LCLS Magnet Damage Management Heinz-Dieter Nuhn, SLAC / LCLS June 19, 2008

1June 19, 2008 Heinz-Dieter Nuhn, SLAC / LCLSLCLS Magnet Damage Management [email protected]

LCLS Magnet Damage ManagementHeinz-Dieter Nuhn, SLAC / LCLS

June 19, 2008

Present Strategies for LCLS Beam Loss Monitoring Review of the Individual Magnet Irradiation Test T-493 Results of Damage Measurements Plans for follow-up Mini-Undulator Irradiation Test

Present Strategies for LCLS Beam Loss Monitoring Review of the Individual Magnet Irradiation Test T-493 Results of Damage Measurements Plans for follow-up Mini-Undulator Irradiation Test


LCLS Beam Loss Monitors (BLMs) Strategies

Radiation protection of the permanent magnet blocks is very important.

Funds have been limited and efforts needed to be focused to minimize costs.

A Physics Requirement Document, PRD 1.4-005 exists, defining the minimum requirements for the Beam Loss Monitors.

The damage estimates are based on published measurement results and a in-house simulations.

Radiation protection of the permanent magnet blocks is very important.

Funds have been limited and efforts needed to be focused to minimize costs.

A Physics Requirement Document, PRD 1.4-005 exists, defining the minimum requirements for the Beam Loss Monitors.

The damage estimates are based on published measurement results and a in-house simulations.


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 exposure to a fast-neutron fluence of 1011 n/cm2.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.

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 exposure to a fast-neutron fluence of 1011 n/cm2.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.


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 simulations predict 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.

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 simulations predict 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.


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-

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-


Total Dose from LCLS e- Beam on C Foil

Corresponding maximum deposited dose.

Maximum Level is

1.0×10-9 rad/e-

Corresponding maximum deposited dose.

Maximum Level is

1.0×10-9 rad/e-


Radiation Limit Estimates

Neutron Fluence for 0.01 % magnet damage from Alderman et al. 1011 n/cm2

Maximum neutron fluence in LCLS magnets from hit on 100 micron C foil from Fasso 1.8×10-4 n/cm2/e-

Maximum total dose in LCLS magnets from hit on 100 micron C foil from Fasso 1.0×10-9 rad/e-

Ratio of neutron fluence per total dose 1.8×105 n/cm2/rad

Maximum total dose in LCLS magnets for 0.01 % damage 5.5×105 rad

Nominal LCLS lifetime 20 years

Number of seconds in 20 years 6.3×108 s

Maximum average permissible energy deposit per magnet 0.88 mrad/s

Corresponding per pulse dose limit during 120 Hz operation 7.3 µrad/pulse

~0.01 mrad/pulse @ 120 Hz; ~1 mrad/s


Neutral; K=3.4881; x= 0.0 mm Neutral; K=3.4881; x= 0.0 mmNeutral; K=3.4881; x= 0.0 mm

Undulator Roll-Away and K Adjustment Function

First; K=3.5000; x=-4.0 mm Roll-Out; K=0.0000; x=+80.0 mm

Horizontal SlideHorizontal Slide

Pole Center LinePole Center Line Vacuum ChamberVacuum Chamber


Maximum Estimated Radiation Dose from BFW Operation

Maximum neutron fluence in magnets of the last undulator due to BFW hit;

based on Fasso simulations; scaled to

Total Charge: 1 nC; Wire Material: C; Wire Diameter 40 µm; RMS Beam radius 37 µm;

1.5×105 n/cm2/pulse

Corresponding radiation dose 1 rad/pulse

Ratio of peak BFW dose to maximum average dose limit 105

Radiation dose received by last undulator by 33 full x and y scans 100 rad

Maximum number of full BFW scans to reach 20 % a maximum dose budget 103

All

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Maximum neutron fluence in magnets of an undulator on same girder due to BFW hit;

based on Fasso simulations; scaled to

Total Charge: 1 nC; Wire Material: C; Wire Diameter 40 µm; RMS Beam radius 37 µm;

1.5×103 n/cm2/pulse

Corresponding radiation dose 10 mrad/pulse

Ratio of peak BFW dose to maximum average dose limit 103

Radiation dose received by last undulator by 33 full x and y scans 1 rad

Maximum number of full BFW scans to reach 20 % a maximum dose budget 105

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The small amount of scans expected, can be ignored for damage purposes; but might require MPS exception.


