9 The MPI-K Accelerator Facilities

9.1 The Accelerators

K. Bechberger, W. Dürr, R. Fleckenstein, M. Frauenfeld, K. Hahn, R. v. Hahn, W. Hahn, K. Hallatschek, K. Hemberger, K. Horn, D. Hübner, C. Kaiser, D. Kaiser, H. Kandler, B. Knape, M. König, V. Kößler, D. Leitner, M. Müller, R. Pfahler, R. Repnow, E. Scheurich, T. Schiffmann, H. Schneider, W. Schreiner, D. Schwalm, A. Seltner, J. Vetter, P. Werle

During the last two years the Heidelberg tandem-postaccelerator system continued to serve as the main injector system for the TSR storage ring providing reliably various kinds of heavy atomic and molecular ions. Additionally, the linac was used successfully to boost the energy of beams generated by the High Current Injector HSI or to transport noble-gas ion beams from the PIXE pelletron. Part of the rf system of the linac is switched to power the HSI resonators.

Most of the cooling circuits of the accelerator building now have been rebuilt, efficiently saving resources and manpower. During the end of the year 2000 most of the MP experimental area has been cleared from old equipment to provide space for the installation of new non-accelerator atomic physics experiments.

9.1.1 The MP-Tandem Accelerator

During the most recent two years the MP-tandem accelerator operated reliably without major problems and almost all requested beam times could be performed as scheduled. The operating hours in 1999 were significantly lower than usual due to several extended shutdowns as the usual service periods for the accelerator were not sufficient for an extensive reconstruction of the cooling and air-conditioning systems of the accelerator building. Therefore, in 1999 the MP was run with voltage for 5634 hours, 3579 hours of which were used for user experiments (Fig. 9.2), while during the year 2000 the performance was with 7043 hours with voltage and 4844 hours for experiments appreciably higher again (fig. 9.3). In Tab. 9.1 the distribution of the total experimental time to the different ion species in use is listed.

Fig. 9.2: Terminal voltage used at the MP-tandem accelerator during the year 1999.

Fig. 9.3: Terminal voltage used at the MP-tandem accelerator during the year 2000.

Besides the two routine service openings of the MP one additional unscheduled tank opening was necessary in October 1999 because of insufficient voltage holding capability. Heavy dust production on one set of pelletron idlers on the high-energy side of the machine obviously caused voltage limiting breakdowns. The central fixing bolt of a large idler had loosened and was found on the tank floor. As this repair happened relatively shortly before the end of the year the following routine service period was postponed and accelerator operation was resumed immediately at the beginning of the year thus compensating some of the losses due to the construction periods.

In spring 2000 again a tank opening became necessary when a terminal cryopump suffered from bad performance causing several emergency stops of the machine, and an electrostatic terminal steerer power supply quit due to a burnt series resistor. The second opening of this year then was due to routine maintenance.

Tab. 9.1: Beams used at the MP-tandem accelerator during the years 1999 and 2000. Terminal voltages are given in MV, user times in hours.

Ion		1999				2000
Voltage	<10	10-11	11-12	Sum	<10	10-11	11-12	Sum
p		31	19	50	40	326		366
d	270			270
^3 He					7			7
^4 He	36			36	189			189
^6 Li	18			18
^7Li	719			719	1507	13		1520
^7 LiH	150			150
^9 Be	496			496	751			751
^12 C	113	229		342	87	459		546
CH	166			166
^13 C	83			83
Li2					281			281
CH2					151			151
^16 O	90	32		122
^19 F	162			162	61	79		140
^20 Ne					52			52
^28 Si	85			85	10			10
C2D2	131			131
^32 S	93			93
O2					105			105
^35Cl					118		41	159
^40Ar					26			26
^45Sc					161	50		211
^48 Ti	103			103
^56 Fe		112		112		161		161
^58 Ni		154		154
^63Cu							126	126
^160 Er	152			152
^167 Er	5			5
^168 Er	75			75
^170 Er	9			9
^238 U	46			46	43			43
Sum	3002	558	19	3579	3471	1206	167	4844

