Wednesday, December 2, 2009
Details of Laser Beam - December 2009
In this post, I will present some details of the optical layout.
1 - This is the side optical table. In the right corner in the front the laser beam transport line can be seen. Through this vacuum line the 800-nm fundamental laser beam from the Ti:S amplifier is transported. Using vacuum reduces instabilities in the laser beam caused by turbulence of air flow.
2 - We choose to transport the stretched amplified laser pulse directly output of the regenerative amplifier. At the output of the laser system a telescope is positioned to shape the laser beam to a smaller size. On this picture you see the compressor that is positioned on the side table.
3 - After the compressor the laser beam passes through the second and third harmonic unit. The third harmonic is used either to generate the electron pulse at the cathode surface of the RF cavity or excite the sample optically. The left over fundamental beam will be used to probe the sample. If necessary this fundamental wavelength can be converted into other wavelengths by using for instance white light generation.
4 - Around the Sample Chamber a frame is mounted to hold the opto-mechanical components. The laser beams (pump and probe) have to be deflected upwards to reach the windows of the vacuum system.
5 - Detail of the UV in coupling. One can see the prism's in the cross.
6 - Detail of the probe laser beam transport line to the window of the Sample Chamber.
Tuesday, December 1, 2009
Details of Sample Chamber - December 2009
In this post, I will introduce some details of the Sample Chamber and explain their function.
1 - At the side of the Sample Chamber one can view through a big window into the chamber and see the carousel holding multiple samples. We have a standard piece mounted with diaphragm’s, a phosphor screen and test samples such as ZnS and ZnSe.
2 - The rotational feed through mounted on a x,y,z stage. We can rotate the right sample into the electron beam, retract the complete carousel out of the electron beam line and displace the sample through the electron beam.
3 - Behind the sample chamber but before the electron beam dump a beam viewer can be inserted into the electron beam. Using a Gigabit Ethernet CCD Camera we are able to follow the electron beam at a high frame rate.
4 - Here you see the beam dump at the deflected output port of the sample chamber. Using this beam dump, we can optimize the electron beam without irradiating the sample and causing unwanted degradation.
5 - Input window of the laser beam to the sample. We are not only able to excite the samples with the electron pulses, but in the same sample chamber we can excite them also with the laser pulse. In this way we can compare laser flash photolysis with electron beam photolysis without exchanging the sample to different experimental setups.
Monday, November 30, 2009
Details of Electron Beamline - December 2009
In this post I will introduce the components of the beamline and explain their function.
1- Directly behind the RF cavity and RF input coupler a valve is positioned to separate the vacuum compartment of the cavity from the rest of the setup.
3 - Next, we have a cross-piece which is used to couple the UV pulse into the vacuum system to illuminate the cathode surface and generate the electron pulse. We use 266-nm laser light, which is the third harmonic of the 800-nm fundamental wavelength coming from a Ti:S amplifier.
5 -In front of the sample chamber a bending magnet is mounted. This enables us to deflect the beam away from the sample into a side beam dump. This function serves multiple purposes: We can scan the electron beam energy; We can optimize the phase injection of the UV laser beam into the RF cavity; We can measure the background level to correct the measurement; By rapid switching of this magnet we prevent the sample from degrading and exposure to excessive electron pulses.
1- Directly behind the RF cavity and RF input coupler a valve is positioned to separate the vacuum compartment of the cavity from the rest of the setup.
2- Then around the bellows a steering magnet is positioned. With this magnet we are able to position the electron beam on the sample and find the overlap with the probe beam. The probe beam is a time delayed ultrashort laser pulse than analyses the status of the sample after being excited by the electron pulse.
Additionally, we are able to displace the electron beam over the full sample surface. This is necessary, because the electron pulse is causing irreversible damage to the sample. By taking each time a fresh piece of sample, the measurement time can be extended before replacing the sample.
3 - Next, we have a cross-piece which is used to couple the UV pulse into the vacuum system to illuminate the cathode surface and generate the electron pulse. We use 266-nm laser light, which is the third harmonic of the 800-nm fundamental wavelength coming from a Ti:S amplifier. In this cross-piece two aluminum coated prim's are mounted on a moving base. This base is constructed in such a way that when rotating the feed through below the gap between the prima's can be varied. One has to realize that the UV beam has to pass through the inner conductor in the coaxline upstream to the cavity. This has a narrow diameter. On the other hand, the prism's have to be placed to the side, because the electron beam is passing through the center. Due to the control of the gap, we can find the optimum position of the prisma's. Finally, the reflection of the UV pulse on the cathode surface can be seen at the output window. This is essential to find with the UV laser beam the center of the cathode surface. One can see all the diamond turning rings in the reflection of the UV laser beam.