Radiation Sources

Possible reasons for generating elevated levels of radiation areElectron 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 operationIs 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 insertionMay only be allowable when all undulators are rolled-out and beam charge is reduced to minimum.

Background Radiation from Upstream Sources including Tune-Up DumpExpected to be sufficiently suppressed by PCMUON collimator.

Beam HaloExpected to be sufficiently suppressed through upstream collimation system.May require halo detection system.


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.

NOT FULLY REALIZED


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.

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.

NOT FULLY REALIZED


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 blocksTwo 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.

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 blocksTwo 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.

NOT FULLY REALIZED


BLM Purpose

The BLM will be used for two purposesA: 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.

The BLM will be used for two purposesA: 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.


ANL Beam Loss Monitor Design

Courtesy of W. Berg, ANLCourtesy of W. Berg, ANL

Rendering of DetectorRendering of Detector

BLM Mounted on BFW in Front of Undulator SegmentBLM Mounted on BFW in Front of Undulator Segment

Beam

A total of 5 BLM deviceswill be installed.


Plan View of Short Drift

Beam Loss MonitorBeam Loss Monitor

Undulators SegmentsUndulators Segments

QuadrupoleQuadrupole

BPMBPM

BFWBFW

Beam Direction


Additional Loss Monitors

Other Radiation Monitoring DevicesDosimeters

Located at each undulator. Routinely replaced and evaluated.

Segmented Long Ion ChambersInvestigated

(Quartz)-FibersInvestigated

Non-Radiative Loss DetectorsPair of Charge Monitors (Toroids)

One upstream and one downstream of the undulator lineUsed 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 ReadbacksUse deviation from setpointsEstimate accumulated kicks to backup calculations based on BPMs.


LCLS Undulator Irradiation Experiment (T-493)

The LCLS electron beam is stopped in a copper dump, and 9 samples of magnet material are positioned at different distances from the dump.

The layout to achieve a range of doses is calculated using FLUKA.

The radiation absorbed will be measured by dosimeters.

Magnetization will be measured before and after exposure.

The integrated beam current will be needed to be recorded to 10%.

The LCLS electron beam is stopped in a copper dump, and 9 samples of magnet material are positioned at different distances from the dump.

The layout to achieve a range of doses is calculated using FLUKA.

The radiation absorbed will be measured by dosimeters.

Magnetization will be measured before and after exposure.

The integrated beam current will be needed to be recorded to 10%.


Linac Coherent Light Source

Near Hall

Far Hall

SLAC LINAC

Undulator Tunnel

Injector

Endstation A

T-493T-493


T-493 Components installed

ESA Beamline with copper cylinder and magnet blocks.

Copper target for 13.7 GeV e- Beam.

Diameter: 4 inches

Length: 10 inches

Dosimeters positioned at in the vicinity of each block.

[See presentation by Johannes Bauer]

ESA Beamline with copper cylinder and magnet blocks.

Copper target for 13.7 GeV e- Beam.

Diameter: 4 inches

Length: 10 inches

Dosimeters positioned at in the vicinity of each block.

[See presentation by Johannes Bauer]

Photo courtesy of J. BauerPhoto courtesy of J. Bauer

BEAM


Magnet Block Assembly

Straight-ahead mounting fixture on work bench with four magnet blocks (viewed in the direction of the beam.)

Straight-ahead mounting fixture on work bench with four magnet blocks (viewed in the direction of the beam.)


Mounted Magnet Block Next to Heat Shield

Magnet block mounted next to heat shield.Magnet block mounted next to heat shield.Mounting fixture with magnet for first forward position with heat shield.

Mounting fixture with magnet for first forward position with heat shield.


