1. ACCELERATOR LABORATORY ( beam.helsinki.fi )

1.1. PREFACE

 

Many far-reaching decisions have been made and projects commenced during 1999. We have resolved to abandon the old Van de Graaff accelerator, now located at the old laboratory facilities at Siltavuorenpenger. These premises will be relinquished when the Department of Physics moves to the new Physicum building at the beginning of 2001. To replace the old apparatus we are striving to obtain a new accelerator. There are many different needs in materials science to be met by such a low energy accelerator and clearly they cannot all be fulfilled. In addition to try to accomplish the requirements of materials characterization, a capability to produce a broad range of ions and large amounts of current suitable for ion implantation below MeV energy has been considered important.

An atomic force microscope has been procured to the laboratory and will be installed at the beginning of 2000. This commendably equipped instrument, acquired in collaboration with a few other laboratories, will open new windows for surface studies of materials. It will promote the strengths of the laboratory, the interplay between experimental and computational studies.

The modification of our main instrument the 5 MV EGP-II tandem accelerator to perform also as an accelerator mass spectroscope is reaching its final stages. The system will be in full flight next year. Construction of a new gas filled detector system for the elastic scattering experiments has also been completed. This equipment will complement the time-of-flight system, its main use being the elastic recoil spectroscopy.

As before, the main enterprise in research has been materials science with ion beams and computational techniques. The experiments concentrated in studies of fusion materials, carbon-like films and hard coatings, in compound semiconductors, sulfides and oxides for optoelectronic devices, and in perusing the more basic processes of diffusion, scattering cross sections and stopping powers. Physics of He-Ne lasers and Raman spectra were investigated and successfully utilized in the analysis of various organic materials.

The computational physics research focused on examining how irradiation damage at interfaces and surfaces in semiconductors and metals differs from that produced in ordinary bulk materials. The results revealed several surprising aspects of damage production, including the massive production of damage by dislocation loop punching in metals and strong asymmetries in the redistribution of atoms across interfaces.

A potentially consequential new collaboration between the laser physics group and the Institute of Biotechnology has been initiated. The aim is to study the processes of laser capture and localizing of micron and sub-micron particles. This is a hot topic in micro- and nanotechnology worldwide, applications ranging from studies of handling viruses to aerosols by the "optical tweezers".

There have been 7 new masters, 6 doctors and one docent achieving their degrees in 1999. Twelve young students in their first and second semesters have worked at the laboratory during summer. We have had almost 20 foreign visitors at the laboratory, in turn our staff has visited more than 20 foreign collaborating laboratories abroad. In addition, we have had fruitful co-operation with several universities, institutions and industrial partners in Finland. The accelerator laboratory was a major organizer of a materials physics summer school in Hyytiälä in August.

The financial resources coming from outside the University budget have maintained their high level. About half of the total funding for the laboratory came from external sources, of which the Academy of Finland was the major contributor with a share of about 75%. Other main sources were TEKES, the European Union and various foundations.

Eero Rauhala

1.2. LABORATORY OPERATION AND DEVELOPMENT

 

Raimo Ingren, Heikki Sepponen, Birger Ståhlberg, Pertti Tikkanen and Kim Wahlström

During the period covered by this annual report the 5MV EGP-10-II tandem accelerator and the 2.5 MV VdG accelerator completed their 17 th and 42nd year in service, respectively. Both accelerators operated reliably.

In April a one-week maintenance work was carried out, with the EGP accelerator due to a short circuit in the high voltage terminal. Some wirings and one transformer were changed. During the maintenance the polarity of the electrostatic steerer after the stripper tube was inverted (the steerer was installed one year earlier, but it didn't have a desirable effect on the ion beam). The steerer’s new performance has increased the maximum final energy of the heavy ions. For example the maximum charge state of 127I was earlier +7 and maximum final energy 37 MeV; now even the charge state +14 can be used giving 72 MeV final energy.

The He ion source of the EGP (Alphatross) was taken into daily use. The He-beam was used 510 h during the year.

A new multi-cathode sputter ion source (MC-SNICS manufactured by NEC) was installed to the injector of the EGP. It can be loaded with 40 sputtering targets simultaneously. This source is intended for future AMS (Accelerator Mass Spectrometry) work. The source has not yet been tested. The installation of a new control system for the EGP accelerator was started. The system is a distributed control system based on home made control nodes. The control nodes are operating under The Forth operating system. CAN-bus (Controller Area Network) connects the nodes and the operator console together via fibre optics. The operator console is a normal PC with InTouch (a man-machine interface program from Wonderware) program and Windows-NT operating system. The main parameters of the system were at the end of the year:

 

1 operator console

6 control nodes

38 analogue output channels (14 bit resolution)

43 analogue input channels (1 6 bit resolution)

29 digital output channels

17 digital input channels

5 stepper motor controls

The VdG required altogether 26 days of maintenance. In May (8 days shutdown) the pressure tank was opened due to service of the ion source and the installation of new bearings to one of the electric motors. In November again an 8 days shutdown was used to ion source service and to the installation of a new vacuum pump to the gas system of the pressure tank. All the other shutdowns lasted 1 - 3 days during which routine service and repairs were carried out.

