- Email: [email protected]
Intensity and bunch profile measurement for ring-shaped electron bunch
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 573 (2007) 172–174 www.elsevier.com/locate/nima
Intensity and bunch profile measurement for ring-shaped electron bunch Anatoly Mal’tsev, Mikhail Mal’tsev, Marina Maslova Joliot-Curie 6, Dubna, Moscow reg., 141980 Russia Available online 20 November 2006
Abstract Methods for measuring the current and geometrical parameters and estimating the energy parameters of electron (or proton) bunches in ring accelerators using synchrotron radiation in the infrared region are reviewed, together with the information-measuring system designed to detect the synchrotron radiation and realize these methods. r 2006 Elsevier B.V. All rights reserved. Keywords: Infrared synchrotron radiation; Accelerator diagnostics; Methods and systems
1. Introduction In some physical experiments performed for the investigation of fast processes in the presence of strong electromagnetic and radiation noise, it is necessary to perform accurate measurements of intensity of thermal radiation and its profile. This problem arose at the JINR an investigation of the intensity of compressible ringshaped bunches of relativistic low-energy electrons with the aid of their synchrotron radiation, whose spectral range falls mainly in the infrared range. 2. Formulation of the problem The ring-shaped electron bunch generating the synchrotron radiation is similar to a thermal emitter whose temperature increases as the ring is compressed (i.e. as the average or equilibrium radius decreases and the electron energy E increases) and in the bunch. The radiation is of a pulsed character with the frequency ranging from 1 to 30 Hz. The linear size of the emitter can change from pulse to pulse in a range from 4 to 12 mm, and the radiated power W ranges from 6.2 103 to 1.8 103 W (this corresponds to Ne ¼ 1 108–3 1013 electrons per bunch. The size of the radiation beam depends on the energy of the electrons and the density n and angular distribution y of the charged particles in the Corresponding author. Tel.: +7 09621 64853; fax:+7 09621 65180.
E-mail address: [email protected] (A. Mal’tsev). 0168-9002/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2006.10.227
bunch. The diameter of the experimental radiation beam in the detector plane is 60 mm. The diagnostics problem was to measure the power of the thermal radiation on the surface of the detector in the range from 2.8 106 to 8.4 101 W/cm2 with a source temperature T ¼ 8 102–2.7 103 1C under conditions of pulsed electromagnetic and radiation noise of accelerator to within 20% and the spatial character of the radiation beam (its profile). 3. Measurement procedure To solve this problem, we developed a special method and to implement the method we created and checked in the physical experiment a noise-proofed informationmeasuring system. The method of measuring and investigating the intensity is based on comparing the integral radiation fluxes, registered in different regions of the spectral distribution of the radiation from the experimental source. The method consists of using two integral photodetectors, which are of different types and manifest the photoeffect differently, and their spectral sensitivity characteristics are different and they record radiation in the spectral range of wavelengths Dl/lb1. The same photodetectors also measure the geometry of the beam. One detector is oriented along the axis of the radiation beam and is stationary. The other detector is moved relative to the stationary detector along a straight line oriented perpendicular to the electron orbits. To measure the profile of the radiation source, an objective lens is inserted
ARTICLE IN PRESS A. Mal’tsev et al. / Nuclear Instruments and Methods in Physics Research A 573 (2007) 172–174
between the radiator and the detector. The lens focuses an image of the source on the flat plane of a sensitive surface of the detector, and the detector is moved relative to the image. This method for measuring the geometry of the radiation beam and the radiator has the drawback that it is impossible to obtain an instantaneous picture of the distribution in each accelerator cycle (duration 1 ms). 