Year 1999 Year 2000

Operations 5634 h 7043 h

Beamtime 3579 h 4844 h

Conditioning, service, test 2055 h 2199 h

Shutdown, maintenance,

holidays 3126 h 1741 h

Several smaller improvements and modifications were realized around the accelerator. The support insulators of the chain diagnostic rings had to be replaced because of brittleness. The faraday cup in the terminal of the MP finally was successfully installed at a new, very restricted location and now can be used routinely. The reason for multiple malfunctions necessitating venting of the tube finally was pinpointed to an overpowered drive magnet, forcing the cup into a blocked position. The gas prestripper canal is available again and the vacuum gauge in the MP terminal is now working reliably. The pairs of regulating slits behind both analyzing magnets have been equipped with a servo drive and can be remotely positioned with an accuracy of 0.05 mm in a reproducible way. The old preacceleration voltage supply caused some problems. In 1999 the oscillator/driver amplifier was rebuilt to continue operation for another year. However, in 2000 two further HV decks of the Deltaray cascade failed and two others were damaged during diagnostic and repair efforts. As neither spare parts nor sufficient documentation was available it was decided to discontinue operation. A new, somewhat smaller power supply was ordered from a renowned supplier as a replacement and will be taken into operation in 2001.

A failure of an insufficiently controlled vacuum system resulted in a catastrophic oil contamination of the HE-chopper RF- and vacuum tank. Though not far from the high-energy acceleration tube, the accelerator vacuum system seems not to be severely affected. However, the doubly walled chopper tank had to be removed from the beam line for a disassembly and a thorough cleaning procedure. A reinstallation was not possible before the end of the year 2000. The vacuum systems of both rf systems (LE buncher and HE chopper) will be modified and equipped with wide range turbo- and oil-free membrane roughing pumps to avoid any further risk.

As may be seen from Tab. 9.1 several new ion species - especially molecular ions - have been delivered to the experiments. In most cases beam development for new molecular ions also had to be done with the ion source of the accelerator, as the superior diagnostic possibilities with the MP are necessary to help identifying the beams produced. While the novel LiH, C₂H₂ and C₂D₂ beams were produced in sufficient intensities for a successful storage in the TSR, the Li₂^–-beam output from the source was reasonable, however only a very small fraction survived the stripping process and were formed into positive Li₂ ions. The noble-gas ions Ar⁺ and Ne⁺ of course were directly produced as positive ions by the PIXE-pelletron and only transported through the MP to the TSR.

Quite some efforts were made to improve the infrastructure of the accelerator building. While in the preceding years most elements of the cooling systems external to the building (cooling towers, pumps, heat exchangers) had been renewed, in 1999 a second step was made: the complete power and sensing wiring system, control and monitoring system, several refrigeration machines, and a considerable part of the in-house water piping system were rebuilt, partly with increased capacity. Most of the system now can be remotely monitored and controlled using a state of the art PLD system connected to the computer network. In addition, the most corroded components of the air-conditioning system could be repaired, while the chillers and the control system still is in a desolate condition. The new system already has proven to run reliably, efficiently and much more economic with respect to manpower and general resources.

During the end of the year the traditional experimental area of the MP-tandem accelerator was reduced and concentrated from previously seven to the three most active beamlines. About 300 m² of floor space was set free for preparation of new experimental facilities producing and using ion beams independent from the MP-postaccelerator system. Fig. 9.1 shows the present floorplan after the rearrangement.

9.1.2 The Heidelberg Postaccelerator

During the last two years the complete linac was in operation only for a few periods. Two weeks of fully used linac operation in 1999 were followed by three weeks in 2000 with a major part of the resonators active. In Tab. 2 ion species, charge states, and beam energies of the six runs are compiled. In some cases only a fraction of the complete linac was necessary to provide the requested beams. The HD⁺ beams had been injected from the HSI for further acceleration by almost the full linac.

