Radiation doses to insertion devices at the advanced photon source

Abstract

Dase measurements made fin and around the insertion devices (IDS) at the Advanced Photon Source are reported. Attempts ar? made to ;c'mpare these dose rates to dose rate> that ha\? been reported to cause rndintipn-induced demagnctlrxion. bur comparisons are complicalted by such factors as the particular magnet material and the techniques used in its manufacture, the spectrum and type of radiation. and rhe demagnetizing field seen by the m.~gnet. The spectxm of radiation at the IDS ha5 been measured .~nd found to include J larse high-energy (7 GeV) component, at least durin,a some runs. Lead shielding installed immediately upstream of the IDS has been found to decrease the dose to the upstream ends of the IDS. It has almost no effect on the dose to the downstream ends of the IDS, however. since much of the radiation travels through the ID vacuum chamber and cannot be readily shielded. Opening the gaps of the IDS during injection and at other times also helps decrease the radiation exposure. INTRODUCTIOS

Radiation-induced demagnetization of Nd-Fe-B permanent magnets.

“…The Nd 2 Fe 14 B sample showed a 1.5% remanence loss that was determined statistically significant. Exposure to bremsstrahlung radiation from an 85-MeV electron beam to a total dose of 450 Mrad resulted in a 14% remanence loss [7,12]. A second Nd-Fe-B sample, from a different manufacturer, displayed a 2% remanence loss after electron-beam irradiation to a total dose of 1370 Mrad, suggesting that magnet composition from different manufacturing processes may have an effect on the rate of remanence loss [7,12].…”

“…The magnetic flux of the sample magnets was measured using an open coil, evaluating the total magnetic flux of the sample [5]. The flux loss at an absorbed dose of 260 Mrad was found to be approximately 9% [5,12], with an increase in flux loss for higher doses [5].…”

“…The estimated absorbed dose to one of the damaged devices was 6.7 Mrad to the first upper magnet, and 5.1 Mrad to the first lower magnet [12]. This dose resulted in a peak magnetic field loss at the upstream end of the device of approximately 8% [12], with demagnetization over one third of the length of the device [6].…”

“…The APS specifically uses Nd-Fe-B permanent magnets in the insertion devices [2]. Although no detectable radiation-induced demagnetization has been observed in the APS insertion devices so far [12], partial demagnetization has been observed in at least one insertion device at the European Synchrotron Radiation Facility (ESRF) [4,6], where Nd-Fe-B permanent magnets are also used.…”

Radiation dose measurements of the insertion devices.

“…Earlier investigations have exhibited varying degrees of demagnetization of these magnets [3] due to irradiation from electron beams [4,5,6], 60 Co γ-rays [5], and high-energy neutrons [7,8]. Although no detectable radiation-induced demagnetization has been observed in the APS insertion devices so far [9], partial demagnetization has been observed in at least one insertion device at the European Synchrotron Radiation Facility (ESRF) [4,6], where Nd-Fe-B permanent magnets are also used. A growing concern for the APS insertion devices, as well as the permanent magnets that will be used in next generation high-power light sources, like the FEL [10,11], resulted from the partial demagnetization observed in the ESRF devices.…”