4. Measurement apparatus Its advantage is that it is simple and hence, reliable and cheap. On the basis of the conditions and requirements of the physical experiment and method of measurement, accurate photodetectors—photodiode and photoresistor— which operate at room temperature were chosen to convert the radiation power into an analog electron signal. This combination makes it possible to register the radiation flux in the spectral range 0.4–4.8 mm, which greatly exceeds the visible range. The channels are independent, and the radiation can be registered simultaneously in both channels (in the case of correlated measurements) or in each channel separately. A photodiode with a 3 mm in diameter sensitive surface is used in the channel with the photodetector. The photodiode is fabricated in a single case with a preamplifier by the integrated technology. The entire photodetection unit does not exceed 1 cm3 in size. Thanks to the small dimensions and the minimization of the electrical contours in the photodetector apparatus, the sensitivity of the apparatus to radiation fields and induction interferences, which makes it possible to work close to the radiation source under conditions of high electromagnetic and radiation noise. Such photodetectors in the case when the synchrotron radiation is registered have an advantage over the previously used photomultipliers. While the photomultipliers are more sensitive, which is not important for the level of synchrotron radiation present in the accelerator, the photodetector has a wider dynamical range and wide bandedness of the spectral characteristic (0.4–1.1 mm). The small dimensions of the photodetector, the insensitivity to external magnetic fields, and the low-power requirements (10 V, 2 mA) simplify the layout of the apparatus and make it convenient to work with. To suppress interference, which can arise in the cable connecting the input circuit with the output registering section, special attention is devoted to the arrangement and screening of the cable. The measured signal is additionally amplified in the registering section up to amplitudes 5 V, which is the maximum limit of the dynamic range of the following analog-to-digital converter (ADC). To eliminate the constant component from the input circuits, a transitional capacitor is inserted in front of the output amplifier, since the measured signal itself is a pulsed signal (duration 1 ms). The measurement channel with an uncooled photoresistor as a detector makes it possible to measure the instantaneous (within 1 106 s) infrared signal using its pulse conversion from the photodetector and introducing a
173
special device [1] for active suppression of interference in the measuring channel before registering in the ADC. The detector consists of two photoresistance with a 0.2 mm sensitive element, one of which is compensating and is covered from infrared radiation. Carefully selected photoresistances with parameters and characteristics that are as close as possible are secured on different sides of the same substrate, which is opaque to infrared radiation but does not screen electromagnetic and radiation fields. This structure of the detector and the use of a differential amplifier made it possible to employ a balanced extraction of the signal from the detector and to decrease substantially the level of in-phase interference on the output signal and drift at the output to the measuring channel. In addition, all input circuits were placed inside electrical screens, the conductors of the photoresistances on the differential inputs of the amplifier were made in the form of twisted pairs, and the amplifier itself was removed from the detector, located directly near the infrared source, at a distance of 2 m. The measured signal from the detectors is transmitted with the aid of a modulating pulse 4 ms from the control unit, triggered by an external triggering pulse. The duration of the modulation pulse was chosen to be equal to 4 ms taking into account the possibilities of the electronic circuits and in order to improve the temporal resolution. This operation can be performed either by pulsed powering of the photoresistors or by a special electronic circuit for commutating the signals from the detectors. From the output of the amplifier, the short measured pulse, whose amplitude is proportional to the instantaneous intensity of the infrared synchrotron radiation at the moment of measurement, is fed along a 50 m long cable into the output amplifier, covered by a wideband negative feedback delayed by 4 ms. This device effectively suppresses the drift of the entire amplifier as well as the interference signals in the range up to 10 kHz but it transmits without any distortions the measured signal with a duration of 4 ms. The moment at which the instantaneous synchrotron radiation is registered is fixed by a 1 106 s gating pulse at the end of the modulation pulse (when its transient process is over) from the control unit, which in turn is triggered by an external pulse. The unit makes it possible to control the delay time in triggering the entire measuring channel relative to the external triggering pulse, it forms the pulse modulating the signal from the detector, and feeds to the ADC, a gating pulse at the end of the modulation pulse. 5. Measurement results The method of measuring the intensity of the thermal radiation and the spatial distribution of the flux was employed and checked in physical experiments performed at the JINR according to a program for developing a collective have-ion accelerator with electron rings [2], on the electron synchrotron at the St. Petersburg Institute of Nuclear Physics in Gatchina [3], and in stand tests of
ARTICLE IN PRESS 174