The EGP and the VdG provided total beam times of 1542 h and 1252 h, respectively. The utilization of the accelerators per month is shown in Fig.1. In July the EGP was shut down due to the annual vacations of the personnel. The distribution of the beam hours divided into 0.5 MV intervals of the terminal voltage of the accelerators is shown in Fig. 2.

The beams provided by the duoplasmatron, the alphatross and the sputtering ion sources of the EGP are summarized in Table 1. At the VdG protons were accelerated for 34 % and 4He+ for 66 % of the total beam time.

In the sample production the isotope separator ion collection energy varied from 100 eV up to 120 keV. Altogether 207 samples were produced from 23 different isotopes.

In the laser laboratory technical work was directed to minimize noise from electric power lines and from radio-frequency sources. During the autumn installations of equipments needed for laser trapping of biological objects were carried out.

 

 

Fig.1. Utilization per month of the EGP-10-II and the VdG accelerators

based on the charging system timers

 

Fig.2. Distribution of the beam hours divided into 0,5 MV intervals of the terminal voltage

 

Table 1. Beam hours for various ions from EGP-10-II

____________________________________________________

Ion

Ion source

Beam hours

Percentage

p

D

211

13.7

4He

A

511

33.2

7Li

SP

35

2.3

11B

SP

106

6.9

12C

SP

88

5.7

28Si

SP

44

2.6

35Cl

SP

9

0.6

127I

SP

485

31.5

186W

SP

9

0.6

197Au

SP

44

2.9

 

____________________________________________________

ª D= Duoplasmatron, A = Alphatross, SP = Sputtering

 

COMPUTER SERVICES

Sisko Vikberg, Emppu Salonen, Kai Arstila, Marcus Gustafsson, Jura Tarus, Jussi Sillanpää and Kai Nordlund

During the recent year, the laboratory computer system was upgraded with 5 new client machines and increased computational capacity. The four PC's handling all the heavy numerical computations were upgraded to 450 MHz dual-PII. A new Lexmark color printer, capable of also printing transparencies was acquired.

The primary operating system which all the client machines run is the freely distributable, UNIX-based Linux operating system (currently Red Hat 6.0). Samba software is used to enable the NT-machines to use the Linux as a fileserver.

The client machines (30 PC's ranging from 120 MHz Pentium to 600 MHz Athlon K7M) are connected through a 100 Mb/s network connection to our Linux-server "beam" (450 MHz dual-PII) and also to the four separate simulation computers.

Most of the application software is free and collected from the Internet. The word-processing is done by using the TeX/LaTeX program (and to a minor extent StarOffice, PowerPoint, and WordPerfect). Commercial software includes Mathematica, Matlab and MicroStation.

The main programming languages used are C, Fortran and different script-languages, such as Awk.

The fast network connections allow us to use the computer resources at the Physics Computation Unit (their DLT-drive is used for making the system backup), the Computer Center of the University and the super computers of the Center of Scientific Computing of Finland.

The machines use ssh (Secure Shell) for secure communication.

A web camera was installed to photograph the construction of the new "Physicum" building in Kumpula. Snapshots taken by the camera, as well as a presentation of the laboratory, are available at our WWW-server http://beam.helsinki.fi/.

 

 

Fig.3. The computer system of the Accelerator Laboratory

INSTRUMENT CONTROL AND DATA ACQUISITION USING THE LINUX-GPIB PACKAGE

Stefan Eriksson, Krister Henriksson and Kai Arstila

The general purpose interface bus (GPIB) uses the IEEE 488.2 standard to transfer information to and from instruments. Most high precision measurement instruments are fitted with this interface. The advantages of the GPIB is that several instruments can be connected to the same bus, thus allowing simultaneous control of these instruments. We have implemented the GPIB package on a standard Pentium PC running the Linux operating system. This provides a highly stable measurement environment that can be accessed from the laboratory network. The Linux environment is also versatile from the programming point-of-view. The measurement system has been used to study the temperature fluctuations of diode lasers and to record spectra in the optical injection experiments.

PUBLIC RELATIONS ACTIVITY

Birger Ståhlberg, Kai Nordlund and Jussi Sillanpää

The Department of Physics has continued the policy to invite students leaving the upper secondary school to visit the laboratories of the Department. In addition, an opportunity to get acquainted with working in a research institute has been offered to a few interested students in the last form of lower secondary schools.

In 1999 the Kumpula premises of the Accelerator laboratory were visited by 37 groups, 600 guests in all. Twenty groups were from upper or lower secondary schools, four groups from technical colleges and 5 groups from the University of Helsinki.