1. DEVELOPMENT OF A BEAM LOSS DETECTION SYSTEM FOR THE CLIC TEST FACILITY 3 T. Lefevre Beam loss monitors for the CLIC Test Facility 3 Preliminary study done in 2003 Geant3 simulations First experimental data Conclusions & Perspectives BIW 2004, 5 May 2004 T. Lefevre, M. Velasco, M. Wood, Northwestern University H. Braun, R. Corsini, M. Gasior, F. Tecker, CERN

2. T. LefevreBIW 2004, 5 May 2004 CLIC Test Facility 3 The CLIC Test Facility 3 is built to demonstrate the Compact LInear Collider feasibility The CLIC Test Facility 3 is built to demonstrate the Compact LInear Collider feasibility - Drive Beam Generation : - Efficient way of producing a high current (35A) high frequency (15GHz) 150MeV and 1.6  s electron beam - Done using a fully loaded linear accelerator (94% RF to beam efficiency) and two rings - Drive Beam Deceleration stability (two beam acceleration section) - The beam is strongly decelerated in order to provide the 30GHz RF source - Study the Beam halo & Beam loss mechanisms - Provide a 30GHz power source to continue the R&D program on high gradient accelerating structures (150MV/m) - Housed in the LEP injector complex and scheduled for completion before 2010. - The construction of the linac will be finished by the end of the year

3. BLM for CTF3 Linac T. Lefevre Northwestern University joined the CTF3 collaboration in 2003 and we are designing and building the beam loss detection system for the CTF3 linac. BIW 2004, 5 May 2004 The operation of a fully loaded linear accelerator Heavy beam loading in accelerating structures  Transient effects where the energy gain per cavity for the beam head can be twice higher than its nominal steady state value Beam transient compensation scheme by adjusting the delay between the beam and the RF signal in the cavities We designed our system to observe the beam transient loss Dangerous beam losses : > 10% of the total beam charge (6  C) The protection system will rely on wall current monitor The BLM system will be a tool for the optimization of the Linac operation

4. T. Lefevre Beam position monitor Accelerating structure Quadrupoles e-e- Beam loss detectors Fast time response (ns-10ns) for beam transient study Segmented X-Y beam loss positioning for tuning Y z x Typical Linac section Design beam optics High probability that beam loss occurs in the quadrupole region BIW 2004, 5 May 2004 Goal : To install the BLM at a position where the beam transient would be lost BLM for CTF3 Linac

5. T. Lefevre Beam pipe simulations : Transverse distribution of the e - /e + shower Geant3 Simulations 100MeV The total flux of electrons in the shower is proportional to the electron energy With higher beam energies, the shower asymmetry is more pronounced BIW 2004, 5 May 2004 Simulations based on a beam loss corresponding to the ‰ of the nominal beam current e-e- Position of observation : 1m dowstream Beam loss at + Y

6. T. Lefevre Beam loss in the Central quadrupole Geant3 Simulations BIW 2004, 5 May 2004 Beam loss Positions of observation e-e- Screening effect of the 3 rd quadrupole which reverses the transverse distribution of the e - /e + Shower Z=25cmZ=75cm Z=120cmZ=155cm

7. T. Lefevre done by Matthew Wood Positions of the beam loss e - shower efficiency e - shower efficiency : Number of particles detected / Number of particles lost Geant3 Simulations BIW 2004, 5 May 2004 e-e- BLM’s (size and position) 35MeV, 0mm beam size, 3mrad beam angle Beam loss at + Y Ø40mm detector installed at 15cm from the beam axis Simulations The shower transverse distribution is affected by the presence of Quadrupoles For losses on the beam pipe the asymmetry corresponds to 50% Beam loss position  more than 2 orders of magnitude difference in the shower efficiency For losses > 1‰ of beam current  Detector must be able to measure currents > 100nA + Y +/- X - Y

