Results from the Cooler and Lead Tests

Abstract

The report presents the results of testing MICE spectrometer magnet current leads on a test apparatus that combines both the copper leads and the high temperature superconducting (HTS) leads with a single Cryomech PT415 cooler and liquid helium tank. The current is carried through the copper leads from 300 K to the top of the HTS leads. The current is then carried through the HTS leads to a feed-through from the vacuum space to the inside of a liquid helium tank. The experiment allows one to measure the performance of both cooler stages along with the performance of the leads. While the leads were powered we measured the voltage drops through the copper leads, through the HTS leads, through spliced to the feed-through, through the feed-through and through the low-temperature superconducting loop that connects one lead to the other.Measurements were made using the leads that were used in spectrometer magnet 1A and spectrometer magnet 2A. These are the same leads that were used for Superbend and Venus magnets at LBNL. The IL/A for these leads was 5.2x10 6 A m -1 . The leads turned out to be too long. The same measurements were made using the leads that were installed in magnet 2B. The magnet 2B leads had an IL/A of 3.3x10 6 A m -1 . This report discusses the cooler performance and the measured electrical performance of the lead circuit that contains the copper leads and the superconducting leads. All of the HTS leads that were installed in magnet 2B were current tested using this apparatus.

Tests of copper and HTS leads with a two-stage pulse tube drop-in cooler

“…This diagram shows the relationship between the first and second-stages of refrigeration. From this diagram, one sees that one needs ~40 W of Q1 in order to get the lowest value of T2 when Q2 = 1.5 W. The operating points for leads 1a and 1b are plotted on FIGURE 6 [11]. The operating points plotted for lead 1a are I = 0, I = 275 A, and I = 275 A plus Q A = 20 W of added heat load to the copper plate.…”

“…These leads have a calculated IL/A of 5.2x 10 6 A m -1 at 275 A [11]. The engineers at the Harbin Institute of Technology calculated IL/A of the MICE coupling magnet leads using Equation 2.…”

What Happened with Spectrometer Magnet 2B

“…The cooler and lead tests [11] results suggest that there may be resistive heating in the HTS leads. The literature from HTS-110, the vendor for the leads does not mention that there is resistive heating in the HTS leads.…”