1. Beam current4 A Beam pulse length1.5 ms Power input/structure 35 MW Ohmic losses (beam on)1.6 MW RF power to load (beam on) 0.4 MW RF-to-beam efficiency ~ 94% Phase variation along pulse±4º RF phase Power to load (beam off) phase Power to load (beam on) ± 4º 1.5  s RF power

2. Beam position monitor Accelerating structures Quadrupoles e-e- Beam loss detectors Y z x Design beam optics

3. Simulations based on a beam loss corresponding to the ‰ of the nominal beam current e-e- Beam loss at + Y

5. (a)(b) (c)(d)

6. + Y +/- X - Y Positions of the beam loss e-e- ACEM’s

7. Collimator BPM 502 BPM 690 Accelerating structures BPM 402 Quadrupoles e - Dipoles Injector Cleaning chicane Steerers First Linac Section

8. - An Aluminum Cathode Electron Multiplier (ACEM) (Ø38mm) e - /e + x &  rays Aluminum cathode 100nm thick e - / e + : [1, 20]MeV  1 – 5 % SEM e -  & x rays : [10keV,20MeV]  4.10 -6 - 2.10 -9 SEM e - e - current amplification < 10 5 - 10 6 e-e- HV Signal 50mV/50Ω  100mA-100nA

9. Calibration using a very intense Cesium source (  - emitter: 53pA) High Voltage (V)500400300 ACEM current (pA)40145.8 Efficiency (%)752611 Output voltage on 50Ω (nV)20.70.3 Calibration : 1mV  xx  A 26.575.7177 ACEM

10. The slit is opened so that the full beam enters the next accelerating structure. The beam transient is then re-accelerated up to 80MeV and is lost somewhere because the beam optics are not adapted to its energy The slit is closed so that the beam transient is stopped in the collimator. The rest of the beam enters the next accelerating structure and is accelerated to 35MeV

11. (a)(b) (c) (d)

12. e - shower efficiency for different beam loss positions and energies Beam loss position1 st Quad2 nd Quad3 rd QuadPipe 0.9mPipe 0.3m Shower efficiency (%)5.25 10 -4 1.4 10 -3 9.3 10 -3 2.7 10 -2 0.2 35MeV, 3mrad, 0mm beam size 80MeV, 3mrad, 0mm beam size Beam loss position1 st Quad2 nd Quad3 rd QuadPipe 0.9mPipe 0.3m Shower efficiency (%)4.6 10 -3 8.9 10 -3 4.5 10 -2 9.9 10 -2 0.28

16. Damage on a Vacuum valve Spectrometer line

17. BLM’s

18. Shower versus beam angle Positions of the beam loss

19. ~ e - / e + shower of 0.3nA, not seen by the ACEM with a 400volts bias

20. ‘BLM signals depend on beam energy, position and current’ Possibility to estimate where the beam transient is lost The different energies are not lost at the same position Beam loss distributed between the detector and the 3 rd quadrupole