For at ændre ”Enhedens

navn” og ”Sted og dato”:

µ RDS111 and Eclipse RD/HP Cyclotron User Meeting 2014

Holger Jensen

PET and Cyclotron unit

Department of Clinical Physiology, Nuclear Medicine & PET

Rigshospitalet,

University of Copenhagen

Denmark.

E-mail: holgerj@pet.rh.dk

Phone: +45 3545 1866

Fax: +45 3545 3896

Copenhagen Eclipse Issues – DV97

Agenda

Side 2

1. RF issues

2. Vacuum issues

3. (Ion source issues)

RF-problems - Burned RF-fuses.

Side 3

• Total number of burned RF-fuses since December-2008 = 46

• Average time interval = 45±86d, minimum = 0d, maximum = 497d

• No systematic recording before 2008, but less faults.

• Similar frequency for many other Siemens/CTI cyclotron users.

0

2

4

6

8

10

12

14

16

18

20 Average time interval [d]

• Last burned RF-fuse in our SCX MC32 cyclotron in 2003, when we had a real problem in

the power amplifier.

• And when a former physicist tried to kill him self by opening the RF-power amplifier

with power on.

• Our other non-Siemens cyclotron colleagues se NO burned fuses.

• Does Siemens have a RF-

design problem?

• We intend to hire our own

RF-expert to investigate the

problem.

RF-problems – Final amplifier, load capacitor

Side 4

• Sparking in the amplifier can cause burned fuses.

• Load capacitor plates ( May-2014) dirty like h... and marks after sparks.

• Do you see a similar effect at your machines?

• Scratches around mounting screws (so avoid burrs).

• Marks from sparking at edge between plate and metal strap to the “line section”.

• RF and HV need rounded corners and NO sharp edges (or redundant holes).

• We plan to make new plates our self.

RF-problems – Final amplifier, load capacitor

Side 5

• Sparking in the ....

...

• Plates were polished and cleaned.

• Fuse-burning ≈ unchanged, but we got more RF-power!

Text book example of damaged Kapton foil (and clear sparking mark) during previous

mounting of RF tube was found and corrected.

RF-problems – Bird directional coupler

Side 6

• Since the installation in January 2005 we have observed 5-10 broken “Bird pickup

directional couplers”

• ELEMENT DIRECTIONAL COUPLER -50 DB 50-100 MHZ FOR 1-5/8" LINE, S/N= 1018 1521

• In most cases the reflected power pickup coupler. But forward- and reflected coupler

are identical! Maybe more critical!

• Never the two 1kW and 10kW pickups at the “Wattmeter line section”

• Is this unique for Copenhagen DV97 or do you see this at other machines too?

• We have managed to repair a few (a broken diode), but often the pickup

loop is broken and un-repairable.

RF-problems – Broken RF-relay board

Side 7

• Since the installation in January 2005 we have twice had burned parts on the RF-relay

board

• 10/2006

• 02/2014,

• Is this unique for Copenhagen DV97 or do you see this at other machines too?

Melted/burned RF cable in 07/2006,

Side 8

RF-problems – Melted/burned RF cables

Wrong impedance match?

Standing waves?

Connector problems?

New home made support

for connector (ver. 1)

Side 9

RF-problems – Melted/burned RF cables

Melted/burned RF cable in 07/2006, 07/2010

Wrong impedance match?

Standing waves?

Connector problems?

New home made support

for connector (ver. 1)

Side 10

RF-problems – Melted/burned RF cables

Melted/burned RF cable in 07/2006, 07/2010 and 04/2014.

Wrong impedance match?

Standing waves?

Connector problems?

New home made support

for connector (ver. 1)

Connector problems?

Support can catch fire?

New support for connector

(ver. 2) in Aluminium.

RF-problems – Fire in RF cable - 1

Side 11

• Problems getting RF on.

• Checking “chamber”, cable and amplifier.

• Found an indication of melted insulation in the cable at

the connector.

• Prepared for mounting a new cable.

• But did not change the cable.

• This was a big mistake.

RF-problems – Fire in RF cable - 2

Side 12

• Manual sweeping for the resonance at a low RFA

(power ) level 10-15 kV .

• Could hear noise/sparks.

• Observed light from behind the shield even after RF

switched off .

• Fire in cable/connector.

• Spare cable damaged too.

• Conclusion: RF trouble shooting should always

be done at very low power level.

