# Presentation: 240703

## The chopper structure-recent developments   F. Caspers, Y. Cuvet

- Where are we today
- According to the original planning, detailed technical drawings should have been ready in June 2004 and all the hardware for the pre-prototype in Sept. 2004
- but there were considerable delays due to other priorities at CERN in 2004
- Since end of December 2004 the detailed technical drawings are ready and have been checked
- We expect the delivery of all bits and pieces by end of March 2005
- Assembly by end of May 2005

## Just a reminder what its about

- A double meander structure (400mm length) printed on an alumina substrate has been designed and developed four our application + parameters (v/c=8%)

- beam

- Metallization:
- Molybden/mangan +
- silver

## Some details (1)

- The printed meander lines on alumina with metallic back-plane

## Some details (2)

## Some details (3)

- Only upper plate cooling circuit shown here

## Some details (4)

## Some details (5)

## Some details (6)

## Some details (7)

## Some details (8)

## What happened in the meantime(1)

- There are considerations and evolutions on the power amplifier side, which could permit us, to come to a coaxial (instead of triax) version.
- If successful wrt power amplifier, we could rather easily modify the chopper structure to coax.
- In this case we would not need to carry out a precise determination of the cross-over frequency between standing wave and traveling wave mode of operation

## What happened in the meantime (2)

- A detailed investigation of  heating of the meander lines as well as heat transfer to the water cooled back plane (in UHV)
- We had already tested a meander structure in air with 10 Ampere DC current  result ok.
- But in vacuum there is not too much convection (hopefully) and there were question marks on the heat transfer by conduction and/or radiation between the alumina ceramic and aluminum back-plane (gap of a few micron). In short we can expect a good heat transfer via “tunneling”

## Thermal analysis (1)

- Assumption: Ceramic substrate with cooled back-plate 160 x 100 x3 mm
- Conducting strip:35 micron copper, 1.8 mm width, 48 Ampere

- By: Dr.J Adam
- Flomerics

## Thermal analysis (2)

- By: Dr.J Adam
- Flomerics

- Heating example of printed 35 micron strip on 0.5 mm thick alumina –no back plane –in air.

- Width of alumina substrate = 100 mm

## Thermal analysis (3)

- By: Dr.J Adam
- Flomerics

- Heating example of printed 35 micron strip on 1 mm thick alumina –no back plane –in air.

- Width of alumina substrate = 100 mm

## Thermal analysis (4)

- By: Dr.J Adam
- Flomerics

- Heating example of printed 35 micron strip on 3 mm thick alumina –back plane watercooled.

- Width of alumina substrate = 100 mm

- Width of metal strip [mm]

- Temperature of metal strip[ deg C]

- IDC = 13 A

## Thermal analysis (refs)

**Literaturangaben**
-  Weitere Infos zum Thema Strombelastbarkeit, insbesondere berechnete Strombelastbarkeitsdiagramme, in:
- Adam, J.: *“New Correlations Between Electrical Current and Temperature Rise in PCB Traces*”. Proc. 20th IEEE SEMI-THERM Symposium, 292-299 (2004)
**[****2]** Adam, J.: „*Neues von der Strombelastbarkeit von Leiterbahnen*“, DVS/GMM-Fachtagung „Elektronische Baugruppen - Aufbau- und Fertigungstechnik. GMM-Fachbericht **44**, 117-123 (2004)
- http://www.flomerics.de/Produkte/Flotherm/Beispiele.html
**[1]** Adam, J.: „*Strombelastbarkeit von Leiterbahnen III. Weitere Diagramme für Multilayer und Umrechnungsregeln*“, PLUS **6** Heft 4,  513-518 (2004)
- Adam, J. : „*IPC-2152 : Neue Richtwerte für die Strombelastbarkeit von Leiterzügen in Leiterplatten*“. Konferenzband 11. FED-Konferenz Ludwigsburg, 11-331 (2003)
- Adam, J.: „*Strombelastbarkeit von Leiterbahnen* *II. Die IPC-Richtlinie IPC-D-275: Mythos und Wirklichkeit“*, PLUS **4** Heft 11, 1817-1823 (2002)
- Adam, J.: „*Strombelastbarkeit von Leiterbahnen* *I. Grundlagen“*, PLUS **4** Heft 10, 1669-1673 (2002)

- By: Dr.J Adam
- Flomerics

## The latest planning

- 	Finalizing design drawings
- mid May until mid July 2004 => Dec 2004
-    Implementation of hardware (preprototype)
- mid July until end of August 2004 =>May2005
- But so far everything looks fine, just delayed..
-    And there is also interest by LBNL and ANL in this kind of printed meander on alumina

## MEBT Chopper Developmentat LBNL for RIA

**S. De Santis**
**J. Byrd**
**J. Staples**
**D. Li**
**R. Keller  **
**	****In collaboration with****	****F. Caspers, CERN**

- This page and the  following 5 slides are copied (with permission) from
-  Berkeley Natl. Lab - Accelerator and Fusion research division

## Rare Isotope Accelerator

**RF chopper****: an essential com- ponent for providing individual intensity adjustment to the beams. Deflects parts of the beam from the RFQ to a high-power stopping target.**

**RIA****: Accelerator system for the production of unstable isotopes. 400 kW beams from H****+**** to U****+28****. Four energy regimes for secondary beams: from stopped beams to 400 MeV/u of in-flight fragments.  **

## Chopper Specifications

| Type | Traveling wave chopper |
| --- | --- |
| Beam velocity | 0.02c |
| q/A | 28/238 – 1/1 |
| Length | 50 cm |
| Voltage | ±2.1 kV |
| Pulse rise/fall time | 12 nsec (5%-95%) |
| Pulse length | 5-22 nsec |
| Repetition rate | up to 28.75 MHz |
| Duty cycle   | ~75 % |

**Transit time > bunch separation (17.4 ns)**

**Wide range of isotopes**
**from H****+**** to U****+28**** **

**82 mrad deflection for U****+28**** of 200 keV/u**

**< 17.4 ns separation between bunches**

**Energy after RFQ**

**Half the RFQ frequency**
**Can chop off every 2****nd**** bunch**

## Slide 22

## Pulse Generator

**Most challenging component: 4.2 kVpp, with 12 ns max. rise time and variable-length flat-top.**
**Two sine-wave generators at 28.75 and 86.25 MHz.**
**CERN SPL design suggests two amplifiers for operation in quasi-static mode during flat-tops and in travelling wave mode during switching. This greatly reduces high power dissipation.**

## First Development Stepsat LBNL

- Extensive modelling of the meander line structure (Microwave Studio, thermal modelling)
- Technology/fabrication tests	-> -> -> -> prototype