Undulator BLM PDR Review Heinz-Dieter Nuhn, SLAC / LCLS January 24, 2008

1. Undulator BLM PDR ReviewHeinz-Dieter Nuhn, SLAC / LCLSJanuary 24, 2008 • Available Damage Data • Requirements • [System Overview] • Charge to the Committee 1

2. Beam Loss Monitors (BLMs) • Radiation protection of the permanent magnet blocks is very important. • Funds are limited and efforts need to be focused to minimize costs. • A Physics Requirement Document, PRD 1.4-005 has been completed, defining the minimum requirements for the Beam Loss Monitors. • The damage estimates are based on published measurement results and a in-house simulations. 2

3. Estimated Radiation-Based Magnet Damage • The loss of magnetization caused by a given amount of deposited radiation has been estimated by Alderman et al. [i] in 2000. • Their results imply that a 0.01% loss in magnetization occurs after absorption of a total fast-neutron fluence of 1011 n/cm2 has been absorbed. • A more recent report by Sasaki et al. [ii] challenges fast neutron fluence as damaging factor and, instead, proposes photons and electrons but does not provide a relation between integrated dose and damage. [i] J. Alderman, et. A., Radiation Induced Demagnetization of Nd-Fe-B Permanent Magnets, Advanced Photon Source Report LS-290 (2001) [ii] S. Sasaki, et al, Radiation Damage to Advanced Photon Source Undulators, Proceedings PAC2005. 3

4. Estimate of Neutron Fluences from LCLS e- Beam • The radiation deposited in the permanent magnets blocks of the LCLS undulator, when a single electron (e-) strikes a 100-µm carbon foil upstream of the first undulator, has been simulated by A. Fasso [iii]. • The results are a peak total dose of 1.0×10-9 rad/e- including a neutron (n) fluence of 1.8×10-4 n/cm2/e-, which translates into 1.8×105 n/cm2 for each rad of absorbed energy. • These numbers are based on peak damage results and should therefore be considered as worst case estimates. [iii] A. Fasso, Dose Absorbed in LCLS Undulator Magnets, I. Effect of a 100 µm Diamond Profile Monitor, RP-05-05, May 2005. 4

5. Simulated Neutron Fluences for LCLS e- Beam on C Foil Simulated neutron fluences in the LCLS undulator magnets (upper jaw) from a single electron hitting a 100-µm-thick carbon foil upstream of the first undulator. Maximum Level is 1.8×10-4 n/cm2/e- 5

6. Total Dose from LCLS e- Beam on C Foil Corresponding maximum deposited dose. Maximum Level is 1.0×10-9 rad/e- 6

7. Radiation Limit Estimates ~0.01 mrad/pulse @ 120 Hz; ~1 mrad/s 7

8. Maximum Estimated Radiation Dose from BFW Operation All Undulators Rolled-In Undulators on DS Girders Rolled-Out (1/100) Small amount of scans expected can be ignored for damage purposes; but might require MPS exception. 8

9. Radiation Sources Possible reasons for generating elevated levels of radiation are • Electron Beam Steering Errors • Will be caught and will lead to beam abort. • Unintentional Insertion of Material into Beam Path • Will be caught and will lead to beam abort. • Intentional Insertion of Material into Beam Path • BFW operation • Is expected to produce the highest levels. May only be allowable when all down-stream undulators are rolled-out and beam charge is reduced to minimum. • Screen insertion • May only be allowable when all undulators are rolled-out and beam charge is reduced to minimum. • Background Radiation from Upstream Sources including Tune-Up Dump • Expected to be sufficiently suppressed through PCMUON collimator. • Beam Halo • Expected to be sufficiently suppressed through upstream collimation system. • May require halo detection system. 9

10. General Requirements • One BLM device will be mounted upstream of each Undulator Segment • The BLM will provide a digital value proportional to the amount of energy deposited in the device for each electron bunch. • The monitor shall be able to detect and measure (with a precision of better than 25%) radiation levels corresponding to magnet dose levels as low as 10 µrad/pulse [0.1 µGy/pulse] and up to the maximum expected level of 10 mrad/pulse [100 µGy/pulse]. • The monitor needs to be designed to withstand the highest expected radiation levels of 1 rad/pulse without damage. • The radiation level received from each individual electron bunch needs to be reported after the passage of that bunch to allow the MPS to trip the beam before the next bunch at 120 Hz. 10