Tab. 9.2 Used beams at the Heidelberg linear postaccelerator (NB) in pulsed mode of operation with 10% duty cycle (P10). Mode HSI indicates injection by High Current Injector.

Ions	EMP[MeV]	QMP	QNB	ENB[MeV]	Time[h]	Mode
HD	(8)	1	1	15	200	HSI
^35Cl	110	9	9	140	41	P10
^45Sc	120	10	10	180	50	P10
^56Fe	130	11	20	280	106	P10
^58Ni	130	12	12	347	150	P10
^63Cu	145	12	25	290	122	P10

However, the Heidelberg linac-postaccelerator system has developed to be the central installation for all accelerator activities. Due to the modularity and reliability of the hardware and the transparency of the control system there are now numerous different modes of operation of the linac system, some of them occasionally are used simultaneously in parallel for different applications. The linac beam transport system is almost permanently in use to deliver beams from the MP-tandem, the PIXE-pelletron or the High Current Injector (HSI) for the TSR experiments. During commissioning of the HSI, the linac beamline has been most valuable for analyzing and optimizing the ion beam properties of the HSI.

Part of the rf power-amplifier system now can be switched between standard linac resonators and one or two modules of the new HSI- cavities. Also the buncher-rf-power amplifiers can be switched. However, the insertion of coaxial switches in the power and signal lines of the linac resonators necessitated a careful recalibration for all amplitude and phase measuring devices. Beams originating from the MP-tandem, the HSI-injector or the PIXE-pelletron now can be selected for further acceleration. The primary rf distribution system (phasing axis) had to be redesigned and modified as variable groups of rf amplifier chains have to be shifted simultaneously against each other. However, continuously working phase shifters for the relatively high power levels of the Heidelberg phasing axis still are a problem and have not yet been implemented. For the time being a software solution is used to replace these missing devices. Separate delays and pulsing units now are necessary to cope with all desired operational modes, e.g., conditioning of linac resonators during TSR beam experiments and HSI beam tests.

The complete beam handling and rf-control system of the postaccelerator is based on a modular CAMAC system driven by a PDP-based CAMAC interface via UNIBUS-DMA-transfers. Attempts to preserve the CAMAC interface but replace the obsolete UNIBUS port by a universal SCSI connection failed because of missing software driver support.

Initially only as an emergency fall back a totally software-based emulator [1] was tested which allows to run virtually all PDP software (operating system and application programs) on a completely standard PC hardware incorporating a PCI-based output card simulating electrically a standard UNIBUS connection. With the CAMAC interface connected and the postaccelerator software loaded into the PC it was possible to operate the complete linac system after only very small efforts for adaptation of the system to our needs.

Fortunately, these tests were sufficiently far advanced when the old PDP 11/44, which had been working very reliably for almost two decades, failed seriously. Without loss of time the linac control was successfully switched to the ‘ERSATZ-11’ system, now consisting only of cheap standard PC hardware components, running noticeably faster than the original system.

The emulator is DOS-based, WINDOWS can be used, too, however with some serious limitations when trying multitasking. A LINUX version of the same emulator soon will be available and might be able to efficiently break the barriers of the 16 bit PDP system, allowing to make a smooth transition from the old linac to the new HSI control system.

9.1.3 The 3 MV-PIXE-Pelletron Accelerator

The PIXE pelletron was routinely operated during the last two years for approximately 6700 hours providing proton beams for the PIXE group as well as various positive molecular and noble-gas ions for TSR experiments. Figs. 9.4 and 9.5 show the used terminal voltage versus time of the year. Standard operating voltage again was only 2.2 MV as the voltage upgrade kit has not yet been installed.

Fig. 9.4: Terminal voltage used at the PIXE pelletron accelerator during 1999.

In 1999 the machine had been opened six times for repair or modifications, in 2000 nine tank openings were necessary for servicing terminal equipment. Not in all cases the apparent problems could be solved by only one interaction, as some defects reappeared almost immediately after repressurizing because only symptoms had been cured. Other problems were directly pressure dependent and did not show up at the opened machine, e.g., problems with electromechanical components or rf interference problems.

