- Email: [email protected]
The H0 beam profile monitor at CELSIUS
Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
The H0 beam pro"le monitor at CELSIUS T. Bergmark!,*, P. Marciniewski", J. Zlomanczuk",# !The Svedberg Laboratory, Box 533, S-751 21 Uppsala, Sweden "Department of Radiation Sciences, Uppsala University, Sweden #Soltan Institute for Nuclear Studies, Warsaw, Poland
Abstract A beam pro"le monitor has been constructed for the observation of the H0 beam emitted from the electron cooler at CELSIUS. The monitor uses a silicon strip detector for position sensitive observation of stripped H0's. A description is given of the detector and the data acquisition system. The performance of the monitor and its use for electron cooling optimization are demonstrated by some recorded examples. ( 2000 Elsevier Science B.V. All rights reserved. PACS: 29.20.Dh; 29.27.-a Keywords: Electron cooling; Pro"le monitor
1. Introduction The CELSIUS ring is equipped with an electron cooler [1]. There are several purposes for the installation of this cooler. It is used for reduction of the transverse emittance during accumulation of ions in the ring. During an experiment it can be used for reduction of both longitudinal and transverse emittance and to counteract the ion beam heating due to interaction with the target or the rest gas of the ring. It may also help in accurate determination of the kinetic energy of the ions. Due to the character of the experimental program of the CELSIUS ring it is foreseen that hydrogen and deuterium ion beams will be commonly used. In these cases ions will be neutralized in the electron cooler and form a neutral beam that will not be bent in the magnetic * Corresponding author. Tel.: #46-18-4713885; fax: #4618-4713833. E-mail address: [email protected] (T. Bergmark)
"eld of the bending section following the electron cooler and eventually leave the ring through a provided exit window. Since the ion beam is immersed in a wider homogeneous electron beam, the pro"le of the neutral beam is the same as the pro"le of the ion beam. This pro"le in its turn depends on the optimization of the electron cooling, especially on the alignment of the electron and the ion beams in the drift tube of the cooler. Thus a measurement of the pro"le of the neutral beam can be used for optimization of the electron cooling and for transverse cooling time measurements. This report will describe the pro"le monitor, which has been built to serve these purposes in CELSIUS.
2. General description In Fig. 1 is shown a top view drawing of the electron cooler and the beginning of the following bending section. It can be seen that the vacuum
0168-9002/00/$ - see front matter ( 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 9 9 ) 0 1 1 1 1 - 0
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
71
Fig. 1. Drawing showing the position of the H0 pro"le monitor (1) straight after the electron cooler (2).
Fig. 2. Block diagram showing the main functional parts of the pro"le monitor.
chamber is extended in the straight direction after the electron cooler in the beginning of the bending section. At the end of this extension, outside the bending magnets, there is a stainless-steel window with a thickness of 0.05 mm. The neutral particles can penetrate this window while they are being ionized. Immediately behind the window and perpendicular to the beam is placed a charged particle
position sensitive detector, a silicon strip detector. Each strip signal from the detector is ampli"ed and discriminated as seen in Fig. 2. The outputs from the discriminators are fed to tapped delay lines for time coding of the position information. By means of a TDC, which is started by a prompt signal, the time coding is obtained in digital form. This information together with pulse-height information
SECTION II.
72
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
is sent to a PC in the CELSIUS control room. The PC can display horizontal and vertical pro"les and information about the time evolution of these pro"les. We have chosen time coding of the position instead of e.g. digital encoding in order to have a low number of cables between the front end ampli"ers and the data acquisition electronics which are separated by about 30 m. This choice also gave a simple connection to the standard CAMAC data acquisition units.
3. The silicon strip detector The silicon strip detector consists of a high resistivity silicon plate with a thickness of 485 lm. A plate area of 40]40 mm was evaluated to be adequate for our pro"le measurements. Since a position resolution of 1 mm is needed, the plate was made with 40 biasing and sensing metal strips with a pitch of 1 mm on each side. The angle between the strips on the di!erent sides is 903 and the plate is mounted in such a way that one will
obtain horizontal and vertical pro"les. A proton in the kinetic energy range of 250 keV to several GeV will deposit at least an energy of 190 keV in the detector. This deposited energy corresponds to a charge of 8 fC. The plate was made by Micron Semiconductor Ltd.. According to the manufacturer an absorbed dose of 1 G increases the detector leakage current by 1 nA/cm2. Assuming that a leakage current of 1 lA is the highest tolerable, one can estimate that the lifetime of the detector is about 103 d in a highintensity beam in CELSIUS. Thus it will be practical to keep the detector in the beam even when measurements are not being done. A photograph of the strip detector mounted in a housing together with electronic units is shown in Fig. 3.
4. Read-out electronics In order to get a convenient modularity for the read-out electronic units, the signals from the outermost four strips at each edge of the plate are
Fig. 3. Photograph showing the silicon strip detector mounted together with electronics.