4 - Sample chamber. It is a very complex piece. The essential function is that a carousel with multiple samples can be positioned with respect to the electron beam using a rotational feed through with x,y,z linear stages. The chamber has four laser windows (two input and two output) mounted at small angles with respect to the electron beam to probe the sample. We like to setup a visible probe line and a infrared probe line.
5 -In front of the sample chamber a bending magnet is mounted. This enables us to deflect the beam away from the sample into a side beam dump. This function serves multiple purposes: We can scan the electron beam energy; We can optimize the phase injection of the UV laser beam into the RF cavity; We can measure the background level to correct the measurement; By rapid switching of this magnet we prevent the sample from degrading and exposure to excessive electron pulses. Saturday, November 28, 2009
Installation of beamline including the Sample Chamber - December 2009
In a previous post, I have introduced the concept of the beamline and Sample Chamber. Due to the failure of the orginal RF Window, the accelerator was out of order for at least two month. Due to this long break, we decided to upgrade the beamline and started to install the Sample Chamber into the beamline.
Below, you will find some pictures of the Sample Chamber. Beginning of December the complete chamber was installed.
Below, you will find some pictures of the Sample Chamber. Beginning of December the complete chamber was installed.
Sample Chamber after the vacuum beaking out procedure.
Viewed from the other side. In the slot of the optical table you can see a large valve in the connection piece to the turbo pump.
Sample Chamber installed on the optical table. The RF cavity is situated at the left side.
Wednesday, September 30, 2009
RF Window problems - September 2009
Shortly after we have achieved very good RF processing results in September 2009, we had a serious RF breakdown event at the RF window. This RF window separates the RF waveguide section at SF6 overpressure from the RF cavity at high vacuum.
In short, while running the klystron at about 7.5 MW output power a breakdown event occurred at the vacuum site of the RF window. We installed photodiodes to monitor breakdown light flashes from the RF cavity and from the RF window. At this specific event the light output from the window was evident. After this event, we had to turn the RF power level down to 1 MW and even then small discharges were appearing each pulse. RF processing did not improve this situation and lead to the conclusion that the RF window has been damages and had to be replaced.
We decided to replace the current CPI RF window of type VWX-1053 with a pillbox type RF window. After consulting some manufactures, we have ordered a RF window from CML Engineering of type 3020-02. This window has higher specifications in terms of peak and average RF power level and therefore will be more reliable. At the end of November 2009 this RF Window and adapter piece has been delivered.
In short, while running the klystron at about 7.5 MW output power a breakdown event occurred at the vacuum site of the RF window. We installed photodiodes to monitor breakdown light flashes from the RF cavity and from the RF window. At this specific event the light output from the window was evident. After this event, we had to turn the RF power level down to 1 MW and even then small discharges were appearing each pulse. RF processing did not improve this situation and lead to the conclusion that the RF window has been damages and had to be replaced.
We decided to replace the current CPI RF window of type VWX-1053 with a pillbox type RF window. After consulting some manufactures, we have ordered a RF window from CML Engineering of type 3020-02. This window has higher specifications in terms of peak and average RF power level and therefore will be more reliable. At the end of November 2009 this RF Window and adapter piece has been delivered.
 The RF window that was installed originally. | |
 The new RF window of CML Engineering installed in the RF section. The connection at the bottom is to the adapter piece for the connection to the RF input coupler of the RF cavity. | |
 Side view of the RF window. |
Thursday, September 17, 2009
Milestones achieved during RF processing - 10th of September 2009
While continuing RF processing of the RF cavity, the level of RF input power is gradually increasing. For instance, on the 10th of September we could ramp up very fast up to 3.9-MW input power and 3.0-MeV electron energy at 50 Hz without experiencing any breakdown.
By the end of the day the level of 7.1-MW input power and 3.8-MeV electron energy has been reached in case of a 1.0-us short pulse and 40-Hz repetition frequency. The measured peak dark current was 0.17 mA and the charge per pulse was 0.079 nC.
By the end of the day the level of 7.1-MW input power and 3.8-MeV electron energy has been reached in case of a 1.0-us short pulse and 40-Hz repetition frequency. The measured peak dark current was 0.17 mA and the charge per pulse was 0.079 nC.