11. Monitor Requirements • Each BLM device will be able to measure the total amount of absorbed dose covering the full area in front of the undulator magnets. • The magnet cross section seen by the beam is 56.5 mm wide by 66 mm high. In their home position, the magnets are located between 6.8 mm and (6.8+66)  mm= 72.8 mm both, above and below the beam axis. Their horizontal extend is ±28.25 mm. They are expected to be moved during operations by 80 mm in positive x-direction and by 6 mm in the opposite direction, which sets the limits horizontal coverage range to +108.25 mm to -34.25 mm. The detector material thus needs to cover an area of about 145×145 mm2 ([2×72.8]×[108.25+34.25] mm2), but is allowed a horizontal cut-out of 7 mm so that it can be mounted without the need for breaking vacuum. • Each BLM device will be calibrated based on the radiation generated by the interaction of a well known beam with the BFW devices. • The calibration geometry will be simulated using FLUKA and MARS to obtain the calibration factors, i.e., the ratio between the maximum estimated damage in a magnet and the voltage produced by each BLM device. 11

12. Beam Loss Monitor Area Coverage • Main purpose of BLM is the protection of undulator magnet blocks. • Less damage expected when segments are rolled-out. • One BLM will be positioned in front of each segment. • Its active area will be able to cover the full horizontal width of the magnet blocks • Two options for BLM x positions will be implemented to be activated by a local hardware switch: • (a) The BLM will be moved with the segment to keep the active BLM area at a fixed relation to the magnet blocks. • (b) The BLM will stay centered on the beam axis to allow radiation level estimates in roll-out position. 12

13. BLM Purpose • The BLM will be used for two purposes • A: Inhibit bunches following an “above-threshold” radiation event. • B: Keep track of the accumulated exposure of the magnets in each undulator. • Purpose A is of highest priority. It will be integrated into the Machine Protection System (MPS) and requires only limited dynamic range from the detectors. • Purpose B is desirable for understanding long-term magnet damage in combination with the undulator exchange program but requires a large dynamic range for the radiation detectors (order 106) and much more sophisticated diagnostics hard and software. 13

14. Additional Loss Monitors • Other Radiation Monitoring Devices • Dosimeters • Located at each undulator. Routinely replaced and evaluated. • Segmented Long Ion Chambers • Investigated • (Quartz)-Fibers • Investigated • Non-Radiative Loss Detectors • Pair of Charge Monitors (Toroids) • One upstream and one downstream of the undulator line • Used in comparator arrangement to detect losses of a few percent • Electron Beam Position Monitors (BPMs) • Continuously calculate trajectory and detect out-of-range situations • Quadrupole Positions and Corrector Power Supply Readbacks • Use deviation from setpoints • Estimate accumulated kicks to backup calculations based on BPMs. 14

15. Other Considerations • Vacuum System • The BLM will not be part of the LCLS Undulator vacuum system. • Alignment • The active volume of each BLM needs only rough alignment to cover the downstream magnet blocks in all roll-in/out locations. 15

16. Other Radiation Monitoring Devices In addition to the BLMs, the use of • TLD monitor • segmented Long Ion Chambers(segmented LIONs), and • Fibers shall be investigated. 16

17. Charge to the Committee • The LCLS ANL and SLAC BLM support groups have developed a Beam Loss Monitor System to support purpose A, i.e., protect the undulator magnets from above-threshold radiation events. • The committee is charged with determining that the Beam Loss Monitor System is ready to enter the final design stage. • The committee is asked to evaluate the following: • Is the Beam Loss Monitor System sufficient for the operational needs of the Undulator System? • Have safety hazards been appropriately identified and mitigated? • Is the interface to the rest of the Undulator system understood and controlled? Are interfaces to other neighboring systems understood and controlled? • Is there a plan in place for assembly, checkout, startup, commissioning, and maintenance? • Are the budget and schedule for fabrication, installation and commissioning of the BLM complete and adequate? • The committee is asked to report on its findings in a written report within a reasonable time following the review. All suggestions and comments are welcome. 17

18. End of Presentation 18