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
73
Fig. 4. Schematic drawing of the preampli"ers and the discriminators.
Fig. 5. Schematic drawing of the delay lines, the trigger generations and the analog channels.
SECTION II.
74
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
paired to two signals thus reducing the position resolution at the edges by a factor of two. On each side odd strips are handled separately from even strips in order to facilitate the sorting out of the strip closest to the hit in cases where the deposited charge is shared between two neighboring strips as seen in Fig. 2. Figs. 4 and 5 show schematic drawings of the preampli"ers, discriminators and time coding electronics. The delay between the taps in the delay lines TZB66-5 is 10$0.5 ns. The total output voltage
Fig. 6. Correlation between pulse amplitudes measured by the odd and the even strips.
noise from the detector and preampli"er is measured to be 5 mV. This corresponds to an input charge noise of 1.3 fC giving a satisfactory large margin to the charges deposited by the particles (58 fC).
5. Data acquisition The principle for the data acquisition has already been shown in Fig. 2. We use standard CAMAC modules for the time-to-digital and analog-todigital conversions (LeCroy 2228A and 2249A, respectively). A special CAMAC parallel output register is used for the transfer of data to the PC ISA-bus. The CAMAC crate controller communicates with the PC via an RS 232 type of serial link. In the PC the pulse-height information is used to determine whether an odd or an even strip was closest to the hit. This is explained in Fig. 6, which shows the correlation between the pulse amplitudes measured by the odd and the even strips. There are three groups of events. Groups E and O correspond to events when one of the even strips (group E) or one of the odd strips (group O) has been hit. Group P corresponds to pedestal values. The slope seen in the A and the O groups shows the magnitude of cross-talk between the even and the odd strips. Events belonging to group P are discarded and then it is straightforward to decide which strip was hit.
Fig. 7. An example of a display of pro"les during cooling of 48 MeV protons.
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
The PC can display horizontal and vertical pro"les at chosen time intervals and/or the time evolution of the FWHM of these pro"les during an accelerator cycle. An example is shown in Fig. 7. The obtained pro"le widths should be multiplied with 0.7 in order to get the ion beam widths in the electron cooler. When the pro"le monitor is used for alignment of the cooler electron beam with
75
the circulating ion beam the resolution is about 0.1 mrad.
Reference [1] M. Sedlacek et al., Workshop on Beam Cooling and related Topics, Montreux, October 4}8 1993, CERN 94}03, p. 235.
SECTION II.
The H0 beam pro"le monitor at CELSIUS T. Bergmark!,*, P. Marciniewski", J. Zlomanczuk",# !The Svedberg Laboratory, Box 533, S-751 21 Uppsala, Sweden "Department of Radiation Sciences, Uppsala University, Sweden #Soltan Institute for Nuclear Studies, Warsaw, Poland
Abstract A beam pro"le monitor has been constructed for the observation of the H0 beam emitted from the electron cooler at CELSIUS. The monitor uses a silicon strip detector for position sensitive observation of stripped H0's. A description is given of the detector and the data acquisition system. The performance of the monitor and its use for electron cooling optimization are demonstrated by some recorded examples. ( 2000 Elsevier Science B.V. All rights reserved. PACS: 29.20.Dh; 29.27.-a Keywords: Electron cooling; Pro"le monitor
1. Introduction The CELSIUS ring is equipped with an electron cooler [1]. There are several purposes for the installation of this cooler. It is used for reduction of the transverse emittance during accumulation of ions in the ring. During an experiment it can be used for reduction of both longitudinal and transverse emittance and to counteract the ion beam heating due to interaction with the target or the rest gas of the ring. It may also help in accurate determination of the kinetic energy of the ions. Due to the character of the experimental program of the CELSIUS ring it is foreseen that hydrogen and deuterium ion beams will be commonly used. In these cases ions will be neutralized in the electron cooler and form a neutral beam that will not be bent in the magnetic * Corresponding author. Tel.: #46-18-4713885; fax: #4618-4713833. E-mail address: [email protected] (T. Bergmark)
"eld of the bending section following the electron cooler and eventually leave the ring through a provided exit window. Since the ion beam is immersed in a wider homogeneous electron beam, the pro"le of the neutral beam is the same as the pro"le of the ion beam. This pro"le in its turn depends on the optimization of the electron cooling, especially on the alignment of the electron and the ion beams in the drift tube of the cooler. Thus a measurement of the pro"le of the neutral beam can be used for optimization of the electron cooling and for transverse cooling time measurements. This report will describe the pro"le monitor, which has been built to serve these purposes in CELSIUS.
2. General description In Fig. 1 is shown a top view drawing of the electron cooler and the beginning of the following bending section. It can be seen that the vacuum
0168-9002/00/$ - see front matter ( 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 9 9 ) 0 1 1 1 1 - 0
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
71
Fig. 1. Drawing showing the position of the H0 pro"le monitor (1) straight after the electron cooler (2).
