Electrical engineering
Introduction
The electrical engineers of the E&I group are responsible for the electronic equipment for the research programmes and projects. The equipment is either selected from commercial suppliers or designed and built in-house. This includes a variety of analog, digital, high voltage, and power electronics. Designs are typically built in small numbers, ranging from a single unit to (in special cases) a few dozen units.
Expertise
The expertise of the electrical engineers in the E&I group covers a number of different electronics technologies, and includes market knowledge, design, simulation, manufacturing, installation and testing.
Design of analog and digital circuits
Typical analog designs are amplifiers and signal generators. More and more designs mix analog and digital techniques, and include VHDL code running on FPGA's, microcontrollers, and components such as integrated Ethernet controllers. The expertise includes custom optical communication links, integrated user interfaces, and computer interfaces.
Design of high-power electronics
Another expertise is the design of high-power electronics, for handling applications up to the range of kilo Amperes, Mega Watts, and/or Mega Volts. Aspects such as grounding, isolation, shielding, mechanical design, thermal design and safety are included in the design process.
Design of high-frequency electronics
The expertise in high-frequency electronics design includes shielding and grounding, and ranges from low-power RF-amplifiers to fast switching of high voltages and/or currents.
Simulation of magnetic fields
A recently acquired expertise is the simulation of magnetic fields, for example for designing magnetic shielding to meet requirements for stray magnetic fields for human safety and reliable machine operation.
Tools
The following EDA tools are used:
- Altium Designer version 6 for electronic schematic entry, simulation and board design
- Xilinx Integrated Software Environment (ISE) for VHDL design entry, synthesis, implementation, simulation and configuration of FPGA’s (Field Programmable Gate Array)
Additionally, we use the following test bench equipment:
- 4 / 16 channel Mixed Signal 5GS/s, 1GHz, 10Msamples memory depth Oscilloscope: Tektronix MSO-4104
- 4 channel 5GS/s, 500MHz oscilloscope: Tektronix TDS3054B
- 2 channel 2GS/s, 500MHz oscilloscope: Hewlett Packard HP 54522A
- 240MHz, 2Gs/s dual Arbitrary/Function Generator: Tektronix AFG3252
- 1100V SourceMeter: Keithley 2410
- Logic Analyser: Hewlett Packard 1661LA
- TTI CPX400 Dual 42V/20A and TTI EL302T Tripple Power Supplies
Usually, our products are produced in small numbers, and as a consequence, outdoor assembly can be relative expensive. For the assembly of small numbers of printed circuit boards, our lab is equipped with SMD soldering and desoldering equipment and a PCB cleaning machine.
Because of the growing complexity of printed circuit boards, the production of printed circuit boards is outsourced.
Projects 2007
In 2007 we have been working on a number of projects, many of them for the FELIX/Felice (Free Electron Laser for Infrared eXperiments/ Free Electron Laser for Intra-Cavity Experiments) system. Additionally, support has been given to the TEC-ECRH research group in Jülich, and local groups such as Pilot-PSI (Plasma-surface Interaction), Molecular Dynamics and nSI (nanolayer Surface & Interface physics). A number of previous and current projects are described below.
Multichannel Timer/AWG
For the Pilot/PSI-, Electronics-, nSI-, Felix and TEC-ECRH groups a Multichannel Timer/AWG (arbitrary wave generator) has been developed.
Because of the different demands of the applications in speed, sample rate and number of channels, a versatile design and a modular setup is chosen. The number of channels can be chosen between 4 and 24, in increments of 4.
The Timer/AWG operates from a remote host via the Rijnhuizen Ethernet Interface connection and a Labview GUI.
The timer channels offer an optical (ST), a contact and a TTL output. Of each timer output the timebase, trigger delay, pulse length and pulse pause can be set, and in addition, each channel supports selection of trigger-, free running-, trigger level-, gate- and burst- mode, and selection of trigger-, gate- and clock- source, and output mode.
The AWG channels have a -10V .. +10V into 50ohm output with a resolution of 12 bits (about 2.5mV). Of each AWG output the time base, trigger delay and the waveform can be programmed, and also features the control of amplitude, phase and bias settings. In addition, each AWG channel supports selection of trigger-, freerunning- , gate- and burst- mode, and selection of trigger-, gate- and clock- source, and output mode.
The Timer/AWG is equipped with a control unit, which maintains the connection to the host and offers four channels of reference inputs. Each reference input channel has an optical (ST), contact and a TTL input and push button.
The use of the reference inputs is highly versatile, as each input can be assigned to multiple timer and/or AWG channels, and can be programmed per channel as a trigger source or gate source. Also the reference inputs can be programmed as a clock source for respectively the timer section and the AWG section.
Current applications are: gasflow control, time sequencing, electron beam deflection systems, ECRH (Electron Cyclotron Resonance Heating) RF-power modulation, and test bench.