A. Mal’tsev et al. / Nuclear Instruments and Methods in Physics Research A 573 (2007) 172–174
diagnostics apparatus and infrared optical systems. The radiation source, the ring-shaped electron bunch, had an equivalent temperature of 103 1C and the number of electrons in the bunch differed from one accelerator pulse to another. The measurements were performed in the range of radiation intensities 3 106–8 101 W/cm2. To ensure that the measuring system operates on the linear section of its sensitivity, a collection of calibrated neutral radiation attenuators and infrared objectives made of optical ceramics for focusing the radiation were used. The temperature range registered in different measurements is 30–2700 1C. The relative instrumental accuracy in the measurement of the intensity of the thermal radiation is equal to 0.2%. The absolute error depends on the calibration of the detectors and may not exceed 5%. 6. Conclusion The measuring system examined above exhibited high noise-resistance, stability, and reliability during long (several week) working sessions. The measurement results were read either according to a digital indicator from the ADC or with the results fed into a computer and printed out together with other registered parameters. Accurate photoresistors determined the possibility of registering with a high relative degree of accuracy of up to 0.2% at room temperature the visible and infrared synchrotron radiation under conditions with a high level of electromagnetic and radiation noise. The described method with modulation of
the measured signal can be used both for one-channel integral measurement of radiation and for multichannel system for registering geometric parameters of the object being observed. The measuring system was calibrated using a thermal standard source, and it was used to measure the absolute values of the current of the electron ring in a collective heavy-ion accelerator [2], and the dimensions of the synchrotron radiation beam were also determined. On account of their unique properties with respect to sensitivity, reliability, operating simplicity, noise-resistance, accuracy, and stability of the parameters, the meter could find application in physical experiments for investigating beams of relativistic charged particles (electrons and protons) in ring accelerators and accumulators—generators of synchrotron (edge) radiation, in linear accelerators for determining the intensity and transverse and longitudinal dimensions of the accelerated beam according to the temperature of the target, through which the beam passes, and in nuclear power plants for monitoring the temperature of units and systems, for metrological purposes, in pulsed photometry, and other fields in optoelectronics.
References [1] A.A. Mal’tsev, Phys. Part. Nucl. 27 (3) (1996) 330. [2] A.A. Mal’tsev, M.A. Mal’tsev, Tech. Phys. 42 (4) (1997) 378. [3] Yu.M. Volkov, et al., Prib. Tekh. Eksp. 5 (1982) 40.
Nuclear Instruments and Methods in Physics Research A 573 (2007) 172–174 www.elsevier.com/locate/nima
Intensity and bunch profile measurement for ring-shaped electron bunch Anatoly Mal’tsev, Mikhail Mal’tsev, Marina Maslova Joliot-Curie 6, Dubna, Moscow reg., 141980 Russia Available online 20 November 2006
Abstract Methods for measuring the current and geometrical parameters and estimating the energy parameters of electron (or proton) bunches in ring accelerators using synchrotron radiation in the infrared region are reviewed, together with the information-measuring system designed to detect the synchrotron radiation and realize these methods. r 2006 Elsevier B.V. All rights reserved. Keywords: Infrared synchrotron radiation; Accelerator diagnostics; Methods and systems
1. Introduction In some physical experiments performed for the investigation of fast processes in the presence of strong electromagnetic and radiation noise, it is necessary to perform accurate measurements of intensity of thermal radiation and its profile. This problem arose at the JINR an investigation of the intensity of compressible ringshaped bunches of relativistic low-energy electrons with the aid of their synchrotron radiation, whose spectral range falls mainly in the infrared range. 2. Formulation of the problem The ring-shaped electron bunch generating the synchrotron radiation is similar to a thermal emitter whose temperature increases as the ring is compressed (i.e. as the average or equilibrium radius decreases and the electron energy E increases) and in the bunch. The radiation is of a pulsed character with the frequency ranging from 1 to 30 Hz. The linear size of the emitter can change from pulse to pulse in a range from 4 to 12 mm, and the radiated power W ranges from 6.2 103 to 1.8 103 W (this corresponds to Ne ¼ 1 108–3 1013 electrons per bunch. The size of the radiation beam depends on the energy of the electrons and the density n and angular distribution y of the charged particles in the Corresponding author. Tel.: +7 09621 64853; fax:+7 09621 65180.