8. T. Lefevre Test on CTF3 in 2003 Using the collimator in the cleaning chicane to study the beam transient BIW 2004, 5 May 2004 Collimator BPM 502 BPM 690 Accelerating structures BPM 402 Quadrupoles e - Beam line layout Dipoles Injector Two Aluminum Cathode Electron Multipliers Ø40mm, Sensitivity range [100nA-100mA] Beam loss monitors Cleaning chicane Steerers First Linac Section

9. T. Lefevre Observation of the beam transient loss Chicane & Collimator Case 1 : Slit opened < 80MeV 35MeV 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 BIW 2004, 5 May 2004 Case 2 : Slit Closed < 35MeV 20MeV 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

10. T. Lefevre Slit closed : Horizontal and Vertical scans BLM Left BLM Right e - Beam goes to the Left Beam goes to the Right Beam goes Down Beam goes Up In vertical scans the beam loss is equally distributed on the two detectors and their output signals are equivalent (<5% difference) In horizontal scans the BLM output signals are different in a ratio of 2 (40-60%) Localizing the beam loss transversely ? BIW 2004, 5 May 2004

11. Geant3 expectations T. Lefevre 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 BIW 2004, 5 May 2004

12. T. Lefevre Vertical scan with the slit opened Close to the detector Detector  3 rd Quad  3 rd Quad 3 rd  2 nd Quad 35 < E < 80MeV E = 35MeV 1.Using BPM data’s to estimate the beam current lost in a linac section 2.Using the BLM measurement to estimate the Z position of the beam loss BIW 2004, 5 May 2004

13. T. LefevreConclusions Beam loss transverse positioning works in agreement with the Geant3 predictions During this test, the beam losses were relatively high (beam transient ~ 1A) and they were located near the quad’s region (which was consistent with the design lattice) Using the BPM’s data & the energy measurements, the BLM system can be used to localize the losses along the accelerator accurately (< 50cm) Without the BPM data, one system per section is not enough to monitor beam loss intensity & position (more complicated for beam losses distributed along the linac) How can we be quantitative : I & Z ? Adding detectors every 50cm to get the Z beam loss position: Longitudinal positioning using a Cherenkov fiber and a time of flight measurement (already developed at SLAC and TTF) BIW 2004, 5 May 2004

14. T. LefevrePerspectives BIW 2004, 5 May 2004 The system to be installed in the next months : The detectors are developed at Northwestern University (M. Velasco and A. Dabrowski) in conjunction with Fermilab (G. Tassotto) 12 sets of 4 detectors (SEM/SIC) located near the quadrupoles region Special set-up to study the losses one a single linac section using 12 detectors The signals are then amplified and acquired using 100MHz ADC’s 1mm gap chamber Can be operated with gas (ionization) or vacuum (SEM) Radiation hard

15. T. Lefevre CTF3 little shop of horrors BIW 2004, 5 May 2004 Damage on a Vacuum valve Spectrometer line

16. Respect the steering limitation T. Lefevre Suggestion ! BIW 2004, 5 May 2004

17. The CLIC Test Facility 3 T. Lefevre Drive Beam generation : Efficient way of producing a 35A beam bunched at 15GHz Acceleration of a high current beam in a 3GHz fully loaded Linac (95% RF to beam efficiency) Production of a high frequency (15GHz) bunched beam using a delay loop and a combiner ring CLEX : CLic EXperimental area: Provide a 30GHz power source for the development of high gradient (150MV/m) accelerating structures Test the Drive beam stability in the Drive Beam Decelerator (beam loss rate) Housed in the LEP Pre-injector complex Scheduled for completion before 2010 BIW 2004, 5 May 2004

18. 30 GHz Power Source and distribution line 3TeV Compact LInear Collider T. Lefevre e - Main Linace + Main Linac BDS Damping rings 4ps, >10  m e - /e + Source 42ns, 2,424GeV 157 bunches (400pC) 4ps, >50  m Main Linac 9  1500GeV 100fs, >1  m Combiner Ring 1 Delay loop Combiner Ring 2 Source 25 Drive Beams Decelerators per linac 1.79GeV, 144A over 56ns 1ps, >50  m Drive Beam Generator 4.5A over 92  s with an final energy of 1.79GeV: 43000 bunches (9.6nC each) 10ps, >50  m BIW 2004, 5 May 2004