Mezzanine FPGA Module
In many new designs, FPGAs are used because of their high integration capabilities (a complete complex design in a single chip) and the flexibility to change the functionality (adding new functions without the need of a board redesign). A Field Programmable Gate Array (FPGA) is a semiconductor device containing programmable components and interconnects. Programmable components can be programmed to perform the function of basic logic gates such as AND, and XOR, or more complex combinational functions such as decoders or simple mathematical functions, and registers, counters, state machines etc. The FPGAs we use have memory blocks and multipliers are embedded on the chip, which makes them suitable for processing analog signals (DSP).
The programmable interconnects allows the programmed components to be interconnected as needed by the system designer, after the FPGA is manufactured, hence the name "field-programmable". The functionality of FPGAs is described by means of a hardware description language, typically VHDL. For many interfaces we have standard VHDL-blocks that are part of our VHDL-library, such as the LCD-module interface, front panel User Interface, Rijnhuizen Ethernet Interface, RS232-, I2C-, Serial Periferal Interface (SPI), full duplex fiber optical interface and interfaces to digital to analogue respectively analogue to digital converters and flash memories.
In order to develop a new FPGA-based design in a cheap, quick and easy way, a generic module has been build around a Xilinx XC3S400 TQFP144 Field Programmable Gate Array. The mezzanine board can be easily implemented on an application specific main board. The main board can be kept relatively simple, because all power supplies needed to feed the FPGA, the configuration PROM and a serial EEPROM (storage medium for application specific settings) are on the mezzanine board. Also the board is equipped with 16 debug-leds. Two fine pitch 80-pole connectors are used to make the connections to the main-board. The FPGA module features:
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The Mezzanine FPGA Module is used in the following applications:
- Digital Signal Processing
- Local and Remote (Ethernet) Interface
- System Control
Projects already build using the Mezzanine FPGA Module are all the projects listed below with a LCD user interface.
Rijnhuizen Ethernet Interface
Because there is an increasing need for Ethernet connectivity on in-house build equipment, in cooperation with the software group a data exchange protocol is developed to communicate between a host machine and an Ethernet device. Examples of devices are the DED modulation circuit (TEC-ECRH), Timer/AWG (Pilot/PSI, nSI, Felix/Felice, MolDyn and E&I), Crystal temperature controller (nSI) and the stepper motor control (Molecular Dynamics, Felice). A variety of data types can be exchanged: settings, status, control and single byte to bulk data, for instance large arrays, which can be of type integer, real or string. To achieve an as large as possible data rate, data is transported in binary format. To avoid conflicts with control characters, data is first converted to the base64 format. Handshaking and error checking by means of a parity bit are supported. For Ethernet connectivity on the in-house build equipment the Lantronix XPORT Embedded Ethernet Device Server is used.
FELIX/Felice
Electron Beam Energy Stabilizer
Electron Beam Energy Stabilizer For alternating Felix and Felice operation, the electron beam is switched between two paths by means of a swiching magnetic field. For keeping the beam on track, the beam-energy for both paths must be kept stable. Therefore, the Electron Beam Energy Stabilizer measures the deviation of the beam, and controls the modulator of Felix/Felice facility. The Electon Beam Energy Stabilizer consists of two units which are situated at different locations. Therefore, a fast full duplex optical link connects the units. Benefits of the optical link are the absence of ground loops, and enabling control of the feedback parameters from both locations.
Magnetic Field Alternation Circuit
For alternating Felix and Felice operation, the electron beam is switched between two paths by means of a pair of swiching magnetic fields with a rate of 20Hz. During the interval the beam is deflected, the current through the magnetic coil is measured and stabilized. In the next period, when the beam goes straight ahead, the magnetic field has to be zero. To eliminate the residual magnetic field, an opposite current is led through the coil. To control this current, the magnetic field insite the magnet is measured through a fluxgate transducer. To control both feedback paths, a Magnetic field Alternation circuit has been developed.
Pyroelectric Array Amplifier Module
For experiments done with the Felice laserbeam facility, the spectum must be known. The spectrum is measured with a monochromator and a pyroelectric array. The pyroelectric array is a DIAS infrared systems pyroelectric linear array 128LT SP1.0, a hybrid detector with 128 responsive elements and an integrated CMOS multiplexer. The pyroelectric chip consists of lithium tantalate (LiTaO3). The size of the responsive elements is 90 μm × 1000 μm with a pitch of 100 μm. The multiplexer includes low-noise preamplifiers for each pixel, analogue switches and an output amplifier. The preamplifiers transform the signal charges of each pixel in a signal voltage, realize a band limiting and give the amplified signal to the sample & hold for the read-out process.
The pyroelectric array is integrated on the Pyroelectric Array Amplifier Module. The timing of the analogue switches and multiplexers is realized by means of a FPGA, which also sets the amplification of the incoming signal and reads out the analogue to digital converter. The digitized data is transmitted through a bidirectional serial communication channel to a remote data-acquisition system. From the remote system it is also possible to optimize the amplification of the incoming signal.