E-mail address: [email protected] (A. Mal’tsev). 0168-9002/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2006.10.227
bunch. The diameter of the experimental radiation beam in the detector plane is 60 mm. The diagnostics problem was to measure the power of the thermal radiation on the surface of the detector in the range from 2.8 106 to 8.4 101 W/cm2 with a source temperature T ¼ 8 102–2.7 103 1C under conditions of pulsed electromagnetic and radiation noise of accelerator to within 20% and the spatial character of the radiation beam (its profile). 3. Measurement procedure To solve this problem, we developed a special method and to implement the method we created and checked in the physical experiment a noise-proofed informationmeasuring system. The method of measuring and investigating the intensity is based on comparing the integral radiation fluxes, registered in different regions of the spectral distribution of the radiation from the experimental source. The method consists of using two integral photodetectors, which are of different types and manifest the photoeffect differently, and their spectral sensitivity characteristics are different and they record radiation in the spectral range of wavelengths Dl/lb1. The same photodetectors also measure the geometry of the beam. One detector is oriented along the axis of the radiation beam and is stationary. The other detector is moved relative to the stationary detector along a straight line oriented perpendicular to the electron orbits. To measure the profile of the radiation source, an objective lens is inserted
ARTICLE IN PRESS A. Mal’tsev et al. / Nuclear Instruments and Methods in Physics Research A 573 (2007) 172–174
between the radiator and the detector. The lens focuses an image of the source on the flat plane of a sensitive surface of the detector, and the detector is moved relative to the image. This method for measuring the geometry of the radiation beam and the radiator has the drawback that it is impossible to obtain an instantaneous picture of the distribution in each accelerator cycle (duration 1 ms). 4. Measurement apparatus Its advantage is that it is simple and hence, reliable and cheap. On the basis of the conditions and requirements of the physical experiment and method of measurement, accurate photodetectors—photodiode and photoresistor— which operate at room temperature were chosen to convert the radiation power into an analog electron signal. This combination makes it possible to register the radiation flux in the spectral range 0.4–4.8 mm, which greatly exceeds the visible range. The channels are independent, and the radiation can be registered simultaneously in both channels (in the case of correlated measurements) or in each channel separately. A photodiode with a 3 mm in diameter sensitive surface is used in the channel with the photodetector. The photodiode is fabricated in a single case with a preamplifier by the integrated technology. The entire photodetection unit does not exceed 1 cm3 in size. Thanks to the small dimensions and the minimization of the electrical contours in the photodetector apparatus, the sensitivity of the apparatus to radiation fields and induction interferences, which makes it possible to work close to the radiation source under conditions of high electromagnetic and radiation noise. Such photodetectors in the case when the synchrotron radiation is registered have an advantage over the previously used photomultipliers. While the photomultipliers are more sensitive, which is not important for the level of synchrotron radiation present in the accelerator, the photodetector has a wider dynamical range and wide bandedness of the spectral characteristic (0.4–1.1 mm). The small dimensions of the photodetector, the insensitivity to external magnetic fields, and the low-power requirements (10 V, 2 mA) simplify the layout of the apparatus and make it convenient to work with. To suppress interference, which can arise in the cable connecting the input circuit with the output registering section, special attention is devoted to the arrangement and screening of the cable. The measured signal is additionally amplified in the registering section up to amplitudes 5 V, which is the maximum limit of the dynamic range of the following analog-to-digital converter (ADC). To eliminate the constant component from the input circuits, a transitional capacitor is inserted in front of the output amplifier, since the measured signal itself is a pulsed signal (duration 1 ms). The measurement channel with an uncooled photoresistor as a detector makes it possible to measure the instantaneous (within 1 106 s) infrared signal using its pulse conversion from the photodetector and introducing a
173