Fig. 9.5: Terminal voltage used at the PIXE pelletron accelerator during 2000.

Appreciable time had to be invested to achieve a better ion-source brightness. The results with the compact magnetron ion source [2] so far were disappointing. Further tests intended to improve the emittance and brightness of the beam were discontinued as the anticipated improvements could not be achieved, probably as the H₁:H₂:H₃ intensity distribution was rather unfavorable with respect to atomic hydrogen.

Instead a brand-new standard rf ion [3] source was installed and tested on the test bench. In contrast to experiments with an old and previously used source the brightness of the beam was surprisingly better by a factor of 80 in comparison with the PIG source. As part of the improvement program it was decided to implement this source quickly in the terminal system in order to benefit in advance from higher brightness beams. Doubly shielded enclosures were built for all control boxes and necessary power supplies, but the source head was installed open and unshielded as it is usual in the terminals of many accelerators. After commissioning the machine behaved well but exhibited various strange instabilities which only became noticeable when focussing down to micrometer beams in the PIXE experiment. Much time had to be invested and various sources for instabilities in the 10^-4 regime were detected. However, the main origin finally was pinpointed in the terminal electronics as the radiation from the unshielded rf source influenced the stabilization circuits of various power supplies. Blocking and rf filtering of all leads going into and out of the supply boxes were tried but the high rf fields influenced virtually all units. Even with the massive terminal shell closed, the power supplies inside the terminal shell were influenced by the position of the pressure vessel of the accelerator. Finally, solid enclosures were built around the ion-source head and the rf generator with massive rf filtering on all connecting lines. This improved the situation considerably and at least allowed to use the high brightness source for µ-beam experiments. As a prototype for the final solution in the upgraded machine a solid pillbox-type common enclosure for source head and rf-oscillator was designed, built and installed in the present terminal, replacing the provisional rf-shielding (Fig. 9.6). The shielded source is now running rather reliably with good initial characteristics. However, the useful lifetime of the source is somewhat limited. A gradual degradation of performance is noticeable and after 2500 hours of operation, the source head normally is changed because of starting problems, instabilities of the discharge and low beam output. Typical performance data measured under identical conditions for the intensities of the three hydrogen lines are given in Tab. 3.

Tab. 3: Hydrogen output of rf ion source

	H1	H2	H3
Fresh source	100 µA	54 µA	15 µA
Source after 2500 h	18 µA	6 µA	0.7µA

Fig. 9.6: Common shielding enclosure for the rf-source head and power oscillator.

During the search for instabilities the properties of various components of the accelerator have been systematically investigated and improvements could be introduced to various systems. The shunt regulation system of the analyzing magnet was replaced by a DC-current transformer to reduce the thermal drifts, steerer power supplies were modified and the computer-controlled terminal stabilization system was improved by the installation of 16 bit ADCs.

9.1.4 Ion Beam Developments

Development work at the ion-source test bench was aimed in two directions. One major effort was made to improve the beam characteristics for the µ-PIXE experiments. A very compact microwave source was purchased which had very attractive specifications for H⁺ beams. After installation at the test bench the total beam output met the specifications, however the H₁/H₂/H₃ ratio was as unfavorable as for the PIG source previously in use and no method was found to increase the H₁ fraction considerably. The emittance and brightness data were not better than the corresponding data of the PIG source. Though the ease of operation and the compactness of the source are very attractive, these experiments were discontinued for the time being.

For direct comparison a factory-fresh standard rf ion source [3] was installed at the test bench. Though the total extracted beam output was lower, the relative H₁ fraction was considerably higher for this source. The brightness was measured to be 3.5 nAmm^–2mrad^–2keV^–1 which was an improvement [4] factor of nearly 80 compared to the presently used source and it was decided to transfer this source to the terminal of the PIXE accelerator. For FCC reasons, the source on the test bench had been operated within a large rf shielding. Therefore none of the interference effects and stability problems were recognized which later on caused serious problems and long delays after installation in the terminal of the accelerator.

