnetometers ................................................................................. 39 5.12 SQUID Applications..................................................................................................... 41 5.13 A Brief History of SQUIDs .......................................................................................... 42 5.14 The SQUID in Mr. SQUID®......................................................................................... 44 6 Troubleshooting and Getting Help........................................................................................ 46 6.1 Problems in V-I Mode................................................................................................... 47 6.2 Problems in V-Φ Mode (Assuming Everything Works in V-I Mode) .......................... 48 6.3 Magnetic Flux Trapping in SQUIDs............................................................................. 49 6.4 Degaussing the Magnetic Shield................................................................................... 50 6.5 RF Interference ............................................................................................................. 50 6.6 Customer Service.......................................................................................................... 52 7 Advanced Experiments ......................................................................................................... 54 7.1 Resistance vs. Temperature of the YBCO SQUID ....................................................... 55 7.2 Building an Analog Flux-Locked Loop........................................................................ 62 7.3 Using a Flux-Locked Loop as a Sensitive Voltmeter ................................................... 66 7.4 The ac Josephson Effect: Microwave-Induced (Shapiro) Steps at 77K and Determining h/e...................................................................................................... 70 7.5 Inductive Measurement of the Superconducting Transition Temperature of an HTS Film ............................................................................................................. 77 7.6 SQUID Properties in Pumped Liquid Nitrogen............................................................ 84 7.7 Building an 8-bit or 12-bit Digital Flux-Locked Loop ................................................. 88 8 About STAR Cryoelectronics............................................................................................. 108 9 Technical Specifications ..................................................................................................... 109 9.1 Electronics................................................................................................................... 109 9.2 Probe ........................................................................................................................... 109 9.3 Magnetic Shield.......................................................................................................... 109 9.4 RF Filter Module......................................................................................................... 110 9.5 Cable ........................................................................................................................... 110 9.6 Dewar.......................................................................................................................... 110 9.7 System Resistances:.................................................................................................... 110 10 References....................................................................................................................... 111 STAR Cryoelectronics, LLC iv Mr. SQUID User’s Guide Revision Record Date Revision Description July 17, 2000 6.1 STAR Cryoelectronics Release © 2000 by STAR Cryoelectronics, LLC, Los Alamos, NM 87544 All rights reserved. No part of this manual may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission of STAR Cryoelectronics. STAR Cryoelectronics reserves the right to change the functions, features, or specifications of its products at any time, without notice. TECHNICAL SUPPORT If you have any questions or comments about this product or other products from STAR Cryoelectronics, please contact: STAR Cryoelectronics 862 Estates Drive Los Alamos, NM 87544 U. S. A. http://www.starcryo.com/ Technical Support: Tel.: (505) 661-6481 FAX: (505) 661-4287 Email: [email protected] STAR Cryoelectronics, LLC v Mr. SQUID User’s Guide WARRANTY STAR Cryoelectronics Limited Warranty STAR Cryoelectronics warrants this product for a period of twelve (12) months from date of original shipment to the customer. Any part found to be defective