Lake Shore 625, User Manual

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Lake Shore Model 625 Superconducting MPS User’s Manual
Introduction 1-1
CHAPTER 1
INTRODUCTION
1.0 GENERAL
This chapter provides an introduction to the Model 625 Superconducting Magnet Power Supply. The Model 625 was
designed and manufactured in the United States of America by Lake Shore Cryotronics, Inc. The Model 625 features
include the following.
• True 4-quadrant (bipolar) 60 A, 5 V output
• 0.1 mA output setting resolution
• Linear regulation minimizes noise and ripple to 0.006% of maximum current into a 1 m

load.
• 1.0 mA stability per hour
• Two units can be connected in parallel for ±120 A operation
• CE compliance to
both the low voltage directive and the electromagnetic compatibility (EMC) directive (pending)
1.1 DESCRIPTION
The Model 625 Superconducting Magnet Power Supply is the ideal supply for small to medium sized superconducting
magnets used in high sensitivity materials research applications. The Model 625 is a practical alternative to both the
larger, one size fits all, superconducting magnet supplies and the endless adaptations of generic power supplies. By
limiting output power, Lake Shore was able to concentrate on the performance requirements of the most demanding
magnet users. The resulting Model 625 provides high precision, low noise, safety, and convenience.
Precision in magnetic measurements is typically defined as smooth continuous operation with high setting resolution and
low drift. Achieving these goals while driving a challenging load, such as a superconducting magnet, requires a unique
solution. The Model 625 delivers up to 60 A at a nominal compliance voltage of 5 V, with the supply acting as either a
source or a sink in true 4-quadrant operation. Its current source output architecture with analog control enables both
smooth operation and low drift. A careful blending of analog and digital circuits provides high setting resolution of
0.1 mA and flexible output programming.
Lake Shore chose linear input and output power stages for the moderate 300 W output of the Model 625. Linear
operation eliminates the radiated radio frequency (RF) noise associated with switching power supplies, allowing the
Model 625 to reduce the overall noise in its output and the noise radiated into surrounding electronics.
Safety should never be an afterthought when combining stored energy and liquid cryogens in a superconducting magnet
system. The Model 625 incorporates a variety of hardware and firmware protection features to ensure the safety of the
magnet and supply. For improved operator safety, the power supply was also designed for compliance with the safety
requirements of the CE mark, including both the low voltage and the electromagnetic compatibility (EMC) directive.
Instrument users have come to rely on Lake Shore for convenience and ease of use. The Model 625 includes the features
necessary to conveniently manage a superconducting magnet. Features such as a persistent switch heater output,
calculated field reading, current ramping, and quench detection are all included. Computer interfaces are also integrated
for automation of the magnet system. The Model 625 is truly an excellent one-box solution for controlling a
superconducting magnet.
Output Architecture
True 4-quadrant output capability of the Model 625 is ideal for the charge and discharge cycling of superconducting
magnets for both positive and negative fields. Tightly integrated analog control of the 4-quadrant output provides smooth
current change with very low overshoot on output change. The Model 625 has the ability to charge and discharge
magnets up to a 5 V rate.
True 4-quadrant operation eliminates the need for external switching or operator intervention to reverse the current
polarity, significantly simplifying system design. The transition through zero current is smooth and continuous, allowing
the user to readily control the magnetic field as polarity changes.