Gate Control Thyristor Stack
The Gate Control Thyristor Stack is part of the modulator of Felix/Felice. The gate control excitates a 20-layer thyristor stack (40kV, 2kA) via a transformer with 1 primary winding and a series of secondary windings. The secondary windings each are connected to the gates of the thyristor stack. The primary winding is connected to a high voltage power source which can deliver an instant current pulse of over 15A.
nSI
Crystal Temperature Controller
The Crystal Temperature Controller is used to heat samples (up to a maximum of 1250 K) in an ultra-high vacuum system in an accurate and reproducible fashion. It can apply pre-programmed heating cycles with continuous feedback control and error checking of the heating parameters. Samples can be heated either by simple radiative heating from a filament, or by e-beam heating by applying a voltage of up to 1 kV to the sample. The unit allows complete flexibility in the selection of the feedback control mechanisms (filament current, filament voltage, sample current or sample voltage). The units "reset-on-error" and the ability to preset upper limits to the internal power supplies ensure that the risk of the sample being damage in the event of a fault developing within the vacuum system is minimized.
Molecular Dynamics / Felice
Stepper Motor Controller
For experiments with the Felix- and Felice laserbeam, a sample is moved along the laserbeam. A stepper motor is used as actuator for the movement of the sample. For control of the stepper motor, a bipolar stepper motor control is developed. The bipolar stepper motor control is a universal motor controller/driver capable to control and drive unipolar and bipolar steppermotors with 4, 5, 6 or 8 wires and up to 50V/5A per phase. Multiple drive modes are supported, namely wave, half step, full step and microstepping in the range 1/2, 1/4, 1/8, 1/16 , 1/32 , 1/64 and 1/128.
For improved motor performance, current control and advanced recirculation modes are applied to:
- avoid overheating,
- accommodate a variety of motors,
- increase torque at higher speed,
- increase top speed,
- improve power efficiency (with chopper style circuit), and
- smooth running.
As an advantage of current control, current though the coils can be limited to prevent overheating when the motor is used in vacuum. The controller is housed in a 3HE 25TE (h=129mm, w=127mm) 19" plug-in unit, offering both local and remote control by means of a LCD module with buttons and a dial, and an Ethernet RJ45 interface.
TEXTOR
DED Modulation Circuit
At Textor (Tokamak Experiment for Technology Oriented Research) in Juelich, Germany, islands in the plasma can be created artificially and in a predictable way by a rotating magnetic field, generated in the center of the Textor-torus, called the DED (Dynamic Ergodic Divertor) modulator. For studies on island suppression in a plasma of a fusion machine, it is interesting to operate with and without ECRH-modulation. The DED modulation Circuit performs a synchronization of the RF-power and the DED-field, and allows phase-shift, duty-cycle and modulation depth control. The DED Modulation Circuit has both local and remote control via Ethernet.
Calorimeter Calibrator
The Calorimeter Calibrator is a calibration tool used at TEXTOR for calibration of the measurement setup of the energy coming from ECRH (Electron Cyclotron Resonance Heating) and dissipated in a waterload.
Projects 2006
In 2006 we have been working on a number of projects, many of them for the FELIX/Felice system. Additionally, support has been given to the research group in Juelich, and local groups such as Pilot-PSI, Moldyn and nSI. A number of previous and current projects are described below.
FELIX/Felice
Gun bias and heater power supply
The Gun Bias and Heater Power Supply controls both the cathode-grid voltage and the filament current of the Felix/Felice gun. It consists of two parts, one at the 100 kV deck and one at the control site. The two parts communicate through a full duplex fiber link. The Power Supply unit at the 100 kV deck consists of the following isolated sources:
- An adjustable 65 … 200 V dual bias supply, for alternating Felix/Felice operation
- A remotely programmable arbitrary wave generator superpositioned to the dual bias supply to compensate for cathode-droop during a Felix or Felice shot
- A 2.5 Amp heater supply
Kicker magnets
The kicker magnets are part of the magnet switching circuit for FELIX/Felice. Both switches (IGBTs) are operating synchronously, When the switches are closed the main power supply build up the main current in the two magnets. On opening, the magnet energy is transferred to a capacitor. The diodes prevent backflow in the circuit. Closing the switches the capacitors energy is transfert back into the magnets. The capacitor voltage and the main power supply voltage are added. The zero power supply is added a reverse current in magnet 1 for creating a zero gauss field. The offset power supply is added a reverse current in magnet 2 for creating the writhe total current for magnet 2. The system successfully keeps the magnetic field below 0.3 Gauss.
Magnum-PSI
Magnetic shielding
The 3 Tesla superconducting magnet for Magnum Psi is creating a large magnetic field that must be shielded. To determine the best shielding option simulations are carried out using OPERA-3D, a three dimensional Simulation software package from Vectorfields.
The left image shows an example result in 3D. The middle image shows the magnetic field of Magnum-PSI in case no shielding is present. The right image shows the effect of 10cm thick shielding all around the Magnum-PSI magnet. A number of other options have been simulated to determine the best trade-off between shielding and cost. Based on these simulations a suitable shielding design has been recommended to the Magnum-PSI project team.