For a further improvement of the beam quality a mass analysis will be performed. A commercial Wien filter was therefore purchased for this purpose. In order to check the matching between source, Wien filter and tube a mock up of the ion optical components including their future control units was built (Fig. 9.7).

Fig. 9.7: Test bench of the ion-optical components of the new 4 MV ion-source terminal.

In spite of the rf-tight shielding of the system, during first operation of the source severe disturbances were realized in the control and regulation systems which need to be cured before integration into the terminal. Several other supply units still have to be redesigned to provide the main ion-source parameters within a very restricted geometrical space.

The second field of activities at the test bench were related to the generation of various molecular ions. Most attention was paid to various suggestions to produce a ⁷Li₂⁺ molecule for storage into the TSR either by acceleration by the MP tandem or the PIXE pelletron. A special oven version of the PIG source was built and operated at the test bench. Some promising lines for A = 12, 13, 14 originally were analyzed, but their relative intensities did not support the assignment to Li₂ molecules and their intensities vanished with time. Other tests were made with modifications to standard negative ion sources of the MP-300 kV injector. Very low ⁷Li₂^– beam intensities were extracted from the Li charge-exchange canal of the duoplasmatron even when operating the canal at extraction potential and using Kr⁺ as primary beam (1 nA/12 nA). In a second attempt the standard sputter source MISS-HD was equipped with a Li-loaded crucible to generate a Li vapor in the Cs primary beam (7 nA). With all these methods only a few pA of ⁷Li₂⁺ beam could be analyzed behind the MP. Finally the standard sputter source was loaded with several different Li compounds containing already Li dimers in their molecules. However, best results were achieved from standard LiO₂-Ag mixtures giving about 120 nA of ⁷Li₂^– output from the source. After acceleration and stripping 400 pA of presumably ⁷Li₂⁺ molecular beam was analyzed proving that a small fraction of Li₂ ions survive the charge exchange process. However, this intensity was found to be insufficient to be used in the storage ring.

The request for LiH⁺ molecular beams could be satisfied somewhat more successfully. From a LiH-Ag-loaded source 300 nA of LiH^– was extracted giving about 2 nA of analyzed LiH⁺ beams at 6 MeV. A reasonable lifetime of the source of about 24 hours allowed almost continuous experiments with the TSR.

9.1.5 Electronic Developments

A major part of the activities was devoted to support the commissioning and operation of the present High Current Injector as well as to prepare the second phase of this project. To improve the stability and reliability of the ion-source control system especially under sparking conditions it was decided to install all major components inside EMI shielded enclosures. The same basic principles were followed during design and definition of the control system of the ECR source, which will be based on the well proven, proprietary EUNET [5] system. Several specialized modules were developed and built to simultaneously ramp different current supplies in parallel using high-resolution DACs, e.g., to support taking intensity distributions of particle spectra of the ECR source automatically. Other modules to read out high-resolution Hall probes and other interfaces with beam diagnostic multiplexers have been built and installed.

For the REX-ISOLDE project a profibus control interface for existing quadrupole power supplies was designed and assembled, the profibus interface of the rf-amplifier was commissioned.

The postaccelerator control system now is equipped with several flatpanel TFT touchpanels which are designed to be at present plug compatible replacements for the old CRT units but later on can be also used as high-resolution VGA displays with standard PC interfaces. Also the general status display of the postaccelerator has been replaced by a TFT device with RGB interface. Also the MP control console has been upgraded with several new flatpanel displays as operator interface via touchpanel and general status and alarm displays.

As the rebuilt cooling systems now allow a remote access via network, a detailed general status display of the system now is available for the operator (Fig. 9.8). In addition a continuous data logging of various parameters and alarms of the accelerator as well as of general supply parameters, e.g., electrical power consumption, water consumption in different places of the institute is done. Thus, a massive leak in an underground water pipe was detected automatically within a
few hours after occurrence.