 7.0 MW and 3.8 MeV |  7.1 MW and 3.8 MeV |
First accelerated electrons - 3th of September 2009
During the first week of September we continued the RF processing of the RF cavity.
The second day we also turned on the main solenoid magnet around the RF cavity. As a result we had to repeat the training session of the day before, because the magnet influences all the processes inside the cavity. For instance, field emitted electrons follow different paths when the magnet is turned on.
On the 2nd of September we soon reached 3.0-MW input power and 2.4-MeV electron energy. We continued the RF processing by replacing the 10-dB attenuator at the input of the preamplifier to 6 dB. Now we sometimes observe breakdown events with a measurable electron signal on the beam dump at the exit of the cavity and at the same time observe a light pulse on the photodiode that looks inside the RF cavity. Surprisingly, not all breakdown events are accompanied by electrons and light. Possibly, these events are taking place outside the RF cavity. By the end of this day, we have reached 3.6-MW input power and 2.9-MeV electron energy operating at 50 Hz.
The 3th of September was a very exciting day, because we observed for the first time dark current coming out the RF cavity. The power level at that moment was 3.7-MW input power and 3.0-MeV electron energy. We were able to optimize the setting of the main solenoid magnet around the cavity by maximizing the dark current on the beam dump. We also observed single-side electron multipacting at the photocathode in the RF gun (see Han et al. in Phys. Rev. ST AB 11, 013501 (2008)). For instance, we have measured at the setting of 3.9-MW input power and 3.0-MeV electron energy a peak dark current of 52 nA and a total charge of 0.11 nC per pulse.
Below you can find two oscilloscope images displaying with the following signals: Light Blue - Modulator current; Purple - Forward RF Pulse; Green - Backward RF pulse; Dark Blue - Beam dump signal.
The second day we also turned on the main solenoid magnet around the RF cavity. As a result we had to repeat the training session of the day before, because the magnet influences all the processes inside the cavity. For instance, field emitted electrons follow different paths when the magnet is turned on.
On the 2nd of September we soon reached 3.0-MW input power and 2.4-MeV electron energy. We continued the RF processing by replacing the 10-dB attenuator at the input of the preamplifier to 6 dB. Now we sometimes observe breakdown events with a measurable electron signal on the beam dump at the exit of the cavity and at the same time observe a light pulse on the photodiode that looks inside the RF cavity. Surprisingly, not all breakdown events are accompanied by electrons and light. Possibly, these events are taking place outside the RF cavity. By the end of this day, we have reached 3.6-MW input power and 2.9-MeV electron energy operating at 50 Hz.
The 3th of September was a very exciting day, because we observed for the first time dark current coming out the RF cavity. The power level at that moment was 3.7-MW input power and 3.0-MeV electron energy. We were able to optimize the setting of the main solenoid magnet around the cavity by maximizing the dark current on the beam dump. We also observed single-side electron multipacting at the photocathode in the RF gun (see Han et al. in Phys. Rev. ST AB 11, 013501 (2008)). For instance, we have measured at the setting of 3.9-MW input power and 3.0-MeV electron energy a peak dark current of 52 nA and a total charge of 0.11 nC per pulse.
Below you can find two oscilloscope images displaying with the following signals: Light Blue - Modulator current; Purple - Forward RF Pulse; Green - Backward RF pulse; Dark Blue - Beam dump signal.
 The first observation of dark current out of the RF cavity measured at the beam dump at the exit. |  Dark current at a higher setting of the acceleration field. |
Wednesday, September 16, 2009
FIrst RF Processing session of RF cavity - 31th of August 2009
On Monday 31th of August 2009 it was the day of starting the RF Processing procedure.
RF Processing is a neccesary step during the installation of the RF accelerator in which gradually increased RF power is applied to the cavity in order to clean and smoothen the inner surface. As a result the cavity can hold increasingly higher electric field levels without resulting in a breakdown event.
In order to perform a successful RF processing procedure, we have equiped the setup with several detection systems:
1- Breakdown detector: A piece of analog electronics monitors the backward reflected RF waves from the cavity and senses very abrupt changes in RF power that will occur upon breakdown inside the cavity. This is due to the change of impedance of the cavity when a breakdown occurs. When a breakdown is detected the RF pulse is immediantely interrupted.
2- Vacuum pressure monitor with switch: When the vacuum pressure inside the cavity exceeds a certain level the RF power to the cavity will be interupted untill the pressure has droped below the level again.