special device [1] for active suppression of interference in the measuring channel before registering in the ADC. The detector consists of two photoresistance with a 0.2 mm sensitive element, one of which is compensating and is covered from infrared radiation. Carefully selected photoresistances with parameters and characteristics that are as close as possible are secured on different sides of the same substrate, which is opaque to infrared radiation but does not screen electromagnetic and radiation fields. This structure of the detector and the use of a differential amplifier made it possible to employ a balanced extraction of the signal from the detector and to decrease substantially the level of in-phase interference on the output signal and drift at the output to the measuring channel. In addition, all input circuits were placed inside electrical screens, the conductors of the photoresistances on the differential inputs of the amplifier were made in the form of twisted pairs, and the amplifier itself was removed from the detector, located directly near the infrared source, at a distance of 2 m. The measured signal from the detectors is transmitted with the aid of a modulating pulse 4 ms from the control unit, triggered by an external triggering pulse. The duration of the modulation pulse was chosen to be equal to 4 ms taking into account the possibilities of the electronic circuits and in order to improve the temporal resolution. This operation can be performed either by pulsed powering of the photoresistors or by a special electronic circuit for commutating the signals from the detectors. From the output of the amplifier, the short measured pulse, whose amplitude is proportional to the instantaneous intensity of the infrared synchrotron radiation at the moment of measurement, is fed along a 50 m long cable into the output amplifier, covered by a wideband negative feedback delayed by 4 ms. This device effectively suppresses the drift of the entire amplifier as well as the interference signals in the range up to 10 kHz but it transmits without any distortions the measured signal with a duration of 4 ms. The moment at which the instantaneous synchrotron radiation is registered is fixed by a 1 106 s gating pulse at the end of the modulation pulse (when its transient process is over) from the control unit, which in turn is triggered by an external pulse. The unit makes it possible to control the delay time in triggering the entire measuring channel relative to the external triggering pulse, it forms the pulse modulating the signal from the detector, and feeds to the ADC, a gating pulse at the end of the modulation pulse. 5. Measurement results The method of measuring the intensity of the thermal radiation and the spatial distribution of the flux was employed and checked in physical experiments performed at the JINR according to a program for developing a collective have-ion accelerator with electron rings [2], on the electron synchrotron at the St. Petersburg Institute of Nuclear Physics in Gatchina [3], and in stand tests of
ARTICLE IN PRESS 174
A. Mal’tsev et al. / Nuclear Instruments and Methods in Physics Research A 573 (2007) 172–174
diagnostics apparatus and infrared optical systems. The radiation source, the ring-shaped electron bunch, had an equivalent temperature of 103 1C and the number of electrons in the bunch differed from one accelerator pulse to another. The measurements were performed in the range of radiation intensities 3 106–8 101 W/cm2. To ensure that the measuring system operates on the linear section of its sensitivity, a collection of calibrated neutral radiation attenuators and infrared objectives made of optical ceramics for focusing the radiation were used. The temperature range registered in different measurements is 30–2700 1C. The relative instrumental accuracy in the measurement of the intensity of the thermal radiation is equal to 0.2%. The absolute error depends on the calibration of the detectors and may not exceed 5%. 6. Conclusion The measuring system examined above exhibited high noise-resistance, stability, and reliability during long (several week) working sessions. The measurement results were read either according to a digital indicator from the ADC or with the results fed into a computer and printed out together with other registered parameters. Accurate photoresistors determined the possibility of registering with a high relative degree of accuracy of up to 0.2% at room temperature the visible and infrared synchrotron radiation under conditions with a high level of electromagnetic and radiation noise. The described method with modulation of
the measured signal can be used both for one-channel integral measurement of radiation and for multichannel system for registering geometric parameters of the object being observed. The measuring system was calibrated using a thermal standard source, and it was used to measure the absolute values of the current of the electron ring in a collective heavy-ion accelerator [2], and the dimensions of the synchrotron radiation beam were also determined. On account of their unique properties with respect to sensitivity, reliability, operating simplicity, noise-resistance, accuracy, and stability of the parameters, the meter could find application in physical experiments for investigating beams of relativistic charged particles (electrons and protons) in ring accelerators and accumulators—generators of synchrotron (edge) radiation, in linear accelerators for determining the intensity and transverse and longitudinal dimensions of the accelerated beam according to the temperature of the target, through which the beam passes, and in nuclear power plants for monitoring the temperature of units and systems, for metrological purposes, in pulsed photometry, and other fields in optoelectronics.
References [1] A.A. Mal’tsev, Phys. Part. Nucl. 27 (3) (1996) 330. [2] A.A. Mal’tsev, M.A. Mal’tsev, Tech. Phys. 42 (4) (1997) 378. [3] Yu.M. Volkov, et al., Prib. Tekh. Eksp. 5 (1982) 40.