Fig. 9.8: On-line status display of the cooling system.

Progress of the improvement program of the PIXE pelletron, however, has been slow. The concept of the new control system for the ion source terminal has been defined, hardware components for the user interface had been prepared. The new compact ion-source terminal assembly including extraction system, Wien-filter mass analyzer and matching lens has been built and the shielded versions of the necessary electronic supplies for the rf oscillator and the HV supplies are going to be tested. Some modifications are still necessary to improve the EMI and sparking immunity of the controls. Fig. 9.7 shows the assembly of the terminal system which will be tested with beam before installation.

A prototype version of the rf ion source previously was installed in the present terminal of the PIXE machine to test its performance. Appropriate rf and voltage supplies were built to power and control this source.

Recently an increasing number of failures was registered on various power supplies because of leaks in the water cooling. It was decided to systematically change the rubber hoses on all first-generation power units which had become brittle after more than 20 years of operation. A considerable number of corroded solderings at the internal water manifolds were detected and had to be reworked at this occasion, too.

The accelerator group now is represented on the web, too, with several pages showing activities and achievements.

[1] ERSATZ-11, V 2.1, DBIT Inc., NY, 1.4.1999

[2] Ishikawa, J., Y. Takeiri, T. Takagi, Rev. of Sci. Instrum. 55 (1984) 449, HVEE Model SO-80-2

[3] HVEE Model SO 173

[4] Scheloske, S., W. Dürr, M. Maetz, R. Pfahler, R. Repnow, H. Schiebler, K. Traxel, Nucl. Instr. Meth. B161-163 (2000) 302

[5] Annual Report MPI-K 1987

9.2 The High-Current Injector HSI

K. Bechberger, R. Cee, R. Fleckenstein, M. Frauenfeld, M. Grieser, K. Hahn, W. Hahn, R. von Hahn, C. Kaiser, D. Kaiser, V. Kößler, S. Papureanu, R. Pfahler, R. Repnow, T. Schiffmann, H. Schneider, W. Schreiner, D. Schwalm, P. Werle

After completion of phase I of the High-Current Injector (HSI) already 22 machine and regular beam times with singly charged molecular and atomic ions were performed in the reporting period. In preparation of phase II at the new injector, which will allow the production and acceleration of highly charged ions, an ECR source has been acquired, which is currently under test in our laboratory, and a charge state separator has been designed, which is presently being installed between the HSI and the post accelerator.

9.2.1 Operation of the High-Current Injector

In the reporting period, the high-current injector HSI delivered several molecular and atomic ions for experiments with the test storage ring. Tab. 9.4 summarizes the atomic and molecular ions delivered by the HSI. For most experiments the RFQ final energy of 0.5 MeV/u was sufficient. A few beam times required higher energies which could be achieved using the 7-gap-resonator section behind the RFQs.

In an experiment with HD⁺ ions the largest possible energy was requested. Therefore the high-current injector and the postaccelerator were operated together for the first time. With the aid of a rebuncher the bunch length of the beam was matched to the acceptance of the postaccelerator and a final energy of 16 MeV was achieved.

For an experiment with ²⁴Mg⁺ ions, on the other hand, the lowest possible energy was requested. We were able to extract an Mg beam from the CHORDIS source and to transport it through the RFQs, operating them with about 40% of the maximum input power. Due to the velocity mismatch, the RFQs were only focussing and not accelerating the beam. The transmission was about 5%. Without the focussing option of the RFQs (no rf power) no beam after the RFQs could be measured.

In several experiments the beam intensities reported in Tab. 9.4 were limited by the experiments. The beam intensities were reduced in these cases by a chopper in front of the RFQs and by the TSR chopper.

In a machine test beam time with He⁺ of 8 MeV and a beam current of 100 µA we investigated the transmission through the whole LINAC. The transmission through the RFQs was found to be 72%, through the Linac 88% and to the postaccelerator also 88% leading to an overall transmission of about 56%. We will try to further improve these values.