19. What have been achieved up to now CTF3 – Preliminary phase - 2002 Low-charge demonstration of electron pulse combination and bunch frequency multiplication by up to a factor 5 Streak camera image of the beam time structure evolution LEP injector EPA ring

20. Operation of a fully loaded linac T. Lefevre Drive beam acceleration in 2003 Beam current – BPM 402 4 A 1.5  s Beam current4 A Beam pulse length1.5  s 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 signals / output coupler of an accelerating cavity RF phase RF power Power to load (beam off) phase Power to load (beam on) ±4º 1.5  s Heavy beam loading in the accelerating structure Beam head sees a much higher accelerating field Strong transient effects so that in the first 50ns of the pulse the beam energy can be twice higher than the energy of the rest of the beam Beam transient compensation by adjusting the delaying the RF pulse in the accelerating structure to suppress the transient effect BIW 2004, 5 May 2004

21. BLM detectors T. Lefevre Two different types of detectors (ns time response) have been tested in parallel - A 4mm thick plastic scintillator (Ø40mm) coupled to XP2020 photomultiplier tube e - /e + Visible Photons 1.75% e-e- Photocathode 25% QE e - / e + : [1, 20]MeV  500 - 1000 photo-e -  & x rays : [10keV,20MeV]  4 - 100 photo-e - e - current amplification <10 6 - 10 7 HV Scintillator Signal x &  rays 50mV/50 Ω   A-pA - 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/50 Ω  100mA-100nA BIW 2004, 5 May 2004

22. For 1.5kV High voltage 20keV energy deposition  0.32±0.03  V 1mV  6.2±0.6MeV (≈ the calibration using radioactive sources) Calibration is done at ESRF using a 20keV X-ray beam BLM detectors : Calibration 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  A26.575.7177 ACEMScintillator + PMT T. LefevreBIW 2004, 5 May 2004

23. Lattice design in a linac section Example in the central Quad:  ≈ 10m  ≈ 100 .mm.mrad  ≈ 80 (40MeV)  ≈ 6mm Beam size Beam emittance Relativistic factor BPM 790 BPM 890 Quadrupoles Steerer Beam loss detectors T. LefevreBIW 2004, 5 May 2004

24. Beam optics reconstructed from experimental data T. Lefevre BLM’s High probability to have beam losses in the quadrupoles region BIW 2004, 5 May 2004

25. 35MeV, 0mm beam size T. Lefevre done by Matthew Wood Beam loss position  more than 2 orders of magnitude difference in the shower efficiency Can the longitudinal beam loss position be determined by the ‘angular shower shape’ ? 80MeV, 0mm beam size Positions of the beam loss Shower asymmetry as a function of the beam loss position Geant3 Simulations BIW 2004, 5 May 2004

26. T. Lefevre done by Matthew Wood Shower versus beam angle During this test we were using very small steering forces (I<1.5A) so that 5mrad can be considered as a maximum deviation angle Beam loss angle effects are small compared to the effect due to the beam loss position 35MeV Positions of the beam loss Geant3 Simulations BIW 2004, 5 May 2004

27. T. Lefevre done by Matthew Wood ~ e - / e + shower of 0.3nA, not seen by the ACEM with a 400volts bias Shower generated by the beam losses in the collimator Geant3 Simulations BIW 2004, 5 May 2004

28. T. Lefevre Example 1 : Observation of the beam transient loss Time – Energy correlation in the beam transient (Each slit aperture selected a given beam energy range between 35-70MeV) You normalize the BLM signals to the beam current loss seen by the BPM502 (≈ BPM690) ‘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 Low - - - - - - - - -  high energy BIW 2004, 5 May 2004