RF-problems – Cable and connector specs. - 1

Side 13

• The RF-cable connectors are VERY shaky.

• Easily damaged by small movements during shield- and tank- openings.

• We (DV97) are not the only customers that experience this problem.

• Siemens/CTI should find an improvement.

• Does Siemens have a RF-design problem?

• Customer complaint sent in April/2014 Reply from Siemens/Knoxville (27/06/2014).

• Has offered to work on a solution together with us. So any input from you?

RF-problems – Cable and connector specs. - 2

Side 14

My “RF”- friend:

Prof. Jong-Seo Chai,

Sung Kyun Kwan University,

Republic of Korea

always say build your own solution if you are not satisfied with the offered solution.

Our connectors are NOT designed for cyclotrons as we use them, but more

likely for fixed mountings in commercial radio-, mobile phone-, ... antenna

systems, ...?

The old connectors were clearly better than the new!

Cable specifications: “LCF78-50JA”

Concerns:

• Power: < 10,6 kW

• Temperature: What is the temperature depense for maximum power?

• Length: within the recommended 222±2”, but I see variations in v/c at

different specification sheets.

• Repeated bending radius: 250 mm!

• Peak voltage: What is the voltage in the cable for our applications?

Jong-Seo Chai: Father of the

KIRAMS-# cyclotron program in

the Republic of Korea.

RF-problems – New cable position - 1

Side 15

• The RF-cable connectors are VERY shaky.

• Easily damaged by small movements during

shield- and tank- openings.

• Suggestion for new solution – 1:

•A fixed RF-line section as in the “Advanced

Cyclotron Systems” (ACS) cyclotrons, TR#:

• Disadvantage when opening and closing tank

RF-problems – New cable position - 2

Side 16

• The RF-cable connectors are VERY shaky.

• Easily damaged by small movements during

shield- and tank- openings.

• Suggestion for new solution – 2:

•A new cable position:

• Disadvantage we have to cut in the shield

RF-problems – documentation, procedures, ...

Side 17

• Siemens should work on all these RF-issues and come up with better technical solutions

• Better and more consistent procedures are demanded. For example: RF-tuning, the use of

dummy loads at various stages in the amplification, ...

• Recommended parameters to measure, like Q-values, gain in tube, impedance mismatch, ...

• Recommended PM procedures

• Advanced RF training course

Agenda

Side 18

1. RF issues

2. Vacuum issues

3. (Ion source issues)

Vacuum issues – why - 1

P19

My favourite discussion subject is ion sources. But today I will have to stop at vacuum.

We all want to have better performing ion sources!

If Siemens want to win the 18F competition with IBA, GE, ACS, ... They have to find a almost factor 2 more beam intensity, due to the low beam-energy!

Is this possible?

Why do CTI, GE, IBA, … machines deliver more or less the same beam?

Vacuum issues – why - 2

0

20

40

60

80

100

120

140

160

180

200

0 100 200 300 400 500 600 700 800 900 1000

Cu

rren

t @

ex

tract

ion

[µ

A]

Ion source current [mA]

MC32 A

MC32 B

MC32 C

PETTrace A

PETTrace B

Cyclone 18 A

Cyclone 18 B

Cyclone 18 C

Eclipse A

Eclipse B

Eclipse C

Eclipse D

• Examples: H- beam current at extraction point.

• 2x GE PETtrace, 3x IBA Cyclone 18/?, 4x Siemens/CTI RDS Eclipse.

• Contributions to my overview is highly appreciated.

Vacuum issues – why - 3

Is there any physics law or technical limitations that prevent us from having 10 times more beam in our Internal Cold Cathode Penning Ion Sources?

I have discussed and discussed with “everybody” and haven’t found any real “experts” or easy solutions.

So it would be nice to get access to what CTI have done to optimize ion source yields.

How far has this “limitation” been explored by CTI/Siemens and is it published?

Field and orbit calculations for central region?

How critical is the alignment of the central region?

Optimization of ion source?

Space charge limitations/effects?

Volume/surface ionization optimization (Cesium?)

Vacuum effects?

Sufficient RF-power?

...

Dual 60μA & T=80% gives Pbeam =2x11x60/0.80 = 1.65 kW,

but

dual 100μA & T=80% gives Pbeam =2x11x100/0.80 = 2.75 kW.