Tab. 9.4: Atomic and molecular ions delivered by the high-current injector.

Beam	Energy [MeV]	Intensity [µA]	Year
HeH^+	2,4	4	1999
He^3D^+	2,4	1	1999
He^+	7,4	300	1999
D2^+	1,9	30	1999
^24Mg^+	0,03	1	1999
H3^+	1,4	60	1999
HD^+	1,4	40	2000
H2^+	2	3	2000
H3^+	1,4	4	2000
HeH^+	2	3	2000
H3^+	1,4	2	2000
D3^+	2,9	2	2000
HD^+	16	1	2000
H^+	0,5	0,2	2000
D2^+	1,9	17	2000
HD^+	16	1	2000

9.2.2 New developments

The residual-gas ionization beam profile monitor. The maximum power dissipation on the grid wires limits the applicable beam current to a few µA depending on the ion species and energy. To be able to measure the beam profiles also at higher currents, a beam profile monitor using residual-gas ionization was developed. This device consists of two plates with an electrical field in between. Residual-gas atoms are ionized by the beam and accelerated to the imaging electrode, where an arrangement of 32 collecting strips made of copper is used to detect the ions. The read-out system was designed in such a way that the electronics used for the profile grids can be used with small modifications also for the residual-gas monitors.

First measurements with 360 µA of ⁴He⁺ at an energy of 1.9 MeV demonstrated the functionality of this new system. To compare the measured beam profile of the residual monitor with the profile grid measurements, a pulsed current of 78 µA with 1.5 ms pulse length was used. This is the highest current the grids can stand. The profiles measured at the same position agreed within 0.1 mm in the measured FWHM value of the beam.

The separator system. To separate the charge states behind the stripper, which will be required in phase II to increase the ionic charge before further acceleration in the postaccelerator, a separator system consisting of 4 identical 45 degree bending magnets has been designed. Allowing for edge angles of 22.5 degree these magnets are rectangular magnets and fulfill the requirement that the dispersion after the separator is zero. The parameters of the 4 dipoles are presented in the following Tab. 9.5.

Tab. 9.5: Parameters of the separator magnets.

Bending angle	45 degree
Edge angles	2x22.5 degree
Bending radius	800 mm
Bmax	1.8 T

At the end of 2000 all 4 magnets were delivered. After a few changes of the alignment ports, the first magnet could already adjusted in the beam line and enabled us to measure the beam energy behind the HSI not having to guide the beam to the magnet D3 behind the postaccelerator. The remaining 3 magnets are presently being installed.

Radiation-cooled cup. An energy dissipation of about 10 W is the maximum dissipation for a standard cup. Assuming a beam intensity of 200 µA at 8 MeV for He, which is easily available at the HSI, the total energy in the beam is about 1.6 kW. Therefore a new radiation-cooled cup was developed. It consists of a standard cup used at the accelerator, housed in a water-cooled copper block. This principle avoids the usual insulation problems with directly water-cooled devices.

Beam transformers. Along the beam line from the high-current injector up to the TSR beam transformers were installed to measure the beam intensity without destruction of the beam. This system enables us to protect the beam line when using high currents by interlocking on the measured currents in each transformer. Any deviation of the beam intensity larger than a specified one leads to stopping of the beam at a water-cooled cup close to the source.

9.2.3 Control System

The control system for the high-current injector was running during the reporting period without major problems.

By applying a new front-end computer (FEC) for the Camac modules, the system is now able to control also the resonators of the high-current injector. The RFQs were equipped with the same CAMAC system as used in the postaccelerator. The software was kept also very similar to the post accelerator to ease the operation. Also an automatic turn-on routine of the resonators was implemented.

Another FEC, the EU-Net, was equipped with a second interface card to optimize transfer rates to the hardware of the separator to be used in phase II.

To support an online fault diagnosis all set and actual values, the vacuum-status and an overview of non-working components are now available via MPI intranet.