ANL Delivery of 12 LCLS Undulator Magnet Blocks

Photo courtesy of S. AndersonPhoto courtesy of S. Anderson

Material: Ne2Fe14B

Block Thickness: 9 mm

Block Height: 56.5 mm

Block Width: 66 mm

Material Density: 7.4 g/cm3

Block Volume: 33.6 cm3

Block Mass: 248.4 g

Curie Point: 310 °C

Material: Ne2Fe14B

Block Thickness: 9 mm

Block Height: 56.5 mm

Block Width: 66 mm

Material Density: 7.4 g/cm3

Block Volume: 33.6 cm3

Block Mass: 248.4 g

Curie Point: 310 °C


Pre-Irradiation Magnetic Moment Measurements

The table shows the results of the measurement of magnetic moments for one of the magnet blocks (Serial No. 00659) as an example.

The Magnetic Moments are measured with a Helmholtz-Coil.

All magnetic measurements have been carried out by Scott Anderson.

The table shows the results of the measurement of magnetic moments for one of the magnet blocks (Serial No. 00659) as an example.

The Magnetic Moments are measured with a Helmholtz-Coil.

All magnetic measurements have been carried out by Scott Anderson.


Magnet Block Assembly (Top View)

Beam Direction

Copper Cylinder

Magnet Blocks

rz

Top View

Heat Shield

4 Magnet blocks in forward direction5 Magnet blocks in transverse direction

3 Magnet blocks kept for reference

M4M3M2M1

M8

M5

M6

M7

M9


Magnet Block Assembly (View in Beam Directions)

yr

View in Beam Direction

Heat Shield

Copper Cylinder

Magnet Blocks

M1-M4M7M8 M6M9

M5


Experiment T-493 Shift Records

Magnet Irradiation Experiment T-493 ran for 38 shifts from7/27-8/09/2007

Magnet Irradiation Experiment T-493 ran for 38 shifts from7/27-8/09/2007


Delivered Power

Delivered power levels alternated between about 125 W during Day and Swing Shifts and 185 W during Owl Shifts.During Day and Swing Shifts the experiment ran parasitically with LCLS commissioning.

Delivered power levels alternated between about 125 W during Day and Swing Shifts and 185 W during Owl Shifts.During Day and Swing Shifts the experiment ran parasitically with LCLS commissioning.


Tunnel Temperature Profile

The temperature in the ESA tunnel stayed between 23-24.6°C during the entire 12-day data collection period.The plot shows diurnal cycle fluctuations.

The temperature in the ESA tunnel stayed between 23-24.6°C during the entire 12-day data collection period.The plot shows diurnal cycle fluctuations.


Magnetic Moment Evaluations: Results Summary

Shown are parameters for the 9 irradiated magnets and the Cu targetthe estimated neutron fluence and dose levelspeak power levelstemperature estimates

The last two columns contain the results of the magnets’ demagnetization measurements.

Shown are parameters for the 9 irradiated magnets and the Cu targetthe estimated neutron fluence and dose levelspeak power levelstemperature estimates

The last two columns contain the results of the magnets’ demagnetization measurements.


Detailed FLUKA model of the experiment

13.7 GeV electron beam impinging on the copper dump

Computation of total dose, electromagnetic dose, neutron energy spectra

Quantity scored using a binning identical to the one used for the mapping of the magnetization loss

BeamM3 M2

M5

M4

M6M7

M1

M8M9

Courtesy of J. Vollaire, SLAC Courtesy of J. Vollaire, SLAC


Damage Gradients

M3

M1

M2

M4 M3

M1

M2

M4

Threshold Estimates for 0.01 % Damage

Source Deposited Energy Dose Dose Neutron Fluence

T-493 0.17 kJ 0.70 kGy 0.070 MRad 0.64×1011 n/cm2

TTF-2 (Lars Fröhlich) 0.5 kGy 0.05 MRad

Previous Estimate 1.4 kJ 5.5 kGy 0.55 MRad 1×1011 n/cm2

FLUKA Simulations by J. Vollaire, SLAC


Additional Evaluation: Field Map Measurements

Grid Size: 26 x 31 Points = 806 Points; Point Spacing: 2 mm; Method: Hall Probe

Reference Magnet SN16673


Field Map Measurements for M1

Absolute Magnetic Field Amplitudes [T]

Reference Magnet Fields subtracted [T]


Example of Dose Mapping for the Four Downstream Samples


Fluence [cm-2] Total Dose [J cm-3]