PRF = 7,0 + 2,75 ≈ Pmax = 10 kW

Vacuum issues – why - 4

Is there any physics law or technical limitations that prevent us from having 10 times more beam in our Internal Cold Cathode Penning Ion Sources?

I have discussed and discussed with “everybody” and haven’t found any real “experts” or easy solutions.

So it would be nice to get access to what CTI have done to optimize ion source yields.

How far has this “limitation” been explored by CTI/Siemens and is it published?

If I want to run tracking codes myself will it be possible to get access to the field mapping data for our DV97?

We want to start on this for our Scanditronix MC32 in 2015 together with Jong-Seo Chai.

Vacuum issues - What IS performance can we obtain?

• Negative ion PIG development was

done in the 60’ and 70’ties.

• Focus today is at other types of IS.

• Most experts are no longer active.

• So we have to read the literature (i.e.

Proceeding of XX’th Int. Conf. on

Cyclotrons)

• Example: G.O. Hendry, T.Y.T. Kuo,

CS15 Compact Cyclotrons and CP42

Cyclotrons.

P23

• Already 30 years ago ≈ 180 µA H- was

reached @ Iarc = 500 mA !!

• This is what we see today.

• But is this the limit?

• P. Schmor, TRIUMF, claims he can make

much more.

• But he wants to have a patent on his

solution. So it is a secret so far.

Vacuum issues – vacuum in the central region

P24

• First question from IS- “experts” at CERN, TRIUMF, ESS is often

“what is your vacuum in the central region”

• A good vacuum is essential for negative ion machines.

• A d… good question and at the same time a d… difficult question.

•

• Vacuum gauges are not sitting in the central region.

• Has CTI/Siemens measured the vacuum profile from the center to the extraction

point?

• For our SCX MC32 we have obtained better IS

performance by improving the pumping

conductance in the central region.

• We want to support this by Monte Carlo

Simulations and predict the effect.

• With access to CAD drawings for the central

region this could be repeated for our DV97 too.

Vacuum issues – backstreaming - 1

P25

• Siemens/CTI is the only cyclotron producer I know about that uses diffusions pumps

without baffles.

• Some producers have started to exchange DP’s with Turbo and Cryo pumps. Maybe

they have a point?

• Black stuff = cracked oil is it normal in other machines?

• Guess if these 3 pictures are from the same machine?

Vacuum issues – backstreaming - 2

P26

• I have asked around among vacuum- and diffusion pump experts (ESS,

Pfeiffer, HSR/Baltzer, ... ) what they think about DP’s without baffles.

• It is a big science and difficult to get a clear answer. For some applications it is

OK for other it is absolutely not.

• For cyclotrons it is so far only the CTI sales people (when we bought the

machine in 2004) that have recommended DP’s without baffles (and even

without HV valves). And I have talked with many about this!

• Back streaming can range over many orders of magnitude. Even with the best

quality oil (i.e. Santovac V) back streaming will still be present (Urs Frick,

HSR)

• The amount of back streaming depends on many factors

The quality of both the DP- and foreline pump oil.

Pump design and Vacuum chamber geometry.

The conditions of both DP- and foreline pumps

A correct alignment of jets in DP,

...

Vacuum issues – example of reduction in back streaming

Side 27

Our VHS-6 with cold cap and/or extended cold cap acts a little bit like a baffle!

Vacuum upgrade for MC32

• Improved cooling of baffles:

a) Present cooling water temperature: 12-14ºC.

b) Replacement with HSR BFC 400 multi baffles

with PCF145-Z refrigerator.

c) Both water and refrigerant (R134a) cooled.

d) T = -13-17ºC

e) Can be cooled with LN2 too.

f) Back streaming down by a factor 10.

g) We have seen an improvement in vacuum.

P28

Vacuum issues – we want to install test baffles - A

Side 29

• Baffles for test on DV97:

a) Adding HSR BFC 160 multi baffles with

PCF245-Z refrigerator.

b) Both water and refrigerant (R134a) cooled.

c) T = -13-17ºC

d) Can be cooled with LN2 too.

e) Back streaming down by a factor ???.

• The space is VERY limited under the magnet!

• We want to start by re-arranging all cables,

gas and cooling pipes.

• The “cyclotron-pit” should have been deeper,

but …

Vacuum issues – we want to install test baffles - B

Side 30

•The “cyclotron-pit” should have been

deeper, but could the legs be extended and

the shielding be made 20 cm higher?

Finito, basta,

Finito, basta, …

Side 31