3- Faraday cup or electron beam dump at the exit of the cavity to monitor the electrons coming out of the cavity. The signal is presented on an oscilloscope.
4- Photodiode that monitors the light output of the cavity to detect the intensity of the breakdown event. The signal is presented on an oscilloscope.
5- Photodiode that monitors the light output near the RF window to detect the intensity of the breakdown event.
We have a few parameters that we can set in the system:
1- RF peak power by changing the RF input power to the Klystron tube by changing a variable discrete attenuator between 0.0 and 15.5 dB in steps of 0.5 dB.
2- RF peak power by changing the high voltage setting of the modulator. This can be seen as a fine adjustment of the RF power as compared to option 1.
3- RF pulse length by changing the modulator pulse length. This can be changed between 0.50 and 2.80 us flat top.
4- RF pulse repetition frequency can be set between 0 - 100 Hz as long as the average power of the modulator does not exceeds 6.5 kW. In general, we do not exceed 50 Hz.
The method that we apply is to start with the setting of the shortest pulse and increase in RF power. After a certain level has been achieved, the pulse length is increased, while keeping the maximum field strength in the cavity constant. Do to this the RF filling time of the cavity has to be taken into account. Once dark current is observed from the cavity, this is easily achieved by keeping the dark current constant. The last step is to increase the pulse repetition frequency. This procedure can be repeated untill the maximum RF input power is reached.
At 18:00 that day we started under supervison of the radiation safety department of TU Delft the RF processing procedure. We replaced the 20 dB attentuator at the input of the preamplifier to a 10 dB. Soon after the start we reached the level of 1 MeV electron energy. By midnight we haved reached 2.9 MW input power and 2.5 MeV electron energy. The estimated electric field inside the cavity is about 60 MV/m.
RF Processing is a neccesary step during the installation of the RF accelerator in which gradually increased RF power is applied to the cavity in order to clean and smoothen the inner surface. As a result the cavity can hold increasingly higher electric field levels without resulting in a breakdown event.
In order to perform a successful RF processing procedure, we have equiped the setup with several detection systems:
1- Breakdown detector: A piece of analog electronics monitors the backward reflected RF waves from the cavity and senses very abrupt changes in RF power that will occur upon breakdown inside the cavity. This is due to the change of impedance of the cavity when a breakdown occurs. When a breakdown is detected the RF pulse is immediantely interrupted.
2- Vacuum pressure monitor with switch: When the vacuum pressure inside the cavity exceeds a certain level the RF power to the cavity will be interupted untill the pressure has droped below the level again.
3- Faraday cup or electron beam dump at the exit of the cavity to monitor the electrons coming out of the cavity. The signal is presented on an oscilloscope.
4- Photodiode that monitors the light output of the cavity to detect the intensity of the breakdown event. The signal is presented on an oscilloscope.
5- Photodiode that monitors the light output near the RF window to detect the intensity of the breakdown event.
We have a few parameters that we can set in the system:
1- RF peak power by changing the RF input power to the Klystron tube by changing a variable discrete attenuator between 0.0 and 15.5 dB in steps of 0.5 dB.
2- RF peak power by changing the high voltage setting of the modulator. This can be seen as a fine adjustment of the RF power as compared to option 1.
3- RF pulse length by changing the modulator pulse length. This can be changed between 0.50 and 2.80 us flat top.
4- RF pulse repetition frequency can be set between 0 - 100 Hz as long as the average power of the modulator does not exceeds 6.5 kW. In general, we do not exceed 50 Hz.
The method that we apply is to start with the setting of the shortest pulse and increase in RF power. After a certain level has been achieved, the pulse length is increased, while keeping the maximum field strength in the cavity constant. Do to this the RF filling time of the cavity has to be taken into account. Once dark current is observed from the cavity, this is easily achieved by keeping the dark current constant. The last step is to increase the pulse repetition frequency. This procedure can be repeated untill the maximum RF input power is reached.
At 18:00 that day we started under supervison of the radiation safety department of TU Delft the RF processing procedure. We replaced the 20 dB attentuator at the input of the preamplifier to a 10 dB. Soon after the start we reached the level of 1 MeV electron energy. By midnight we haved reached 2.9 MW input power and 2.5 MeV electron energy. The estimated electric field inside the cavity is about 60 MV/m.
