First spectral measurements of a cryogenic high-field short-period undulator

Abstract

Further development of synchrotron light sources and new concepts for free electron lasers require undulators with short periods and high magnetic fields. A promising approach is the cryogenic permanent magnet undulator concept based on an advanced magnet material. This new rare earth alloy ðPr; NdÞ 2 Fe 14 B, shows an increasing remanent field of up to 1.7 T without the limits of spin reorientation transition. This work presents first spectral measurements of a prototype cryogenic permanent magnet undulator, consisting of 20 periods of 9 mm in length, cooled by a closed cycle cryo-cooler to temperatures below 30 K. The K parameter of 0.837 at RT is increased by more than 15% to 0.966, and an increase of the third harmonics photon flux of up to 66% was achieved. A possible degradation of the on-axis field quality due to thermally induced magnetic field errors, deduced from the measured bandwidth of the spectrum, is below the limits of the detector resolution of 2%.

Challenges of in-vacuum and cryogenic permanent magnet undulator technologies

“…Another material, (PrNd)-Fe-B alloy, was developed for low temperature applications and an optimized composition of ðPr 0.8 Nd 0.2 Þ 2 Fe 14 B is proposed [50]. At 30 K, the remanence and coercivity of ðPr 0.8 Nd 0.2 Þ 2 Fe 14 B reach 1.69 T and 5700 kA=m, respectively, which shows that the field gain is 15% when cooled down to 80 K [27]. After the performance of a PrFeB and (PrNd)FeB CPMU has been proven, the use of these materials has become the preferred choice for the development of CPMUs.…”

“…Early developments of CPMUs have been pursued at SPring-8 [23,24], and the desired magnetic field quality was demonstrated in a 0.6-m NdFeB-CPMU prototype with a 14-mm period length. The magnetic characteristics of several magnet materials were explored at SPring-8 [22], SOLEIL [25] and HZB [26,27] to characterize the magnetic performance of CPMUs. At ESRF in 2008, a 2-m long CPMU with a period length of 18 mm was built based on NdFeB magnets [28] becoming the first full-scale CPMU operating in a storage ring [29,30] followed by other CPMUs operating in storage rings such as SOLEIL [31], DLS [32], SLS [33] and ESRF [34].…”

Free electron lasers driven by plasma accelerators: status and near-term prospects

“…Owing to the ultra-short nature of the electron beam, a comparably compact magnetic chicane is sufficient to stretch the bunch. To increase the Pierce parameter, a specific undulator design was proposed [ 64 ] : it minimizes the undulator period and maximizes the undulator parameter by using a cryogenically cooled in-vacuum design [ 67 , 68 ] . A cryogenic undulator, as described in Ref.…”

Development of a new magnetic measurement bench for in-vacuum undulators

“…The absence of a vacuum chamber between the magnet arrays and relativistic electron beam in IVUs, allow for operation of the device at lower vertical aperture, thus increasing the magnetic field. IVUs are usually designed with short magnetic periods, as low as 15 mm for operation at room temperature and down to 9 mm [2] for operation at cryogenic temperatures, where the permanent magnets yield higher remanence and higher coercivity fields [3].…”

“…The vacuum chamber surrounding the magnetic array results in limited accessibility to adjust individual magnetic poles, and thus optimisation of the magnetic array is usually performed without the vacuum chamber, which is installed at a later stage. This procedure is a time consuming one, and compromises the quality of the (1) = u 2n 2 1 + 1 2…”