Dose Profile versus Magnetization Loss Profile



Next Experiments

T-493 was a measurement of the demagnetization of stand-alone magnets with no significant demagnetizing fields present.Inside an undulator, the magnet blocks will be tightly packaged next to one another and magnet blocks might experience the magnetic fields of the neighboring magnets.This scenario will be covered by the “Mini – Undulator Irradiation Test”.Ben Poling, SLAC, has designed and built a Mini-Undulator from spare LCLS Undulator magnet and pole pieces. A second Mini-Undulator (for reference) will be built before the first irradiation run.The magnetization of individual magnet pieces as well as the on-axis magnetic field of the assembled Mini-Undulators will be measured before and after the irradiation processes. Irradiation will be done similar to T-493: A radiation field will be generated by the LCLS electron beam hitting a copper target in ESA.This time, irradiation will be done in phases.


Courtesy of B. Poling, SLACCourtesy of B. Poling, SLAC

Mini-Undulator Design by Ben Poling


Mini-Undulator Design by Ben Poling

Courtesy of B. Poling, SLACCourtesy of B. Poling, SLAC

Made from spare LCLS undulator magnet blocks (2 x 2 x 3) and pole pieces (2 x 2 x 5).

Total number of periods: 3.

Gap height and period length identical to LCLS undulator.

Made from spare LCLS undulator magnet blocks (2 x 2 x 3) and pole pieces (2 x 2 x 5).

Total number of periods: 3.

Gap height and period length identical to LCLS undulator.


Schedule for Test Sequence

Friday, May 16, 2008 20:00- Monday, May 19, 2008 07:00 First irradiation run.

Thursday, June 19, 2008 Irradiation Collaboration Meeting

Friday, June 27, 2008 20:00- Monday, June 30, 2008 07:00 Second irradiation run.

Friday, July 11, 2008 20:00- Monday, July 14, 2008 07:00 Third irradiation run.

Friday, August 1, 2008 20:00- Monday, August 4, 2008 07:00 Fourth irradiation run.

May 2008May 2008Sun Mon Tue Wed Thu Fri Sat

27 28 29 30 1 2 3

4 5 6 7 8 9 10

11 12 13 14 15 16 17

18 19 20 21 22 23 24

25 26 27 28 29 30 31

1 2 3 4 5 6 7

June 2008June 2008Sun Mon Tue Wed Thu Fri Sat

25 26 27 28 29 30 31

1 2 3 4 5 6 7

8 9 10 11 12 13 14

15 16 17 18 19 20 21

22 23 24 25 26 27 28

29 30 1 2 3 4 5

July 2008July 2008Sun Mon Tue Wed Thu Fri Sat

29 30 1 2 3 4 5

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August 2008August 2008Sun Mon Tue Wed Thu Fri Sat

27 28 29 30 31 1 2

3 4 5 6 7 8 9

10 11 12 13 14 15 16

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31 1 2 3 4 5 6

MINI-UND RUN 1 MINI-UND RUN 2 MINI-UND RUN 4MINI-UND RUN 3

CANCELED


Summary

The plan for monitoring and protecting the LCLS undulators from radiation was presented.Irradiation test at SLAC have been carried out in August 2007:

Nine of the spare Nd2Fe14B permanent magnet pieces for the LCLS undulators have been exposed to radiation fields of various intensities under conditions that can be precisely calculated by FLUKA simulations.The total exposure time was 12.5 days during which a copper target was hit by the 13.7 GeV LCLS electron beam. The total energy of the 36.8x1015 electrons that hit the target was 80 MJ.After a cool-down period, the magnetization levels of the magnets have been measured and compared with the pre-irradiation values. The difference is being compared to the (FLUKA) estimated radiation levels received.In addition, Mini-Undulators (3 periods, each) have been prepared for testing. The magnetic moments of each of the magnets as well as the on-axis magnetic fields after assembly will be measured and recorded. The plan is to irradiate one of them in up to four periods.The present plan to do the irradiation before the August shutdown will probably not work out.


End of Presentation

LCLS Magnet Damage Management Heinz-Dieter Nuhn, SLAC / LCLS June 19, 2008

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Transcript of LCLS Magnet Damage Management Heinz-Dieter Nuhn, SLAC / LCLS June 19, 2008