Several smaller changes made the machine control more comfortable. As an example, a coupling of channels to give all resonator phases of the used resonators the same offset is now implemented. Due to its reliability this control system will also be used to control the ECR ion source and the new electron target.

9.2.4 The ECR Source

In preparation of phase II of the high-current injector an ECR Source for the production of highly charged ions was bought, which is presently installed on a test bench. The next aim is to collect experience with operating the source and to optimize all ion production methods, i.e. gas, oven and sputter modes.

The system consists of the source itself, a solenoid and a double focussing magnet to determine the charge state and the energy. Due to the required input energy of 4 keV/u of the first RFQ, the source has to be operated at potentials up to 36 kV for A/Q = 9. All acceptance tests at the manufacturer were very successful. We achieved stable operating conditions at 36 kV, and all required intensities with specified charge states could be produced.

It is planned to install the source at the HSI in 2002.

9.3 The Heavy-Ion Storage Ring TSR

M. Beutelspacher, M. Frauenfeld, M. Grieser, K. Hahn, R. von Hahn, K. Horn, V. Kößler, R. Repnow, W. Schreiner, D. Schwalm, P. Werle, A. Wolf

In 44 beam times molecular ions and atomic ions with masses up to 63 were successfully stored and cooled in the TSR.

In the reporting period, the TSR was used for atomic-, molecular- and accelerator-physics experiments for more than 6500 hours in 44 beam times. Ion species stored in 1999-2000 with ion currents > 1µA are listed in Tab. 9.6. For some molecular and atomic ion beams the beam intensities were below 1 mA and could not be measured with the current transformer of the TSR. The beam lifetimes listed in Tab. 9.6 refer to the average TSR vacuum between 3´10^–11 and 8´10^–11 mbar. The heaviest ion species stored in 1999-2000 was ⁶³Cu²⁵⁺. For Coulomb-explosion imaging experiments the following molecules were extracted from the TSR: H₃⁺, HeH⁺, D₂H⁺, D₃⁺, LiH⁺, CH⁺, CH₂⁺, C₂D₂⁺ .

In 1999 the TSR was modified to provide the infrastructure for the new electron target: The support of the laser cooling section was placed on rails and rebuilt. Also the rails for the supports of the electron target were installed in the reporting period. To provide space for the new electron target and the laser section, it was necessary to change the position of the induction accelerator (INDAC) towards a position in front of the electron cooler; due to the limited space, a new support for the induction accelerator had to be constructed. Moreover, the cold atom target consisting of a small cold Cs cloud in a magnetic optical trap was installed into the TSR behind the electron cooler.

Also in 1999 the cathode of the electron cooler had to be replaced. After outbaking of the cooler and one third of the TSR, leaks appeared in the electron cooler: For unidentified reasons three feed-throughs of NEC pumps were leaking and had to be replaced. Unfortunately, one of these feed-throughs was located in a unfavorable place in a toroid chamber of the electron cooler and its repair required to dismount one arm of the electron gun. Moreover, a water leak in the cooling coil of the electron cooler collector required also its replacement.

Tab.9.6 Measured beam lifetimes and beam currents in the TSR during 1999-2000

Beam	Energy [MeV]	Intensity [mA]	Lifetime [s]
H2^+	1.9	5	9
HD^+	11.9	23	39
D2^+	1.9	< 1µA	20
HeH^+	2.38	50	29
^9Be^+	7.3	25	29
^16O^2+	6.1	130	14
^19F^3+	11.6	200	18
^19F^6+	74	335	118
^32S^9+	20	80	9
^35Cl^13+	140	750	103
^45Sc^18+	178	380
^48Ti^13+	35.7	6	25
^48Ti^17+	106	2	100
^58Ni^25+	342.4	600	60
^56Fe^9+	100	36	38
^56Fe^10+	123.5	31	45
^56Fe^11+	121.9	58	61
^56Fe^12+	145	65	44
^56Fe^20+	280	71	600
^63Cu^25+	290	280	49