 The accelerator is control from the control room. Left to right: Juleon Schins, Laurens Siebbeles, Koos van Kammen and Walter Knulst. |  Walter Knulst is controling RF processing from the accelerator GUI build in LabView. |
 Walter Knulst together with Martien Vermeulen who is the allround electron accelerator engineer. |  Another look at the control room. |
 A breakdown event is recorded by the oscilloscoop. In green you can see the abrupt change in RF reflection from the cavity and 400 ns later the breakdown detector has switched of the RF power. |  Another breakdown event, which has unfortunately not been detected by the breakdown detector due to the fact that the rising edge is less steap than the event to the left. |
Low power tests of RF Cavity - 27th of August 2009
On Thursday 27th of August 2009 the system was ready to be switched on. All subsystems have been tested before. We connected on this day the RF waveguide for the first time to the accelerator cavity.
The first test is to use very low power RF and measure the resonance frequency as a function of cavity temperature. This test is very exciting, because all RF parts have never been tested as one assembly.
The RF cavity has been checked by measuring the resonance frequency using a network analyzer after manufacturing. You can read more about electrical validation in a post from 2006. It has been observed that the resonance frequency is 2997.802 MHz at 20 oC in air.
In between the RF waveguide section and the RF cavity, a RF window and input coupler is placed. You can read more about the RF waveguide section in a post from 2006. The input coupler has been tuned in such a way that maximal RF power is coupled from the rectangular waveguide into the coaxial waveguide feeding the RF cavity. However, this has never been tested in combination with the actual cavity.
For the lower power test of the RF cavity, we have modified the RF system so that the maximum output power is reduced by 20 dB, i.e. 0.1 MW instead of 10 MW. This is done by inserting a 20 dB attenuator at the input of the 100 W preamplifier. You can read more about the RF system in a post form 2007. This safety measure protects the RF cavity from severe breakdown events.
We started by putting the RF cavity at 20 oC. We achieved a perfect incoupling at a frequency of 2999.080 MHz. The difference of -1.28 MHz with the measurement shortly after manufacturing is more than can be explained by the difference between air and vacuum of -0.95 MHz.
We continued the test by increasing the temperature by steps of 5 oC up to 35 oC. The resonance frequency shifts to lower frequencies when increasing the temperature. The resulting coefficient of 48 kHz/K is very close to the theoretical value of 48.5 kHz/K.
The conclusion is that the resonance frequency at 30 oC of the RF cavity (2998.600) is very close to the center frequency of the PLL. Therefore, we have decided to operate the RF cavity at this temperature setting.
We finished the low power test of the RF cavity by increasing the RF power.
Below you will find several scoop displays showing the reflection of RF power at the resonance frequency of the RF cavity at different temperatures. Dark blue: high tention of modulator; Light blue: current of modulator; Purple: Forward RF pulse; Green: Backward RF Pulse.
The first test is to use very low power RF and measure the resonance frequency as a function of cavity temperature. This test is very exciting, because all RF parts have never been tested as one assembly.
The RF cavity has been checked by measuring the resonance frequency using a network analyzer after manufacturing. You can read more about electrical validation in a post from 2006. It has been observed that the resonance frequency is 2997.802 MHz at 20 oC in air.
In between the RF waveguide section and the RF cavity, a RF window and input coupler is placed. You can read more about the RF waveguide section in a post from 2006. The input coupler has been tuned in such a way that maximal RF power is coupled from the rectangular waveguide into the coaxial waveguide feeding the RF cavity. However, this has never been tested in combination with the actual cavity.
For the lower power test of the RF cavity, we have modified the RF system so that the maximum output power is reduced by 20 dB, i.e. 0.1 MW instead of 10 MW. This is done by inserting a 20 dB attenuator at the input of the 100 W preamplifier. You can read more about the RF system in a post form 2007. This safety measure protects the RF cavity from severe breakdown events.
We started by putting the RF cavity at 20 oC. We achieved a perfect incoupling at a frequency of 2999.080 MHz. The difference of -1.28 MHz with the measurement shortly after manufacturing is more than can be explained by the difference between air and vacuum of -0.95 MHz.
We continued the test by increasing the temperature by steps of 5 oC up to 35 oC. The resonance frequency shifts to lower frequencies when increasing the temperature. The resulting coefficient of 48 kHz/K is very close to the theoretical value of 48.5 kHz/K.
The conclusion is that the resonance frequency at 30 oC of the RF cavity (2998.600) is very close to the center frequency of the PLL. Therefore, we have decided to operate the RF cavity at this temperature setting.
