Summary of Tests of SIC and SEM as Beam Loss Devices at CTF3

Summary of Tests of SIC and SEM as Beam Loss Devices at CTF3 Anne Dabrowski Thibaut Lefevre October 29 2004

SIC as Ionization Chamber RAW signal (no amplifier or electronics – just cable to digitizer) Voltage Dependence on SICvisible: ~8 mV • average of 5 measurements at each voltage and constant beam loss • Signal other than ionization Dominant ~3 mV

Beam Loss Conditions based on Matthew’s simulation (CTF3_NOTE_061) Charged particles gammas Number of particles / 0.25 MeV Flux (1/cm2 s) 1012 10-2 10-3 1011 10-4 0 100 Radius (cm) 0 Energy 25MeV

Flux of photons ~ order of magnitude higher than e+e- for E < 5 MeV t, atomic photo-effect (electron ejection, photon absorption); Energy Distribution for a beam energy of 25 MeV at a distance of 100 cm Total photon cross section in lead, as a function of energy

Beam Loss: SIC Faraday Cup Girder 5 beam energy ~ 20 MeV Electronics: Amplification Factor: 20 or 200 Amplifier Saturates at ~1.6V. read over a 50 ohm resistor Currently operating at the lower gain or 20 SIC, Faraday cup

Sensitivity Girder 5, beam energy ~ 20 MeV 0.8 A of beam loss F-cup is saturated 0.25 A of beam loss Less than 0.025 A beam loss [between % and ‰]

Look for linearity between the Faraday cup and SIC within pulse On Girder 6, Beam Energy > 35 MeV Saturation of SIC not visible at ~ 40% of loss of beam current Faraday cup saturated but not visible from last bin of -1600 … would need to go to higher intensities to check saturation of SIC

Voltage Scan of Chambers at Girder 7 : SIC and SEM give same signal with the electronics (50ohm resistor to an amplifier) Estimate 1 mA/cm2 of current from the beam going through the chambers. This is a high beam loss region.

Z-mapping to localize losses Girder 6 Setup : 3 SIC’s 1Atm Middle of first cavity Middle of second cavity After the quadrupole

Nominal Beam Optics Just after the quadruple Middle of the first cavity Middle of the second cavity

Huge Loss in the 2nd Cavity Just after the quadruple Middle of the first cavity Middle of the second cavity

Conclusion • Negatives: • Since the SIC / SEM is sensitive to X-rays, and X-ray cross sections depend on energy, the device is difficult to calibrate ... • There are sources of X-rays in the machine not correlated to beam loss eg dark current in the cavities • To go to the ‰ level SIC lacks sensitivity (close to the noise), at least at the 20 – 30 MeV region. • Positives: • SIC, SEM and Faraday cup correlate to the beam loss in amplitude and pulse time. • SIC and SEM have same sensitivity since the dominant process is photo-electric effect, with fast response. • Can be used to give additional beam loss information, eq z position of the loss.

Future improvements • Shielding from noise to improve the actual system • Seal the shielding boxes • Question for the future ? • Detecting the ‰ of beam loss • Only sensitive to charged particles (calibration) :important to do reliable quantitative measurements • Fast time response : important for transient study (quantitative beam loss measurements) We need to work on a new detector : (Richardson ? ..)

Response of SIC 1 Torr vs SIC 1 Atm within the pulse SIC 1 Torr SIC 1 Atm SIC 1 Atm SIC 1 Torr

Summary of Tests of SIC and SEM as Beam Loss Devices at CTF3