In situcorrection of field errors induced by temperature gradient in cryogenic undulators

Abstract

A new technique of undulator field correction for cryogenic permanent magnet undulators (CPMUs) is proposed to correct the phase error induced by temperature gradient. This technique takes advantage of two important instruments: one is the in-vacuum self-aligned field analyzer with laser instrumentation system to precisely measure the distribution of the magnetic field generated by the permanent magnet arrays placed in vacuum, and the other is the differential adjuster to correct the local variation of the magnet gap. The details of the two instruments are described together with the method of how to analyze the field measurement data and deduce the gap variation along the undulator axis. The correction technique was applied to the CPMU with a length of 1.7 m and a magnetic period of 14 mm. It was found that the phase error induced during the cooling process was attributable to local gap variations of around 30 m, which were then corrected by the differential adjuster.

Short period, high field cryogenic undulator for extreme performance x-ray free electron lasers

“…While SmCo's gains are relatively small, continuing to 4.2 K, NdFeB sees large increases in energy product as the material is cooled down to 135 K. At this point the material undergoes a spin-axis reorientation due to competition between anisotropy and exchange forces, the latter being dominant at room temperature, and the useful field created by the magnet begins to drop with continued cooling [13]. Cryogenic undulators using NdFeB have been built, cooling to above the spin-axis reorientation onset [14][15][16].…”

“…At the same time a special set of pole clamps can be created, either intentionally or otherwise, with an assortment of differing heights to hold the poles in place at the desired height as the poles are naturally pulled out by the forces between the undulator halves. To compensate for the materials shrinking during cooling, it may be necessary to employ mechanical distorting techniques to the undulator such as that used in the SPring-8 design [32].…”

Radiation-induced magnetization reversal causing a large flux loss in undulator permanent magnets

“…This can be done on site without moving the undulators to a dedicated facility, by means of a portable and precise magnetic measurement system13. We carried out the measurements at the minimum gap of 3.5 mm for eight undulator segments from the most upstream side.…”

Shaping Photon Beams with Undulators and Wigglers

“…For IVUs, the introduced geometric pole height error is effectively hidden behind a CuNi foil which is installed after shimming. Long-range phase errors can still be compensated under vacuum and cooled conditions via a length tuning of the columns which supports the in-vacuum magnet girders (Tanaka et al 2009). …”

“…The field of a CPMU exceeds that of an IVU by a factor of about 1.4, where 15 % are due to the negative temperature coefficient of the remanence and the rest is related to the selected grade with higher remanence (less coercivity) at room temperature. Several CPMUs have been built and installed at 3GSRs: ESRF (Chavanne et al 2009a(Chavanne et al ,b, 2010, PSI (Tanaka et al 2009), DIAMOND (Ostenfeld and Pedersen 2010), and SOLEIL (Benabderrahmane et al 2013). The period lengths are oe 0 D 18 mm (ESRF, SOLEIL), 14 mm (PSI), and 17.7 mm (DIAMOND).…”