We finished the low power test of the RF cavity by increasing the RF power.
Below you will find several scoop displays showing the reflection of RF power at the resonance frequency of the RF cavity at different temperatures. Dark blue: high tention of modulator; Light blue: current of modulator; Purple: Forward RF pulse; Green: Backward RF Pulse.
 RF Cavity at 20 oC and frequency 2999.080 MHz. |  RF Cavity at 30 oC and frequency 2998.600 MHz. |
 The temperature dependence of the RF Cavity. |  RF Cavity at 30 oC and frequency 2998.600 MHz. Modulator pulse setting is 0.90 us and higher RF power. |
Friday, August 21, 2009
Temperature Control of RF Cavity - 21th of August 2009
We have constructed and tested the temperature control system of the RF Cavity.
This system has been designed to serve two purposes: 1- keeping the RF cavity at a constant temperature, so that the drift of the resonance frequency is as small as possible; 2- Cooling when RF pulses are applied and heating during intervening times.
The temperature control system consists of three segments: 1- Cathode section, 2- Cell sections and 3- Input Coupler section. Each section has one cooling water channel, one Thermocoax heating element and one thermocouple temperature sensor. The temperature of the section is controlled by a Eurotherm controller. The flow of the cooling water can be adjusted by remote control of a valve. The heating rate can be controlled by remote control of power supplies connected to the heating elements.
You can see the cooling water channel of the Cathode and Cell section very clearly at the photo's of the RF cavity model. In the same pictures one thermocouple is visible at the outer diameter of the full cell. There is also a thermocouple at the outer diameter of the half cell. So, we can control the temperature of each cell individually. However, due to the fact that the RF cavity is a big peace of high conductance copper, the thermal conductivity is very high and therefore the three sections are well coupled. This is a great factor of complexity.
Nevertheless, we were able to select the settings of the Eurotherm controllers in such a way that we have reached a very good temperature stability of less than 0.1 degrees Celsius.
A special feature that we have applied in the system is a cooling bias, so that there is always a minimal flow of cooling water. Therefore, the heating elements should deliver a minimal power to get the RF cavity at a constant temperature. Now, we have chosen the minimal flow values in such a way that the ratio of the heat input in the cathode section to the cell section is roughly the same as the expected ratio of the heat dissipation of the RF field inside the cavity from full cell to half cell. We hope that in this way the transient effects will be minimized due to the switching on and off of the RF pulses. This can only be tested when the RF pulses are applied.
On top the three Eurotherm temperature controllers. Below the three power supplies feeding the heating elements. To the left all the connections to the RF cavity are visible.
This system has been designed to serve two purposes: 1- keeping the RF cavity at a constant temperature, so that the drift of the resonance frequency is as small as possible; 2- Cooling when RF pulses are applied and heating during intervening times.
The temperature control system consists of three segments: 1- Cathode section, 2- Cell sections and 3- Input Coupler section. Each section has one cooling water channel, one Thermocoax heating element and one thermocouple temperature sensor. The temperature of the section is controlled by a Eurotherm controller. The flow of the cooling water can be adjusted by remote control of a valve. The heating rate can be controlled by remote control of power supplies connected to the heating elements.
You can see the cooling water channel of the Cathode and Cell section very clearly at the photo's of the RF cavity model. In the same pictures one thermocouple is visible at the outer diameter of the full cell. There is also a thermocouple at the outer diameter of the half cell. So, we can control the temperature of each cell individually. However, due to the fact that the RF cavity is a big peace of high conductance copper, the thermal conductivity is very high and therefore the three sections are well coupled. This is a great factor of complexity.
Nevertheless, we were able to select the settings of the Eurotherm controllers in such a way that we have reached a very good temperature stability of less than 0.1 degrees Celsius.
A special feature that we have applied in the system is a cooling bias, so that there is always a minimal flow of cooling water. Therefore, the heating elements should deliver a minimal power to get the RF cavity at a constant temperature. Now, we have chosen the minimal flow values in such a way that the ratio of the heat input in the cathode section to the cell section is roughly the same as the expected ratio of the heat dissipation of the RF field inside the cavity from full cell to half cell. We hope that in this way the transient effects will be minimized due to the switching on and off of the RF pulses. This can only be tested when the RF pulses are applied.
On top the three Eurotherm temperature controllers. Below the three power supplies feeding the heating elements. To the left all the connections to the RF cavity are visible.
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