Fig. 2. Block diagram showing the main functional parts of the pro"le monitor.
chamber is extended in the straight direction after the electron cooler in the beginning of the bending section. At the end of this extension, outside the bending magnets, there is a stainless-steel window with a thickness of 0.05 mm. The neutral particles can penetrate this window while they are being ionized. Immediately behind the window and perpendicular to the beam is placed a charged particle
position sensitive detector, a silicon strip detector. Each strip signal from the detector is ampli"ed and discriminated as seen in Fig. 2. The outputs from the discriminators are fed to tapped delay lines for time coding of the position information. By means of a TDC, which is started by a prompt signal, the time coding is obtained in digital form. This information together with pulse-height information
SECTION II.
72
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
is sent to a PC in the CELSIUS control room. The PC can display horizontal and vertical pro"les and information about the time evolution of these pro"les. We have chosen time coding of the position instead of e.g. digital encoding in order to have a low number of cables between the front end ampli"ers and the data acquisition electronics which are separated by about 30 m. This choice also gave a simple connection to the standard CAMAC data acquisition units.
3. The silicon strip detector The silicon strip detector consists of a high resistivity silicon plate with a thickness of 485 lm. A plate area of 40]40 mm was evaluated to be adequate for our pro"le measurements. Since a position resolution of 1 mm is needed, the plate was made with 40 biasing and sensing metal strips with a pitch of 1 mm on each side. The angle between the strips on the di!erent sides is 903 and the plate is mounted in such a way that one will
obtain horizontal and vertical pro"les. A proton in the kinetic energy range of 250 keV to several GeV will deposit at least an energy of 190 keV in the detector. This deposited energy corresponds to a charge of 8 fC. The plate was made by Micron Semiconductor Ltd.. According to the manufacturer an absorbed dose of 1 G increases the detector leakage current by 1 nA/cm2. Assuming that a leakage current of 1 lA is the highest tolerable, one can estimate that the lifetime of the detector is about 103 d in a highintensity beam in CELSIUS. Thus it will be practical to keep the detector in the beam even when measurements are not being done. A photograph of the strip detector mounted in a housing together with electronic units is shown in Fig. 3.
4. Read-out electronics In order to get a convenient modularity for the read-out electronic units, the signals from the outermost four strips at each edge of the plate are
Fig. 3. Photograph showing the silicon strip detector mounted together with electronics.
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
73
Fig. 4. Schematic drawing of the preampli"ers and the discriminators.
Fig. 5. Schematic drawing of the delay lines, the trigger generations and the analog channels.
SECTION II.
74
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
paired to two signals thus reducing the position resolution at the edges by a factor of two. On each side odd strips are handled separately from even strips in order to facilitate the sorting out of the strip closest to the hit in cases where the deposited charge is shared between two neighboring strips as seen in Fig. 2. Figs. 4 and 5 show schematic drawings of the preampli"ers, discriminators and time coding electronics. The delay between the taps in the delay lines TZB66-5 is 10$0.5 ns. The total output voltage
Fig. 6. Correlation between pulse amplitudes measured by the odd and the even strips.
noise from the detector and preampli"er is measured to be 5 mV. This corresponds to an input charge noise of 1.3 fC giving a satisfactory large margin to the charges deposited by the particles (58 fC).
5. Data acquisition The principle for the data acquisition has already been shown in Fig. 2. We use standard CAMAC modules for the time-to-digital and analog-todigital conversions (LeCroy 2228A and 2249A, respectively). A special CAMAC parallel output register is used for the transfer of data to the PC ISA-bus. The CAMAC crate controller communicates with the PC via an RS 232 type of serial link. In the PC the pulse-height information is used to determine whether an odd or an even strip was closest to the hit. This is explained in Fig. 6, which shows the correlation between the pulse amplitudes measured by the odd and the even strips. There are three groups of events. Groups E and O correspond to events when one of the even strips (group E) or one of the odd strips (group O) has been hit. Group P corresponds to pedestal values. The slope seen in the A and the O groups shows the magnitude of cross-talk between the even and the odd strips. Events belonging to group P are discarded and then it is straightforward to decide which strip was hit.
Fig. 7. An example of a display of pro"les during cooling of 48 MeV protons.
T. Bergmark et al. / Nuclear Instruments and Methods in Physics Research A 441 (2000) 70}75
The PC can display horizontal and vertical pro"les at chosen time intervals and/or the time evolution of the FWHM of these pro"les during an accelerator cycle. An example is shown in Fig. 7. The obtained pro"le widths should be multiplied with 0.7 in order to get the ion beam widths in the electron cooler. When the pro"le monitor is used for alignment of the cooler electron beam with
75
the circulating ion beam the resolution is about 0.1 mrad.
Reference [1] M. Sedlacek et al., Workshop on Beam Cooling and related Topics, Montreux, October 4}8 1993, CERN 94}03, p. 235.
SECTION II.